Makine Mühendisliği
2019 |
Sindirac, Can; Buyukaksoy, Aligul; Akkurt, Sedat Electrical properties of gadolinia doped ceria electrolytes fabricated by infiltration aided sintering Journal Article SOLID STATE IONICS, 340 , 2019, ISSN: 0167-2738. @article{ISI:000493220600015, title = {Electrical properties of gadolinia doped ceria electrolytes fabricated by infiltration aided sintering}, author = {Can Sindirac and Aligul Buyukaksoy and Sedat Akkurt}, doi = {10.1016/j.ssi.2019.115020}, issn = {0167-2738}, year = {2019}, date = {2019-11-01}, journal = {SOLID STATE IONICS}, volume = {340}, abstract = {Common solid oxide fuel cell (SOFC) electrolyte materials (e.g., gadolinia doped ceria - GDC) demand temperatures exceeding 1400 degrees C for densification by conventional solid state sintering. It is very desirable to reduce the densification of the SOFC electroltytes to i) avoid microstructural coarsening of the composite anode layers, which are co-sintered with the electolyte layer in the anode supported SOFC fabrication scheme and ii) reduce energy consumption during SOFC manufacturing. We have recently demostrated a novel infiltration-aided sintering route to densify GDC ceramics at 1200 degrees C. In the present work, we present the electrical properties of GDC ceramics fabricated thusly. Comparison of high density (>= 95%) samples fabricated by conventional or infiltration-aided sintering reveal that at 700 degrees C, similar total electrical conductivities are obtained, while at 300 degrees C, specific grain boundary resistivity is smaller in the latter. Bulk (grain) conductivity is higher in porous GDC ceramics (relative density <= 90%) fabricated by infiltration-aided sintering than the conventionally sintered ones with similar porosities. Finally, open circuit voltage of 0.84 V at 700 degrees C, obtained under dilute hydrogen and stagnant air conditions suggests that GDC ceramics densified by infiltration-aided sintering are suitable for use as SOFC electrolytes.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Common solid oxide fuel cell (SOFC) electrolyte materials (e.g., gadolinia doped ceria - GDC) demand temperatures exceeding 1400 degrees C for densification by conventional solid state sintering. It is very desirable to reduce the densification of the SOFC electroltytes to i) avoid microstructural coarsening of the composite anode layers, which are co-sintered with the electolyte layer in the anode supported SOFC fabrication scheme and ii) reduce energy consumption during SOFC manufacturing. We have recently demostrated a novel infiltration-aided sintering route to densify GDC ceramics at 1200 degrees C. In the present work, we present the electrical properties of GDC ceramics fabricated thusly. Comparison of high density (>= 95%) samples fabricated by conventional or infiltration-aided sintering reveal that at 700 degrees C, similar total electrical conductivities are obtained, while at 300 degrees C, specific grain boundary resistivity is smaller in the latter. Bulk (grain) conductivity is higher in porous GDC ceramics (relative density <= 90%) fabricated by infiltration-aided sintering than the conventionally sintered ones with similar porosities. Finally, open circuit voltage of 0.84 V at 700 degrees C, obtained under dilute hydrogen and stagnant air conditions suggests that GDC ceramics densified by infiltration-aided sintering are suitable for use as SOFC electrolytes. |
Mobedi, Emir; Dede, Mehmet Ismet Can Geometrical analysis of a continuously variable transmission system designed for human-robot interfaces Journal Article MECHANISM AND MACHINE THEORY, 140 , pp. 567-585, 2019, ISSN: 0094-114X. @article{ISI:000478967700033, title = {Geometrical analysis of a continuously variable transmission system designed for human-robot interfaces}, author = {Emir Mobedi and Mehmet Ismet Can Dede}, doi = {10.1016/j.mechmachtheory.2019.06.024}, issn = {0094-114X}, year = {2019}, date = {2019-10-01}, journal = {MECHANISM AND MACHINE THEORY}, volume = {140}, pages = {567-585}, abstract = {New robotic systems are placed out of their constrained workspaces in order to work alongside humans. Consequently, these applications call for robots monitoring and regulating physical human-robot interaction. These robots' mechanical compliance should be varied when they are in physical contact with the human or their changing environments. This compliance variation can be achieved in a variety of ways. However, one common idea is the variation of joint stiffness mechanically, electromechanically or by control. The solution presented in this paper is an electromechanical way of varying the joint stiffness. Among the electromechanical methods for varying the joint stiffness, continuously variable transmission (CVT) systems can be used in human-robot interfaces if a set of design criteria are met. These criteria include backdrivability, independent output position and stiffness variation, shock absorbing and low mass/inertia. In this paper, a novel two-cone CVT design with a double spherical transmission element is introduced by taking into account the abovementioned criteria. Additionally, design parameters are identified via carrying out a geometrical analysis of this new CVT system. (C) 2019 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } New robotic systems are placed out of their constrained workspaces in order to work alongside humans. Consequently, these applications call for robots monitoring and regulating physical human-robot interaction. These robots' mechanical compliance should be varied when they are in physical contact with the human or their changing environments. This compliance variation can be achieved in a variety of ways. However, one common idea is the variation of joint stiffness mechanically, electromechanically or by control. The solution presented in this paper is an electromechanical way of varying the joint stiffness. Among the electromechanical methods for varying the joint stiffness, continuously variable transmission (CVT) systems can be used in human-robot interfaces if a set of design criteria are met. These criteria include backdrivability, independent output position and stiffness variation, shock absorbing and low mass/inertia. In this paper, a novel two-cone CVT design with a double spherical transmission element is introduced by taking into account the abovementioned criteria. Additionally, design parameters are identified via carrying out a geometrical analysis of this new CVT system. (C) 2019 Elsevier Ltd. All rights reserved. |
Yenigun, Onur; Barisik, Murat Electric Field Controlled Heat Transfer Through Silicon and Nano-confined Water Journal Article NANOSCALE AND MICROSCALE THERMOPHYSICAL ENGINEERING, 23 (4), pp. 304-316, 2019, ISSN: 1556-7265. @article{ISI:000472928800001, title = {Electric Field Controlled Heat Transfer Through Silicon and Nano-confined Water}, author = {Onur Yenigun and Murat Barisik}, doi = {10.1080/15567265.2019.1628136, Early Access Date = JUN 2019}, issn = {1556-7265}, year = {2019}, date = {2019-10-01}, journal = {NANOSCALE AND MICROSCALE THERMOPHYSICAL ENGINEERING}, volume = {23}, number = {4}, pages = {304-316}, abstract = {Nanoscale heat transfer between two parallel silicon slabs filled with deionized water was studied under varying electric field in heat transfer direction. Two oppositely charged electrodes were embedded into the silicon walls to create a uniform electric field perpendicular to the surface, similar to electrowetting-on-dielectric technologies. Through the electrostatic interactions, (i) surface charge altered the silicon/water interface energy and (ii) electric field created orientation polarization of water by aligning dipoles to the direction of the electric field. We found that the first mechanism can manipulate the interface thermal resistance and the later can change the thermal conductivity of water. By increasing electric field, Kapitza length substantially decreased to 1/5 of its original value due to enhanced water layering, but also the water thermal conductivity lessened slightly since water dynamics were restricted; in this range of electric field, heat transfer was doubled. With a further increase of the electric field, electro-freezing (EF) developed as the aligned water dipoles formed a crystalline structure. During EF (0.53 V/nm), water thermal conductivity increased to 1.5 times of its thermodynamic value while Kapitza did not change; but once the EF is formed, both Kapitza and conductivity remained constant with increasing electric field. Overall, the heat transfer rate increased 2.25 times at 0.53 V/nm after which it remains constant with further increase of the electric field.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Nanoscale heat transfer between two parallel silicon slabs filled with deionized water was studied under varying electric field in heat transfer direction. Two oppositely charged electrodes were embedded into the silicon walls to create a uniform electric field perpendicular to the surface, similar to electrowetting-on-dielectric technologies. Through the electrostatic interactions, (i) surface charge altered the silicon/water interface energy and (ii) electric field created orientation polarization of water by aligning dipoles to the direction of the electric field. We found that the first mechanism can manipulate the interface thermal resistance and the later can change the thermal conductivity of water. By increasing electric field, Kapitza length substantially decreased to 1/5 of its original value due to enhanced water layering, but also the water thermal conductivity lessened slightly since water dynamics were restricted; in this range of electric field, heat transfer was doubled. With a further increase of the electric field, electro-freezing (EF) developed as the aligned water dipoles formed a crystalline structure. During EF (0.53 V/nm), water thermal conductivity increased to 1.5 times of its thermodynamic value while Kapitza did not change; but once the EF is formed, both Kapitza and conductivity remained constant with increasing electric field. Overall, the heat transfer rate increased 2.25 times at 0.53 V/nm after which it remains constant with further increase of the electric field. |
Sen, Tumcan; Barisik, Murat Pore connectivity effects on the internal surface electric charge of mesoporous silica Journal Article COLLOID AND POLYMER SCIENCE, 297 (10), pp. 1365-1373, 2019, ISSN: 0303-402X. @article{ISI:000488511000011, title = {Pore connectivity effects on the internal surface electric charge of mesoporous silica}, author = {Tumcan Sen and Murat Barisik}, doi = {10.1007/s00396-019-04555-w}, issn = {0303-402X}, year = {2019}, date = {2019-10-01}, journal = {COLLOID AND POLYMER SCIENCE}, volume = {297}, number = {10}, pages = {1365-1373}, abstract = {Nano-scale confinements within mesoporous systems develop overlapping electric double layers (EDL) such that the existing theoretical models cannot predict the electric potential distributions and resulting surface charges. In addition, ionic conditions undergo local variation through connections between the pore voids and pore throats. For the first time in literature, we studied the charging behavior of mesoporous silica in terms of the pore to throat size ratio (R-pt) to characterize the pore connectivity effects, in addition to porosity (epsilon) and pore size (H). Both local and average surface charge densities inside mesoporous silica were examined by varying these parameters systematically. Results showed that the magnitude of surface charge density decreased with increasing EDL overlap and decreasing connectivity effects. We formulized this behavior and developed an extended model to predict mesoporous silica's internal charge as a function of porosity, pore size, and pore to throat size ratio.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Nano-scale confinements within mesoporous systems develop overlapping electric double layers (EDL) such that the existing theoretical models cannot predict the electric potential distributions and resulting surface charges. In addition, ionic conditions undergo local variation through connections between the pore voids and pore throats. For the first time in literature, we studied the charging behavior of mesoporous silica in terms of the pore to throat size ratio (R-pt) to characterize the pore connectivity effects, in addition to porosity (epsilon) and pore size (H). Both local and average surface charge densities inside mesoporous silica were examined by varying these parameters systematically. Results showed that the magnitude of surface charge density decreased with increasing EDL overlap and decreasing connectivity effects. We formulized this behavior and developed an extended model to predict mesoporous silica's internal charge as a function of porosity, pore size, and pore to throat size ratio. |
Sindirac, Can; Buyukaksoy, Aligul; Akkurt, Sedat JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY, 92 (1), pp. 45-56, 2019, ISSN: 0928-0707. @article{ISI:000483728100005, title = {Electrochemical performance of La0.6Sr0.4Co0.2Fe0.8O3-Ce0.9Gd0.1O2-delta composite SOFC cathodes fabricated by electrocatalyst and/or electrocatalyst-ionic conductor infiltration}, author = {Can Sindirac and Aligul Buyukaksoy and Sedat Akkurt}, doi = {10.1007/s10971-019-05073-5}, issn = {0928-0707}, year = {2019}, date = {2019-10-01}, journal = {JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY}, volume = {92}, number = {1}, pages = {45-56}, abstract = {Infiltration of electrocatalyst precursor solutions into previously sintered porous ionic conductor scaffolds has been used recently as an alternative method to the conventional co-sintering route to fabricate electrocatalyst-ionic conductor composites for solid oxide fuel cell (SOFC) cathode applications. However, the aqueous nitrate solutions generally used to perform the infiltration process results in electrocatalyst precipitates that are disconnected from each other, yielding poor electrode performance. In this work, polymeric electrocatalyst (La0.6Sr0.4Co0.2Fe0.8O3-LSCF) precursors that produce interconnected thin films upon heat treatment were used to infiltrate porous ionic conductor Ce0.9Gd0.1O2-delta (GDC) scaffolds to overcome these issues. In addition, for the first time in the literature, a mixture of LSCF and GDC polymeric precursors, which would yield LSCF-GDC nanocomposite coatings on the grains of the porous GDC scaffold were used as the infiltration solution. Thus, further enhancement of the electrocatalyst/ionic conductor interfacial area and achievement of improved electrode performance was aimed. As a result of the optimization studies, the lowest measured area specific polarization resistance (ASR(cathode)) values of 0.47 and 0.73 omega.cm(2) were obtained for polymeric LSCF+GDC and LSCF precursor infiltrations respectively at 700 degrees C, in air. In addition, LSCF+GDC infiltration yielded electrodes with much improved long-term stability in comparison to those obtained by LSCF infiltration. [GRAPHICS] .}, keywords = {}, pubstate = {published}, tppubtype = {article} } Infiltration of electrocatalyst precursor solutions into previously sintered porous ionic conductor scaffolds has been used recently as an alternative method to the conventional co-sintering route to fabricate electrocatalyst-ionic conductor composites for solid oxide fuel cell (SOFC) cathode applications. However, the aqueous nitrate solutions generally used to perform the infiltration process results in electrocatalyst precipitates that are disconnected from each other, yielding poor electrode performance. In this work, polymeric electrocatalyst (La0.6Sr0.4Co0.2Fe0.8O3-LSCF) precursors that produce interconnected thin films upon heat treatment were used to infiltrate porous ionic conductor Ce0.9Gd0.1O2-delta (GDC) scaffolds to overcome these issues. In addition, for the first time in the literature, a mixture of LSCF and GDC polymeric precursors, which would yield LSCF-GDC nanocomposite coatings on the grains of the porous GDC scaffold were used as the infiltration solution. Thus, further enhancement of the electrocatalyst/ionic conductor interfacial area and achievement of improved electrode performance was aimed. As a result of the optimization studies, the lowest measured area specific polarization resistance (ASR(cathode)) values of 0.47 and 0.73 omega.cm(2) were obtained for polymeric LSCF+GDC and LSCF precursor infiltrations respectively at 700 degrees C, in air. In addition, LSCF+GDC infiltration yielded electrodes with much improved long-term stability in comparison to those obtained by LSCF infiltration. [GRAPHICS] . |
Gur, Sebnem; Korkmaz, Koray; Kiper, Gokhan DESIGN OF ANTI-PARALLELOGRAM LOOP ASSEMBLIES Journal Article JOURNAL OF THE INTERNATIONAL ASSOCIATION FOR SHELL AND SPATIAL STRUCTURES, 60 (3), pp. 232-240, 2019, ISSN: 1028-365X. @article{ISI:000488985500006, title = {DESIGN OF ANTI-PARALLELOGRAM LOOP ASSEMBLIES}, author = {Sebnem Gur and Koray Korkmaz and Gokhan Kiper}, doi = {10.20898/j.iass.2019.201.006}, issn = {1028-365X}, year = {2019}, date = {2019-09-01}, journal = {JOURNAL OF THE INTERNATIONAL ASSOCIATION FOR SHELL AND SPATIAL STRUCTURES}, volume = {60}, number = {3}, pages = {232-240}, abstract = {Scissor mechanisms are frequently used for deployable structures and many studies have been conducted on the subject. Most of the studies consider scissor units as modules in the design process. An alternative approach is to utilize loops as the modules for design. In this paper, the design alternatives of single degree-of-freedom planar linkages comprising anti-parallelogram loops using the loop assembly method is presented. First, scissor mechanisms are reviewed. Next, the types of four-bar loops and the resulting linkages in the literature are introduced and those which are yet to be explored, anti-parallelogram being one of them, are identified. Then the loop assembly method and the examples in the literature are reviewed. As a method to form as many alternatives as possible, symmetry operations are proposed. Suitable frieze symmetry groups utilized for obtaining the assemblies are explained and the anti-parallelogram loop patterns are derived. Next, the single degree-of-freedom linkages are obtained from the loop assemblies. Finally, a selection of the resulting linkages with novel properties are presented. This study shows that loop assemblies are efficient in systematic type synthesis of scissor linkages, some types of which could not be foreseen by using units as modules.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Scissor mechanisms are frequently used for deployable structures and many studies have been conducted on the subject. Most of the studies consider scissor units as modules in the design process. An alternative approach is to utilize loops as the modules for design. In this paper, the design alternatives of single degree-of-freedom planar linkages comprising anti-parallelogram loops using the loop assembly method is presented. First, scissor mechanisms are reviewed. Next, the types of four-bar loops and the resulting linkages in the literature are introduced and those which are yet to be explored, anti-parallelogram being one of them, are identified. Then the loop assembly method and the examples in the literature are reviewed. As a method to form as many alternatives as possible, symmetry operations are proposed. Suitable frieze symmetry groups utilized for obtaining the assemblies are explained and the anti-parallelogram loop patterns are derived. Next, the single degree-of-freedom linkages are obtained from the loop assemblies. Finally, a selection of the resulting linkages with novel properties are presented. This study shows that loop assemblies are efficient in systematic type synthesis of scissor linkages, some types of which could not be foreseen by using units as modules. |
Gorgulu, Ibrahimcan; Dede, Mehmet Ismet Can A New Stiffness Performance Index: Volumetric Isotropy Index Journal Article MACHINES, 7 (2), 2019, ISSN: 2075-1702. @article{ISI:000475300300024, title = {A New Stiffness Performance Index: Volumetric Isotropy Index}, author = {Ibrahimcan Gorgulu and Mehmet Ismet Can Dede}, doi = {10.3390/machines7020044}, issn = {2075-1702}, year = {2019}, date = {2019-06-01}, journal = {MACHINES}, volume = {7}, number = {2}, abstract = {A new index for a precise calculation of a manipulator's stiffness isotropy is introduced. The proposed index is compared with the conventionally used stiffness isotropy index by making use of the investigation on R-CUBE manipulator. The proposed index is shown to produce relatively more precise results from which a higher number of isotropic poses are detected.}, keywords = {}, pubstate = {published}, tppubtype = {article} } A new index for a precise calculation of a manipulator's stiffness isotropy is introduced. The proposed index is compared with the conventionally used stiffness isotropy index by making use of the investigation on R-CUBE manipulator. The proposed index is shown to produce relatively more precise results from which a higher number of isotropic poses are detected. |
Toksoy, Muhammet Fatih; Haber, Richard A Modification of commercial boron carbide powder using Rapid Carbothermal Reduction Journal Article INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, 16 (3), pp. 1120-1125, 2019, ISSN: 1546-542X. @article{ISI:000463236200025, title = {Modification of commercial boron carbide powder using Rapid Carbothermal Reduction}, author = {Muhammet Fatih Toksoy and Richard A Haber}, doi = {10.1111/ijac.13130}, issn = {1546-542X}, year = {2019}, date = {2019-05-01}, journal = {INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY}, volume = {16}, number = {3}, pages = {1120-1125}, abstract = {Non-uniform morphology and existence of free carbon are two main problems for commercial boron carbide powders. This work proposes a method for eliminating free carbon and changing the morphology of commercial powders using Rapid Carbothermal Reduction (RCR) process. Free carbon is eliminated from commercial boron carbide powders and morphology is evolved to less angular shapes with limited particle size growth. Commercial and modified powders were densified by Spark Plasma Sintering at 1900 degrees C with 0, 5, and 20 minutes dwell. Despite the particle size growth, modified boron carbide powders reached >99% TD with shorter dwell times compared with commercial starting powders. Improved microhardness observed with dense modified samples as a result of enhanced morphology and increased twinning.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Non-uniform morphology and existence of free carbon are two main problems for commercial boron carbide powders. This work proposes a method for eliminating free carbon and changing the morphology of commercial powders using Rapid Carbothermal Reduction (RCR) process. Free carbon is eliminated from commercial boron carbide powders and morphology is evolved to less angular shapes with limited particle size growth. Commercial and modified powders were densified by Spark Plasma Sintering at 1900 degrees C with 0, 5, and 20 minutes dwell. Despite the particle size growth, modified boron carbide powders reached >99% TD with shorter dwell times compared with commercial starting powders. Improved microhardness observed with dense modified samples as a result of enhanced morphology and increased twinning. |
Acarer, Sercan; Ozkol, Unver Off-Design Analysis of Transonic Bypass Fan Systems Using Streamline Curvature Through-Flow Method Journal Article INTERNATIONAL JOURNAL OF TURBO & JET-ENGINES, 36 (2), pp. 137-146, 2019, ISSN: 0334-0082. @article{ISI:000477662600002, title = {Off-Design Analysis of Transonic Bypass Fan Systems Using Streamline Curvature Through-Flow Method}, author = {Sercan Acarer and Unver Ozkol}, doi = {10.1515/tjj-2016-0083}, issn = {0334-0082}, year = {2019}, date = {2019-05-01}, journal = {INTERNATIONAL JOURNAL OF TURBO & JET-ENGINES}, volume = {36}, number = {2}, pages = {137-146}, abstract = {The two-dimensional streamline curvature through-flow modeling of turbomachinery is still a key element for turbomachinery preliminary analysis. Basically, axisymmetric swirling flow field is solved numerically. The effects of blades are imposed as sources of swirl, work input/output and entropy generation. Although the topic is studied vastly in the literature for compressors and turbines, combined modeling of the transonic fan and the downstream splitter of turbofan engine configuration, to the authors' best knowledge, is limited. In a prior study, the authors presented a new method for bypass fan modeling for inverse design calculations. Moreover, new set of practical empirical correlations are calibrated and validated. This paper is an extension of this study to rapid off-design analysis of transonic by-pass fan systems. The methodology is validated by two test cases: NASA 2-stage fan and GE-NASA bypass fan case. The proposed methodology is a simple extension for streamline curvature method and can be applied to existing compressor methodologies with minimum numerical effort.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The two-dimensional streamline curvature through-flow modeling of turbomachinery is still a key element for turbomachinery preliminary analysis. Basically, axisymmetric swirling flow field is solved numerically. The effects of blades are imposed as sources of swirl, work input/output and entropy generation. Although the topic is studied vastly in the literature for compressors and turbines, combined modeling of the transonic fan and the downstream splitter of turbofan engine configuration, to the authors' best knowledge, is limited. In a prior study, the authors presented a new method for bypass fan modeling for inverse design calculations. Moreover, new set of practical empirical correlations are calibrated and validated. This paper is an extension of this study to rapid off-design analysis of transonic by-pass fan systems. The methodology is validated by two test cases: NASA 2-stage fan and GE-NASA bypass fan case. The proposed methodology is a simple extension for streamline curvature method and can be applied to existing compressor methodologies with minimum numerical effort. |
Yenigun, Onur; Barisik, Murat Effect of nano-film thickness on thermal resistance at water/silicon interface Journal Article INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, 134 , pp. 634-640, 2019, ISSN: 0017-9310. @article{ISI:000462418300056, title = {Effect of nano-film thickness on thermal resistance at water/silicon interface}, author = {Onur Yenigun and Murat Barisik}, doi = {10.1016/j.ijheatmasstransfer.2019.01.075}, issn = {0017-9310}, year = {2019}, date = {2019-05-01}, journal = {INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER}, volume = {134}, pages = {634-640}, abstract = {Parallel to the developments in micro/nano manufacturing techniques, component sizes in micro/nano electro mechanical systems have been decreasing to nanometer scales. Decrease in lengths in heat transfer direction below the heat carrier phonon length scales reduces thermal conduction in semiconductors. This study shows that such altered phonon spectrums with the decrease of size also reduce the heat transfer at the solid/liquid interfaces and can be correlated with the thermal conductivity of the slab. Using Molecular Dynamics (MD), we measured heat transfer between water and silicon of different thickness between 5 nm and 60 nm. Silicon slabs exhibit a linear temperature profile through the bulk where thermal conductivities measured based on Fourier law decreased by the decreasing slab thickness. We applied a semi-theoretical formulism on variation of conductivity by slab thickness. At the interface of these slabs and water, heat passage is disturbed due to the phonon mismatch of dissimilar materials, which is mostly considered as solid/liquid couple interface properties by the earlier literature. Resistance for phonon passage characterized as Kapitza length (L-K) is measured for different slab thicknesses at different surface wetting conditions varying between hydrophilic to hydrophobic. Increasing surface wetting decreases the L-K while at a certain wetting, decreasing the slab thickness increases the L-K. Once the L-K of different size slabs normalized by its bulk value (assumed to be the L-K of the thickest slab at the corresponding wetting), L-K variation by silicon thickness shows a universal behavior independent of surface wetting. A mathematical model describing the exponential increase of L-K by decreasing thickness was developed and validated by an earlier model. We further developed a correlation between the corresponding changes of L-K and conductivity with respective to their bulk values by analytically combining two models as (L-K/L-K-(Bulk)) = exp (3.94(k(Bulk) - k)/(k x k(Bulk))), using which L-K can be predicted from available thermal conductivities of a certain material. Results are crucial for thermal management of current and future electronics. (C) 2019 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Parallel to the developments in micro/nano manufacturing techniques, component sizes in micro/nano electro mechanical systems have been decreasing to nanometer scales. Decrease in lengths in heat transfer direction below the heat carrier phonon length scales reduces thermal conduction in semiconductors. This study shows that such altered phonon spectrums with the decrease of size also reduce the heat transfer at the solid/liquid interfaces and can be correlated with the thermal conductivity of the slab. Using Molecular Dynamics (MD), we measured heat transfer between water and silicon of different thickness between 5 nm and 60 nm. Silicon slabs exhibit a linear temperature profile through the bulk where thermal conductivities measured based on Fourier law decreased by the decreasing slab thickness. We applied a semi-theoretical formulism on variation of conductivity by slab thickness. At the interface of these slabs and water, heat passage is disturbed due to the phonon mismatch of dissimilar materials, which is mostly considered as solid/liquid couple interface properties by the earlier literature. Resistance for phonon passage characterized as Kapitza length (L-K) is measured for different slab thicknesses at different surface wetting conditions varying between hydrophilic to hydrophobic. Increasing surface wetting decreases the L-K while at a certain wetting, decreasing the slab thickness increases the L-K. Once the L-K of different size slabs normalized by its bulk value (assumed to be the L-K of the thickest slab at the corresponding wetting), L-K variation by silicon thickness shows a universal behavior independent of surface wetting. A mathematical model describing the exponential increase of L-K by decreasing thickness was developed and validated by an earlier model. We further developed a correlation between the corresponding changes of L-K and conductivity with respective to their bulk values by analytically combining two models as (L-K/L-K-(Bulk)) = exp (3.94(k(Bulk) - k)/(k x k(Bulk))), using which L-K can be predicted from available thermal conductivities of a certain material. Results are crucial for thermal management of current and future electronics. (C) 2019 Elsevier Ltd. All rights reserved. |
Beylergil, Bertan; Tanoglu, Metin; Aktas, Engin Mode-I fracture toughness of carbon fiber/epoxy composites interleaved by aramid nonwoven veils Journal Article STEEL AND COMPOSITE STRUCTURES, 31 (2), pp. 113-123, 2019, ISSN: 1229-9367. @article{ISI:000464609300001, title = {Mode-I fracture toughness of carbon fiber/epoxy composites interleaved by aramid nonwoven veils}, author = {Bertan Beylergil and Metin Tanoglu and Engin Aktas}, doi = {10.12989/scs.2019.31.2.113}, issn = {1229-9367}, year = {2019}, date = {2019-04-01}, journal = {STEEL AND COMPOSITE STRUCTURES}, volume = {31}, number = {2}, pages = {113-123}, abstract = {In this study, carbon fiber/epoxy (CF/EP) composites were interleaved with aramid nonwoven veils with an areal weight density of 8.5 g/m(2) to improve their Mode-I fracture toughness. The control and aramid interleaved CF/EP composite laminates were manufactured by VARTM in a [0]4 configuration. Tensile, three-point bending, compression, interlaminar shear, Charpy impact and Mode-I (DCB) fracture toughness values were determined to evaluate the effects of aramid nonwoven fabrics on the mechanical performance of the CF/EP composites. Thermomechanical behavior of the specimens was investigated by Dynamic Mechanical Analysis (DMA). The results showed that the propagation Mode-I fracture toughness values of CF/EP composites can be significantly improved (by about 72%) using aramid nonwoven fabrics. It was found that the main extrinsic toughening mechanism is aramid microfiber bridging acting behind the crack-tip. The incorporation of these nonwovens also increased interlaminar shear and Charpy impact strength by 10 and 16.5%, respectively. Moreover, it was revealed that the damping ability of the composites increased with the incorporation of aramid nonwoven fabrics in the interlaminar region of composites. On the other hand, they caused a reduction in in-plane mechanical properties due to the reduced carbon fiber volume fraction, increased thickness and void formation in the composites.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, carbon fiber/epoxy (CF/EP) composites were interleaved with aramid nonwoven veils with an areal weight density of 8.5 g/m(2) to improve their Mode-I fracture toughness. The control and aramid interleaved CF/EP composite laminates were manufactured by VARTM in a [0]4 configuration. Tensile, three-point bending, compression, interlaminar shear, Charpy impact and Mode-I (DCB) fracture toughness values were determined to evaluate the effects of aramid nonwoven fabrics on the mechanical performance of the CF/EP composites. Thermomechanical behavior of the specimens was investigated by Dynamic Mechanical Analysis (DMA). The results showed that the propagation Mode-I fracture toughness values of CF/EP composites can be significantly improved (by about 72%) using aramid nonwoven fabrics. It was found that the main extrinsic toughening mechanism is aramid microfiber bridging acting behind the crack-tip. The incorporation of these nonwovens also increased interlaminar shear and Charpy impact strength by 10 and 16.5%, respectively. Moreover, it was revealed that the damping ability of the composites increased with the incorporation of aramid nonwoven fabrics in the interlaminar region of composites. On the other hand, they caused a reduction in in-plane mechanical properties due to the reduced carbon fiber volume fraction, increased thickness and void formation in the composites. |
Ozcelik, Gokberk H; Barisik, Murat Electric charge of nanopatterned silica surfaces Journal Article PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21 (14), pp. 7576-7587, 2019, ISSN: 1463-9076. @article{ISI:000464580600033, title = {Electric charge of nanopatterned silica surfaces}, author = {Gokberk H Ozcelik and Murat Barisik}, doi = {10.1039/c9cp00706g}, issn = {1463-9076}, year = {2019}, date = {2019-04-01}, journal = {PHYSICAL CHEMISTRY CHEMICAL PHYSICS}, volume = {21}, number = {14}, pages = {7576-7587}, abstract = {The most recent technologies employ nanoscale surface patterning or roughening in order to engineer desired properties on a surface. Electrokinetic properties at the interface of such surfaces and ionic liquids show different behavior to the well-known theoretical descriptions. Basically, the ionic distribution on the surface differs due to electrical double layer overlap effects in the pits and curvature effects at the tips of surface structures. Generally, the charge density of a surface is assumed to be a material property and surface roughness effects are overlooked in most of the literature. In contrast, we properly calculated the local surface charges based on surface chemistry at the corresponding local ionic concentration (charge regulation) for various surface roughness and solution conditions. The results showed that the surface charge density of silica decreased at the pits but increased at the tips of surface patterns. Even for the simplest case of self-repeating surface structures, the average of local surface charges becomes lower than the theoretical predictions. Based on numerical calculations, a phenomenological model was developed as an extension to the existing flat surface theory, which can successfully predict the average surface charge on a nano patterned surface as a function of the surface pattern size, ionic concentration and pH.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The most recent technologies employ nanoscale surface patterning or roughening in order to engineer desired properties on a surface. Electrokinetic properties at the interface of such surfaces and ionic liquids show different behavior to the well-known theoretical descriptions. Basically, the ionic distribution on the surface differs due to electrical double layer overlap effects in the pits and curvature effects at the tips of surface structures. Generally, the charge density of a surface is assumed to be a material property and surface roughness effects are overlooked in most of the literature. In contrast, we properly calculated the local surface charges based on surface chemistry at the corresponding local ionic concentration (charge regulation) for various surface roughness and solution conditions. The results showed that the surface charge density of silica decreased at the pits but increased at the tips of surface patterns. Even for the simplest case of self-repeating surface structures, the average of local surface charges becomes lower than the theoretical predictions. Based on numerical calculations, a phenomenological model was developed as an extension to the existing flat surface theory, which can successfully predict the average surface charge on a nano patterned surface as a function of the surface pattern size, ionic concentration and pH. |
Maden, Feray; Akgun, Yenal; Kiper, Gokhan; Gur, Sebnem; Yar, Mujde; Korkmaz, Koray A CRITICAL REVIEW ON CLASSIFICATION AND TERMINOLOGY OF SCISSOR STRUCTURES Journal Article JOURNAL OF THE INTERNATIONAL ASSOCIATION FOR SHELL AND SPATIAL STRUCTURES, 60 (1, SI), pp. 47-64, 2019, ISSN: 1028-365X. @article{ISI:000464014000005, title = {A CRITICAL REVIEW ON CLASSIFICATION AND TERMINOLOGY OF SCISSOR STRUCTURES}, author = {Feray Maden and Yenal Akgun and Gokhan Kiper and Sebnem Gur and Mujde Yar and Koray Korkmaz}, doi = {10.20898/j.iass.2019.199.029}, issn = {1028-365X}, year = {2019}, date = {2019-03-01}, journal = {JOURNAL OF THE INTERNATIONAL ASSOCIATION FOR SHELL AND SPATIAL STRUCTURES}, volume = {60}, number = {1, SI}, pages = {47-64}, abstract = {When the existing literature on the research of scissor structures is thoroughly investigated, it is seen that different researchers use different terminologies and classifications especially for the definition of the primary units and the motion type. Some of the studies define the whole geometry based on the geometric properties of the primary scissor units and the unit lines while some other studies define it according to the loops. All these studies use different names for similar elements. This article aims to review the literature on the classification and terminology of scissor structures and represent the state of art on the studies. Tables are represented showing all approaches in the literature. In addition, the article criticizes the missing points of each terminology and definition, and proposes some new terminology. In order to arrive at this aim, different definitions of the primary scissor units and motion types used in key studies in the literature are investigated thoroughly. With several examples, it is demonstrated that naming the scissor units according to the resulting motion type might be misleading and it is better to specify the motion type for the whole structure. A classification for transformation of planar curves is presented.}, keywords = {}, pubstate = {published}, tppubtype = {article} } When the existing literature on the research of scissor structures is thoroughly investigated, it is seen that different researchers use different terminologies and classifications especially for the definition of the primary units and the motion type. Some of the studies define the whole geometry based on the geometric properties of the primary scissor units and the unit lines while some other studies define it according to the loops. All these studies use different names for similar elements. This article aims to review the literature on the classification and terminology of scissor structures and represent the state of art on the studies. Tables are represented showing all approaches in the literature. In addition, the article criticizes the missing points of each terminology and definition, and proposes some new terminology. In order to arrive at this aim, different definitions of the primary scissor units and motion types used in key studies in the literature are investigated thoroughly. With several examples, it is demonstrated that naming the scissor units according to the resulting motion type might be misleading and it is better to specify the motion type for the whole structure. A classification for transformation of planar curves is presented. |
Cetkin, Erdal; Miguel, Antonio F Constructal branched micromixers with enhanced mixing efficiency: Slender design, sphere mixing chamber and obstacles Journal Article INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, 131 , pp. 633-644, 2019, ISSN: 0017-9310. @article{ISI:000456761100057, title = {Constructal branched micromixers with enhanced mixing efficiency: Slender design, sphere mixing chamber and obstacles}, author = {Erdal Cetkin and Antonio F Miguel}, doi = {10.1016/j.ijheatmasstransfer.2018.11.091}, issn = {0017-9310}, year = {2019}, date = {2019-03-01}, journal = {INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER}, volume = {131}, pages = {633-644}, abstract = {Here we uncover the passive micromixer designs with the maximum mixing efficiency under a lesser flow impedance. Three different designs of micromixers were considered for volume constrained systems: branched systems of ducts, branching ducts with sphere mixing chamber and branching ducts with obstacles. The best performing designs, with maximum mixing efficiency and minimum flow impedance, are uncovered numerically by considering three degrees of freedom (ratios between diameters, between lengths, and between length and diameter) under total volume constraint. The mixing efficiency, the flow impedance and the mixer performance (or mixer quality) for all the designs are determined based on numerical results. The results uncover that the branched micromixer should have long mother ducts with larger diameter than daughter ducts. Our results also show that branching ducts with sphere mixing chambers and obstacles also enhance the mixing efficiency but with an additional penalty on flow impedance. Besides, systems with a sphere mixing chamber insertion in the junction between mother and daughter ducts have greater mixing efficiency than systems with embedded obstacles into the mother channel. However, for a given flow impedance, the mixing efficiency is greater for branched systems of ducts than for branching ducts with sphere mixing chamber and with obstacles. For mixer systems built in a space with limited size, branching ducts with sphere mixing chamber may be a good option because they require less space than the other systems. Here new analytical models are also proposed to predict the mixing efficiency and mixer performance based on numerical results. In summary, this paper provides important insights for the designers of micromixer based on Constructal law. (C) 2018 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Here we uncover the passive micromixer designs with the maximum mixing efficiency under a lesser flow impedance. Three different designs of micromixers were considered for volume constrained systems: branched systems of ducts, branching ducts with sphere mixing chamber and branching ducts with obstacles. The best performing designs, with maximum mixing efficiency and minimum flow impedance, are uncovered numerically by considering three degrees of freedom (ratios between diameters, between lengths, and between length and diameter) under total volume constraint. The mixing efficiency, the flow impedance and the mixer performance (or mixer quality) for all the designs are determined based on numerical results. The results uncover that the branched micromixer should have long mother ducts with larger diameter than daughter ducts. Our results also show that branching ducts with sphere mixing chambers and obstacles also enhance the mixing efficiency but with an additional penalty on flow impedance. Besides, systems with a sphere mixing chamber insertion in the junction between mother and daughter ducts have greater mixing efficiency than systems with embedded obstacles into the mother channel. However, for a given flow impedance, the mixing efficiency is greater for branched systems of ducts than for branching ducts with sphere mixing chamber and with obstacles. For mixer systems built in a space with limited size, branching ducts with sphere mixing chamber may be a good option because they require less space than the other systems. Here new analytical models are also proposed to predict the mixing efficiency and mixer performance based on numerical results. In summary, this paper provides important insights for the designers of micromixer based on Constructal law. (C) 2018 Elsevier Ltd. All rights reserved. |
Sarikaya, Mustafa; Tasdemirci, Alper; Guden, Mustafa Impact loading and modelling a multilayer aluminium corrugated/fin core: The effect of the insertion of imperfect fin layers Journal Article STRAIN, 55 (1), 2019, ISSN: 1475-1305. @article{ISI:000455963900004, title = {Impact loading and modelling a multilayer aluminium corrugated/fin core: The effect of the insertion of imperfect fin layers}, author = {Mustafa Sarikaya and Alper Tasdemirci and Mustafa Guden}, doi = {10.1111/str.12298}, issn = {1475-1305}, year = {2019}, date = {2019-02-01}, journal = {STRAIN}, volume = {55}, number = {1}, abstract = {The quasi-static compression (0.0048 m/s) and Taylor-like impact (135, 150, and 200 m/s) loading of a multilayer 1050 H14 aluminium corrugated core were investigated both experimentally and numerically in LS-DYNA using the perfect and imperfect sample models. In the imperfect sample models, one or two layers of corrugated fin structure were replaced by the fin layers made of bent-type cell walls. The localised deformation in the quasi-static imperfect models of cylindrical sample started at the imperfect layers, the same as the tests, and the layers were compressed until about the densification strain in a step-wise fashion. The localised deformation in the perfect models, however, started at the layers at and near the top and bottom of the test sample. In the shock mode, the sample crushed sequentially starting at the impact end layer regardless the perfect or imperfect sample models were used. Furthermore, the perfect and imperfect models resulted in nearly the same initial crushing stresses in the shock mode. The layer strain histories revealed a velocity-dependent layer densification strain. Both model types, the imperfect and perfect, well approximated the stress-time histories and layer deformations of the shock mode. The rigid perfectly plastic locking model based on the numerically determined densification strains also showed well agreements with the experimental and numerical plateau stresses of the shock mode.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The quasi-static compression (0.0048 m/s) and Taylor-like impact (135, 150, and 200 m/s) loading of a multilayer 1050 H14 aluminium corrugated core were investigated both experimentally and numerically in LS-DYNA using the perfect and imperfect sample models. In the imperfect sample models, one or two layers of corrugated fin structure were replaced by the fin layers made of bent-type cell walls. The localised deformation in the quasi-static imperfect models of cylindrical sample started at the imperfect layers, the same as the tests, and the layers were compressed until about the densification strain in a step-wise fashion. The localised deformation in the perfect models, however, started at the layers at and near the top and bottom of the test sample. In the shock mode, the sample crushed sequentially starting at the impact end layer regardless the perfect or imperfect sample models were used. Furthermore, the perfect and imperfect models resulted in nearly the same initial crushing stresses in the shock mode. The layer strain histories revealed a velocity-dependent layer densification strain. Both model types, the imperfect and perfect, well approximated the stress-time histories and layer deformations of the shock mode. The rigid perfectly plastic locking model based on the numerically determined densification strains also showed well agreements with the experimental and numerical plateau stresses of the shock mode. |
Sarikaya, Mustafa; Tasdemirci, Alper; Guden, Mustafa Impact loading and modelling a multilayer aluminium corrugated/fin core: The effect of the insertion of imperfect fin layers Journal Article STRAIN, 55 (1), 2019, ISSN: 1475-1305. @article{ISI:000455963900004b, title = {Impact loading and modelling a multilayer aluminium corrugated/fin core: The effect of the insertion of imperfect fin layers}, author = {Mustafa Sarikaya and Alper Tasdemirci and Mustafa Guden}, doi = {10.1111/str.12298}, issn = {1475-1305}, year = {2019}, date = {2019-02-01}, journal = {STRAIN}, volume = {55}, number = {1}, abstract = {The quasi-static compression (0.0048 m/s) and Taylor-like impact (135, 150, and 200 m/s) loading of a multilayer 1050 H14 aluminium corrugated core were investigated both experimentally and numerically in LS-DYNA using the perfect and imperfect sample models. In the imperfect sample models, one or two layers of corrugated fin structure were replaced by the fin layers made of bent-type cell walls. The localised deformation in the quasi-static imperfect models of cylindrical sample started at the imperfect layers, the same as the tests, and the layers were compressed until about the densification strain in a step-wise fashion. The localised deformation in the perfect models, however, started at the layers at and near the top and bottom of the test sample. In the shock mode, the sample crushed sequentially starting at the impact end layer regardless the perfect or imperfect sample models were used. Furthermore, the perfect and imperfect models resulted in nearly the same initial crushing stresses in the shock mode. The layer strain histories revealed a velocity-dependent layer densification strain. Both model types, the imperfect and perfect, well approximated the stress-time histories and layer deformations of the shock mode. The rigid perfectly plastic locking model based on the numerically determined densification strains also showed well agreements with the experimental and numerical plateau stresses of the shock mode.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The quasi-static compression (0.0048 m/s) and Taylor-like impact (135, 150, and 200 m/s) loading of a multilayer 1050 H14 aluminium corrugated core were investigated both experimentally and numerically in LS-DYNA using the perfect and imperfect sample models. In the imperfect sample models, one or two layers of corrugated fin structure were replaced by the fin layers made of bent-type cell walls. The localised deformation in the quasi-static imperfect models of cylindrical sample started at the imperfect layers, the same as the tests, and the layers were compressed until about the densification strain in a step-wise fashion. The localised deformation in the perfect models, however, started at the layers at and near the top and bottom of the test sample. In the shock mode, the sample crushed sequentially starting at the impact end layer regardless the perfect or imperfect sample models were used. Furthermore, the perfect and imperfect models resulted in nearly the same initial crushing stresses in the shock mode. The layer strain histories revealed a velocity-dependent layer densification strain. Both model types, the imperfect and perfect, well approximated the stress-time histories and layer deformations of the shock mode. The rigid perfectly plastic locking model based on the numerically determined densification strains also showed well agreements with the experimental and numerical plateau stresses of the shock mode. |
Aydin, Levent; Aydin, Olgun; Artem, Secil H; Mert, Ali Design of dimensionally stable composites using efficient global optimization method Journal Article PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART L-JOURNAL OF MATERIALS-DESIGN AND APPLICATIONS, 233 (2), pp. 156-168, 2019, ISSN: 1464-4207. @article{ISI:000459891100006, title = {Design of dimensionally stable composites using efficient global optimization method}, author = {Levent Aydin and Olgun Aydin and Secil H Artem and Ali Mert}, doi = {10.1177/1464420716664921}, issn = {1464-4207}, year = {2019}, date = {2019-02-01}, journal = {PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART L-JOURNAL OF MATERIALS-DESIGN AND APPLICATIONS}, volume = {233}, number = {2}, pages = {156-168}, abstract = {Dimensionally stable material design is an important issue for space structures such as space laser communication systems, telescopes, and satellites. Suitably designed composite materials for this purpose can meet the functional and structural requirements. In this paper, it is aimed to design the dimensionally stable laminated composites by using efficient global optimization method. For this purpose, the composite plate optimization problems have been solved for high stiffness and low coefficients of thermal and moisture expansion. Some of the results based on efficient global optimization solution have been verified by genetic algorithm, simulated annealing, and generalized pattern search solutions from the previous studies. The proposed optimization algorithm is also validated experimentally. After completing the design and optimization process, failure analysis of the optimized composites has been performed based on Tsai-Hill, Tsai-Wu, Hoffman, and Hashin-Rotem criteria.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Dimensionally stable material design is an important issue for space structures such as space laser communication systems, telescopes, and satellites. Suitably designed composite materials for this purpose can meet the functional and structural requirements. In this paper, it is aimed to design the dimensionally stable laminated composites by using efficient global optimization method. For this purpose, the composite plate optimization problems have been solved for high stiffness and low coefficients of thermal and moisture expansion. Some of the results based on efficient global optimization solution have been verified by genetic algorithm, simulated annealing, and generalized pattern search solutions from the previous studies. The proposed optimization algorithm is also validated experimentally. After completing the design and optimization process, failure analysis of the optimized composites has been performed based on Tsai-Hill, Tsai-Wu, Hoffman, and Hashin-Rotem criteria. |
Sindirac, Can; Cakirlar, Seda; Buyukaksoy, Aligul; Akkurt, Sedat Lowering the sintering temperature of solid oxide fuel cell electrolytes by infiltration Journal Article JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 39 (2-3), pp. 409-417, 2019, ISSN: 0955-2219. @article{ISI:000450379400035, title = {Lowering the sintering temperature of solid oxide fuel cell electrolytes by infiltration}, author = {Can Sindirac and Seda Cakirlar and Aligul Buyukaksoy and Sedat Akkurt}, doi = {10.1016/j.jeurceramsoc.2018.09.029}, issn = {0955-2219}, year = {2019}, date = {2019-02-01}, journal = {JOURNAL OF THE EUROPEAN CERAMIC SOCIETY}, volume = {39}, number = {2-3}, pages = {409-417}, abstract = {A dense electrolyte with a relative density of over 95% is vital to prevent gas leakage and thus the achievement of high open circuit voltage in solid oxide fuel cells (SOFCs). The densification process of ceria based electrolyte requires high temperatures heat treatment (i.e. 1400-1500 degrees C). Thus, the minimum co-sintering temperatures of the anode-electrode bilayers are fixed at these values, resulting in coarse anode microstructures and consequently poor performance. The main purpose of this study is to densify gadolinia doped ceria (GDC), a common SOFC electrolyte, at temperatures lower than 1400 degrees C. By this aim, an approach involving the infiltration of polymeric precursors into porous electrolyte scaffolds, a method commonly used for composite SOFC electrodes, is proposed. By infiltrating polymeric precursors of GDC into porous GDC scaffolds, a reduction in the sintering temperature by at least 200 degrees C is achieved with no additives that might affect the electrical properties. Energy dispersive x-ray spectroscopy line scan analyses performed on porous GDC scaffolds infiltrated by a marker solution (polymeric FeOx precursor in this case) reveals a homogeneous infiltrated phase distribution, demonstrating the effectiveness of polymeric precursors.}, keywords = {}, pubstate = {published}, tppubtype = {article} } A dense electrolyte with a relative density of over 95% is vital to prevent gas leakage and thus the achievement of high open circuit voltage in solid oxide fuel cells (SOFCs). The densification process of ceria based electrolyte requires high temperatures heat treatment (i.e. 1400-1500 degrees C). Thus, the minimum co-sintering temperatures of the anode-electrode bilayers are fixed at these values, resulting in coarse anode microstructures and consequently poor performance. The main purpose of this study is to densify gadolinia doped ceria (GDC), a common SOFC electrolyte, at temperatures lower than 1400 degrees C. By this aim, an approach involving the infiltration of polymeric precursors into porous electrolyte scaffolds, a method commonly used for composite SOFC electrodes, is proposed. By infiltrating polymeric precursors of GDC into porous GDC scaffolds, a reduction in the sintering temperature by at least 200 degrees C is achieved with no additives that might affect the electrical properties. Energy dispersive x-ray spectroscopy line scan analyses performed on porous GDC scaffolds infiltrated by a marker solution (polymeric FeOx precursor in this case) reveals a homogeneous infiltrated phase distribution, demonstrating the effectiveness of polymeric precursors. |
Celik, Hasan; Mobedi, Moghtada; Nakayama, Akira; Ozkol, Unver JOURNAL OF POROUS MEDIA, 22 (5), pp. 511-529, 2019, ISSN: 1091-028X. @article{ISI:000466845700001, title = {A STUDY ON NUMERICAL DETERMINATION OF PERMEABILITY AND INERTIA COEFFICIENT OF ALUMINUM FOAM USING X-RAY MICROTOMOGRAPHY TECHNIQUE: FOCUS ON INSPECTION METHODS FOR RELIABILITY (PERMEABILITY AND INERTIA COEFFICIENT BY TOMOGRAPHY)}, author = {Hasan Celik and Moghtada Mobedi and Akira Nakayama and Unver Ozkol}, doi = {10.1615/JPorMedia.2019028887}, issn = {1091-028X}, year = {2019}, date = {2019-01-01}, journal = {JOURNAL OF POROUS MEDIA}, volume = {22}, number = {5}, pages = {511-529}, abstract = {The volume-averaged (i.e., macroscopic) transport properties such as permeability and inertia coefficient of two aluminum foams with 10 and 20 pores per inch (PPI) pore density are found using microtomography images. It is shown that a comparison between the numerical values and the experimental results may not be sufficient to prove the correctness of the obtained results. Hence, in addition to traditional validation methods such as grid independency and comparison with reported results in literature, further inspections such as (a) checking the development of flow, (b) inspection of Darcy and non-Darcy regions, (c) conservation of flow rate through the porous media, (d) sufficiency of number of voxels in the narrow throats, and (e) observation of transverse velocity gradients in pores for high and low Reynolds numbers can be performed to further validate the achieved results. These techniques have been discussed and explained in detail for the performed study. Moreover, the obtained permeability and inertia coefficient values are compared with 19 reported theoretical, numerical, and experimental studies. The maximum deviation between the present results and the reported studies for 10 PPI is below 25%, while for 20 PPI it is below 28%.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The volume-averaged (i.e., macroscopic) transport properties such as permeability and inertia coefficient of two aluminum foams with 10 and 20 pores per inch (PPI) pore density are found using microtomography images. It is shown that a comparison between the numerical values and the experimental results may not be sufficient to prove the correctness of the obtained results. Hence, in addition to traditional validation methods such as grid independency and comparison with reported results in literature, further inspections such as (a) checking the development of flow, (b) inspection of Darcy and non-Darcy regions, (c) conservation of flow rate through the porous media, (d) sufficiency of number of voxels in the narrow throats, and (e) observation of transverse velocity gradients in pores for high and low Reynolds numbers can be performed to further validate the achieved results. These techniques have been discussed and explained in detail for the performed study. Moreover, the obtained permeability and inertia coefficient values are compared with 19 reported theoretical, numerical, and experimental studies. The maximum deviation between the present results and the reported studies for 10 PPI is below 25%, while for 20 PPI it is below 28%. |
Ates, Gizem; Majani, Ronny; Dede, Mehmet Ismet Can Design of a Teleoperation Scheme with a Wearable Master for Minimally Invasive Surgery Inproceedings {Carbone, G; Ceccarelli, M; Pisla, D} (Ed.): NEW TRENDS IN MEDICAL AND SERVICE ROBOTICS: ADVANCES IN THEORY AND PRACTICE, pp. 45-53, Int Federat Promot Mech & Machine Sci, Tech Comm Biomechan Engn, Robot & Mechantron; Int Federat Promot Mech & Machine Sci, Tech Comm Computat Kinemat 2019, ISSN: 2211-0984, (6th International Workshop on Medical and Service Robots (MESROB), Univ Cassino & S Latium, Sch Engn, Cassino, ITALY, 2018). @inproceedings{ISI:000460759400006, title = {Design of a Teleoperation Scheme with a Wearable Master for Minimally Invasive Surgery}, author = {Gizem Ates and Ronny Majani and Mehmet Ismet Can Dede}, editor = {G {Carbone and M Ceccarelli and D} Pisla}, doi = {10.1007/978-3-030-00329-6_6}, issn = {2211-0984}, year = {2019}, date = {2019-01-01}, booktitle = {NEW TRENDS IN MEDICAL AND SERVICE ROBOTICS: ADVANCES IN THEORY AND PRACTICE}, volume = {65}, pages = {45-53}, organization = {Int Federat Promot Mech & Machine Sci, Tech Comm Biomechan Engn, Robot & Mechantron; Int Federat Promot Mech & Machine Sci, Tech Comm Computat Kinemat}, series = {Mechanisms and Machine Science}, abstract = {Minimally invasive surgery is increasingly being preferred over conventional surgery, however many problems still persist in longer surgeries such as pituitary surgeries, where surgeons are still required to hold an endoscope in their hand for prolonged periods of time. Many modern approaches have recently been proposed in literature to reduce the surgeon's effort. In this paper we extended upon these previous attempts and presented a promising solution; a real time teleoperation scheme with 3 different modes of operation, composed of a wearable ring system that captures and transmits voluntary hand motions over a wireless connection to a slave system. Accordingly, this slave system processes the received data to generate velocity demands for the robot endoscope controller. Finally, the feasibility of the proposed modes of operation are demonstrated and compared by measuring their learning curve and effort by running a set of training simulations on human subjects.}, note = {6th International Workshop on Medical and Service Robots (MESROB), Univ Cassino & S Latium, Sch Engn, Cassino, ITALY, 2018}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } Minimally invasive surgery is increasingly being preferred over conventional surgery, however many problems still persist in longer surgeries such as pituitary surgeries, where surgeons are still required to hold an endoscope in their hand for prolonged periods of time. Many modern approaches have recently been proposed in literature to reduce the surgeon's effort. In this paper we extended upon these previous attempts and presented a promising solution; a real time teleoperation scheme with 3 different modes of operation, composed of a wearable ring system that captures and transmits voluntary hand motions over a wireless connection to a slave system. Accordingly, this slave system processes the received data to generate velocity demands for the robot endoscope controller. Finally, the feasibility of the proposed modes of operation are demonstrated and compared by measuring their learning curve and effort by running a set of training simulations on human subjects. |
Isitman, O; Ayit, O; Vardarli, E; Hanalioglu, S; Isikay, I; Berker, M; Dede, M I C Viscoelastic Modeling of Human Nasal Tissues with a Mobile Measurement Device Inproceedings {Carbone, G; Ceccarelli, M; Pisla, D} (Ed.): NEW TRENDS IN MEDICAL AND SERVICE ROBOTICS: ADVANCES IN THEORY AND PRACTICE, pp. 216-224, Int Federat Promot Mech & Machine Sci, Tech Comm Biomechan Engn, Robot & Mechantron; Int Federat Promot Mech & Machine Sci, Tech Comm Computat Kinemat 2019, ISSN: 2211-0984, (6th International Workshop on Medical and Service Robots (MESROB), Univ Cassino & S Latium, Sch Engn, Cassino, ITALY, 2018). @inproceedings{ISI:000460759400025, title = {Viscoelastic Modeling of Human Nasal Tissues with a Mobile Measurement Device}, author = {O Isitman and O Ayit and E Vardarli and S Hanalioglu and I Isikay and M Berker and M I C Dede}, editor = {G {Carbone and M Ceccarelli and D} Pisla}, doi = {10.1007/978-3-030-00329-6_25}, issn = {2211-0984}, year = {2019}, date = {2019-01-01}, booktitle = {NEW TRENDS IN MEDICAL AND SERVICE ROBOTICS: ADVANCES IN THEORY AND PRACTICE}, volume = {65}, pages = {216-224}, organization = {Int Federat Promot Mech & Machine Sci, Tech Comm Biomechan Engn, Robot & Mechantron; Int Federat Promot Mech & Machine Sci, Tech Comm Computat Kinemat}, series = {Mechanisms and Machine Science}, abstract = {Modeling the dynamic of tool-tissue interaction for the robotic minimally invasive surgeries is one of the main issues for designing appropriate robot controllers. A mobile measurement device is produced in order to model some nasal tissues of a human. This mobile device is a hand-held one which measures the applied moments and relative angular displacements about a fixed pivot point. The ex-vivo measurements are realized by surgeons on a relatively fresh human cadaver head. The tip of the nose and the nasal concha are the two tissues that are investigated. In this study, five different viscoelastic models are considered; Elastic, Kelvin-Voight, Kelvin-Boltzmann, Maxwell and Hunt-Crossley. The results are evaluated and cross-validated on each data set. Hunt-Crossley and Kelvin-Boltzmann models provided the minimum root-mean-square (RMS) error among the other models.}, note = {6th International Workshop on Medical and Service Robots (MESROB), Univ Cassino & S Latium, Sch Engn, Cassino, ITALY, 2018}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } Modeling the dynamic of tool-tissue interaction for the robotic minimally invasive surgeries is one of the main issues for designing appropriate robot controllers. A mobile measurement device is produced in order to model some nasal tissues of a human. This mobile device is a hand-held one which measures the applied moments and relative angular displacements about a fixed pivot point. The ex-vivo measurements are realized by surgeons on a relatively fresh human cadaver head. The tip of the nose and the nasal concha are the two tissues that are investigated. In this study, five different viscoelastic models are considered; Elastic, Kelvin-Voight, Kelvin-Boltzmann, Maxwell and Hunt-Crossley. The results are evaluated and cross-validated on each data set. Hunt-Crossley and Kelvin-Boltzmann models provided the minimum root-mean-square (RMS) error among the other models. |
Sen, Tumcan; Barisik, Murat Internal surface electric charge characterization of mesoporous silica Journal Article SCIENTIFIC REPORTS, 9 , 2019, ISSN: 2045-2322. @article{ISI:000455593600022, title = {Internal surface electric charge characterization of mesoporous silica}, author = {Tumcan Sen and Murat Barisik}, doi = {10.1038/s41598-018-36487-w}, issn = {2045-2322}, year = {2019}, date = {2019-01-01}, journal = {SCIENTIFIC REPORTS}, volume = {9}, abstract = {Mesoporous silica is an emerging technology to solve problems of existing and to support projected revolutionary applications ranging from targeted drug delivery to artificial kidney. However, one of the major driving mechanisms, electric charging of internal mesoporous surfaces, has not been characterized yet. In the nanoscale confinements of mesoporous structures made of pore throats and pore voids, surface charges diverge from existing theoretical calculations and show local variation due to two occurrences. First, when the size of pore throat becomes comparable with the thickness of ionic layering forming on throats' surfaces, ionic layers from opposite surfaces overlap so that ionic concentration on the surface becomes different than Boltzmann distribution predicts, and there will no longer be an equilibrium of zero electric potential at pore throat centers. Second, when this non zero potential inside throats becomes different than the potential of pore voids, ionic diffusion from void to throat creates axial ionic variation on surfaces. For such a case, we performed a pore level analysis on mesoporous internal surface charge at various porosities and ionic conditions. Pore parameters strongly affected the average internal charge which we characterized as a function of overlap ratio and porosity, first time in literature. Using this, a phenomenological model was developed as an extension of the existing theory to include nano-effects, to predict the average mesoporous internal surface charge as a function of EDL thickness, pore size and porosity.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Mesoporous silica is an emerging technology to solve problems of existing and to support projected revolutionary applications ranging from targeted drug delivery to artificial kidney. However, one of the major driving mechanisms, electric charging of internal mesoporous surfaces, has not been characterized yet. In the nanoscale confinements of mesoporous structures made of pore throats and pore voids, surface charges diverge from existing theoretical calculations and show local variation due to two occurrences. First, when the size of pore throat becomes comparable with the thickness of ionic layering forming on throats' surfaces, ionic layers from opposite surfaces overlap so that ionic concentration on the surface becomes different than Boltzmann distribution predicts, and there will no longer be an equilibrium of zero electric potential at pore throat centers. Second, when this non zero potential inside throats becomes different than the potential of pore voids, ionic diffusion from void to throat creates axial ionic variation on surfaces. For such a case, we performed a pore level analysis on mesoporous internal surface charge at various porosities and ionic conditions. Pore parameters strongly affected the average internal charge which we characterized as a function of overlap ratio and porosity, first time in literature. Using this, a phenomenological model was developed as an extension of the existing theory to include nano-effects, to predict the average mesoporous internal surface charge as a function of EDL thickness, pore size and porosity. |
2018 |
Konan, H C; Cetkin, E Snowflake shaped high-conductivity inserts for heat transfer enhancement Journal Article INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, 127 (C), pp. 473-482, 2018, ISSN: 0017-9310. @article{ISI:000445984500046, title = {Snowflake shaped high-conductivity inserts for heat transfer enhancement}, author = {H C Konan and E Cetkin}, doi = {10.1016/j.ijheatmasstransfer.2018.08.063}, issn = {0017-9310}, year = {2018}, date = {2018-12-01}, journal = {INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER}, volume = {127}, number = {C}, pages = {473-482}, abstract = {Here, we show numerically how thermal resistance in a two-dimensional domain with a point heat source can be reduced with embedded high-conductivity snowflake shaped pathways. The external shape of the domain is square, and its boundaries are heat sink. The geometry of the inserted pathways which corresponds to the minimum T-max was uncovered with the consideration of Constructal Theory, i.e. the constructal design. In the first assembly, number of mother (big) fins was uncovered as the area fraction increases. The results of the first assembly indicate that the increase in number of mother fins does not increase heat transfer after a limit number for the fins. After uncovering the mother pathway geometry corresponding to the minimum T-max the daughter (small) fins inserted at the tip of them, i.e. second assembly. In the second assembly, the fin ratios, small fin location and angle were discovered when the area fraction is fixed. In addition, in the third assembly, larger daughter fins were attached to mother fins. The results of the second and third assemblies document what should be the geometric length scales and the number of daughter fins in order to minimize T-max. The constructal design uncovered is similar to the shape of snowflakes. Therefore, the results also uncover snowflakes correspond to the designs with minimum thermal conductivity, i.e., not mimicking the nature but understanding it with physics. (C) 2018 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Here, we show numerically how thermal resistance in a two-dimensional domain with a point heat source can be reduced with embedded high-conductivity snowflake shaped pathways. The external shape of the domain is square, and its boundaries are heat sink. The geometry of the inserted pathways which corresponds to the minimum T-max was uncovered with the consideration of Constructal Theory, i.e. the constructal design. In the first assembly, number of mother (big) fins was uncovered as the area fraction increases. The results of the first assembly indicate that the increase in number of mother fins does not increase heat transfer after a limit number for the fins. After uncovering the mother pathway geometry corresponding to the minimum T-max the daughter (small) fins inserted at the tip of them, i.e. second assembly. In the second assembly, the fin ratios, small fin location and angle were discovered when the area fraction is fixed. In addition, in the third assembly, larger daughter fins were attached to mother fins. The results of the second and third assemblies document what should be the geometric length scales and the number of daughter fins in order to minimize T-max. The constructal design uncovered is similar to the shape of snowflakes. Therefore, the results also uncover snowflakes correspond to the designs with minimum thermal conductivity, i.e., not mimicking the nature but understanding it with physics. (C) 2018 Elsevier Ltd. All rights reserved. |
Sankaya, Mustafa; Tasdemirci, Alper; Guden, Mustafa Dynamic crushing behavior of a multilayer thin-walled aluminum corrugated core: The effect of velocity and imperfection Journal Article THIN-WALLED STRUCTURES, 132 , pp. 332-349, 2018, ISSN: 0263-8231. @article{ISI:000449569000026, title = {Dynamic crushing behavior of a multilayer thin-walled aluminum corrugated core: The effect of velocity and imperfection}, author = {Mustafa Sankaya and Alper Tasdemirci and Mustafa Guden}, doi = {10.1016/j.tws.2018.06.029}, issn = {0263-8231}, year = {2018}, date = {2018-11-01}, journal = {THIN-WALLED STRUCTURES}, volume = {132}, pages = {332-349}, abstract = {The crushing behavior of a multilayer 1050 H14 aluminum corrugated core was investigated both experimentally and numerically (LS-Dyna) using the perfect and imperfect models between 0.0048 and 90 m s(-1). The dynamic compression and direct impact tests were performed in a compression type and a modified Split Hopkinson Pressure Bar set-up, respectively. The investigated fully imperfect model of the corrugated core sample represented the homogenous distribution of imperfection, while the two-layer imperfect model the localized imperfection. The corrugated core experimentally deformed by a quasi-static homogenous mode between 0.0048 and 22 m s(-1), a transition mode between 22 and 60 m s(-1) and a shock mode at 90 m s(-1). Numerical results have shown that the stress-time profile and the layer crushing mode of the homogeneous and transition mode were well predicted by the two-layer imperfect model, while the stress-time profile and the layer crushing mode were well approximated by the fully imperfect model. The fully imperfect model resulted in complete sequential layer crushing at 75 and 90 m s(-1), respectively. The imperfect layers in the shock mode only affected the distal end stresses, while all models implemented resulted in similar impact end stresses. The distal end initial crushing stress increased with increasing velocity until about 22 m s(-1); thereafter, it saturated at similar to 2 MPa, which was ascribed to the micro inertial effect. Both the stress-time and velocity-time history of the rigid perfectly-plastic-locking model and the critical velocity for the shock deformation were well predicted when a dynamic plateau stress determined from the distal end stresses in the shock mode was used in the calculations.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The crushing behavior of a multilayer 1050 H14 aluminum corrugated core was investigated both experimentally and numerically (LS-Dyna) using the perfect and imperfect models between 0.0048 and 90 m s(-1). The dynamic compression and direct impact tests were performed in a compression type and a modified Split Hopkinson Pressure Bar set-up, respectively. The investigated fully imperfect model of the corrugated core sample represented the homogenous distribution of imperfection, while the two-layer imperfect model the localized imperfection. The corrugated core experimentally deformed by a quasi-static homogenous mode between 0.0048 and 22 m s(-1), a transition mode between 22 and 60 m s(-1) and a shock mode at 90 m s(-1). Numerical results have shown that the stress-time profile and the layer crushing mode of the homogeneous and transition mode were well predicted by the two-layer imperfect model, while the stress-time profile and the layer crushing mode were well approximated by the fully imperfect model. The fully imperfect model resulted in complete sequential layer crushing at 75 and 90 m s(-1), respectively. The imperfect layers in the shock mode only affected the distal end stresses, while all models implemented resulted in similar impact end stresses. The distal end initial crushing stress increased with increasing velocity until about 22 m s(-1); thereafter, it saturated at similar to 2 MPa, which was ascribed to the micro inertial effect. Both the stress-time and velocity-time history of the rigid perfectly-plastic-locking model and the critical velocity for the shock deformation were well predicted when a dynamic plateau stress determined from the distal end stresses in the shock mode was used in the calculations. |
Oztoprak, Nahit; Gunes, Mehmet Deniz; Tanoglu, Metin; Aktas, Engin; Egilmez, Oguz Ozgur; Senocak, Ciler; Kulac, Gediz Developing polymer composite-based leaf spring systems for automotive industry Journal Article SCIENCE AND ENGINEERING OF COMPOSITE MATERIALS, 25 (6), pp. 1167-1176, 2018, ISSN: 0792-1233. @article{ISI:000449094200012, title = {Developing polymer composite-based leaf spring systems for automotive industry}, author = {Nahit Oztoprak and Mehmet Deniz Gunes and Metin Tanoglu and Engin Aktas and Oguz Ozgur Egilmez and Ciler Senocak and Gediz Kulac}, doi = {10.1515/secm-2016-0335}, issn = {0792-1233}, year = {2018}, date = {2018-11-01}, journal = {SCIENCE AND ENGINEERING OF COMPOSITE MATERIALS}, volume = {25}, number = {6}, pages = {1167-1176}, abstract = {Composite-based mono-leaf spring systems were designed and manufactured to replace existing mono-leaf metal leaf spring in a light commercial vehicle. In this study, experimentally obtained mechanical properties of different fiber-reinforced polymer materials are presented first, followed by the description of the finite element analytical model created in Abaqus 6.12-1 (Dassault Systemes Simulia Corp., RI, US) using the obtained properties. The results from the finite element analysis are presented next and compared with actual size experimental tests conducted on manufactured prototypes. The results demonstrated that the reinforcement type and orientation dramatically influenced the spring rate. The prototypes showed significant weight reduction of about 80% with improved mechanical properties. The hybrid composite systems can be utilized for composite-based leaf springs with considerable mechanical performance.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Composite-based mono-leaf spring systems were designed and manufactured to replace existing mono-leaf metal leaf spring in a light commercial vehicle. In this study, experimentally obtained mechanical properties of different fiber-reinforced polymer materials are presented first, followed by the description of the finite element analytical model created in Abaqus 6.12-1 (Dassault Systemes Simulia Corp., RI, US) using the obtained properties. The results from the finite element analysis are presented next and compared with actual size experimental tests conducted on manufactured prototypes. The results demonstrated that the reinforcement type and orientation dramatically influenced the spring rate. The prototypes showed significant weight reduction of about 80% with improved mechanical properties. The hybrid composite systems can be utilized for composite-based leaf springs with considerable mechanical performance. |
Sankaya, Mustafa; Tasdemirci, Alper; Guden, Mustafa Dynamic crushing behavior of a multilayer thin-walled aluminum corrugated core: The effect of velocity and imperfection Journal Article THIN-WALLED STRUCTURES, 132 , pp. 332-349, 2018, ISSN: 0263-8231. @article{ISI:000449569000026b, title = {Dynamic crushing behavior of a multilayer thin-walled aluminum corrugated core: The effect of velocity and imperfection}, author = {Mustafa Sankaya and Alper Tasdemirci and Mustafa Guden}, doi = {10.1016/j.tws.2018.06.029}, issn = {0263-8231}, year = {2018}, date = {2018-11-01}, journal = {THIN-WALLED STRUCTURES}, volume = {132}, pages = {332-349}, abstract = {The crushing behavior of a multilayer 1050 H14 aluminum corrugated core was investigated both experimentally and numerically (LS-Dyna) using the perfect and imperfect models between 0.0048 and 90 m s(-1). The dynamic compression and direct impact tests were performed in a compression type and a modified Split Hopkinson Pressure Bar set-up, respectively. The investigated fully imperfect model of the corrugated core sample represented the homogenous distribution of imperfection, while the two-layer imperfect model the localized imperfection. The corrugated core experimentally deformed by a quasi-static homogenous mode between 0.0048 and 22 m s(-1), a transition mode between 22 and 60 m s(-1) and a shock mode at 90 m s(-1). Numerical results have shown that the stress-time profile and the layer crushing mode of the homogeneous and transition mode were well predicted by the two-layer imperfect model, while the stress-time profile and the layer crushing mode were well approximated by the fully imperfect model. The fully imperfect model resulted in complete sequential layer crushing at 75 and 90 m s(-1), respectively. The imperfect layers in the shock mode only affected the distal end stresses, while all models implemented resulted in similar impact end stresses. The distal end initial crushing stress increased with increasing velocity until about 22 m s(-1); thereafter, it saturated at similar to 2 MPa, which was ascribed to the micro inertial effect. Both the stress-time and velocity-time history of the rigid perfectly-plastic-locking model and the critical velocity for the shock deformation were well predicted when a dynamic plateau stress determined from the distal end stresses in the shock mode was used in the calculations.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The crushing behavior of a multilayer 1050 H14 aluminum corrugated core was investigated both experimentally and numerically (LS-Dyna) using the perfect and imperfect models between 0.0048 and 90 m s(-1). The dynamic compression and direct impact tests were performed in a compression type and a modified Split Hopkinson Pressure Bar set-up, respectively. The investigated fully imperfect model of the corrugated core sample represented the homogenous distribution of imperfection, while the two-layer imperfect model the localized imperfection. The corrugated core experimentally deformed by a quasi-static homogenous mode between 0.0048 and 22 m s(-1), a transition mode between 22 and 60 m s(-1) and a shock mode at 90 m s(-1). Numerical results have shown that the stress-time profile and the layer crushing mode of the homogeneous and transition mode were well predicted by the two-layer imperfect model, while the stress-time profile and the layer crushing mode were well approximated by the fully imperfect model. The fully imperfect model resulted in complete sequential layer crushing at 75 and 90 m s(-1), respectively. The imperfect layers in the shock mode only affected the distal end stresses, while all models implemented resulted in similar impact end stresses. The distal end initial crushing stress increased with increasing velocity until about 22 m s(-1); thereafter, it saturated at similar to 2 MPa, which was ascribed to the micro inertial effect. Both the stress-time and velocity-time history of the rigid perfectly-plastic-locking model and the critical velocity for the shock deformation were well predicted when a dynamic plateau stress determined from the distal end stresses in the shock mode was used in the calculations. |
Deveci, Arda H; Artem, Secil H On the estimation and optimization capabilities of the fatigue life prediction models in composite laminates Journal Article JOURNAL OF REINFORCED PLASTICS AND COMPOSITES, 37 (21), pp. 1304-1321, 2018, ISSN: 0731-6844. @article{ISI:000449554200002, title = {On the estimation and optimization capabilities of the fatigue life prediction models in composite laminates}, author = {Arda H Deveci and Secil H Artem}, doi = {10.1177/0731684418791231}, issn = {0731-6844}, year = {2018}, date = {2018-11-01}, journal = {JOURNAL OF REINFORCED PLASTICS AND COMPOSITES}, volume = {37}, number = {21}, pages = {1304-1321}, publisher = {SAGE PUBLICATIONS LTD}, address = {1 OLIVERS YARD, 55 CITY ROAD, LONDON EC1Y 1SP, ENGLAND}, abstract = {In this study, the estimation and optimization capabilities of the multiaxial fatigue life prediction models, namely, Failure Tensor Polynomial in Fatigue, Fawaz-Ellyin, Sims-Brogdon and Shokrieh-Taheri are investigated comparatively. Fatigue life predictions are obtained for multidirectional graphite/epoxy, glass/epoxy, carbon/epoxy and carbon/PEEK composite laminate data taken from the literature. The prediction study shows that the models can predict the fatigue behavior of the multidirectional laminates at different degrees of proximity. In the optimization, a hybrid algorithm combining particle swarm algorithm and generalized pattern search algorithm is used to search the optimum stacking sequence designs of the laminated composites for maximum fatigue life. The hybrid algorithm shows superior performance in terms of computational time and finding improved global optima compared to the best results presented in the literature. After the capability of the models and the reliability of the algorithm are revealed, several lay-up design problems involving different cyclic loading scenarios are solved. The results indicate that the reliability of the optimization may considerably change according to the used model even if the model may yield reasonable prediction results.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, the estimation and optimization capabilities of the multiaxial fatigue life prediction models, namely, Failure Tensor Polynomial in Fatigue, Fawaz-Ellyin, Sims-Brogdon and Shokrieh-Taheri are investigated comparatively. Fatigue life predictions are obtained for multidirectional graphite/epoxy, glass/epoxy, carbon/epoxy and carbon/PEEK composite laminate data taken from the literature. The prediction study shows that the models can predict the fatigue behavior of the multidirectional laminates at different degrees of proximity. In the optimization, a hybrid algorithm combining particle swarm algorithm and generalized pattern search algorithm is used to search the optimum stacking sequence designs of the laminated composites for maximum fatigue life. The hybrid algorithm shows superior performance in terms of computational time and finding improved global optima compared to the best results presented in the literature. After the capability of the models and the reliability of the algorithm are revealed, several lay-up design problems involving different cyclic loading scenarios are solved. The results indicate that the reliability of the optimization may considerably change according to the used model even if the model may yield reasonable prediction results. |
Tasdemirci, Alper; Akbulut, Emine Fulya; Guzel, Erkan; Tuzgel, Firat; Yucesoy, Atacan; Sahin, Selim; Guden, Mustafa Crushing behavior and energy absorption performance of a bio-inspired metallic structure: Experimental and numerical study Journal Article THIN-WALLED STRUCTURES, 131 , pp. 547-555, 2018, ISSN: 0263-8231. @article{ISI:000445311400043, title = {Crushing behavior and energy absorption performance of a bio-inspired metallic structure: Experimental and numerical study}, author = {Alper Tasdemirci and Emine Fulya Akbulut and Erkan Guzel and Firat Tuzgel and Atacan Yucesoy and Selim Sahin and Mustafa Guden}, doi = {10.1016/j.tws.2018.07.051}, issn = {0263-8231}, year = {2018}, date = {2018-10-01}, journal = {THIN-WALLED STRUCTURES}, volume = {131}, pages = {547-555}, abstract = {A thin-walled structure inspired from a biologic creature known as balanus was investigated experimentally and numerically under quasi-static and dynamic loads for load-carrying and energy absorption properties. The structure was composed of an inner conical core with a hemispherical cap and an outer shell in frusto-conical shape and formed by deep drawing. The applied deep drawing process was modelled using nonlinear finite element code LS-DYNA to determine the residual stress/strain and the non-linear thickness distribution after the forming process. It was also shown that the load carried by the balanus structure was greater than the arithmetic sum of the load carried by the inner core and by the outer shell separately. Although the mean force increase due to interaction effect at quasi-static strain rate was approximately 5%, while it increased to roughly 26% at dynamic strain rates in drop weight experiments. The numerical models also showed that the outer shell absorbed more energy than the inner core while the difference between the energy absorbing performance of the core and shell decreased with increasing deformation rate. The effect of strain rate and inertia on the increase in crush load increased with increasing impact velocity, while the strain rate effect had greater influence than the inertia on the crush load. The increased load carrying capacity of the balanus at quasi-static and dynamic strain rates was ascribed to the interaction between the core and shell and the confinement effect of the outer shell particularly at dynamic strain rate.}, keywords = {}, pubstate = {published}, tppubtype = {article} } A thin-walled structure inspired from a biologic creature known as balanus was investigated experimentally and numerically under quasi-static and dynamic loads for load-carrying and energy absorption properties. The structure was composed of an inner conical core with a hemispherical cap and an outer shell in frusto-conical shape and formed by deep drawing. The applied deep drawing process was modelled using nonlinear finite element code LS-DYNA to determine the residual stress/strain and the non-linear thickness distribution after the forming process. It was also shown that the load carried by the balanus structure was greater than the arithmetic sum of the load carried by the inner core and by the outer shell separately. Although the mean force increase due to interaction effect at quasi-static strain rate was approximately 5%, while it increased to roughly 26% at dynamic strain rates in drop weight experiments. The numerical models also showed that the outer shell absorbed more energy than the inner core while the difference between the energy absorbing performance of the core and shell decreased with increasing deformation rate. The effect of strain rate and inertia on the increase in crush load increased with increasing impact velocity, while the strain rate effect had greater influence than the inertia on the crush load. The increased load carrying capacity of the balanus at quasi-static and dynamic strain rates was ascribed to the interaction between the core and shell and the confinement effect of the outer shell particularly at dynamic strain rate. |
Tasdemirci, Alper; Akbulut, Emine Fulya; Guzel, Erkan; Tuzgel, Firat; Yucesoy, Atacan; Sahin, Selim; Guden, Mustafa Crushing behavior and energy absorption performance of a bio-inspired metallic structure: Experimental and numerical study Journal Article THIN-WALLED STRUCTURES, 131 , pp. 547-555, 2018, ISSN: 0263-8231. @article{ISI:000445311400043b, title = {Crushing behavior and energy absorption performance of a bio-inspired metallic structure: Experimental and numerical study}, author = {Alper Tasdemirci and Emine Fulya Akbulut and Erkan Guzel and Firat Tuzgel and Atacan Yucesoy and Selim Sahin and Mustafa Guden}, doi = {10.1016/j.tws.2018.07.051}, issn = {0263-8231}, year = {2018}, date = {2018-10-01}, journal = {THIN-WALLED STRUCTURES}, volume = {131}, pages = {547-555}, abstract = {A thin-walled structure inspired from a biologic creature known as balanus was investigated experimentally and numerically under quasi-static and dynamic loads for load-carrying and energy absorption properties. The structure was composed of an inner conical core with a hemispherical cap and an outer shell in frusto-conical shape and formed by deep drawing. The applied deep drawing process was modelled using nonlinear finite element code LS-DYNA to determine the residual stress/strain and the non-linear thickness distribution after the forming process. It was also shown that the load carried by the balanus structure was greater than the arithmetic sum of the load carried by the inner core and by the outer shell separately. Although the mean force increase due to interaction effect at quasi-static strain rate was approximately 5%, while it increased to roughly 26% at dynamic strain rates in drop weight experiments. The numerical models also showed that the outer shell absorbed more energy than the inner core while the difference between the energy absorbing performance of the core and shell decreased with increasing deformation rate. The effect of strain rate and inertia on the increase in crush load increased with increasing impact velocity, while the strain rate effect had greater influence than the inertia on the crush load. The increased load carrying capacity of the balanus at quasi-static and dynamic strain rates was ascribed to the interaction between the core and shell and the confinement effect of the outer shell particularly at dynamic strain rate.}, keywords = {}, pubstate = {published}, tppubtype = {article} } A thin-walled structure inspired from a biologic creature known as balanus was investigated experimentally and numerically under quasi-static and dynamic loads for load-carrying and energy absorption properties. The structure was composed of an inner conical core with a hemispherical cap and an outer shell in frusto-conical shape and formed by deep drawing. The applied deep drawing process was modelled using nonlinear finite element code LS-DYNA to determine the residual stress/strain and the non-linear thickness distribution after the forming process. It was also shown that the load carried by the balanus structure was greater than the arithmetic sum of the load carried by the inner core and by the outer shell separately. Although the mean force increase due to interaction effect at quasi-static strain rate was approximately 5%, while it increased to roughly 26% at dynamic strain rates in drop weight experiments. The numerical models also showed that the outer shell absorbed more energy than the inner core while the difference between the energy absorbing performance of the core and shell decreased with increasing deformation rate. The effect of strain rate and inertia on the increase in crush load increased with increasing impact velocity, while the strain rate effect had greater influence than the inertia on the crush load. The increased load carrying capacity of the balanus at quasi-static and dynamic strain rates was ascribed to the interaction between the core and shell and the confinement effect of the outer shell particularly at dynamic strain rate. |
Beylergil, Bertan; Tanoglu, Metin; Aktas, Engin Effect of polyamide-6,6 (PA 66) nonwoven veils on the mechanical performance of carbon fiber/epoxy composites Journal Article COMPOSITE STRUCTURES, 194 , pp. 21-35, 2018, ISSN: 0263-8223. @article{ISI:000432490400003, title = {Effect of polyamide-6,6 (PA 66) nonwoven veils on the mechanical performance of carbon fiber/epoxy composites}, author = {Bertan Beylergil and Metin Tanoglu and Engin Aktas}, doi = {10.1016/j.compstruct.2018.03.097}, issn = {0263-8223}, year = {2018}, date = {2018-06-01}, journal = {COMPOSITE STRUCTURES}, volume = {194}, pages = {21-35}, abstract = {In this study, carbon fiber/epoxy (CF/EP) composites were interleaved with polyamide-6,6 (PA 66) nonwoven veils at two different areal weight densities (17 and 50 gsm) to improve their delamination resistance against Mode-I loading. Mode-I fracture toughness (DCB), tensile, open hole tensile (OHT), flexural, compression, short beam shear (ILSS) and Charpy-impact tests were performed on the reference and PA 66 interleaved composite specimens. The DCB test results showed that the initiation and propagation Mode-I fracture toughness values of the composites were significantly improved by 84 and 171% using PA 66-17 gsm veils respectively, as compared to reference laminates. The use of denser PA 66-50 gsm veils in the interlaminar region led to higher improvement in fracture toughness values (349% for initiation and 718% for propagation) due to the higher amount of veil fibers involved in fiber bridging toughening mechanism. The incorporation of PA 66-50 gsm nonwoven veils also increased the ILSS and Charpy impact strength of the composites by 25 and 15%, respectively. On the other hand, the PA 66 veils reduced in-plane mechanical properties of CF/EP composites due to lower carbon fiber volume fraction and increased thickness.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, carbon fiber/epoxy (CF/EP) composites were interleaved with polyamide-6,6 (PA 66) nonwoven veils at two different areal weight densities (17 and 50 gsm) to improve their delamination resistance against Mode-I loading. Mode-I fracture toughness (DCB), tensile, open hole tensile (OHT), flexural, compression, short beam shear (ILSS) and Charpy-impact tests were performed on the reference and PA 66 interleaved composite specimens. The DCB test results showed that the initiation and propagation Mode-I fracture toughness values of the composites were significantly improved by 84 and 171% using PA 66-17 gsm veils respectively, as compared to reference laminates. The use of denser PA 66-50 gsm veils in the interlaminar region led to higher improvement in fracture toughness values (349% for initiation and 718% for propagation) due to the higher amount of veil fibers involved in fiber bridging toughening mechanism. The incorporation of PA 66-50 gsm nonwoven veils also increased the ILSS and Charpy impact strength of the composites by 25 and 15%, respectively. On the other hand, the PA 66 veils reduced in-plane mechanical properties of CF/EP composites due to lower carbon fiber volume fraction and increased thickness. |
Kandemir, Sinan Development of Graphene Nanoplatelet-Reinforced AZ91 Magnesium Alloy by Solidification Processing Journal Article JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE, 27 (6, SI), pp. 3014-3023, 2018, ISSN: 1059-9495, (International Conference on Emerging Trends in Nanoscience and Nanotechnology (ICETINN), Sikkim Manipal Inst Technol, Majitar, INDIA, MAR 16-18, 2017). @article{ISI:000435416000050, title = {Development of Graphene Nanoplatelet-Reinforced AZ91 Magnesium Alloy by Solidification Processing}, author = {Sinan Kandemir}, doi = {10.1007/s11665-018-3391-x}, issn = {1059-9495}, year = {2018}, date = {2018-06-01}, journal = {JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE}, volume = {27}, number = {6, SI}, pages = {3014-3023}, abstract = {It is a challenging task to effectively incorporate graphene nanoplatelets (GNPs) which have recently emerged as potential reinforcement for strengthening metals into magnesium-based matrices by conventional solidification processes due to their large surface areas and poor wettability. A solidification processing which combines mechanical stirring and ultrasonic dispersion of reinforcements in liquid matrix was employed to develop AZ91 magnesium alloy matrix composites reinforced with 0.25 and 0.5 wt.% GNPs. The microstructural studies conducted with scanning and transmission electron microscopes revealed that fairly uniform distribution and dispersion of GNPs through the matrix were achieved due to effective combination of mechanical and ultrasonic stirring. The GNPs embedded into the magnesium matrix led to significant enhancement in the hardness, tensile strength and ductility of the composites compared to those of unreinforced AZ91 alloy. The strength enhancement was predominantly attributed to the grain refinement by the GNP addition and dislocation generation strengthening due to the coefficient of thermal expansion mismatch between the matrix and reinforcement. The improved ductility was attributed to the refinement of beta eutectics by transforming from lamellar to the divorced eutectics due to the GNP additions. In addition, the strengthening efficiency of the composite with 0.25 wt.% GNP was found to be higher than those of the composite with 0.5 wt.% GNP as the agglomeration tendency of GNPs is increased with increasing GNP content. These results were compared with those of the GNP-reinforced magnesium composites reported in the literature, indicating the potential of the process introduced in this study in terms of fabricating light and high-performance metal matrix composites.}, note = {International Conference on Emerging Trends in Nanoscience and Nanotechnology (ICETINN), Sikkim Manipal Inst Technol, Majitar, INDIA, MAR 16-18, 2017}, keywords = {}, pubstate = {published}, tppubtype = {article} } It is a challenging task to effectively incorporate graphene nanoplatelets (GNPs) which have recently emerged as potential reinforcement for strengthening metals into magnesium-based matrices by conventional solidification processes due to their large surface areas and poor wettability. A solidification processing which combines mechanical stirring and ultrasonic dispersion of reinforcements in liquid matrix was employed to develop AZ91 magnesium alloy matrix composites reinforced with 0.25 and 0.5 wt.% GNPs. The microstructural studies conducted with scanning and transmission electron microscopes revealed that fairly uniform distribution and dispersion of GNPs through the matrix were achieved due to effective combination of mechanical and ultrasonic stirring. The GNPs embedded into the magnesium matrix led to significant enhancement in the hardness, tensile strength and ductility of the composites compared to those of unreinforced AZ91 alloy. The strength enhancement was predominantly attributed to the grain refinement by the GNP addition and dislocation generation strengthening due to the coefficient of thermal expansion mismatch between the matrix and reinforcement. The improved ductility was attributed to the refinement of beta eutectics by transforming from lamellar to the divorced eutectics due to the GNP additions. In addition, the strengthening efficiency of the composite with 0.25 wt.% GNP was found to be higher than those of the composite with 0.5 wt.% GNP as the agglomeration tendency of GNPs is increased with increasing GNP content. These results were compared with those of the GNP-reinforced magnesium composites reported in the literature, indicating the potential of the process introduced in this study in terms of fabricating light and high-performance metal matrix composites. |
Nguyen, Chinh Thanh; Barisik, Murat; Kim, BoHung Wetting of chemically heterogeneous striped surfaces: Molecular dynamics simulations Journal Article AIP ADVANCES, 8 (6), 2018, ISSN: 2158-3226. @article{ISI:000436855300003, title = {Wetting of chemically heterogeneous striped surfaces: Molecular dynamics simulations}, author = {Chinh Thanh Nguyen and Murat Barisik and BoHung Kim}, doi = {10.1063/1.5031133}, issn = {2158-3226}, year = {2018}, date = {2018-06-01}, journal = {AIP ADVANCES}, volume = {8}, number = {6}, abstract = {Using molecular dynamics simulations, we thoroughly investigated the wetting behaviors of a chemically heterogeneous striped substrate patterned with two different wetting materials, face-centered cubic gold and face-centered cubic silver. We analyzed the density distributions, normal stress distributions, surface tensions, and contact angles of a water droplet placed on the substrates at different heterogeneities. We found that the density and stress profile of the water droplet near the substrate-water interface were noticeably affected by altering the gold and silver contents in the substrate. Specifically, a greater portion of gold (more wetting) or smaller portion of silver (less wetting) in the substrate composition induced higher densities and higher normal stresses in the vicinity of the substrate surface. Also, it was observed that the surface tensions at liquid-vapor interface and solid-vapor interface were not largely impacted by the change of the substrate composition while the solid-liquid surface tension decreased exponentially with increasing fraction of gold. Most importantly, we found that contact angle of a nanometer-sized water droplet resting on the chemically heterogeneous striped substrate does not show linear dependence on corresponding surface fractions like that predicted by Cassie-Baxter model at the macro-scale. Consequently, we proposed a method for successfully predicting the contact angle by including the critical effects of the substrate heterogeneity on both surface tensions and line tension at the three-phase contact line of the water droplet and the chemically striped substrate. (C) 2018 Author(s).}, keywords = {}, pubstate = {published}, tppubtype = {article} } Using molecular dynamics simulations, we thoroughly investigated the wetting behaviors of a chemically heterogeneous striped substrate patterned with two different wetting materials, face-centered cubic gold and face-centered cubic silver. We analyzed the density distributions, normal stress distributions, surface tensions, and contact angles of a water droplet placed on the substrates at different heterogeneities. We found that the density and stress profile of the water droplet near the substrate-water interface were noticeably affected by altering the gold and silver contents in the substrate. Specifically, a greater portion of gold (more wetting) or smaller portion of silver (less wetting) in the substrate composition induced higher densities and higher normal stresses in the vicinity of the substrate surface. Also, it was observed that the surface tensions at liquid-vapor interface and solid-vapor interface were not largely impacted by the change of the substrate composition while the solid-liquid surface tension decreased exponentially with increasing fraction of gold. Most importantly, we found that contact angle of a nanometer-sized water droplet resting on the chemically heterogeneous striped substrate does not show linear dependence on corresponding surface fractions like that predicted by Cassie-Baxter model at the macro-scale. Consequently, we proposed a method for successfully predicting the contact angle by including the critical effects of the substrate heterogeneity on both surface tensions and line tension at the three-phase contact line of the water droplet and the chemically striped substrate. (C) 2018 Author(s). |
Sen, Tumcan; Barisik, Murat Size dependent surface charge properties of silica nano-channels: double layer overlap and inlet/outlet effects Journal Article PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 20 (24), pp. 16719-16728, 2018, ISSN: 1463-9076. @article{ISI:000436032900043, title = {Size dependent surface charge properties of silica nano-channels: double layer overlap and inlet/outlet effects}, author = {Tumcan Sen and Murat Barisik}, doi = {10.1039/c8cp01906a}, issn = {1463-9076}, year = {2018}, date = {2018-06-01}, journal = {PHYSICAL CHEMISTRY CHEMICAL PHYSICS}, volume = {20}, number = {24}, pages = {16719-16728}, abstract = {Transport inside nano-channels and tubes is highly dependent on their surface charge properties. While previous studies assume that the charge density of a surface is a material property and independent of confinement size, this study properly characterized the surface charge of a nanochannel as a function of channel height and length under various solution conditions. By calculating the local surface charge based on local ionic concentrations, the surface charge of a nano-channel was studied by considering the effects of both overlapping electrical double layers (EDLs) and inlet/outlet regions. First, the surface charge of silica decreased with the increase in EDL overlap, which is characterized by the ratio of EDL thickness to channel height. Second, the local surface charge showed variation at the inlet/outlet regions where the channel's electrokinetics was in development. We defined a general entrance length as a function of EDL thickness for the electrokinetically developing part of different cases, after which the surface charge reached its equilibrium value and remained constant. Based on such length scales, we extended the existing theory to include nano-effects. A phenomenological model was developed, which can predict the average nano-channel surface charge as a function of EDL thickness, pH, channel length and channel height.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Transport inside nano-channels and tubes is highly dependent on their surface charge properties. While previous studies assume that the charge density of a surface is a material property and independent of confinement size, this study properly characterized the surface charge of a nanochannel as a function of channel height and length under various solution conditions. By calculating the local surface charge based on local ionic concentrations, the surface charge of a nano-channel was studied by considering the effects of both overlapping electrical double layers (EDLs) and inlet/outlet regions. First, the surface charge of silica decreased with the increase in EDL overlap, which is characterized by the ratio of EDL thickness to channel height. Second, the local surface charge showed variation at the inlet/outlet regions where the channel's electrokinetics was in development. We defined a general entrance length as a function of EDL thickness for the electrokinetically developing part of different cases, after which the surface charge reached its equilibrium value and remained constant. Based on such length scales, we extended the existing theory to include nano-effects. A phenomenological model was developed, which can predict the average nano-channel surface charge as a function of EDL thickness, pH, channel length and channel height. |
Kor, Orcun; Acarer, Sercan; Ozkol, Unver Aerodynamic optimization of through-flow design model of a high by-pass transonic aero-engine fan using genetic algorithm Journal Article PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART A-JOURNAL OF POWER AND ENERGY, 232 (3), pp. 211-224, 2018, ISSN: 0957-6509. @article{ISI:000435491500001, title = {Aerodynamic optimization of through-flow design model of a high by-pass transonic aero-engine fan using genetic algorithm}, author = {Orcun Kor and Sercan Acarer and Unver Ozkol}, doi = {10.1177/0957650917730466}, issn = {0957-6509}, year = {2018}, date = {2018-05-01}, journal = {PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART A-JOURNAL OF POWER AND ENERGY}, volume = {232}, number = {3}, pages = {211-224}, abstract = {This study deals with aerodynamic optimization of a high by-pass transonic aero-engine fan module in a through-flow inverse design model at cruise condition. To the authors' best knowledge, although the literature contains through-flow optimization of the simplified cases of compressors and turbines, an optimization study targeting the more elaborate case of combined transonic fan and splitter through-flow model is not considered in the literature. Such a through-flow optimization of a transonic fan, combined with bypass and core streams separated by an aerodynamically shaped flow splitter, possesses significant challenges to any optimizer, due to highly non-linear nature of the problem and the high number of constraints, including the fulfillment of the targeted bypass ratio. It is the aim of this study to consider this previously untouched area in detail and therefore present a more sophisticated and accurate optimization environment for actual bypass fan systems. An in-house optimization code using genetic algorithm is coupled with a previously developed in-house through-flow solver which is using a streamline curvature technique and a set of in-house calibrated empirical models for incidence, deviation, loss and blockage. As the through-flow models are the backbone of turbo-machinery design, and great majority of design decisions are taken in this phase, such a study is assessed to result in significant guidelines to the gas turbine community.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This study deals with aerodynamic optimization of a high by-pass transonic aero-engine fan module in a through-flow inverse design model at cruise condition. To the authors' best knowledge, although the literature contains through-flow optimization of the simplified cases of compressors and turbines, an optimization study targeting the more elaborate case of combined transonic fan and splitter through-flow model is not considered in the literature. Such a through-flow optimization of a transonic fan, combined with bypass and core streams separated by an aerodynamically shaped flow splitter, possesses significant challenges to any optimizer, due to highly non-linear nature of the problem and the high number of constraints, including the fulfillment of the targeted bypass ratio. It is the aim of this study to consider this previously untouched area in detail and therefore present a more sophisticated and accurate optimization environment for actual bypass fan systems. An in-house optimization code using genetic algorithm is coupled with a previously developed in-house through-flow solver which is using a streamline curvature technique and a set of in-house calibrated empirical models for incidence, deviation, loss and blockage. As the through-flow models are the backbone of turbo-machinery design, and great majority of design decisions are taken in this phase, such a study is assessed to result in significant guidelines to the gas turbine community. |
Cetkin, E THE EFFECT OF COOLING ON MECHANICAL AND THERMAL STRESSES IN VASCULAR STRUCTURES Journal Article JOURNAL OF THERMAL ENGINEERING, 4 (2, 7), pp. 1855-1866, 2018, ISSN: 2148-7847. @article{ISI:000431972300010, title = {THE EFFECT OF COOLING ON MECHANICAL AND THERMAL STRESSES IN VASCULAR STRUCTURES}, author = {E Cetkin}, doi = {10.18186/journal-of-thermal-engineenng.382916}, issn = {2148-7847}, year = {2018}, date = {2018-02-01}, journal = {JOURNAL OF THERMAL ENGINEERING}, volume = {4}, number = {2, 7}, pages = {1855-1866}, abstract = {Here, we show how the vascular channel configuration and its shape affect the mechanical strength which is simultaneously subjected to heating and mechanical load. The material properties were defined as functions of temperature. The effect of channel cross-section on the coolant mass flow rate, peak temperature and peak stresses are documented. The results show that the resistances to flow of stresses and fluid is minimum with the circular channels while the resistance to the heat flow is the smallest with semi-circular channels. In addition, morphing the vascular design provides almost the smallest resistance to the heat flow with circular channels (0.3% difference in the peak temperature). This shows that even the convective resistances are the smallest with circular-cross section, overall thermal resistance is smaller in semi-circular design for the fixed fluid volume. The peak stress is smaller with hybrid design than the parallel designs for the entire pressure drop range. In addition, the effects of mechanical load, heating rate and reference temperature on the stress distribution are also documented. Furthermore, the thermal and mechanical stresses are also documented separately, and then compared with the coupled solution cases. The chief result of this paper is that for a coupled system minimizing only one of the resistance terms is not sufficient, all the resistances considered simultaneously in order to uncover the best performing design. In coupled solutions, we documented the simulation results with temperature dependent material properties and the resistances to the heat and fluid flow is affected by the mechanical deformations. In addition, the results show that the designs should be free to vary, the unexpected designs can be the best performing designs for the given parameters and constraints. Therefore, the design parameters based on the experience does not always yield the best performing designs as the objectives and constraints vary.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Here, we show how the vascular channel configuration and its shape affect the mechanical strength which is simultaneously subjected to heating and mechanical load. The material properties were defined as functions of temperature. The effect of channel cross-section on the coolant mass flow rate, peak temperature and peak stresses are documented. The results show that the resistances to flow of stresses and fluid is minimum with the circular channels while the resistance to the heat flow is the smallest with semi-circular channels. In addition, morphing the vascular design provides almost the smallest resistance to the heat flow with circular channels (0.3% difference in the peak temperature). This shows that even the convective resistances are the smallest with circular-cross section, overall thermal resistance is smaller in semi-circular design for the fixed fluid volume. The peak stress is smaller with hybrid design than the parallel designs for the entire pressure drop range. In addition, the effects of mechanical load, heating rate and reference temperature on the stress distribution are also documented. Furthermore, the thermal and mechanical stresses are also documented separately, and then compared with the coupled solution cases. The chief result of this paper is that for a coupled system minimizing only one of the resistance terms is not sufficient, all the resistances considered simultaneously in order to uncover the best performing design. In coupled solutions, we documented the simulation results with temperature dependent material properties and the resistances to the heat and fluid flow is affected by the mechanical deformations. In addition, the results show that the designs should be free to vary, the unexpected designs can be the best performing designs for the given parameters and constraints. Therefore, the design parameters based on the experience does not always yield the best performing designs as the objectives and constraints vary. |