@article{salah_hatem_khalil_bedair_2019, title={Embedded void approach effects on intrinsic stresses in laterally grown GaN-on-Si substrate}, volume={242}, ISSN={["1873-4944"]}, DOI={10.1016/j.mseb.2019.02.016}, abstractNote={Laterally grown GaN-on-Si substrate is promising for solid state lighting, high power density devices, and wireless communication applications among others. Despite their superior optical and electrical properties, they suffer from high dislocation-densities due to high lattice and thermal expansion coefficients mismatch between both crystalline materials. Different approaches have been suggested to reduce defects in GaN-on-Si technology. One of these approaches is Embedded Void Approach (EVA), which has been employed to control defects mobility in GaN thin-film on Si substrate by inserting micro-voids near the interface. In the current study, a three-dimensional multiple-slip crystal plasticity model and specialized finite-element formulations were used to address GaN growth on Si substrate. Furthermore, EVA has been studied to understand the effectiveness of the experimentally developed approach in reducing defects mobility. Additionally, a parametric study has been conducted to examine the effect of voids size and aspect ratio on the intrinsic stresses. It was found that EVA results in considerable reduction in the stresses in the mid surface of the structure near the voids and consequently the dislocation density at the top surface, enhancing the performance of the proposed system.}, journal={MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS}, author={Salah, Salma I. and Hatem, Tarek M. and Khalil, Essam E. and Bedair, Salah M.}, year={2019}, month={Mar}, pages={104–110} }
 @article{khafagy_hatem_bedair_2019, title={Modelling of III-Nitride Epitaxial Layers Grown on Silicon Substrates with Low Dislocation-Densities}, volume={4}, ISSN={["2059-8521"]}, DOI={10.1557/adv.2019.49}, abstractNote={Large lattice and thermal expansion coefficients mismatches between III-Nitride ( III N ) epitaxial layers and their substrates inevitably generate defects on the interfaces. Such defects as dislocations affect the reliability, life time, and performance of photovoltaic (PV) devices. High dislocation densities in epitaxial layer generate higher v-shaped pits densities on the layer top surface that also directly affect the device performance. Therefore, using an approach such as the embedded void approach (EVA) for defects reduction in the epitaxial layers is essential. EVA relies on the generation of high densities of embedded microvoids (~10^8/cm^2), with ellipsoidal shapes. These tremendous number of microvoids are etched near the interface between the III N thin-film and its substrate where the dislocation densities present with higher values. This article used a 3-D constitutive model that accounts the crystal plasticity formulas and specialized finite element (FE) formulas to model the EVA in multi-junction PV and therefore to study the effect of the embedded void approach on the defects reduction. Mesh convergence and 2-D analytical solution validation is conducted with accounting thermal stresses. Several aspect and volume ratios of the embedded microvoids are used to optimize the microvoid dimensions.}, number={13}, journal={MRS ADVANCES}, author={Khafagy, Khaled H. and Hatem, Tarek M. and Bedair, Salah M.}, year={2019}, pages={755–760} }
 @article{khafagy_hatem_bedair_2018, title={Three-Dimensional Crystal-Plasticity Based Model for Intrinsic Stresses in Multi-junction Photovoltaic}, ISBN={["978-3-319-72361-7"]}, ISSN={["2367-1181"]}, DOI={10.1007/978-3-319-72362-4_41}, abstractNote={Our understanding for intrinsic stresses and defects evolution in photovoltaic devices has became an essential part of new developments. In particular, Multi-Junction Photovoltaic (MJ-PV) modules depend on multi-layer structures that may suffer high dislocation-densities as a result of high lattice and thermal expansion coefficient mismatch. These defects limit the performance, reliability, and lifetime of PV devices. In the current study, a three-dimensional multiple-slip crystal-plasticity model and specialized finite-element formulations are used to investigate InGaN growth on Si substrates. The formulation is based on accounting for thermal and intrinsic stresses as a result of different processing conditions and microstructures. Furthermore, the formulation was used to investigate a recently developed technique, Embedded Void Approach (EVA), which can be used to address both the high density of defects and the cracking/bowing of InGaN growth on Si. The current work lays the groundwork for more extensive use of silicon in MJ-PV devices.}, journal={ENERGY TECHNOLOGY 2018: CARBON DIOXIDE MANAGEMENT AND OTHER TECHNOLOGIES}, author={Khafagy, Khaled H. and Hatem, Tarek M. and Bedair, Salah M.}, year={2018}, pages={453–461} }
 @article{hatem_zikry_2011, title={A model for determining initial dislocation-densities associated with martensitic transformations}, volume={27}, ISSN={["0267-0836"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-80054886787&partnerID=MN8TOARS}, DOI={10.1179/1743284711y.0000000079}, abstractNote={ A three-dimensional multiple-slip dislocation-density-based crystal plasticity formulation, and specialised finite element formulations were used to determine the initial dislocation-densities associated with martensitic transformations in steel alloys. The analysis is based on modelling the shear part from the phenomenological theory of martensitic transformation to obtain both the transformation mobile and immobile dislocation-densities. The model was validated with experiments related to the transformation of lath martensite in high-strength low-alloying steels. }, number={10}, journal={MATERIALS SCIENCE AND TECHNOLOGY}, author={Hatem, T. M. and Zikry, M. A.}, year={2011}, month={Oct}, pages={1570–1573} }
 @article{hatem_zikry_2010, title={Deformation and failure of single-packets in martensitic steels}, volume={17}, number={2}, journal={Computers Materials & Continua}, author={Hatem, T. M. and Zikry, M. A.}, year={2010}, pages={127–147} }
 @article{hatem_zikry_2010, title={Dynamic shear-strain localization and inclusion effects in lath martensitic steels subjected to high pressure loads}, volume={58}, ISSN={["1873-4782"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-80052492778&partnerID=MN8TOARS}, DOI={10.1016/j.jmps.2010.04.009}, abstractNote={A three-dimensional multiple-slip dislocation-density based crystalline formulation, specialized finite-element formulations, and specialized Voronoi tessellations adapted to martensitic orientations, were used to investigate shear–strain localization, and dislocation-density evolution in martensitic microstructures under dynamic compressive loading conditions. The formulation is based on accounting for variant morphologies and orientations, secondary-phase structures, and initial dislocations-densities that are uniquely inherent to martensitic microstructures. The effects of strain rate and inclusions on the evolution of shear–strain localization were investigated. The analysis indicates that variant morphology and orientations have a direct consequence on dislocation-density accumulation and inelastic localization in martensitic microstructures, and that lath directions, orientations, and arrangements are critical characteristics of high-strength martensitic dynamic behavior. It is shown that tensile hydrostatic pressure due to the unloading of the plastic waves at the free boundary and extensive shear–strain accumulation occurs at certain triple junctions. Furthermore, plastic shear-slip accumulation between inclusions and the surrounding martensitic matrix results in shear–strain localization and increases in the tensile hydrostatic pressure at critical locations, such as trip junctions.}, number={8}, journal={JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS}, author={Hatem, T. M. and Zikry, M. A.}, year={2010}, month={Aug}, pages={1057–1072} }
 @article{hatem_zikry_2009, title={Dislocation density crystalline plasticity modeling of lath martensitic microstructures in steel alloys}, volume={89}, ISSN={["1478-6443"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-70449117497&partnerID=MN8TOARS}, DOI={10.1080/14786430903185999}, abstractNote={A three-dimensional multiple-slip dislocation density-based crystalline formulation, specialized finite-element formulations and Voronoi tessellations adapted to martensitic orientations were used to investigate large strain inelastic deformation modes and dislocation density evolution in martensitic microstructures. The formulation is based on accounting for variant morphologies and orientations, retained austenite and initial dislocation densities that are uniquely inherent to martensitic microstructures. The effects of parent austenite orientation and retained austenite were also investigated for heterogeneous fcc/bcc crystalline structures. Furthermore, the formulation was used to investigate microstructures mapped directly from SEM/EBSD images of martensitic steel alloys. The analysis indicates that variant morphology and orientations have a direct effect on dislocation density accumulation and inelastic localization in martensitic microstructures, and that lath directions, orientations and arrangements are critical characteristics of high strength martensitic deformation and behavior.}, number={33}, journal={PHILOSOPHICAL MAGAZINE}, author={Hatem, T. M. and Zikry, M. A.}, year={2009}, pages={3087–3109} }
 @article{hatem_zikry_2009, title={Modeling of Lath Martensitic Microstructures and Failure Evolution in Steel Alloys}, volume={131}, ISSN={["0094-4289"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-77955251717&partnerID=MN8TOARS}, DOI={10.1115/1.3183780}, abstractNote={A multiple-slip dislocation-density-based crystalline formulation, specialized finite-element formulations, and Voronoi tessellations adapted to martensitic orientations were used to investigate dislocation-density activities and crack tip blunting in high strength martensitic steels. The formulation is based on accounting for variant morphologies and orientations, retained austenite, and initial dislocations densities that are uniquely inherent to martensitic microstructures. The effects of variant distributions and arrangements are investigated for different crack and void interaction distributions and arrangements. The analysis indicates that for certain orientations related to specific variant block arrangements, which correspond to random low angle orientations, cracks can be blunted by dislocation-density activities along transgranular planes. For other variant block arrangements, which correspond to random high angle orientations, sharp crack growth can occur due to dislocation activities along intergranular planes.}, number={4}, journal={JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY-TRANSACTIONS OF THE ASME}, author={Hatem, T. M. and Zikry, M. A.}, year={2009}, month={Oct} }
 @article{hatem_zikry_2009, title={Shear pipe effects and dynamic shear-strain localization in martensitic steels}, volume={57}, ISSN={["1873-2453"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-67849128240&partnerID=MN8TOARS}, DOI={10.1016/j.actamat.2009.06.028}, abstractNote={A three-dimensional, multiple-slip, dislocation-density-based crystalline formulation, specialized finite-element formulations, and Voronoi tessellations adapted to martensitic orientations were used to investigate dislocation-density activities and shear-strain localization in high-strength martensitic steels under quasi-static and dynamic loading conditions. The formulation is based on accounting for variant morphologies and orientations, retained austenite, and initial dislocations densities that are uniquely inherent to martensitic microstructures. The effects of variant distributions and arrangements, loading directions, and microcracks on the evolution of shear-strain localization are investigated. The analysis indicates that shear-strain localization occurs due to slip-system compatibilities relative to the loading direction and the long direction of laths, which result in shear-strain accumulation. At specific triple junctions, rotation misalignments due to lattice and slip incompatibilities occur, and these incompatibilities are further exacerbated by the presence of defects, such as microcracks.}, number={15}, journal={ACTA MATERIALIA}, author={Hatem, T. M. and Zikry, M. A.}, year={2009}, month={Sep}, pages={4558–4567} }