@article{bahei-el-din_rajendran_zikry_2004, title={A micromechanical model for damage progression in woven composite systems}, volume={41}, ISSN={["1879-2146"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-1842484113&partnerID=MN8TOARS}, DOI={10.1016/j.ijsolstr.2003.12.006}, abstractNote={Damage progression in woven composites is modeled for multiscale analysis of structures. The proposed model is a representative volume element (RVE) of the woven material, derived from micrographs. In principle, it is applicable to any woven system with periodic fiber placement; however, the focus in this paper is on 3D weaves. The domain and boundary conditions of the RVE are selected such that the model can serve as a repository for predicting the overall behavior under general, multiaxial stress states. The overall response due to applied stress, or strain, and local damage is evaluated by a transformation field analysis (TFA) scheme. Damage mechanisms observed under quasi-static and impact loads are implemented. This includes matrix cracking, frictional sliding and debonding of the fiber bundles, and fiber rupture. The local stress components affected by the active damage modes are removed or reduced by superimposing a transformation stress field on the elastic field caused by the overall loads in the undamaged material. This results in a local stress field that is within the affordable local strength magnitudes, and an overall transformation stress, which modifies the elastic estimate. Implementation of the material model in quasi-static and dynamic finite element procedures is discussed, and examples, which illustrate the model capabilities, are presented.}, number={9-10}, journal={INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES}, author={Bahei-El-Din, YA and Rajendran, AM and Zikry, MA}, year={2004}, month={May}, pages={2307–2330} }
 @article{bahei-el-din_botrous_2003, title={Analysis of progressive fiber debonding in elastic laminates}, volume={40}, ISSN={["1879-2146"]}, DOI={10.1016/S0020-7683(03)00353-6}, abstractNote={The evolution of fiber debonding, and sliding, in fibrous laminates is modeled by a coupled micro/macro-mechanical analysis scheme. The laminates under consideration have a symmetric layup, and are subjected to mechanical loads. The individual plies are elastic, have a unidirectional reinforcement, and can suffer local damage at the fiber/matrix interface when the resolved normal and shear stresses exceed their ultimate magnitudes. The local fields in the plies are assumed to be periodic, and are approximated by the finite element method for overall loads and local resolved stresses that are in excess of the interface strength. Local effects in the individual plies are scaled up to the laminate analysis through stress transformation factors, which are a function of the elastic properties of the plies and their stacking configuration. The proposed analysis was implemented for a periodic array model of the laminas, and for in-plane loading of the laminate. The model predictions for a unidirectional steel/epoxy system subjected to transverse loading compare remarkably well with experimental measurements. This result, and several other examples given for axial and off-axis loading of SiC/CAS laminates, illustrate the model capabilities in predicting the overall strains in the presence of simultaneous, progressive debonding in the individual plies.}, number={25}, journal={INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES}, author={Bahei-El-Din, YA and Botrous, AG}, year={2003}, month={Dec}, pages={7035–7053} }
 @article{bahei-el-din_zikry_2003, title={Impact-induced deformation fields in 2D and 3D woven composites}, volume={63}, ISSN={["0266-3538"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0037403705&partnerID=MN8TOARS}, DOI={10.1016/S0266-3538(03)00021-6}, abstractNote={The deformation fields and kinematics of woven composite material systems, due to impact loads, were analyzed and characterized for various structural and load parameters. Target plates comprising of woven composites with 3D and 2D preforms were considered. Kinetic energies in the range of 18–39,000 J, due to projectile velocities in the range of 2–1000 m/s, were investigated. The impact problem model accounts for geometrical details of the flat target plates and the hemispherical projectile. Contact solutions at dissimilar surfaces were modeled with gap elements, and the solution of the nonlinear dynamic problem was obtained by the finite element method. In the present study, we investigated wave propagation effects, and how their spatial and temporal distribution is related to the evolution of multi-dimensional elastic fields and potential damage modes. Unit cells representative of the 2D and 3D woven composites were used to obtain estimates of the overall elastic moduli. It was found that the compression wave induced by impact reflected several times between the free surfaces of the target plate before fiber failure initiated, and that this was one of the major mechanisms leading to penetration. At low velocity impact, the deformations were similar to quasi-static bending deformation modes, and failure is predicted to be due to fiber breakage at the backside of the target plate. At higher impact velocities, wave propagation effects are more significant and lead to penetration at the impact face. For all material systems, localized shear damage in 3D woven systems and extensive shear delamination in 2D woven systems preceded complete penetration.}, number={7}, journal={COMPOSITES SCIENCE AND TECHNOLOGY}, author={Bahei-El-Din, YA and Zikry, MA}, year={2003}, month={May}, pages={923–942} }
 @article{bahei-el-din_zikry_rajendran_2003, title={Impact-induced deformation fields in 3D cellular woven composites}, volume={34}, ISSN={["1359-835X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0041631068&partnerID=MN8TOARS}, DOI={10.1016/S1359-835X(03)00143-X}, abstractNote={Abstract The deformation fields and kinematics of nonporous and porous three-dimensional (3D) woven composite material systems were analyzed and characterized under an incident impact energy of 560 J caused by a 78 g projectile at a velocity of 120 m/s. The analysis quantifies experimental observations of the effects of porosity on the impact resistance and behavior of 3D woven composites. The dynamic nonlinear impact solution was obtained by the finite element method, in which contact between the projectile and the target plate was modeled with gap elements. In the present study, we investigated the spatial and temporal evolution of multi-dimensional elastic fields and potential damage modes in the target plates. A unit cell, representative of the 3D woven composite, was used to obtain estimates of the overall elastic moduli. These estimates were then used with two material models to represent the porous system in the finite element analysis of the target plate. One material model, which had explicit geometrical distributions of 3D voids, was used in the impact region, and the other material model, which was based on a representation of smeared voids, was used in regions removed from the impact zone. The analysis indicates that wave propagation effects at the incident energy applied here are significant, and these effects can lead to projectile penetration at the impact face. Localized shear damage in the 3D woven system precedes penetration in both the nonporous and the porous systems. Experimental observations, which indicate that a porous system can dissipate more energy than the nonporous system before penetration, are found to be mainly attributed to the confinement of local damage fields, which emanate from the boundaries of the embedded voids.}, number={8}, journal={COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING}, author={Bahei-El-Din, YA and Zikry, MA and Rajendran, AM}, year={2003}, pages={765–778} }