@article{xu_rezvanian_zikry_2013, title={Electro-mechanical modeling of the piezoresistive response of carbon nanotube polymer composites}, volume={22}, ISSN={["1361-665X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84876921770&partnerID=MN8TOARS}, DOI={10.1088/0964-1726/22/5/055032}, abstractNote={A coupled electro-mechanical FE approach was developed to investigate the piezoresistive response of carbon nanotube polymer composites. Gauge factors (GFs) and resistance variations of CNT–polymer composite systems were obtained by coupling Maxwell equations to mechanical loads and deformations through initial piezoresistive coefficients of the CNTs, the epoxy, and the tunnel regions, for different arrangements, percolated paths, tunnel distances, and tensile, compressive, and bending loading conditions. A scaling relation between GFs and applied strains was obtained to understand how variations in loading conditions and CNT arrangements affect sensing capabilities and piezoresistive carbon nanotube polymer composite behavior. These variations in GFs were then used to understand how the coupled strains, stresses and current densities vary for aligned and percolated paths for the different loading conditions, CNT arrangements, and tunnel distances. For the percolated path under tensile loading conditions, elastic strains as high as 16% and electrical conductivities that were four orders in magnitude greater than the initial matrix conductivity were obtained. Results for the three loading conditions clearly demonstrate that electrical conductivity and sensing capabilities can be optimized as a function of percolation paths, tunneling distance, orientation, and loading conditions for piezoresistive applications with large elastic strains and conductivities.}, number={5}, journal={SMART MATERIALS AND STRUCTURES}, author={Xu, S. and Rezvanian, O. and Zikry, M. A.}, year={2013}, month={May} }
 @article{xu_rezvanian_zikry_2013, title={Electrothermomechanical Modeling and Analyses of Carbon Nanotube Polymer Composites}, volume={135}, ISSN={["1528-8889"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84888342251&partnerID=MN8TOARS}, DOI={10.1115/1.4023912}, abstractNote={A new finite element (FE) modeling method has been developed to investigate how the electrical-mechanical-thermal behavior of carbon nanotube (CNT)–reinforced polymer composites is affected by electron tunneling distances, volume fraction, and physically realistic tube aspect ratios. A representative CNT polymer composite conductive path was chosen from a percolation analysis to establish the three-dimensional (3D) computational finite-element (FE) approach. A specialized Maxwell FE formulation with a Fermi-based tunneling resistance was then used to obtain current density evolution for different CNT/polymer dispersions and tunneling distances. Analyses based on thermoelectrical and electrothermomechanical FE approaches were used to understand how CNT-epoxy composites behave under electrothermomechanical loading conditions.}, number={2}, journal={JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY-TRANSACTIONS OF THE ASME}, author={Xu, S. and Rezvanian, O. and Zikry, M. A.}, year={2013}, month={Apr} }
 @article{xu_rezvanian_peters_zikry_2013, title={The viability and limitations of percolation theory in modeling the electrical behavior of carbon nanotube-polymer composites}, volume={24}, ISSN={["1361-6528"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84875677113&partnerID=MN8TOARS}, DOI={10.1088/0957-4484/24/15/155706}, abstractNote={A new modeling method has been proposed to investigate how the electrical conductivity of carbon nanotube (CNT) reinforced polymer composites are affected by tunneling distance, volume fraction, and tube aspect ratios. A search algorithm and an electrical junction identification method was developed with a percolation approach to determine conductive paths for three-dimensional (3D) carbon nanotube arrangements and to account for electron tunneling effects. The predicted results are used to understand the limitations of percolation theory and experimental measurements and observations, and why percolation theory breaks down for specific CNT arrangements.}, number={15}, journal={NANOTECHNOLOGY}, author={Xu, S. and Rezvanian, O. and Peters, K. and Zikry, M. A.}, year={2013}, month={Apr} }
 @article{xu_bourham_rabiei_2010, title={A novel ultra-light structure for radiation shielding}, volume={31}, ISSN={["1873-4197"]}, DOI={10.1016/j.matdes.2009.11.011}, abstractNote={A new ultra-light structure based on the application of open-cell metal foams has been designed and investigated to determine its ability for attenuation of γ-rays and thermal neutrons. Open-cell metal foam, a unique class of material, has been employed in the structure and is studied in this work where radiation attenuation abilities of foams and foams filled with water and borated water have been compared with bulk Aluminum. The γ-ray attenuation measurements were performed using γ-ray at 0.662, 1.173 and 1.332 MeV photon energies and thermal neutron attenuation measurements were conducted using a polyenergetic thermal neutron beam. The results show that the metallic foam by itself attenuates less γ-ray as compared to bulk material, while the mass attenuation coefficients of foams filled with water is higher than that of bulk metals. The thermal neutron experiment, on the other hand, has shown a dramatic attenuation improvement in foams filled with water and particularly with borated water as compared to bulk metal and foam.}, number={4}, journal={MATERIALS & DESIGN}, author={Xu, Siqi and Bourham, Mohamed and Rabiei, Afsaneh}, year={2010}, month={Apr}, pages={2140–2146} }