Yield behavior of extremely porous solid foams under multiaxial states of stress is of significant importance because, unlike pressure... Show moreYield behavior of extremely porous solid foams under multiaxial states of stress is of significant importance because, unlike pressure independent yield response of the majority of engineering materials, solid foams exhibit quadratic as well as linear dependence on hydrostatic stress component in their yield behavior. Therefore, there exists a critical need to analyze and use specimen geometries that allow biaxial and triaxial experiments through which yield surface can be probed under varying amounts of mean stress. This study investigates, through FE analysis, the feasibility of Maltese-Cross (MC) specimen geometry as a potential candidate for using in biaxial and triaxial experiments. Although solid foams have a pressure dependent yield behavior, the current study adopted a linear elastic-hardening J2 flow rule to keep the analysis reasonably simple and focus on the fundamental effect of specimen geometry on strain field and, more importantly, the extraction of yield point from multiaxial force-displacement data. One must recognize that in multiaxial experiments, particularly in triaxial loading, forces and displacements experienced by the nominal gage section cannot be directly measured for practical reasons. Instead, far field forces and displacements have to be used to calculate average measures of stress and strain within the gage section. This study shows through FE analyses that MC specimens can be used to determine the onset of macroscopic yielding under varying amount of mean stress component, provided that certain stress/strain paths, which cause premature deformation localization out of the gage section, are avoided. M.S. in Mechanical and Aerospace Engineering, December 2011 Show less
