***<br/>CMS-9816976<br/>Chang<br/>Failure surfaces in macroscopic stress space of honeycombs, fiber reinforced composites and foams under triaxial loading are studiesd. Both macroscopic and microscopic failure surfaces are addressed within the scope of progressive failure of periodic solids. Correlation with experimental work will be established through collaborations with Prof. Kyriakides of University of Texas-Austin.***