%T Theoretical and numerical investigation on internal instability phenomena in composite materials %P 5928-5933 %O 11th International Conference on Fracture, Turin, Italy, March 20-25, 2005 %B Proceedings of the 11th International Conference on Fracture 2005 (ICF11) %D 2005 %A Alberto Carpinteri %A Marco Paggi %A Giorgio Zavarise %X Instability phenomena occurring in the microstructure of composite materials are investigated. To this aim, a complete description of the mechanical behavior of bi-material interfaces in composite materials requires the definition of both a cohesive law involving damage for the debonding stage, and a contact model during the closure of the interface. Both formulations are herein presented and implemented in the FE code FEAP. Numerical examples showing the transition from a snap-back instability to a stable mechanical response are presented. %L eprints1927 %I Curran Associates