This three-year award provides support for US-France cooperative research aimed at the development of methods to predict the constitutive behavior of nonlinear composite materials. The collaboration involves Pedro Ponte Castaneda and John Bassani of the University of Pennsylvania and the research group of Pierre Suquet at the Mechanics and Acoustics Laboratory of the French National Center for Scientific Research in Marseille, France. The investigators will focus their research on self-consistent models of nonlinear composites and applications to polycrystals. They will also investigate material behavior at the single-crystal level, including elasto-viscoplasticity, multiple-slip hardening, and size-scale efforts. The US researchers bring to this collaboration expertise in theoretical work on nonlinear homogenization and crystal plasticity. This is complemented by experimental facilities in Marseille and French expertise in numerical methods. The project will advance understanding of nonlinear microscopic mechanisms involved in deformation and fracture of materials, such as plastics and metals.