This proposed project will focus on the numerical and theoretical study of plastic deformation and fracture behavior of nanotwinned materials. That is, the project will develop reliable methods for the generation of the simulation model of nanotwinned materials, study the plastic deformation and fracture behaviors of these materials, try to find out the underlying physical and mechanical mechanisms and construct theoretical models on the yield and fracture strengths. The outcomes of the project will provide basic information for tailoring the material microstructures and for the fabrication and application of new nanotwinned materials with high strength and good ductility.