Development of a new nonlinear numerical material model for woven composite materials accounting for permanent deformation and damage

Due to their draping, stiffness, improved ductility and damage tolerance properties woven composites are being increasingly used for the construction of crash-relevant structural parts. Textile composites may depict a nonlinear behavior along several directions. Moreover, considerably-thick composite structures are likely to be used in order to increase energy absorption and to comply with the crash validation criteria. Therefore, a nonlinear numerical material model for textile composite materials has been developed for shells and thick shells. The model has been implemented as a user-defined subroutine (UMAT) in the LS-DYNA finite element code featuring with explicit time integration. The nonlinear behavior until failure is modeled in each in-plane material direction by a user-defined load curve or the Ramberg-Osgood equation. A plasticity formulation coupled with the nonlinearity accounts for permanent deformations. The failure is predicted using either a maximal stress criterion or the quadratic Tsai-Wu criterion. In order to model damage propagation, different post-failure damage definitions have been developed and implemented for each main in-plane material direction. A smeared formulation ensures the mesh independence in the presence of strain localization. The model has been assessed using characterization tensile and compressive tests on plain-weave and twill-weave carbon fiber composites.