A constitutive model for fiber-reinforced polymer plies accounting for plasticity and brittle damage including softening – Implementation for implicit FEM

A constitutive ply model is developed to allow for the simulation of laminated structures made of fiber-reinforced polymers. The model accounts for stiffness degradation accompanied by strain hardening (i.e. distributed brittle damage), unrecoverable strain accumulation (i.e. multi-surface plasticity), and stiffness degradation accompanied by strain softening (i.e. localized brittle damage). Owing to the characteristics of such ply materials the model handles these effects and their evolutions in an anisotropic manner.The constitutive model is briefly reviewed with respect to distributed damage and plasticity, and the extension to incorporate softening is given in detail. The implementation as material routine for an implicit FEM package and the computation of the material Jacobian matrix is presented. Additional measures are adopted for improving/achieving convergence, as being required for the treatment of material softening within numerical solution schemes.The application of the constitutive model for structural analysis is demonstrated by presenting simulation results from Open Hole Tension configurations. The predictions include the overall non-linear response until structural failure and the local distribution and evolution of the mechanisms incorporated in the constitutive ply model. Discussion of these results and comparison to literature show that crucial intra-ply mechanisms are captured well by the proposed constitutive model.