Computational analysis of fracture and fatigue in overmolded thermoplastic composites: Time-homogenized viscoplasticity, cohesive fracture and processing effects

A numerical framework is presented for simulating fracture and fatigue in a T-section, cut from an overmolded thermoplastic composite panel made of CF/PEEK. The framework combines a cohesive zone model for the overmolded interface with an anisotropic viscoplasticity model for the laminate and accounts for processing effects. For high-cycle fatigue analyses, a two-scale time-homogenized version of the viscoplasticity model is derived. The numerical framework is applied to the analysis of a rib pull-off test and is used to gain insights into the influence on the short- and long-term response of two typical processing effects: out-of-plane deformations of the laminate that occur during thermoforming and non-uniform healing profiles resulting from spatially varying thermal histories. Furthermore, the effects of various modeling assumptions are studied, such as modeling the local fiber orientations of each ply in the laminate with a mesoscopic ply-by-ply approach, the effect of viscoplastic deformations in the laminate, the influence of non-uniform local stress ratios, and the effect of the boundary conditions. The analyses demonstrate that the framework is capable of efficiently simulating a large number of cycles. The simulation results show that the local wrinkles in the laminate as a result of thermoforming have a significant effect on the mechanical response, especially under cyclic loading. Moreover, accounting for viscoplastic deformations appears more important when high degrees of bonding of the overmolded interface are achieved. Finally, it is shown that changes to the boundary conditions have a significant effect on the short and long-term response of the T-section, challenging the validity of the test for characterizing fracture and fatigue properties of the overmolded interface.