A new integrated modeling method for predicting low-velocity impact behavior and residual tensile failure of Z-pinned T-joints

Composite T-joints are highly susceptible to low-velocity impact, which can significantly affect their residual performance due to the primary working condition of bearing out-of-plane tensile loads. Currently, most methods that employ multiple models or analytical steps to sequentially assess the mechanical properties of composites generally exhibit certain limitations, leaving room for improvement. This study has developed a finite element (FE) model to simulate the low-velocity impact and post-impact tensile behaviors of carbon fiber reinforced polymers (CFRP) T-joints using an integrated analysis method. The model is based on stress failure criteria and continuous stiffness degradation theory and incorporates corrections to the damage variables. Both the low-velocity impact and quasi-static tensile portions of the model are implemented using an explicit solver with the VUMAT subroutine for calculations in Abaqus. The element damage states are transferred between the two models via a Python script, mitigating the inefficiencies and uncontrollable errors associated with the traditional method of transferring element information between multiple models or analytical steps. Finally, the numerical results of mechanical response and damage states are compared with experimental findings from various perspectives, and the bridging mechanism of Z-pins is thoroughly investigated. The results show that the model exhibits a maximum error of 10.41 % in the main key parameters during low-velocity impact and a maximum error of 10.30 % in the ultimate load during post-impact tension. The model's delamination damage state and final tensile failure mode closely align with the experimental results. Furthermore, a comprehensive analysis of the FE model indicates that the pull-out force of the Z-pin is unrelated to its implantation position or pull-out rate, and the reinforcing effect of the Z-pin becomes significantly apparent only after the CFRP T-joint reaches a certain degree of initial damage.