An Efficient Material Model to Simulate the Effects of z-pin Reinforcement

Interlaminar delamination has been identified as a dominant damage mode for laminated composites subjected to impact. Even small impact energies can cause a major drop in residual strength. In order to overcome delamination, through the thickness reinforcement (TTR), such as z-pinning and stitching, have been used frequently and have shown substantial improvements in delamination resistance and residual strength of laminated composites. Modeling the impact experiments using finite element simulations would be a useful tool to predict performance of z-pinned composites. Considering the small size of individual z-pins (less than 1 mm) relative to the size of the laminate, modeling detailed geometric features of z-pins is computationally expensive. In this work, a two-stage strategy for efficient simulation of pin reinforcement is proposed. In the first stage, a small scale, detailed single pin geometric model is analyzed to capture different failure modes of the pin. Results from this detailed simulation are then used to develop an equivalent material model for z-pin reinforcement using discrete cohesive surfaces. This eliminates the need for detailed computational models including the pin geometry. This method is implemented to estimate the load-displacement response and delamination area of a laminates subjected to impact. The comparison with experimentally observed results shows good correlation.