Numerical study on curing residual stresses in compression of Z-pinned composites

The Z-pinning technology can effectively improve the interlaminar properties of composite materials, yet the implantation of Z-pins causes fiber distortion, resin-rich zones, and reduced in-plane properties. This paper proposes a numerical method to predict the in-plane compressive properties of Z-pinned composites, with curing effects into consideration. A representative unit cell model is established by analyzing the fine morphology of the Z-pinned structure. Considering the time-dependent properties of the cure process, we develop a coupled thermo-chemo-mechanical multi-field model for Z-pinned structures. The residual stress field obtained from the previous calculation is introduced as a predefined field in the calculation of in-plane compressive performance, and the simulated results are in good agreement with the experimental results. It is found that a large amount of residual stress accumulates around the Z-pin during the cure. Therefore, under compressive loads, weaker material properties around the Z-pin will first develop crack defects, gradually extending to the resin-rich regions. The presence of fiber orientation, resin-rich regions, and cure-induced residual stresses significantly reduce the in-plane compressive performance of Z-pinned composites.