Analysis and modeling of the Z-pin insertion in prepreg based on contact mechanism

Z-pinning is increasingly applied to improve the fracture toughness in fiber-reinforced laminated composites. Force modeling during Z-pin insertion into prepreg is crucial for the manufacturing technology of Z-pinned laminates. In this paper, the effect of lay-up sequence on the Z-pin insertion force is investigated. Experimental testing reveals that the change of ply structure can result in two main force-displacement relationships in the compression phase, namely linear growth and nonlinear growth. Through analyzing the contact mechanism, the force-displacement relationship depends highly on the contact area between Z-pin and prepreg, which is validated by insertion experiments with different conical tipped Z-pins. Two models based on different contact modes of Z-pin insertion are proposed: the analytical model for the unidirectional prepreg and the finite element model for the cross-ply prepreg. The advantage of this approach is its ability to capture the contact behavior during the insertion process, thus predicting the insertion force more accurately. The analysis results are in good agreement with experiments.