A multiscale study on warpage of multi-pinned composites induced by curing process

In this paper, we studied the curing process and curing-induced warpage of multi-pinned composite structures through a novel multiscale methodology. This method interconnects the curing kinetics, composite micromechanics, mesoscale depiction and equivalent property calculation of Z-pinned regions, and macroscale warpage prediction by transmitting the evolving degree of cure and cure-dependent material properties. This methodology was then experimentally validated. We also systemically illustrated how the multi-pinned composites evolve through the curing process and further analyzed the effects of Z-pin diameter, spacing, material, composite layup, and cure temperature profile on the curing-induced warpage. It shows that Z-pinning primarily alters the tensile, through-thickness thermal expansion, and through-thickness chemical shrinkage properties of composites throughout the curing. Composites with medium-diameter Z-pins, larger Z-pinning spacing, and carbon fiber Z-pins are found to show larger macroscale warpages. Compared with other unidirectional patterns, the [45°]_n layup is more susceptible to curing-induced warpage. Furthermore, the cure temperature profile affects the warpages through the final degrees of cure.