Residual stress and interface stress in symmetric laminated composites

An uneven strain model for analyzing the residual stress and interface stress in laminate composite was proposed. The analytic formulas of residual-stress in the laminate with symmetrical structure were presented and the variations of the residual-stress and interface stress with location were studied. This study revealed two important facts: (1) for a single layer in laminate, the residual stress is a function of location along length; (2) there exist normal stresses in the interface and it varies along the length direction. Experiments of mechanical properties were performed, using Si₃N₄/TiN-Si₃N₄ laminate sample with symmetrical three-layer and multilayer (2N+1), to investigate the effect of residual stress. The results suggest that the mechanical properties depend on the distribution of residual stress and is consistent with the theoretic prediction.