The effect of interfacial imperfection on the nonlinear dynamic behavior of composite laminates under low-velocity impact

Interfacial imperfection usually exists in composite laminates, which are widely used in the aerospace and shipbuilding industries. Such laminates are usually impacted by external loads in practical applications, and there are very few impact studies considering the interfacial imperfection. Therefore, based on Reddy's shear deformation theory, zigzag displacement theory, Hertz's contact law and layer spring model, a 2-dimensional numerical model is proposed to more effectively study the effects of interfacial imperfection on the low- velocity impact behavior of composite laminates. In addition, the rationality of the numerical model is verified by combining numerical examples from other references. It can be clearly seen from the numerical results that due to the interfacial imperfection, the normal stresses in the fiber direction of each layer increase while the maximum contact force decreases simultaneously. As the dimensionless interface parameter \(R\) $R$ increases, the transverse shear stress \({\sigma }_{xz}\) ${\sigma }_{\mathit{xz}}$ of the middle local layer decreases, while the transverse shear stress \({\sigma }_{xz}\) ${\sigma }_{\mathit{xz}}$ in both side layers increases. Although the transverse shear stress \({\sigma }_{yz}\) ${\sigma }_{\mathit{yz}}$ along the entire plate thickness decreases as \(R\) $R$ increases from 0 to 0.2, \({\sigma }_{yz}\) ${\sigma }_{\mathit{yz}}$ shows a similar pattern when \(R\) $R$ ranges between 0.2 and 0.3. Furthermore, based on the principle of energy balance, we further propose a semi-theoretical formula to predict the damage degree of composite laminates when the interfacial bonding gradually weakens under low-velocity impact. Research results show that when \(R\) $R$ increases from 0 to 1.0, relative sliding between layers will cause the damage of composite laminates to increase sharply. But when \(R\) $R$ is greater than 1.0, the damage degree is no longer sensitive to the increase in \(R\) $R$ .