Residual properties of composite plates subjected to impact fatigue

This work deals with post-impact residual mechanical behavior of composite plates made with glass fiber cloth and two different thermosetting resins (epoxy and polyester). It is well known that damages induced by multiple impacts greatly reduce the residual properties. How are the residual strength or stiffness affected by the impacts? How does impact energy and number of impacts contribute to the degradation of mechanical properties? What kind of supports induces more damages and consequently a larger reduction in residual properties? These are some questions that we attempt to clarify in this paper. To investigate and assess the effect of the energy level and number of impacts on the total induced damage and residual properties, impact fatigue tests were carried out at selected energy range of: 3 J, 4 J, 5 J, and 6 J. Then, coupons containing the damaged area are cut out, in order to estimate the tensile, compressive, and shear residual properties, particularly residual strength. The energy level and number of impacts are major factors influencing the loss of stiffness and strength. However, stiffness is more affected than strength by the repeated impacts. A clear decrease of compressive residual strength with the number of impacts for the two fixture conditions (clamped on two opposite sides and a circular clamp) is demonstrated. The drop in the case of the circular clamping is more visible, confirming a greater extent of damages. A three-parameter damage model is proposed and applied, with some conclusions are withdrawn in this investigation.