Abstract
Instrumented drop weight impact testing has been used to study the impact performance of fiber reinforced polymer composites. Deformation processes and fracture mechanisms of thin-plate composite laminates were examined as a function of material parameters, plate thickness, stacking sequence, and impact loading rate. For the lami nates containing tough fibers, such as high-strength polyethylene, plastic deformation was found to be an important energy absorbing mechanism. High flexibility of these fibers allows the incident energy to be dispersed in a wider area and the impact load to be shared by a greater volume of material. A clean penetration crack was observed in the samples that contain primarily brittle fibers, such as graphite. This failure mode absorbed very lit tle incident energy. In addition, both matrix-fiber interfacial debonding and interlaminar cracking were shown to be effective in dissipating impact energy. Mechanistic study in dicated that the impact response of the laminates can be described by an initial stage of elastic deformation, followed by three stages of plastic deformation. Also, impact testing data showed that interlaminar hybridization with thermoplastic laminates was able to im prove the impact toughness of the otherwise brittle epoxy laminates. Fiber-matrix debon ding in thermoplastic laminates and interlaminar debonding between thermoplastic and epoxy laminates enhanced the impact energy absorption capacity of hybrid-matrix com posites. However, due to this poor interfacial adhesion, the result of post-impact three- point bending tests indicated an inferior damage tolerance for hybrid-matrix laminates. A simplified theory for impact failure mechanisms of composite laminates is proposed. It provides a mechanistic basis for the development of a practical model for the prediction of impact failure modes. This theory has proved to be useful in the studies on the impact penetration of more brittle composites.