Using the drop weight impact tower to evaluate impact resistance of FRP composite plates

Drop weight impact towers are frequently used to assess the dynamic response of plate materials including glass fiber reinforced thermoset composites. There has been confusion over how to interpret the results of such testing, however, as evidenced by the absence of an ASTM or other authoritative test standard. The composites community has attempted to develop "impact metrics" but these efforts are hampered by inadequate understanding of the interactions between test apparatus and material specimen which include both geometric and material parameter effects.;It is demonstrated experimentally and analytically that the impact response is a path dependent function of impact velocity and tup mass up to a point labeled the Linear Inelastic Limit where damage becomes severe enough to commence decoupling the local and global plate reactions. These observations indicate why it has been so difficult to interpret the apparent impact response in a manner which permits useful comparison of different composite systems. An impact metric called the decoupling contact force is proposed. Key variables which define the decoupling contact force are identified.;The quantity of energy returned inelastically to the crosshead following a particular impact provides a useful measure of impact performance. When this returned energy is plotted over a range of impact energies it becomes possible to trace damage development and identify transitions in the dynamic response. Inelastic Energy Curves are used to evaluate the impact resistance of numerous resin transfer molded composite plates and to probe the fundamental interactions between test apparatus and specimen.