Dynamic study of energy loss mechanisms during ballistic impact of polymer composites

The objective of this study is to determine the energy dissipation mechanisms in polymer-matrix composites during the impact of high velocity projectiles. At the microscopic level, these processes include heat, fiber deformation and breakage, matrix deformation and fracture, interfacial debonding and fiber pullout. Macroscopic failure modes include plastic deformation, perforation and delamination. In this study, precision measurements were made, using specialized specimen designs and innovative test methods, to determine the fraction of the energy consumed by each of these processes during impact. Using well designed experiments, relationships between material parameters and energy dissipation were obtained. The results of this basic study provide a scientific basis for the predictions and designs of protective materials which are lighter and more resistant to impact energy. Matrix was found to be one of the most important energy absorption mechanisms during impact, especially in ductile samples such as Spectra-900 PE and Kevlar-49 reinforced polymer. On the other hand, delamination dominates the energy dissipation in brittle composites, as illustrated in graphite reinforced materials. A series of experiments were designed and conducted to elucidate the contribution from each energy loss mechanism. In these experiments, the contributions from fiber breakage, fiber deformation, matrix cracking, delamination, friction, and strain rate effects were individually measured. A semi-empirical model was tested using these results, and a correlation was made with the composite system. Based on this study, more effective energy absorbing composites with tailored properties must be considered by composite designers.