Evaluation of the damaged area of glass-fiber-reinforced epoxy-matrix composite materials submitted to ballistic impacts

Fiber-reinforced composites submitted to ballistic impact show large, and sometimes irregular, areas of delamination. The evaluation of these damaged areas is important to assess the effects of the laminate microstructure on the response of the material to the imposed loading. In this paper bulletproof laminates were obtained using 30 plies of glass-fiber reinforced-epoxy matrix composites. The ballistic performance of these laminates was varied by modifying the properties of the constituent laminate or by changing the laminate assemblage. An automated digital analysis procedure was developed in order to determine size and shape parameters that characterize the damaged areas. The procedure developed proved to be robust and sensible enough to cope with subtle variations on the damaged areas, which are due to the differences on the mechanical response of the composites caused by modifications on their microstructure. The results obtained show that not only the area of delamination is important to quantify the ballistic performance. The isotropy of the ballistic response, determined measuring the Feret Ratio or the Circular Shape Factor, is also important.