Laminated fiber-reinforced composites are engineering materia1s with many desirab1e properties inc1uding high stiffness and strength. However, the 1ack of fiber reinforcement in the through-thickness direction makes composite 1aminates vu1nerab1e to foreign object impact loading. Transverse impact loading can 1ead to a variety of damages inc1uding matrix cracking, de1amination and fiber breakage. De1aminations can reduce the strength of a 1aminate, especia11y the compressive strength after impact. Impact loading typica11y causes multiple de1aminations that vary in size and shape by depth location. The frac ture behavior of impact damages has been a topic of extensive research [1). Recent1y significant advances have been made in the area of nondestructive eva1uation (NDE) of impact damages in composites. For examp1e, u1trasound is used to map out the detai1s of impact-induced de1aminations with p1y-by-p1y reso1ution [2).In this work u1trasonic NDE is used to address three prob1ems in impact-induced de1amination. First, quantitative corre1ation between the energy dissipated in the 1aminate and the total area of de1amination is investigated. The resu1ts are compared to mechanica1 properties of the composite, such as the frac ture toughness. Second, the abi1ity of a de1amination to b10ck the passage of u1trasound and the associate "s hadowing" effects are studied. Fina11y the impact resistance in terms of the area of de1amination per unit of dissipated energy is compared for a thermoset and a thermop1astic composite.
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