Instrumented Impact and Static Indentation of Composites

Abstract

The low velocity impact behavior of several laminate systems has been studied. Instrumented impact tests were compared with static indentation tests using the same specimen and test configurations. The impact behavior, defined by impact force, damage size and energy absorption, was found to be similar to the static indentation response. The damage growth process during impact as the force surged to its maximum value can be visualized from the static indentation damage induced at incrementally increased force levels. Delamination impact damage suddenly appeared only when the impact force reached a threshold value which was dependent on laminate fracture toughness. Further force increase resulted in gradual damage size growth until fiber damage caused the force to level off. There was evidence that laminate fracture toughness also affected the level-off force. Fiber damage not only absorbed significant energy but also allowed for further delamination damage growth. Overall, the characteristics of impact force versus damage size varied with materials. As the impact energy levels varied, different stages of the impact failure process would be reached. Simple mode I or mode II delamination was not sufficient to describe all the possible failure modes involved in either impact or compression after impact.