IMPACT STUDY OF SANDWICH COMPOSITE STRUCTURES WITH DELAMINATION

Finite element analyses were conducted to analyze the dynamic response of an unbalanced sandwich beam, a balanced sandwich beam, and a balan ced sandwich plate subject to a low energy impact. In particular, stra in versus time history, failure location and mode, and the influence o f an existing delamination crack on the failure were investigated. It was found that, in the presence of a small delamination crack, the fai lure load of a sandwich composite structure increased compared to that of the non-delaminated structure. For a small crack, failure under im pact loading was core shearing, that occurred away from the crack tip. However, as the delamination crack length increased, the core shearin g failure occurred at the crack tip under a reduced impact load. Thus, the failure location shifted moving away from the crack tip to the cr ack tip as the delamination crack size increased from a small size to a large size. The failure load for a large crack structure was signifi cantly smaller than that of the non-delaminated structure. Core sheari ng failure was followed by delmaination at the core/faceplate interfac es. When the initial delamination crack size became longer than half o f the beam length, the crack further propagated through the interface. Furthermore, a delamination crack did not result in a substantial inc rease in the maximum deflection compared to that of the non-delaminate d specimen. Thus, detection of delamination cracks was difficult from the deflection measurement under a low energy impact. Finally, the eff ect of crack surface friction on the dynamic behaviour and failure of the sandwich structures was small.