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 balanced sandwich plate subject to a low energy impact. In particular, strain versus time history, failure location and mode, and the influence of an existing delamination crack on the failure were investigated. It was found that, in the presence of a small delamination crack, the failure load of a sandwich composite structure increased compared to that of the non-delaminated structure. For a small crack, failure under impact loading was core shearing, that occurred away from the crack tip. However, as the delamination crack length increased, the core shearing failure occurred at the crack tip under a reduced impact load. Thus, the failure location shifted moving away from the crack tip to the crack tip as the delamination crack size increased from a small size to a large size. The failure load for a large crack structure was significantly smaller than that of the non-delaminated structure. Core shearing failure was followed by delmaination at the core/faceplate interfaces. When the initial delamination crack size became longer than half of the beam length, the crack further propagated through the interface. Furthermore, a delamination crack did not result in a substantial increase in the maximum deflection compared to that of the non-delaminated specimen. Thus, detection of delamination cracks was difficult from the deflection measurement under a low energy impact. Finally, the effect of crack surface friction on the dynamic behaviour and failure of the sandwich structures was small.