Compression Behavior of FRP Sandwich Specimens with Interface Debonds

Local regions of bond failure between face sheet and core are often observed when sandwich structures are exposed to low energy impacts. Similarly, impact loads frequently result in delaminations within the face sheets. In the absence of any delaminations in the sandwich structure the buckling strain of the debonded region is in this work shown to be the key parameter in assessing the structural integrity of a sandwich component in compression. The objective of this study was to predict the buckling of the debonded region and to investigate the parameters controlling this instability. A large number of analyses of the delamination buckling problem, which in many ways may appear similar to the debond problem, have been carried out in the past. However, the debond-buckling problem has not been addressed before and as shown in this work there are significant differences. The Finite Element method was found able to predict all the experimentally observed phenomena accurately. These calculations were expensive, and a simple one-dimensional closed form solution is proposed for qualitative parametric investigations. Effects of material properties and initial imperfections were examined. Analyses of the buckling of a delamination suggest that the effect of the core can be ignored. In contrast, the results presented in this paper show that the core cannot be ignored in the case of buckling of a debond nor can it be simulated in terms of simple boundary conditions.