Buckling and Vibration of Composite Laminate with Multiple Delaminations

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Buckling and vibration of composite laminates with multiple delaminations subjected to compressive loading were studied theoretically and experimentally.First, the theoretical and experimental investigations of the buckling behavior of composite laminates with single delamination were performed. The effects of the delamination length and depth on the buckling load were clarified, It was found that the load carried by the laminate increases even after the bifurcation. While the load in the thinner part of the delaminated region remains constant, the load in the thicker part increases after the buckling. The possibility of the growth of delamination due to the buckling deformations was investigated based on the potential energy release rate at the delamination tips.Next, the theoretical and experimental studies of the buckling behavior of composite laminates with multiple delaminations were conducted. The buckling load was found to be lowered by the multiple delaminations. Like for the case of single delamination, the load carried by the laminate increases even after the bifurcation. The delamination growth is prone to occur due to the higher potential energy release rate at the multiple delamination tips. The analytical solutions obtained for the buckling behavior were verified by the finite element solutions and the experimental observations.Finally, the vibration of the composite laminates with multiple delaminations was studied. By investigating the laminate without inplane loading, the effects of the delamination length and depth on the natural frequencies were clarified. And the analysis of the laminate subjected to inplane loading showed that the natural frequency decreases drastically due to the inplane compression. The results of the vibration analysis of laminates with multiple delaminations contribute to the development of the method to detect the delaminations in composite laminates.