By taking account of partial closure of delamination, the buckling analysis of elliptically delaminated composite laminates under in-plane compressive loads is made using a finite element method. In order to deal with the contact problem for the partial closure of delamination, a penalty function method is proposed. In the method, fictitious springs are inserted iteratively at all of the overlapped points. Stiffness of each spring is calculated by considering the overlap and stiffness of the structure at that point. Numerical calculations were carried out to clarify the effects of delamination size, shape, position through thickness and ply angle of delaminated layer on the buckling load and buckling mode. The results are shown in graphs.
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