A finite element method is applied to explain significant reduction of compressive properties of composite cross-ply laminates owing to multiple delaminations and the instability of the delamination cracks. Through-width multiple delaminations with equal length are considered. The contact problem is considered by using one-dimensional GAP elements on delaminated surfaces, which can realize piecewise linear force-displacement relation. The postbuckling behavior is numerically obtained and the energy release rates
GI and
GII at each delamination edge are calculated through virtual crack closure technique at each step. The postbuckling behaviors obtained by the finite element method agree well with those observed in the experiment and obtained by Rayleigh-Ritz approximation technique. The mode I energy release rate
GI, however, increases very little as expected from the postbuckling deformation. The mode II energy release rate
GII increases proportional to the end-shortening after the buckling. The distributions of total energy release rates
G=
GI+
GII at the delamination edges are discussed.
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