THE STABILITY OF DELAMINATION GROWTH IN COMPRESSIVELY LOADED COMPOSITE PLATES

The stability of growth of internal delaminations in composite plates subjected to compressive loading is investigated. Due to the compressi ve loading, these structures can undergo buckling of the delaminated l ayer and subsequently growth of the delamination. The study does not i mpose any restrictive assumptions regarding the delamination thickness and plate length (as opposed to the usual thin film assumptions). The growth characteristics of the delamination under monotonic compressiv e loading are obtained on the basis of a combined delamination bucklin g/postbuckling and fracture mechanics model. The postbuckling solution is derived through a perturbation procedure, which is based on an asy mptotic expansion of the load and deformation quantities in terms of t he distortion parameter of the delaminated layer, the latter being con sidered a compressive elastica. The closed form solutions for the ener gy release mte at the delamination tip versus applied compressive stra in during the initial postbuckling phase are used to define the combin ations of delamination length and applied strain that lead to unstable growth. This would practically cause either contained ''jump'' growth or complete (catastrophic) growth of the delamination. Estimates for the lower and upper bounds of the jump distance (unstable growth) are provided. Moreover, a study of the influence of the mode dependence of interface toughness on the conditions of initiation and extent of del amination growth is performed.