GROWTH-BEHAVIOR OF INTERNAL DELAMINATIONS IN COMPOSITE BEAM PLATES UNDER COMPRESSION - EFFECT OF THE END CONDITIONS/

The effect of the end conditions, i.e. clamped-clamped vs. simply-supp orted ends on the initial postbuckling and growth behavior of delamina tions in plates is studied. The study does not impose any restrictive assumptions regarding the delamination thickness and plate length. Fir st, a closed form solution for the mode mixity, energy release rate an d deformation quantities is derived for the case of a clamped-clamped delaminated plate, which complements the already existing solution for a delaminated simply-supported plate. A perturbation procedure is fol lowed, which is based on an asymptotic expansion of the load and defor mation quantities in terms of the distortion parameter of the delamina ted layer, the latter being considered a compressive elastica. The add itional complication in the clamped-clamped case arises because now th e amplitude at the clamped end needs to be expanded in terms of the di stortion parameter of the delaminated part, in addition to the amplitu de at the common section and the distortion parameter of the base plat e. The effects of the end conditions on the growth behavior are found to depend on the relative location of the delamination through the thi ckness. For the same plate length and thickness and the same delaminat ion length and applied strain, delaminations located closer to the sur face exhibit nearly the same energy release rate and mode mixity eithe r in a clamped-clamped or a simply supported configuration. However, i n delaminations located further away from the surface, for the same ap plied strain, the energy release rate is larger and there is also a hi gher mode II component in the simply-supported case. Moreover, the mid -point transverse displacement of the delaminated layer as well as tha t of the substrate part, is larger in the simply supported case. The s ame major trend that has been observed in the simply supported case, i .e. the increased growth resistance of the delaminations located near the surface relative to the ones located further inside the plate, is also observed in the clamped-clamped case.