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The compressive stability of delaminated random short-fiber composites is con sidered. A mechanistic model is introduced for the problem. Both buckling stability and crack stability (i.e., delamination growth) are investigated. Two analytical methods are developed for studying the buckling stability of the delaminated com posites. The first is formulated on the basis of the well-known Rayleigh-Ritz method, including transverse shear in the composite and distorsional deformation in the delaminated ligament. The second method employs a plane-elasticity, finite-element buckling analysis. Both local buckling and coupled global and local buckling are ex amined. A fracture mechanics approach is used to study the possible compressive crack growth at buckling. The validity of the model and the accuracy and efficiency of the methods of analysis are demonstrated and discussed.

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The interlaminar fracture behavior of a random short-fiber SMC composite is studied both experimentally and analytically. In the experimental phase of the study, the random short-fiber SMC-R50 composite with different thicknesses is used. The commonly used double-cantilever-beam (DCB) fracture test is employed to evaluate the mode-I interlaminar fracture toughness. In the analytical portion of the research, owing to significant deformation in the DCB test, a geometrically nonlinear analysis is introduced to account for large deflection and nonlinear load-deflection curves in the evaluation of the interlaminar fracture toughness. For the SMC-R50 material studied, the interlaminar toughness of the composite is found to be an order of magnitude higher than that of unreinforced neat resin due to unusual damage mechanisms ahead of the crack tip and significant fiber bridging across crack surfaces. The effect of com posite thickness on the interlaminar fracture is appreciable. The influence of the SMC material microstructure on interlaminar crack resistance is discussed in detail.