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This paper treats the failure characteristics of [0/90/0] and [90/0/90] cross-ply laminates based upon the statistical strength analysis. The stress redistributions at the failure of the 90 ° ply are analyzed using a shear-lag model, taking the thermal residual stresses and Poisson effect into consideration. The formulae for determining first cracking, subsequent multiple cracking and ultimate fracture are derived. The present analysis is compared with the existing experimental results for graphite/epoxy cross-ply laminates, and reasonable agreements have been obtained.

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Graphite epoxy cross ply laminates show multiple cracking in the 90 ° ply before final rupture occurs. By the aid of a piezo-electric load cell crack formation was measured as a function of the applied load in (02/902)s, (02/903)s and (02/906) s laminates. With these experimental results and a shear lag analysis, to account for the non-homogeneous stress distribution in cracked 90° plies, it was possible to estimate the Weibull strength distribution of the respective 90° ply. it was found that at decreasing 90° ply thickness the shape factor increases. This can be attributed to a suppression of defect growth close to the 90°/0° interface. Because of the changing shape parameter at decreasing ply thickness a description of the thickness effect by a Weibull shape parameter is im possible.

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