The Influence of Layer Waviness on the Stress State in Hydrostatically Loaded Cylinders: Failure Predictions

Abstract

This paper extends the work of two previous papers by using the stress analysis techniques described in those papers to predict the failure pressure of imperfect thick multilayer composite cylinders, the imperfection being due to layer waviness. The past work is briefly reviewed and then the discussion focuses on failure predictions. The maximum stress failure criterion is used. Waves of varying length and amplitude are con sidered. Failure pressures in the presence of waviness are compared with failure pressures for perfect cylinders. Failure mode and location are predicted. Residual thermal stresses due to curing are included in the analysis. The results indicate that the primary modes of failure are fiber compression or interlaminar shear. Fiber compression stresses are aggravated due to the eccentricities associated with waviness. Interlaminar shear stresses occur due both to the geometry of the wave, and to the shear-extension coupling associated with local anisotropy of the material. A third failure mode, interlaminar normal tension, is also possible. Residual thermal stresses influence failure to some degree. Finally, it is shown that because of the higher stresses at the inner radial location of a thick cylinder, mild levels of waviness occurring away from the inner radial location have no influence on failure.