Hydrostatic Response of Thick Laminated Composite Cylinders

Abstract

This study discusses the results of a layer-by-layer analysis of a thick-walled cross-ply graphite-epoxy cylinder subjected to external hydrostatic pressure. The analysis, which is valid away from the ends of the cylinder and is based on a generalized plane deformation elasticity solution for each layer, considers inter- and intralaminar stresses. Cylinders with 102 layers and radius to wall thickness ratios of 5 and 10 are studied. The influence of cur ing stresses are evaluated. For possible application to testing, the response of a thick lami nated ring is compared to the response of a cylinder. The idea of smearing the 102 layers into an equivalent single layer is discussed and the results of a smeared analysis are com pared with the layer-by-layer analysis. Finally, the responses of glass-epoxy and metallic cylinders are compared with the response of the graphite-epoxy cylinder. The primary findings of the study are: (1) the radial strain distribution through the thickness of the graphite-epoxy cylinder changes from extension at the inner radius to compression at the outer radius. This is different than the radial strain distributions through the glass-epoxy and metallic cylinders. The radial strains for these cylinders are everywhere extensional. (2) The magnitude of the curing stresses are much smaller than the stresses due to hydro static pressure. (3) The smearing technique works very well, the response predicted by the single-layer analysis being indistinguishable from the response predicted by the layer-by- layer analysis. (4) The high level of orthotropy of the graphite-epoxy causes a higher fiber loading than occurs for glass-epoxy. This effect could amplify any imperfections, e.g., fiber waviness, in the compressively loaded fibers and could lead to premature failure.