Biaxial testing of fiber composites using tubular specimens

The failure of advanced continuous fiber laminates is not well understood. Stresses on a ply level are usually multiaxial, and reliable rules for the prediction of laminate failure are not generally available. Experiments to measure laminate-failure properties are difficult to perform and to relate to composite structures, being complicated for example by stress concentrations at the free edges of laboratory specimens. A multiaxial laminate specimen based on internal pressure and axial-force loading of a cylinder has been developed that appears to give reliable response and failure data. The purpose of this paper is to present in detail the design and show the supporting analysis of the specimen. In addition recent results on the failure of carbon/epoxy laminates are reviewed.