A multiaxial failure criterion for a brittle orthotropic composite

A multiaxial failure criterion is validated for a brittle orthotropic composite, namely a tridirectional carbon–carbon composite (3D CC). It is aimed at designers of 3D CC structures. The composite is subjected to a triaxial strain state along its reinforcement axes, which is representative of its in-service loading conditions. A multiaxial test rig is designed in order to reproduce this required strain state. Its mock-up dimensions are optimised by combining Taguchi experimental strategy with tridimensional finite element modelling. Comparison of experimental results with numerical modelling shows that failure occurs due to the required strain state; failure is brittle and corresponds to simultaneous breakage of carbon yarns along the three reinforcement axes. Subsequently, the experiment validates a failure criterion, which assumes linear coupling between the three principal strains.