Fibre Break Failure Processes in Unidirectional Composites. Part 3: Unidirectional Plies Included in Laminates

Abstract

The purpose of these three papers is not to just revisit the modelling of unidirectional composites. It is to provide a robust framework based on physical processes that can be used to optimise the design and long term reliability of internally pressurised filament wound structures. The results given in paper Parts 1 and 2 concerning the behaviour of unidirectional composites, such as carbon fibre reinforced epoxy resin, are, here, extended to the behaviour of cross-plied composites consisting of unidirectional plies orientated at different angles with respect to the loading direction. In these laminates the plies orientated parallel to the loading direction (at 0∘) control the ultimate failure of the composite. This paper shows that the development of fibre breaks in analogous to that seen in the studies described in Part 1 and 2. Clustering of fibre breaks, shown by the development of 32-plets, preceedes failure just before specimen loaded monotonically break but develop in a more stable manner when subjected to steady high level loads. The effect of separating the 0∘ plies into thinner layers impedes the development of fibre breaks clusters and increases ultimate lifetimes.