Effect of the Loading Rate on Failure of Composite Pressure Vessel

A multi-scale model has been successfully applied to the simulation of the effects of pressurisation rate on damage accumulation in carbon fibre/epoxy plates and composite pressure vessels. The results of the simulations agree with experimental results and reveal that the point at which the structures become unstable in a monotonic pressurisation test depends on the speed of loading. The faster the loading rate the higher the applied stress at which the composite structure becomes unstable. The mechanism which governs this behaviour is seen to be the viscoelastic nature of the matrix material through which stresses are transferred from broken to neighbouring intact fibres. At loading rates that allow greater relaxation of the resin around fibre breaks neighbouring fibres are subjected to increased loads over a significantly greater length, leading to further earlier breaks.