Micromechanisms of load transfer in a unidirectional carbon fibre–reinforced epoxy composite due to fibre failures. Part 2: Influence of viscoelastic and plastic matrices on the mechanisms of load transfer

A local three-dimensional (3D) finite element analysis (FEA), of the mechanisms governing composite damage (in the region around a fibre break), has been carried out. The model considers viscoelastic and plastic matrix behaviours with and without debonding at the broken fibre/matrix interface. The finite element analysis has shown that even a simple viscoelastic law describing the behaviour of the epoxy resin leads to an increasing load on the neighbouring intact fibres, as a function of time. The plastic behaviour of the matrix has been shown to have consequences on reloading after unloading. In contrast to other studies reported in the literature, the calculations were carried out on different representative 3D unit cells, corresponding to different states of composite damage. In this way, the usual limitations of the finite element approach have been overcome as the number of fibres considered has not been restricted to only the fibres nearest to the broken fibre and the evaluation of the stress field is more accurate. This study follows a previous study (Part 1) which considered the behaviour of a unidirectional composite consisting of both elastic fibres and matrix which is used to validate the approach taken in the present paper.