Thermal residual microstress generation during the processing of unidirectional carbon fibre/epoxy resin composites: random fibre arrays

Abstract

Finite element models are developed to predict the thermal residual stresses generated during the processing of carbon fibre/epoxy resin composites. A previous analysis that assumed regular arrays of fibres is extended to include random fibre arrays, which are thought to be more appropriate to the actual fibre distributions. The stresses are local to single fibres under conditions of plane strain. Initially a hypothetical distribution is assumed which is intermediate between a hexagonal and square array. This model consists of a representative selection of the unit cells used in the analysis of the regular fibre arrays. The fibre volume fraction of the model is 27% and the fibre separation ranges from 1.0 to 12.0 μm. Subsequently a computer program is used to generate random fibre arrays and a region local to a single fibre in a 50% fibre volume fraction array is meshed for finite element analysis. The results are compared with those obtained assuming regular fibre arrays. Observations are made also of actual fibre arrays under an optical microscope; these are compared with the fibre arrays assumed in the modelling. The change from a regular to a random arrangement generally increases the maximum tensile stress produced in the epoxy resin. This tends to occur at positions within the smallest gap between two fibres.