High-fidelity computational micromechanics of first-fibre failure in unidirectional composites: Deformation mechanisms and stress concentration factors

Stress redistribution and damage phenomena in the vicinity of the first-fibre break in unidirectional composites under longitudinal tensile loads are investigated by means of high-fidelity computational micromechanics based on experimentally characterised material constituents. In this framework, periodic microstructures with statistically representative random fibre packings are analysed, and transient dynamic analyses are performed to take into account the progressive failure and recoiling of a breaking fibre. The effects of mechanisms such as curing residual stresses, fibre/matrix debonding and matrix inelastic deformation on the first-fibre failure process are investigated. The stress concentration factors on intact fibres are found to depend on the statistical failure stress of the breaking fibres, and decrease with increasing strength. For the AS4/8552 composite with average constituent properties, maximum stress concentration factors of 20.6%, 16.1% and 14.2% are predicted, respectively, for fibre volume fractions of 50%, 60%, 70%. Material systems with lower fibre-to-matrix stiffness ratios, such as glass/epoxy, result in lower stress concentration factors. The fibre/matrix interface strength is found to have a limited overall influence on stress redistribution around fibre breakage. (C) 2020 Elsevier Ltd. All rights reserved.