Finite element analysis of the effect of longitudinal debonding on stress redistributions around fibre breaks in randomly packed fibres

Abstract

One of the challenges in longitudinal strength models of unidirectional composites is to comprehensively simulate the stress redistribution around a broken fibre. This redistribution is affected by the interfacial debonding of the broken fibre from the matrix. In the present work, a novel approach using finite element modelling is developed that considers all primary contributors to the longitudinal debonding in randomly packed fibre configurations. The parametric study revealed that a larger friction coefficient, interfacial fracture toughness and interfacial shear strength shorten the debond length and increase the stress concentration factor (SCF) on the neighbouring intact fibres. The magnitude of the SCFs strongly depends on the local fibre volume fraction, the radial distance between the intact fibres and the broken fibre, and the debond length. Incorporating interfacial debonding considerably reduces the SCF overpredictions by the well-bonded models. The presence of a matrix crack, encircling the broken fibre, locally increases the SCFs in the adjacent intact fibres and marginally shortens the debond length of the broken fibre. By incorporating these results into a strength model, the influence of the longitudinal debonding and co-existing matrix cracks on failure strain of unidirectional composites can be further tuned.