Keywords: cross-ply laminates, discrete element method, contact softening model, microstructure, transverse cracking.

Damage and failure of the fibre reinforced laminate composites remains a challenging research subject in the area of material science and engineering. Most of the existing numerical approaches to study microscopic damage evolution in composite materials can be referred to as top-down approaches [1]. The basic idea is to embed developing cracks, that are discontinuities in the displacement field, in the continuum, e.g., by fictitious representations. Therefore, these approaches can only deal with materials with a small number of major voids and relatively little disorder, and can rarely make any statement on the relationship between material microstructure and macro fracture behavior. On the basis of certain reasonable assumptions, some of the macro models can match the failure curves from experimental results. However, they cannot explain how the damage starts and develops inside a composite during the whole loading process.

This paper follows a completely different route, which can be understood as a bottom-up strategy [2]. In this study a novel particle assembly model is developed using two dimensional discrete element method (DEM) for the purpose of simulating micro to macro damage and failure process of the fibre reinforced cross-ply laminate composites. Fibre and matrix are represented, respectively, using DEM models that have different particle and bond properties which are calibrated by a series of numerical tests. The fibre-matrix and ply-ply interfaces are treated by the contact softening model in the DEM which is similar to the cohesive zone model (CZM) in the continuum mechanics, with a bilinear traction-separation law. A DEM model for 90°/0°/90° cross-ply laminates is formed by using the above calibrated properties, and later adopted to simulate the dynamic damage evolution process of the laminates, by which matrix cracking, debonding and delamination are captured simultaneously. The numerical results have demonstrated the capability of the DEM model developed in simulating the entire failure process of the composite laminate, from micro cracking in matrix and interfaces to the formation of the macro cracks and delamination until the eventual failure. This study has also confirmed that the DEM model has unique advantages over the conventionally numerical models in terms of dealing with the evolution of microscopic damage in composite materials.

1

B. Cotterell, "The Past, Present and Future of Fracture Mechanics", Engineering Fracture Mechanics, 69, 533, 2002. doi:10.1016/S0013-7944(01)00101-1

2

F. Wittel, "Fragmentation of shells", Physical Review Letters, 93, 035504, 2004. doi:10.1103/PhysRevLett.93.035504

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