A micromechanically inspired model for compressive and shear failure in fibre-reinforced composites

This paper introduces a 3D continuum damage mechanics (CDM) model formulated with nonlinear kinematics to describe the mechanical response of CFRP composites, focusing on their behaviour under compression and shear. The CFRP is modelled using matrix and fibre phases, where a computationally efficient mean-field averaging approach is used to obtain the homogenised composite response at the ply level. The two phases are modelled as hyperelastic materials, and continuum damage induced by shear degrades the matrix. To obtain a well-posed homogenisation in terms of a fluctuating displacement field in the Hill–Mandel condition, the model incorporates a rotation-neutralised formulation alongside matrix-fibre coupling formulated in terms of the consequent Biot stress. The performance of the model was assessed using measurements from the Third World-Wide Failure Exercise and experimental laminate tests. Using material parameters calibrated on the compressive curves for the IM7/8552 plies, the model results in biaxial failure envelopes with good qualitative and quantitative agreement with the LaRC05 and Hashin criteria. The computational model was also used to predict the compressive strength of multidirectional T700/epoxy laminates. On average, the strength predictions differed from the experimental mean by 6.1%, while the measurements showed an average difference from the mean of 3.8% based on three measurements for each lay-up. The model also compares favourably with two other representative models in the literature.