Finite element modelling of frictional bridging during fatigue crack growth in fibre-reinforced metal matrix composites

In this study, the influence of thermal expansion mismatch, fibre debonding, interface friction and interface degradation on crack-tip shielding due to crack face bridging is investigated for fatigue of a Ti–6–4 matrix reinforced with unidirectional SiC-fibres using a three-dimensional finite element model of a compact tension specimen. The crack-tip stress intensity factors resulting from the residual stresses due to thermal expansion mismatch are calculated. For several levels of applied external loads, the crack-tip stress intensity factors are calculated for cyclic loading to assess the influence of friction on the build-up of crack-tip shielding during crack growth. The results show that fibre bridging, residual stresses and elastic mismatch produce crack-tip stress intensity factors that are widely different from the externally applied stress intensity factor. The numerical results show that an increase in the friction coefficient leads to a reduction of the crack-tip stress intensity factor, whereas thermal expansion mismatch leads to an increase of the crack-tip load. Finally, the degradation of the interface, modelled by a selective reduction of the friction coefficient, leads to a decrease in crack-tip shielding.