Fatigue crack growth in fibre reinforced metal laminates

In order to increase understanding of the mechanisms involved in the fatigue crack growth behaviour of fibre reinforced metal laminates (FRMLs), experimental and theoretical studies have been carried out at DERA. A wide variety of FRMLs has been investigated, including ARALL 1, 2, 3 and 4 laminates with unidirectional aramid fibres and GLARE 1, 2, 3 and 4 laminates with unidirectional and cross-plied glass fibres. The FRMLs had from two to five metal layers, each 0.2mm or 0.3mm thick. Fatigue crack growth rates were measured for constant amplitude loading at different stress levels and R-ratios. Damage in the laminates, including delamination and broken fibres, was measured fractographically. SPATE scans were also used to monitor delamination. A three-dimensional FE model has been developed specifically for stress analysis of FRMLs, including prediction of stress intensity factors and crack growth rates. The FE model incorporates delamination and other features observed in the experimental work, and allows for thermal residual stresses within the FRMLs. A simple elastoplastic one-dimensional model has also been developed for estimating stress intensity factors in the absence of delamination. The predictions of the models have been found to be in good agreement with the experimental results.