Mixed-mode fatigue crack growth of thin aluminium panels with single-side repair using experimental and numerical methods

In this paper, experimental and numerical fatigue crack growth of thin aluminium panels containing a central inclined crack of 45° with single-side glass/epoxy composite patch are performed. Effects of patch lay-up configuration on the restarting crack growth (crack re-initiation) life and crack growth rate of the repaired panels are investigated. The obtained experimental results are compared with those predicted using finite element analysis based on both mid-plane and unpatched surface fracture parameters. In the finite elements analyses, it is assumed that the crack-front remains perpendicular to the panel's surfaces during its propagation. It is shown that the finite element crack re-initiation and propagation lives predictions using the unpatched surface results are too conservative. However, the finite element mid-plane results lead to a non-conservative life prediction. It is experimentally shown that, the most effective patch lay-up configurations to retard the crack growth of the repaired panels is ?45/+45]₂; however, the most life extension including the crack propagation cycles belongs to the patch lay-up of 90₄]. It is also shown that using the asymmetric patch lay-up configuration similar to 90₂/0₂] with a proper bonding process may lead to a very slow crack growth rate, even slower than the patch lay-up of 90₄].