Experimental investigations on fatigue crack growth of repaired thick aluminium panels in mixed-mode conditions

In this paper, experimental fatigue crack growth of thick aluminium panels containing a central inclined crack of 45° repaired with single-side glass/epoxy composite patch are performed. It is shown that, the technique of single-side repair using glass/epoxy composite patch is effective in the crack growth life extension of the thick panels in mixed-mode conditions. It is also shown that the crack-front of the propagated cracks of the repaired panels has a curvilinear shape which is the effect of the existed out-of-plane bending due to the asymmetry conditions in the single-side repaired panels. It is indicated that the crack propagation path at patched surface is different from the un-patched surface of the panels. In the primary stages of the crack growth, the crack surfaces through the thickness, in the vicinity of the mid-plane propagate without surface twisting. There are considerable differences between the obtained crack growth path at patched and un-patched surfaces of the panels which mean that the crack propagation surfaces have three-dimensional patterns. Using the various thin patch lay-ups has minor effects on the crack re-initiation life of the repaired thick panels. It is shown that using various four layers patch lay-up configurations, the crack propagation life of the cracked panels may increase by the order of 30–85%. The most fatigue crack growth life extension belongs to the repaired panel with the patch lay-up of [90]4.