Experimental and Numerical Damage Tolerance Analysis of Cracked Stiffened Aluminum Plates Repaired by Composite Patches

In the present study, the fatigue crack growth behavior of build-up stiffened panels containing cracks in both skin and stringer repaired with single sided 4-ply [02/±45] UD glass/epoxy composite patch is investigated by the experimental and finite element method. Two sets of specimens containing crack in skin only, panel (a), and crack in both skin and stringer, panel (b) are prepared. Initial cracks are made by wire cut tool and under tension–tension constant amplitude fatigue loading, the lives of unrepaired specimens are obtained. Then the composite patches are bonded to the next set of specimens properly and cured using hot-press machine. Under the same loading condition, the a-N data (crack length vs. number of cycles) of the specimens are obtained and compared with unrepaired ones. For panel (b) the cracks in both skin and stringer are traced and the results are obtained. Also a 2D FE model is developed to find the stress intensity factors at the crack tip and using the fatigue crack growth relationships the lives of the panels are calculated. The results show the effect of patch repair that increase the life of the structure. For panel containing crack in both skin and stringer, after failure of the skin the patch carries the load as a bridge and stringer crack advances to the web until failure of the specimen.