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Repairs have been made to cracked thin-walled structures by bonding a
fibre reinforced polymer composite patch which reduces the crack opening
displacement. Here we describe the mechanism of a fatigue crack growth in a
composite repaired thick plate. Experimental results of a cracked plate overlaid
by a bonded composite patch and cyclically loaded, is presented first.
Subsequently, a three dimensional nonlinear finite element study is carried out to
determine the required condition for the crack arrest. Both crack bridging by
fibres and plasticity-induced crack closure contribute to the arrest. The results of
this investigation indicate that the plasticity-induced crack closure phenomenon is
beneficial to the repair when the crack tip in the base structure under goes plastic
deformation. The effect of the applied patch is most significant at the outer
surface, and its influence decreases from the location adjacent to the outer surface
through the thickness.