Modelling composite repairs to cracked metal structures

Composite patches (usually made from carbon-fibre reinforced plastic (CFRP)) are frequently used for localised structural strengthening. They can also be used to repair fatigue cracks in metallic structures in situations where welded repairs are unsuitable: for example, cracks in stress concentrations may re-appear soon after a welded repair is attempted. This application is, however, hampered by the difficulty of predicting the fatigue life extension produced by the repair. This paper presents work which shows that the growth of patched and unpatched fatigue cracks can be predicted using finite-element analysis, allowing the benefits of a potential patch repair to be quantitatively assessed. Simulations of the crack propagation are performed and show a good correlation with test results. The tested repair was successful in significantly reducing the fatigue crack growth rate.