Composite patches as reinforcements and crack arrestors in aircraft structures

The application of adhesively bonded composite patches as reinforcements and crack arrestors for a multisite damaged aircraft structure is investigated. Experiments are performed to test the ability of a bonded composite reinforcement to prevent cracks from coalescing. With a finite element model developed for composite patch repairs, the effect of thermal residual stresses on the stress-intensity factor and the resulting fatigue crack growth rate is demonstrated. An effective thermal stress is estimated by comparing experimental results with model predictions. Reinforcement for a multiple-site damage situation is analyzed by modeling an infinite row of closely spaced cracked rivet holes. The composite reinforcement is shown to dramatically reduce the stress-intensity factor, increase fatigue life, and protect against catastrophic failure.