Fatigue behavior of bonded composite repairs

In this study, recent efforts into the research and development of composite repairs bonded to defective aircraft structures are discussed, The fatigue crack growth (FCG) behavior of precracked Al 7075/T6 substrates with bonded composite patches was investigated experimentally and analytically. Boron-epoxy patches with 2-, 4- and 6-plies were installed on Al substrates with single-side-crack. Tension-tension fatigue tests were also conducted on Al substrates to establish their fatigue behavior for comparing with the repaired specimens. A considerable increase in the fatigue life and a decrease in the stress intensity factor (SIF) were observed as the number of plies increased. An analytical model, based on Rose's analytical solution and Paris' power law, was developed to predict the FCG behavior of the repaired substrates. The analytical and experimental results are found to be in good agreement.