Fatigue crack growth behavior of bonded composite repairs

In this study, fatigue crack growth (FCG) behavior of pre-cracked Al 7075/T6 substrates with bonded composite patches is investigated experimentally and analytically. Boron/epoxy patches with 2-, 4- and 6-ply are installed on Al substrates with single-side-crack. Tension-tension fatigue tests are 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) are observed as the number of plies increased. An analytical model, based on Rose's analytical solution and Paris' power law, is developed to predict the FCG behavior of the repaired substrates. The analytical and experimental results are in good agreement.