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Composite patches are bonded to a cracked metallic surface either symmetrically (double sided) or unsymmetrically (single sided) to extend service life. The stresses in the metallic panel are greatly affected by the repair symmetry. Unsymmetric repairs present the greatest challenge because of the presence of out-of-plane bending. Thermal residual stresses are present because of the thermal coef cient mismatch of the patch and the aluminum plate. Debonding along an adhesive-adherend interface can reduce the patch effectiveness. A simple analysis with Mindlin plate theory is investigated to model the host and the repair plate. The two plates are connected by an adhesive layer modeled by effective springs. Large de ection theory is used in the case of unsymmetric repairs. The springs are ineffective in the debond zone and are removed. Both the aluminum and the debond cracks are characterized by fracture mechanics by use of the stress intensity factor and strain-energy release rate, respectively. Experiments on aluminum 2024-T3 plate, AS4/3501-6 carbon/epoxy composite patch and FM73 adhesive include determining the thermal residual stresses in the aluminum plate and observation of debond development by use of an ultrasonic C-scan. Tests are conducted to examine the metallic and debond crack growth interaction on unsymmetric repairs.

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