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This paper describes the initial development of methods for predicting the fatigue life of bonded composite repairs applied to cracked aluminum aircraft structures. Bonded repairs offer great potential in stopping or slowing crack growth. The benefits of bonded repairs when compared to riveted repairs are significant, and include improvements in fatigue life, inspectability, and cost. The main barrier to the widespread use of this technology is the lack of methods for ensuring damage tolerance and durability [1–3]. In this paper, approximate analytical equations are developed to characterize both disbonding and crack growth in a repair applied to a center-cracked plate. The equations are in a form suitable for use in probabilistic risk assessments and inclusion in industry codes and standards, and have been validated against a boundary element model.

In this paper, the authors review damage mechanisms and failure modes of bonded composite repairs applied to aluminum aircraft structures, with a focus on the effects of bending on the performance of asymmetric or one-sided repairs. Failure mechanisms are elucidated using results from testing carried out during the course of the University of British Columbia Bonded Composite Repair Program (UBC-BCRP). The authors then outline the regulatory requirements for damage tolerance and describe the new methods and test data developed under the UBC-BCRP to improve the analysis of bending repairs.