Fatigue evaluation of thick monolithic aluminum structures repaired using composite bonded doublers

Abstract

The composite repair of metallic aircraft structures is a proven technology used in many repair applications on both military and commercial aircraft. Composite bonded repairs to metallic aircraft structures are generally used for fatigue enhancement, crack patching, as well as in different kinds of damage repairs. A classical research approach has been adopted for the project. A literature review has been conducted to become acquainted with the crack initiation and crack growth prediction methods in composite bonded repair situations and to gather experimental data for validation purposes. Test data generated by DERA and the USAF has been used to evaluate crack growth and crack initiation analysis tools. Both classical and FEA based fatigue analysis have been evaluated for accuracy. From the evaluation, a list of deficiencies has been developed, and a new methodology proposed to improve the fatigue life prediction for thick cracked aluminum structures. The new methodology provides a good compromise between accuracy and complexity in the analysis of bonded repair designs. A new set of data was generated, due to the lack of experimental crack growth data available for typical CF18 materials and spectrum loading. The proposed methodology has been evaluated against existing and new test data generated for the project. The designed test coupons had a centre section of 6.35 mm (0.25 inch) of thickness and were made of 7050-T7451 Aluminum. Coupon testing was realized using spectrum loading representative of CF-18 usage. This project has been realized in collaboration with the Canadian Department of National Defence (DND), Martec Limited and the Université de Sherbrooke"--Résumé abrégé par UMI