Durability of bonded crack retarders for aerospace

The increase in demand for aircraft focuses the structural designers and manufacturers towards the reduction of manufacturing cost and structural weight while maintaining high safety, damage tolerance, and structural integrity. These weight savings can be achieved by using large integral structures. However, large integral structures show reduced performance with respect to damage tolerant design due to lack of physical barriers that can arrest a growing crack such as presently exist in structures joined with rivets and bolts. Fibre metal laminates such as Glass Laminated Aluminium Reinforced Epoxy (GLARE) have been proven effective as bonded crack retarders (BCR) in reducing the fatigue crack growth rate and improving the life of metallic aircraft structures. A major problem associated with bonded crack retarders is the development of thermal residual stresses which may have negative impact on the performance of the structure. Hence, the objectives of this research are to investigate the thermal residual stress developed during the strap bonding process and the fatigue durability of bonded crack retarders. Extensive research performed in this dissertation covers the detailed investigation of thermal residual stresses and the fatigue durability of GLARE bonded crack retarders when incorporated onto different structural coupons and on an aircraft mock-up panel. Thermal residual stresses developed during the strap bonding process are very low and the application of a bonded crack retarder improved the fatigue performance of the specimen. The experimental data on residual stress measurements and fatigue testing provides information for researchers and aircraft structural designers to improve the performance and life of critical aircraft structures and the possibilities of incorporating the bonded crack retarder concept in the initial design and fabrication stages