Local CFRP/Metal Hybrid Material Improving Composite Bolted Joints

Abstract

One of the main methods currently used for joining composite components for aircraft and spacecraft applications is still mechanical fastening, which shows the advantage of reliability, detachability and inspectability and represents a well-established and well-known method from its origin in the design of metallic structures. However, to attain a satisfactory structural coupling efficiency with composite materials is much more challenging than it is for metals due to the low bearing and shear strengths, the higher notch sensitivity and the dependence on laminate configuration. These properties represent a limiting factor on the structural performance of composite structures and require additional special reinforcement techniques.

One effective method of increasing the mechanical joint efficiency of highly loaded composite joints entails the reinforcement of the joining area with thin high-strength metal foils. These foils are locally embedded into the composite laminate by means of ply substitution techniques, thus avoiding any local laminate thickening and providing for a local hybrid laminate with high bearing and shear capabilities and high robustness. The local hybrid reinforcement technique is deemed an efficient approach to increase the joint efficiency of composite bolted joints, thus resulting in considerable mass savings, assembly work reductions and an increase of robustness.

The present paper is intended to provide an overview about the mechanical performance and manufacturing of local hybrid CFRP/Ti and CFRP/St material as a reinforcement approach of highly loaded bolted joints highlighting some specific applications for aircraft and spacecraft structures.