Robust Bonded Joints with Surface Toughening design feature

Abstract

The certification of safety relevant bonded joints in carbon reinforced composites remains a major challenge within the aerospace industry. Three methods are allowed to achieve compliance to the regulations like CS 25.571 and their accompanying documents (e.g. AMC20-107b). A non-destructive testing of bonded joints which determines its actual strength is not yet available. A proof test of each and every joint under its loading and environmental conditions is not economically affordable or technically feasible. Only the usage of design features to limit the size of a potential disbond presents a reasonable approach. Within the EU-FP7 research project BOPACS various technologies for such design features have been investigated. Conventional rivets have been found as a feasible solution. Although rivets have been proven as mechanically suitable they come with known downsides for composite structures like interrupting fibres, inhibiting orthotropic composite layups and preventing a carbon dust-free assembly. This leaves the need for design features with high mechanical efficiency and less negative impact on the composite structure and its bonds. The work presented here gives an overview of the Surface Toughening design feature which overcomes the downsides of the original hybrid bond line concept developed by Löbel et al. It summarizes the previous work of the authors and relates it to the context of damage tolerance joining of military aerospace composite structures.