A numerical and experimental study on reverse-bent joints for composite substrates

Abstract

Adhesive bonding is used increasingly by the aerospace industry to join structural components made from composite materials. One of the most common joint configurations is the lap shear joint. However, the potential strength of joints made with fibre reinforced composites is rarely achieved because of delamination and premature failure caused by out-of-plane stresses. Common approaches for managing stress include the introduction of adhesive fillets at the overlap ends, tapering of the substrates, the use of ’multi-modulus adhesives’, and geometric modifications to reduce peel stresses. McLaren and MacInnes suggested simply deforming the substrate at the end of the overlap length to improve the stress distribution within the overlap area. In previous work by Fessel et al 1 this idea was developed further and applied in a numerical and experimental study on various thin metallic substrates which are commonly used in the automotive industry. The required design changes to the substrates were minor but significant joint strength improvement resulted. In this follow-on paper the reverse-bent joint was applied to composite substrates, which were compared numerically and experimentally with the traditional lap shear joint configuration. Due to a reduction in peel stresses the joint strength of the lap shear joint was significantly increased, by up to 190%, depending upon the chosen material combination.