Experiments and modelling of competitive failure behaviour of CFRP stepped-lap repairs with different design parameters

Abstract

Stepped-lap bonding has been preferably applied in composite repairing. Nevertheless, the design of repairs presents challenges due to the complex failure mechanism. This paper aims to investigate the mechanical performance and failure mechanism of Carbon Fibre Reinforced Polymer (CFRP) repairs with stepped-lap under tensile loading. Two design parameters are studied, i.e. step numbers and slope combinations. Furthermore, the two different configuration methods of Cohesive Zone Model (CZM) are creatively employed in the developed numerical models, i.e. the adhesive interface adopts cohesive contact, while zero-thickness cohesive elements are inserted in the interlayer between the first two plies of CFRP to simulate possible delamination. Simulations are verified against experimental failure loads, as well as damage evolutions in the repaired adhesive interface, ply interlayer and CFRP laminate. Results showed that the tensile strength of stepped-lap repairs increased with step numbers. The three-step stepped-lap repair with a slope combination of 1/20–1/20–1/20 bears the strongest tensile strength and greatest load-bearing capacity. This work reveals the competitive failure mechanism in adhesively repaired composites and offers a reliable prediction approach for the design of bonded CFRP repairs in practical aeronautic applications.