Numerical analysis of the mixed-mode fracture of bonded joints depending on the adhesive thickness

Abstract

The mixed-mode strength of bonded joints can be predicted by techniques such as cohesive zone models (CZM), which requires the estimation of the adhesive strength and fracture toughness ( GC). Under the scope of fracture properties, the tensile and shear fracture toughness ( GIC and GIIC, respectively) and the corresponding mixed-mode behaviour are particularly relevant. Moreover, these parameters highly depend on the adhesive thickness ( tA), making it relevant to validate and propose CZM laws for bonded joint design. This work numerically addressed the tA influence on the mixed-mode fracture process of adhesive joints. For this purpose, single-leg bending (SLB) test experimental data was used, considering joints with composite adherends and a ductile adhesive, and tA from 0.1 to 2.0 mm. A numerical CZM analysis was performed, including the experimental and numerical load-displacement ( P- δ) curves’ comparison for validation, followed by the CZM law estimation and fracture envelope validation, for all tA. The effect of the different CZM parameters on the results was finally evaluated. Overall, it was possible to numerically ascertain the tA effect on the fracture behaviour of adhesive joints and to propose a numerical technique for mixed-mode bonded joint analysis.