Adhesive thickness effects on the mixed-mode fracture toughness of bonded joints

Abstract

ABSTRACTAiming to predict the strength of bonded joints by techniques such as cohesive zone models (CZM), it is highly relevant to estimate the adhesive strength and fracture toughness (GC). Here, the tensile and shear fracture toughness (GIC and GIIC, respectively) and the corresponding mixed-mode behaviour acquire special relevancy. However, it is known that these parameters are highly dependent on the adhesive thickness (tA). The present work experimentally addresses the tA effect on the mixed-mode behaviour of bonded joints, namely on the tensile and shear fracture energies (GI and GII, respectively), using the Single-Leg Bending (SLB) test. Different data reduction schemes were applied. With this purpose, the respective resistance curves (R-curves) were calculated, which enabled plotting the respective fracture envelope for a sample tA by the knowledge of the pure-mode GIC and GIIC. Overall, it was possible to obtain a good agreement between methods for the mixed-mode GI and GII calculation and to estimate the most suitable fracture envelope of the adhesive for a given tA. The compliance-based beam method (CBBM) was found to be particularly suited to perform data reduction, since it accounts for the adhesives’ ductility and it is not affected by crack length (a) measuring errors.