Impact of surface preparation method on the fracture toughness of adhesive joints subjected to diverse loading modes

While research has explored surface treatment effects on fracture energies in pure modes (I or II), there is a lack of research under mixed-mode loading. The aim of this paper is to investigate the influence of surface treatment approaches on the fracture behaviour and fracture energy of adhesive joints at different loading modes. To achieve this, double cantilever beam (DCB) adhesive joints were manufactured considering two different surface treatment methods namely grit blasting and mechanical bristle blasting. The joints were subjected to five different mode mixities. Fracture energy for each tested condition was calculated based on a compliance-based approach. The fracture energies in mode I reached an increase of 55 % when grit blasting surface treatment was applied, while for mode II the fracture energy reached a value three times higher for mechanical bristle blasting surface treatment, both energies from the mixed mode tests. The failure mechanisms were also evaluated for joints with different surface treatments as a function of loading mode. In all tested conditions, a cohesive failure mode was observed; however, the results underscore the substantial influence of the surface treatment method on the fracture energy of adhesive joints. This is attributed to the distinct failure mechanisms observed under varying surface treatment conditions.