Influence of laser ablation-induced surface topology on the mechanical behaviour of aluminium bonded joints

Abstract

The state of the surface plays a crucial role in defining the mechanical properties of bonded joints, in particular, the chemical state of the adherend surface and its structural morphology have been proved to be the main elements of the bonding process. The structural morphology of the surface strictly depends from its topological features, like roughness, presence and distribution of grooves, homogeneity, etc. In a previous work, the effect provided by pulsed Yb-laser ablation on the mode I energy release rate of aluminium double cantilever beam joints was evaluated, in order to identify a relation between the combination of laser parameters and the morphological characteristics of the ablated surfaces which can support in identifying the optimal process configuration. The experimental tests showed that the fracture toughness of the double cantilever beam joints grew up as the surface roughness increased until a threshold value, after which the grooves resulted too narrow to allow the adhesive to completely fill them, inducing a higher amount of entrapped air into the grooves and therefore reducing the level of failure propagation energy. In this work, the problem dealing with the influence that the presence of air bubbles has over the mechanical behaviour of bonded joints was considered and the study went deeper into the investigation on the relation between laser-induced surface topology and mechanical response of joints. Different surface textures involving different directions and conditions of treatment were realized and their effect on the mechanical properties of aluminium bonded specimens was evaluated through experimental tests. The characterization of the treated surfaces was carried out by observing them with a 3D optical profiler and with SEM analysis and by measuring some geometrical features of the patterns created as a result of laser ablation.