On enhancement of fracture resistance of adhesive joints by surface micropatterning using a femtosecond laser

This study focuses on the influence of surface micropatterns, including uniform and nonuniform grooves fabricated by selective removal of a designed volume from aluminum alloy substrates using a femtosecond laser, on the mode I fracture behavior of adhesively bonded interfaces. The morphology, wettability, chemistry and microstructure of the patterned surfaces have been analyzed. The mode I fracture behavior of adhesive joints was characterized by measuring the fracture resistance using a J-integral approach, and the fracture process in the joint was investigated numerically using a continuum damage model. The results show that the laser patterning has modified the surface roughness, wettability and surface chemistry such that the fracture resistance could be greatly increased. It also reveals the significance of patterning uniformity across the surfaces and the existence of a limiting effective patterning ratio (the ratio of the patterned area to the flat bonding area) on enhancing the fracture resistance. Local plastic deformation that occurred in the adhesive at the patterned structures due to stress concentration was found to be one toughening mechanism although it tended to induce crack growth close to one substrate-adhesive interface.