A study on the effect of surface roughness on the strength of single lap joints

Summary form only given. Many surface treatments to improve adhesion roughen the surface. Treatments such as abrasion and etching remove the weak boundary layer and improve wetting behavior. Liquid adhesives that are spread during application do not ensure removal of air from cavities on the surface. Adhesive penetration into substrate pores is influenced by capillary forces and retarded by viscosity. Surface roughness can affect adhesive spreading and contact angle. In order to investigate aspects of surface roughness, surface profile, resin viscosity, and surface morphology, experiments were conducted using two steels (1018 cold rolled and hot rolled weld steel). Four surface modifications were performed on these samples by grit blasting at 552 kPa and 276 kPa from a distance of 25.4 mm and chemical etching using chromic acid for 2 mins and 10 mins. Crossed patterns were also obtained by an etch technique which involved changing the metal sample dip angle into the etch solution. Two resins were used to assess viscosity effects in interaction with different surface topographies. Contact angles were measured on all surfaces using these resins. Metal specimens were bonded under pressure and oven cured at 121/spl deg/C for 2 hours. To gain insight into the effect of surface topography, SEM was used to observe the modified surfaces. Average roughness was measured using a profilometer and surface profiles were obtained for all samples. The strength and displacement values were measured at crosshead speeds of 1 and 100 mm/min, to assess the interrelation between failure mechanisms and joint displacements, surface topography and resin viscosity.