Effects of surface treatment and adhesive thickness on the shear strength of precision bonded joints

In the present work single-lap-joint specimens with an adhesive layer of micron-scale thickness were prepared, and the effects of adhesive thickness and surface treatments (Milling, SAA, PAA, and SB + SAA) on the bond strength were investigated by tensile tests and surface analyses. The shear strength increases with the increase of adhesive thickness for the milling surface, while it is not presented for the other treated surfaces. PAA treatment can significantly improve the bond strength, while the sandblasting treatment cannot despite the surface roughness greatly increased. The bond strength depends on many surface characteristics, such as the peak density, nano-scale pores, and texture direction, instead of only the roughness value or wettability. The shear energy consumption of the single-lap joints is positively correlated with the shear strength, which evaluates the surface treatment methods for improving the bond strength at a thin adhesive thickness as PAA > Milling > SB + SAA > SAA.