The influence of adherend surface roughness on the failure at adhesive-adherend interface is analyzed experimentally for the adhesive joints of two types. Anisotropy of roughness undulation at adhesive-adherend interface produces the mechanical intertwining effect, and contributes to increase of shearing strength of adhesive bonding. The adherend surface roughness Ry' that minimizes the adhesive bonding strength is observed for simple lap joints. When the adherend surface roughness Ry is larger than Ry', it is general view that the larger the adherend surface roughness Ry is, the higher the bonding strength becomes. In the domain Ry < Ry' conversely, the strength of adhesive bonding extremely increases for small decrease of roughness. Randomly scratched adherend surface with minimum Ry shows high strength of adhesive bonding. Moreover, experimental analysis is carried out about strength characteristics of butt joints acted normal load for adhesive layer.
