Behaviour of adhesive-bonded assemblies of galvanized steel sheets under shear loading

The mechanical properties of bonded galvanized steel structures may be improved by using different surface treatments. Results indicate that degreasing with trichloroethane leads to the highest failure stress, followed by a 2 M sodium hydroxide etch, an 0.5 M sodium hydroxide etch and treatment with Parcodine; a 1 N sulphuric acid etch is the least effective. In addition, the examination of fracture surfaces reveals four distinct zones which correspond to the following four delamination steps: a zone of purely adhesive failure accompanied by cracking and partial debonding of the zinc layer; a zone of mixed failure (adhesive and cohesive); a zone of purely cohesive failure; and a zone of mixed failure which is the source of final fracture.