Evaluation of Interfacial Fracture Toughness between Paint and Steel Sheet in Paint-coated Steel Sheet System Using DCB Specimen

A method for evaluating the interfacial adhesion strength between paint layer and chromate-coated steel sheet in the paint-coated steel sheet system was proposed. Three kinds of the steel sheets modified with chromic acid which contained various content of colloidal silica and a paint composed of a mixture of alkyd resin and silica particles were used as specimens for the experiment. The adhesion strength was evaluated by the critical strain energy release rate at interfacial crack initiation. To measure the critical strain energy release rate, an asymmetric double cantilever beam specimen was used, where an interfacial pre-crack was induced between the paint layer and steel sheet. When the crack propagates along the interface between paint layer and chromate-coated steel sheet, it was observed that the critical strain release rate increase with increasing the content of colloidal silica in the chromate-coated steel sheet. Similar dependency of the silica content on the adhesion strength had been also confirmed in the cross cut tests. This signified that the interfacial adhesion strength could be evaluated quantitatively by the critical energy release rate.