Experimental evaluation of mode I fracture toughness of dissimilar-material joints with thermal residual stresses

The mode I interlaminar fracture toughness of dissimilar-material joints with thermal residual stresses is experimentally evaluated. The double cantilever beam (DCB) test is commonly used to assess the interlaminar fracture toughness of composites but is inadequate when dissimilar materials are joined owing to the mixed mode, which arises from differences in the bending stiffness and the thermal residual stresses formed during manufacturing because of differences in the linear expansion coefficient of the adherends. To address these difficulties, a new test, named the constant-load DCB test, was developed to evaluate the mode I interlaminar fracture toughness. In this study, a testing machine, based on the theoretical method previously established to derive the mode I interlaminar fracture toughness of dissimilar-material joints, is manufactured, and the fracture toughness is experimentally determined. As a result, good agreement between the theoretical value and experimental results is obtained, and the mode mixity ratio is significantly decreased compared with that of the general DCB test.