Mixed mode fracture toughness of adhesively bonded joints with residual stress

Adhesively bonded double cantilever beam (DCB) test specimens with residual stress were manufactured. Deforming the adherends during the curing process caused the DCB specimens to curve due to the residual stress and shear load arose at the adhesive layer. Therefore, mixed mode fractures were generated by applying mode I loading to the specimens. The relation between the specimen curvature and the strain energy due to the residual stress was theoretically investigated and the mode II energy release rate for each specimen was calculated using measured specimen curvature. Because the mode I energy release rate for each specimen can be calculated with the DCB test result, the fracture toughness in mixed mode conditions was discussed. By manufacturing the specimens with different residual stresses, mixed mode fracture tests with various mixed mode ratios were conducted and the effect of the mixed mode ratio on the energy release rates was investigated.