Investigation on the measurement of pure mode-Ⅲ delamination fracture toughness of CFRPs

This study focuses on the characterization of pure mode-Ⅲ delamination behavior of continuous carbon fiber reinforced polymer (CFRP) laminated composites. Compared to mode-Ⅰ, mode-Ⅱ and mixed mode-Ⅰ/Ⅱ delamination, studies on the mode-Ⅲ delamination and mixed mode delamination with mode-Ⅲ are relatively rare and insufficient. Currently, there is still no international universal test standard established for pure mode-Ⅲ delamination, as well as mixed mode delamination with mode-Ⅲ. For characterization of pure mode-Ⅲ delamination fracture toughness, the most challenge is to obtain a pure mode-Ⅲ delamination with a uniform strain energy release rate (SERR) distribution along the delamination front. The development for pure mode-Ⅲ delamination testing methods is summarized. The testing method for pure mode-Ⅲ delamination, edge crack torsion (ECT) and edge ring crack torsion (ERCT) are evaluated. Numerical results show that the unwanted mode-Ⅰ and mode-Ⅱ components can be neglected for both unidirectional and woven carbon epoxy composites. In addition, with the optimization of specimen configuration, a more uniform distribution of mode-Ⅲ SERR along delamination front is obtained. ECT and ERCT are compared experimentally.