Characterization of crack propagation in mode I delamination of multidirectional CFRP laminates

During the experimental characterization of the mode I interlaminar fracture toughness of multidirectional composite laminates, the crack tends to migrate from the propagation plane (crack jumping) invalidating the tests. In an earlier numerical study [9], we reported that this problem could be eliminated by choosing the appropriate bending stiffness of the beam arms. In the current paper, six stacking sequences were defined numerically and checked experimentally to validate the methodology presented in the numerical study. The results showed that crack jumping could be avoided by increasing the stiffness of the crack arms. Micrographies of the tested specimens showed that the delamination was not a perfect interlaminar fracture, as is usually considered. Instead, the propagation of delamination occurred with fiber tearing. The toughness values showed a dependency upon both the amount of fiber bridging and the interface angles.