Discussions of Mode III Fracture Mechanisms in CFRP Laminates under ECT Tests Based on Non-destructive Observations

Abstract

In this study, mode III interlaminar fracture mechanisms were investigated using edge crack torsion (ECT) tests of carbon fiber reinforced plastic (CFRP) laminates. As mode III interlaminar fractures propagate within the closed interlayers, the optimal methods for observing fracture mechanisms are non-destructive. Thus, ultrasonic flaw detection and X-ray phase imaging methods were adopted. In the vicinity of the crack tip in the center region of the CFRP laminate, it was observed that cracks migrated from the initial interlayer to the neighboring one via the transverse cracks that precede delamination. Numerical simulations suggested that these transverse cracks were caused by out-of-plane shear stresses in the center region of the ECT test specimens. From these results, the effects of transverse cracks preceded by the delamination and the migration of crack propagating interlayers are not negligible in the evaluation of Mode III interlaminar fracture toughness using ECT tests.