Experimental–Numerical Investigation of Mode I, Mode
II,
and Mixed‐Mode Delamination in a Multidirectional Carbon/Epoxy Laminate
K. J. Wong, K. C. Ting, M. N. Tamin ABSTRACT
To enable directional comparison of delamination behavior in multidirectional laminates across different mode ratios, elastic mismatch between laminate arms must be eliminated. This study examines Mode I, Mode II, and mixed‐Mode I/II delamination in a fully isotropic multidirectional carbon/epoxy composite, with identical elastic properties ensured for both the laminate and its sub‐laminates. Experimental characterization using Double Cantilever Beam (DCB), End Notched Flexure (ENF), and Single Leg Bending (SLB) tests showed that fracture toughness increased with mode ratio, from 687 N/m in Mode I to 933 N/m in mixed‐mode and 1708 N/m in Mode II. The Benzeggagh–Kenane criterion yielded a mode interaction parameter of 1.7. Fractographic observations revealed matrix cracking and fiber/matrix debonding as the dominant mechanisms in Mode I, while shear cusps governed Mode II behavior. A unified cohesive zone modeling framework using a single parameter set showed reasonable agreement with experimental force–displacement responses, with deviations of 3%–18% in peak force and initial slope, and 3% in the dissipated energy for the element furthest from the crack tip. Crack initiation occurred at mid‐width for DCB and SLB specimens and at the edge for ENF, followed by self‐similar growth.