U-notch fracture analysis in laminated E-glass/epoxy composites under out-of-plane shear loading: Theories versus experiments

This study investigates the mode III translaminar fracture behavior of U-notched E-glass/epoxy laminates through combined experimental and theoretical analyses. Although stress-based fracture criteria have been successfully applied to unidirectional U-notched laminates under mode III loading, their applicability to multidirectional configurations remains limited. The present study extends the analysis to cross-ply and quasi-isotropic laminates within a unified fracture assessment framework. ASFPB tests are conducted on laminate with different configurations and notch-tip radii. The virtual isotropic material concept (VIMC) represents the anisotropic laminates as equivalent isotropic plates. Within this framework, a methodology is proposed for determining the mode III critical stress parameter and characteristic distances of the laminates, rather than directly adopting the tensile strength as the fracture-controlling stress. The fracture resistance is predicted using the point stress (PS) and mean stress (MS) criteria. The experimental results reveal that fracture resistance is governed by both notch-tip radius and laminate configuration. Increasing the notch-tip radius from 0.35 to 2 mm enhances the measured fracture resistance by approximately 29−67%, depending on the laminate configuration. The unidirectional laminate exhibits the highest resistance, followed by the quasi-isotropic and cross-ply laminates. VIMC-PS predicts the experimental findings with discrepancies of 3.2−26.1%, whereas VIMC-MS shows discrepancies of 6.4−27.4%.