Interlaminar Fracture Behavior of Composites: The Role of Interface Layers Angle and Cure State in Mode I Delamination Growth

Composite laminates are widely used in structural applications due to their high stiffness-to-weight ratio and tailoring capability; however, their durability is often limited by interlaminar crack growth. Under Mode I loading, the strain-energy release rate governs delamination resistance and is influenced by both interfacial fiber orientation and the curing condition of the polymer matrix. This study presents a systematic experimental investigation of the effects of interface ply angle and curing temperature on crack propagation behavior using Double Cantilever Beam (DCB) tests on glass/epoxy laminates. Four interface configurations (0//0, 0//30, 0//45, and 0//90) were examined under different curing schedules, including room-temperature cure and thermally post-cured conditions. The results show that interfacial fiber orientation significantly affects the crack-growth resistance and the shape of the R-curve, with misaligned interfaces exhibiting higher propagation toughness than the baseline 0//0 configuration. Off-axis interfaces (0//30 and 0//45) displayed elevated energy dissipation during crack growth, while the 0//90 interface exhibited the highest propagation toughness, associated with non-planar crack advance and repeated crack arrest events. Post-curing led to a consistent increase in the measured propagation strain-energy release rate across all interface configurations, indicating improved resistance to stable delamination growth. Overall, the findings demonstrate that both interfacial architecture and curing history play important roles in governing Mode I delamination behavior in composite laminates. The results provide experimental insight into how ply orientation and post-curing can be used as practical parameters to tailor crack-growth resistance and improve interlaminar fracture performance.