This study presents a comprehensive quantitative investigation into the material properties and damage behavior of unidirectional carbon fiber reinforced plastic laminates with ply discontinuities. Laminates with varying resin gap lengths were evaluated. In situ edge observations and X-ray computed tomography were employed to assess the damage processes in the area of the ply discontinuity. These methods examined initially occurring cracks, secondary cracks, and delamination. Some unexpected cracking behavior was observed in this study. For instance, initial cracks were observed to form not at the interface but at a distance from the resin–ply interface, likely due to a constraint condition caused by the chemical shrinkage of the resin during the curing process. Furthermore, all cracks in the resin region curved toward the center, with successively formed cracks having higher curvatures. This behavior can be attributed to the redistribution of principal stresses within the resin pocket following the initial cracks. The matrix cracking was followed by delamination that started from the tips of the matrix cracks and progressed toward the ends of the specimen. Additionally, the number and locations of cracks in the resin pocket were influenced by the length of the resin gap and the uniformity of the thickness and width of the specimen. In addition to the experimental investigation, a stress-based variational analysis was employed to predict crack onset stresses in the laminates. The analysis successfully calculated the energy release rate for laminates with varying resin pocket lengths and provided predictions for crack onset stresses. The analytical predictions demonstrated good agreement with the experimental observations, enhancing the understanding of resin pocket behavior in CFRP laminates.

Carbon fiber-reinforced plastics (CFRPs) offer excellent in-plane mechanical performance, but their relatively low interlaminar fracture toughness makes them vulnerable to delamination, particularly around intralaminar discontinuities such as resin-rich regions or fiber gaps. This study investigates the effectiveness of polyamide (PA) mesh inserts in improving interlaminar toughness and suppressing delamination in CFRP laminates with such features. Two PA mesh configurations were evaluated: a fully embedded continuous layer and a 20 mm cut mesh strip placed between continuous and discontinuous plies near critical regions. Fracture toughness tests showed that PA mesh insertion improved interlaminar toughness approximately 2.4-fold compared to neat CFRP, primarily due to a mechanical interlocking mechanism that disrupts crack propagation and enhances energy dissipation. Uniaxial tensile tests with digital image correlation revealed that while initial matrix cracking occurred at similar stress levels, the stress at which complete delamination occurred was approximately 60% higher in specimens with a 20 mm mesh and up to 92% higher in specimens with fully embedded mesh. The fully embedded mesh provided consistent delamination resistance across the laminate, while the 20 mm insert localized strain redistribution and preserved global mechanical performance. These findings demonstrate that PA mesh is an effective interleaving material for enhancing damage tolerance in CFRP laminates with internal discontinuities.

Matrix cracking in CFRP laminates results in mechanical properties degradation of the material such as the stiffness reduction, the existence of residual strains, etc. Usually, the damage parameters used for matrix cracking are stiffness reduction, Poisson’s ratio reduction and the change in thermal expansion coefficients. In this study, a damage parameter: the existence of the

Matrix cracking in CFRP laminates results in mechanical properties degradation of the material such as the stiffness reduction, the existence of residual strains, etc. Usually, the damage parameters used for matrix cracking are stiffness reduction, Poisson’s ratio reduction and the change in thermal expansion coefficients. In this study, a damage parameter: the existence of the