Size‐Dependent Strength and Failure Mechanisms of Cross‐Ply Thick Composite Laminates Under Flexural and Interlaminar Shear Loading

ABSTRACT The size effects on the flexural strength and interlaminar shear strength for cross‐ply thick composite laminates are systematically investigated, with particular emphasis on the coupled influence of specimen thickness and curing‐induced overheating. Cross‐ply specimens with thicknesses ranging from 2.4 to 16.2 mm are experimentally tested, and the failure mechanisms are analyzed through microscopic observations and numerical simulations. The curing‐induced overheating is exacerbated by increasing specimen thickness, leading to matrix degradation and a quantitative correlation with strength reduction. To overcome the limitation of existing size effect models, which primarily attribute strength reduction to statistical variability or fracture‐mechanics‐based scaling, an improved energetic‐statistical size effect law is proposed by incorporating a physically defined damage variable λ T accounting for curing‐induced overheating. The results indicate that the flexural strength and interlaminar shear strength have a tendency to decrease by about 40% and 22% with the increase of specimen thickness, while the dominant failure mechanisms remain statistically invariant. The proposed model demonstrates improved predictive accuracy over the classical Bazant and Carpinteri model, particularly for thick laminates where curing‐induced overheating cannot be neglected. From an engineering perspective, the proposed model provides a rational basis for strength prediction and structural design of thick composite components, such as center wing box, wind turbine blade and satellite support structures, where thickness often exceeds standard coupon dimensions and curing‐induced thermal gradients may significantly influence load‐bearing capacity.