Test and Prediction of <scp>ESET</scp> Fracture Toughness of Fiber‐Reinforced Composite Under Different Orientations

ABSTRACT Precisely elucidating the influence of various orientations on the fracture performance of unidirectional fiber‐reinforced composites (UD FRCs) is crucial for evaluating the structural integrity of defect UD FRCs. Existing studies lack in‐depth analysis of failure mechanisms and accurate prediction of fracture toughness for different orientations. Quasi‐static eccentrically‐loaded single edge crack tension (ESET) fracture tests were conducted in air on compression‐molded unidirectional T300 carbon fiber/7901 epoxy composites with fiber orientations spanning 0°–90° (15° increments). The digital image correlation technology was used to reveal the deformation and failure mechanisms during the fracture process. Then, the mixed‐mode I‐II trilinear cohesive zone model (CZM) was developed and used to predict fracture behavior under different orientations. It was found that increasing the orientation angle leads to a higher initiation fracture toughness, consistent with the observed trend in maximum tensile strain ε yy . The relationship between fracture toughness and ε yy has been established. Moreover, combined with microanalysis, it can be observed that as the orientation angle increases, the failure mechanism shifts from fiber–matrix interface debonding, matrix cracking, and fiber bridging to matrix shear failure, fiber breakage, and pull‐out. Finally, the CZM method combined with the established B‐K parameters relationship can quickly and accurately predict fracture toughness under any orientations, and the maximum error is less than 3%. The current research on the damage mechanism and reliability evaluation of FRCs is of great significance.