Shear Strength Prediction and Interfacial Damage Mechanisms in High‐Silica Woven Composites Under Aging and Fatigue

ABSTRACT The quasi‐static shear mechanical behavior and damage mechanisms of high‐silica woven fiber‐reinforced phenolic interfaces after thermal‐oxidative aging and fatigue were investigated through shear tests in conjunction with digital image correlation (DIC) and scanning electron microscopy (SEM). The residual shear strength of interface progressively decreases with increasing fatigue amplitude, cycles, and duration of thermal‐oxidative aging. Up to 20,000 cycles, the residual strengths under fatigue loadings , , , and decreased by 8.9%, 12.9%, 21.3%, and 30.3%, respectively. At fatigue amplitude , thermo‐oxidative aging for 36, 76, and 103 days caused reductions of 30.4%, 34.6%, and 38.4% relative to the unaged specimens. DIC and SEM reveal that interfacial shear damage initiates at defects along the biphasic interface, progresses through microcrack propagation with concurrent penetration into the interlaminar region, and ultimately results in crack coalescence and macroscopic delamination‐induced instability failure. Under fatigue‐dominated loading, damage is characterized by fiber fracture and interlaminar debonding, whereas thermo‐oxidative aging suppresses fiber tearing but markedly exacerbates interlaminar debonding. Based on the equivalence principle of residual strength under fatigue loading‐cycling‐aging, a predictive model for residual shear strength was developed to account for the effects of thermal‐oxidative aging and fatigue. Experimental validation showed that the model achieved an average relative error of approximately 10%, demonstrating good agreement with the measured data.