Effect of time-varying on interface synergy and fractional-order modeling of nonlinear strength degradation in SiCf/PyC/SiC composites under 1350 ℃

This study investigates the influence of time-varying effects on the microstructural evolution and mechanical properties of SiCf/PyC/SiC composites under 1350 °C dynamic thermal scouring. Based on the capability of fractional calculus to describe systems with memory effects and long-range correlations, a High-Temperature Time-Dependent Strength Damage Model (HTDDM) was established using Caputo-type fractional derivatives. Systematic experiments and theoretical analysis reveal that the tensile strength exhibits a non-monotonic variation with thermal-scouring time, increasing followed by a subsequent decline. Results indicate that 2–3 h of thermal scouring represents the optimal process window. During this period, the interfacial bonding strength enters an adaptive-range, maintaining essential fiber pull-out mechanisms while in-situ Si-O-C whiskers trigger secondary toughening. Conversely, thermal scouring exceeding 5 h induces excessive volumetric expansion from SiO₂ formation, a reversal from compressive to tensile residual stresses, and complete degradation of the PyC interphase. Ultimately, this leads to the collapse of the synergistic load-bearing system.