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Currently, considerable attention has been directed towards the significant role of the interphase in dictating the mechanical properties of composites. Herein, the mechanical behavior of SiC f /SiC composites with two distinct interphases, BN and BN/SiC, was delved into under a three-point bending. Meanwhile, analyses of the damage process and failure mechanism of the composites were conducted using acoustic emission (AE), digital image correlation (DIC), and dynamic mechanical analysis (DMA) methods. The results demonstrated the moderate interfacial bond strength of composites with BN/SiC interphase. Cracks were observed to be repeatedly deflected at the matrix/SiC interphase and fiber/BN interphase, leading to a larger bending strength and a pseudoplastic fracture mode. Ultimately, shear forces led to the failure of the composites. Overall, this study indicates that damage analysis provides a theoretical basis for comprehending potential damage in composites and optimizing interphase design. • Multi-scale analysis of damage mechanisms using non-destructive testing. • The crack deflection mechanisms of different interphases were analyzed. • The correlation of AE, DIC and DMA test methods in damage monitoring was established. [ABSTRACT FROM AUTHOR]

[Display omitted] • The damage evolution of SiC f /SiC composites with a BN/SiC multilayer interface oxidized at elevated temperature was analysed by acoustic emission. • The interface microstructure evolution depended on oxidation temperature was analysed, which controlled the mechanical behavior of SiC f /SiC composites. • Two different degradation mechanisms for oxidized composites are proposed based on characterization results. • The study provides guidance for the service life design of SiC f /SiC composites. In this study, the mechanical properties of SiC f /SiC composites with a BN/SiC multilayer interface was evaluated after oxidized at 800 °C, 1100 °C and 1400 °C for 200 h. The damage evolution of the fabricated and oxidized composites were analyzed by acoustic emission techniques. The chemical composition and structural evolution of the SiC f /SiC composites after oxidation were observed by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and energy dispersive spectroscopy. Significant temperature-dependent strength degradation of the SiC f /SiC composites was observed. The results indicated that the interfacial microstructure change caused by oxidation had a significant impact on the damage process of the composites, and two different degradation mechanisms for oxidized composites are discussed. The toughening mechanism of crack deflection and fiber pull out failed after oxidation at 800 °C. The degradation of the mechanical properties after oxidation at 1100 and 1400 °C was attributed to the hysteresis of fiber breakage caused by weak interface bonding. This work could predict the service life of SiC f /SiC composites and contribute to their early application in aerospace. [ABSTRACT FROM AUTHOR]