Mechanical behavior and failure analysis of 2D-C/SiC composite under on- and off-axis loading

Mechanical behavior and failure mechanisms of two-dimensional plain-woven carbon fiber-reinforced silicon carbide (2D-C/SiC) composite were investigated under on- and off-axis loading conditions. Detailed analysis of the off-axis loading effect was conducted by employing the digital image correlation (DIC) technique, acoustic emission (AE) monitoring, high-speed imaging, and fractographic analysis. The results reveal obvious tension–compression asymmetry and angular dependence in mechanical response. Compared to the weak nonlinear stress–strain response under on-axis loading, off-axis tensile responses exhibit pronounced nonlinearity, due to elevated damage in the matrix and fiber/matrix interface. The absence of fibers in the loading direction and the intensified damage under off-axis loading contributes to the strength degradation. A gradual transition in failure mode from tensile-dominated to tensile-shear-coupled is observed as the off-axis angle increases. Furthermore, the applicability of the Tsai-Wu failure criterion to 2D-C/SiC was evaluated based on experimental data. The Tsai-Wu criterion, with interaction coefficient calibrated with the 45° off-axis test, provides a practical and reliable approach for strength prediction of 2D-C/SiC composite.