Damage mechanism and acoustic emission-based modeling of SiC/SiC tubes under combined tension-torsion loading

Ceramic matrix composites are ideal for thermo-structural components, where they often encounter complex multiaxial stress states. This study investigated damage evolution in plain-woven SiC/SiC tubes under combined tension-torsion loading using acoustic emission, three-dimensional digital image correlation, and fractography. Results demonstrated that the mechanical behavior was significantly influenced by the stress state. AE analysis revealed this was due to competitive and synergistic tensile-shear interactions, which intensify damage accumulation and drive a transition in the dominant energy dissipation mechanism. To quantify this damage evolution and identify the governing stress type, an AE-based damage initiation criterion and a failure progression envelope model were developed. Fractography further indicated that while the fracture path is governed by the governing stress type, a transition in governing stress type can occur during loading, specifically when tensile and shear stresses co-dominate. This shift directed fracture along the direction of maximum shear stress, consistent with observed fracture angles.