New insights into interface characterization of ceramic matrix composites: Theory and application of hysteresis loops with Coulomb friction

To better predict the stress–strain relationship during unloading/reloading cycles in unidirectional fiber-reinforced ceramic matrix composites (FRCMCs), a comprehensive micromechanical hysteresis loop model is proposed, considering Coulomb friction and incorporating effects of interphase thickness, Poisson effect, residual thermal stress (RTS), and interfacial roughness. Based on the model, the hysteresis behavior is categorized into three distinct domains, i.e., small debonding energy (SDE), large debonding energy (LDE), and overlarge debonding energy (OLDE). For FRCMCs with low debonding toughness and thin interphase, the SDE scenario is more prevalent. By applying the model to interface characterization, we propose a more scientific set of parameters for interfacial performance description, including frictional coefficient, initial interfacial radial pressure, debonding toughness, and axial RTS. Furthermore, a method for obtaining the interfacial parameters based on tensile hysteresis tests is established, taking into account all the three domains. Especially, an innovative two-stage fitting approach is designed to derive interfacial properties for the SDE case, addressing the gaps in prior research. The comparison of the current model with experimental data for C_f/PyC/SiC and Nicalon/CAS composites demonstrates the reliability in hysteresis testing analysis.