Effects of single-phase and Co-deposited interphases on mechanical hysteresis behavior in T700^TM mini-C_f/SiC composites

Hysteresis behavior in C_f/SiC composites is affected by the interface properties. The objective of this paper is to establish the relationship between the mechanical hysteresis behavior of mini-C_f/SiC composites and interphase type (i.e., single-phase PyC interphase and co-deposited (PyC + SiC) interphase) and thickness (i.e., 300 ∼ 2000 nm). Cyclic tensile loading/unloading experiments were conducted for different mini-C_f/SiC composites. Evolution of composite's cyclic strain, hysteresis width, and secant modulus with increasing peak stress were analyzed. The composite's thermal residual stress (TRS) was obtained through the common intersection compliance point (CIP) method. Micro damage mechanisms of surface cracking in the matrix and fiber's pullout at the fracture surface were observed under the SEM to characterize composite's internal damage state. A micromechanical first loading–unloading-reloading constitutive model was developed to predict cyclic mechanical response. The values of interface slip ratio (ISR) and interface shear stress (ISS) were obtained through the hysteresis analysis. For the same interphase thickness and similar fiber volume of PyC and (PyC + SiC) interphase, the ultimate tensile strength (UTS) of mini-C_f/SiC composites with the PyC interphase was higher than that of the samples with the (PyC + SiC) interphase. The values of ISS for the mini-C_f/SiC with the (PyC + SiC) interphase were much higher than those of mini-C_f/SiC with PyC interphase.