Characterization of hysteresis stress-strain behaviors of C/SiC composites under different fiber pre-treatments

Three different pre-treatments on the carbon fiber preform were performed for several C/ S/'C composites and the respective mechanical hysteresis behaviors were compared by a loading/unloading test. An increase in residual strain, loop width and area, and a decrease in secant modulus with increasing peak stress were observed for all the composites. However, the composite with heat treatment has the steepest evolution of hysteresis characteristics owning to the largest thermal residual stress (TRS), which can be evidently alleviated by the pyrocarbon interphase between C fibers and SiC matrix. A proper interfacial bonding can be achieved by a heat treatment on the fiber preform previously coated with a thin pyrocarbon material, which enables the composite to possess excellent strength and toughness.