Tension–tension fatigue behavior and residual strength evolution of SiC/(PyC/SiC)2/SiC minicomposites prepared by CVI+MI and CVI+PIP processes

Abstract

Abstract The residual tensile strength (RTS) evolution of SiC/(PyC/SiC)2/SiC samples, prepared by chemical vapor impregnation (CVI) combined with either melting reaction sintering (MI) or polymer impregnation and pyrolysis (PIP), was investigated after 106 cycles as the pre-fatigue stress increased. The fatigue limits of the two tested specimen types, CVI\xa0+\xa0MI and CVI\xa0+\xa0PIP, were 760 and 660\xa0MPa, respectively, corresponding to 95% and 75% of the tensile strength, respectively. Although the RTS of the two specimen types first increased and then decreased, it was interesting that after pre-fatigue, the maximum RTS of the CVI\xa0+\xa0PIP-prepared sample at 680\xa0MPa, was 16\xa0MPa higher than that of the CVI\xa0+\xa0MI-prepared sample at 590\xa0MPa. The nanoindentation results indicate that the matrix prepared by CVI could protect the fiber from heavy damage in subsequent preparation, and the matrix modulus and hardness were higher in samples prepared by PIP than those prepared by MI. According to the microstructure observations and hysteresis characteristics, it was concluded that the differences mainly came from the internal stress state, matrix, and fiber properties.