Comparison of bend stress relaxation and tensile creep of SVD SiC fibers

Three different CVD SiC fibers were tested for bend stress relaxation (BSR) and tensile creep over a wide range of temperatures, times, and stresses, Primary creep was always observed, even for creep strains on the order of 2%. The BSR and tensile creep results were compared using simple linear viscoelastic principles. It was found that BSR results could predict the same time and temperature dependence as tensile creep; however, BSR-predicted creep strains usually overestimated the magnitude of tensile creep strain. The time, temperature, and stress dependence were determined for all the fibers for the experimental conditions of this study. Some of the primary creep behavior can be explained by load-sharing effects between the core and the CVD SIC substrate and some microstructural changes; however, the extent of primary creep cannot fully be accounted for from this work.