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 usin g simple linear viscoelastic principles. It was found that BSR results could predict the same time and temperature dependence as tensile cre ep; however, BSR-predicted creep strains usually overestimated the mag nitude of tensile creep strain. The time, temperature, and stress depe ndence were determined for all the fibers for the experimental conditi ons of this study. Some of the primary creep behavior can be explained by load-sharing effects between the core and the CVD SIC substrate an d some microstructural changes; however, the extent of primary creep c annot fully be accounted for from this work.