CYCLIC-FATIGUE BEHAVIOR OF SIC SIC COMPOSITES AT ROOM AND HIGH-TEMPERATURES/

Tension-tension cyclic-fatigue tests of a two-dimensional-woven-SiC-fi ber-SiC-matrix composite (SiC/SiC) prepared by chemical vapor infiltra tion (CVI) were conducted in air at room temperature and in argon at 1 000 degrees C, The cyclic-fatigue limit (10(7) cycles) at room tempera ture was similar to 160 MPa, which was similar to 80% of the monotonic tensile strength of the composite, However, the fatigue limit at 1000 degrees C was only 75 MPa, which was 30% of the tensile strength of t he composite, No difference was observed in cyclic-fatigue life at roo m temperature and at 1000 degrees C at stresses >180 MPa; however cycl ic-fatigue life decreased at 1000 degrees C at stresses < 180 MPa. The fracture mode changed from fracture in 0 degrees and 90 degrees bundl es at high stresses to fracture mainly in 0 degrees bundles at low str esses, Fiber-pullout length at 1000 degrees C was longer than that at room temperature, and, in cyclic fatigue, it was longer than that in m onotonic tension, The decrease in the fatigue limit at 1000 degrees C was concluded to be possibly attributed to creep of fibers and the red uction of the sliding resistance of the interface between the matrix a nd the fibers.