FREQUENCY-DEPENDENCE OF FATIGUE LIFE AND INTERNAL HEATING OF A FIBER-REINFORCED CERAMIC-MATRIX COMPOSITE

The influence of loading frequency on the fatigue life and internal (frictional) heating of unidirectional SiC-fiber/ calcium aluminosilicate-matrix composites was investigated at room temperature. Specimens mere subjected to tension-tension fatigue at sinusoidal loading frequencies from 25 to 350 Hz and maximum fatigue stresses of 180 to 240 MPa. The key findings of the study were that (1) fatigue life decreased sharply as the loading frequency was increased, (2) for all loading frequencies, fatigue failures occurred at stress levels that mere significantly below the monotonic proportional limit stress of similar to 285 MPa, and (3) pronounced internal heating occurred during fatigue, with the surface temperature of the fatigue specimens increasing by 160 K during 350-Hz fatigue at a peak stress of 240 MPa.