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 (f rictional) heating of unidirectional SiC-fiber/ calcium aluminosilicat e-matrix composites was investigated at room temperature. Specimens me re subjected to tension-tension fatigue at sinusoidal loading frequenc ies 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 sha rply as the loading frequency was increased, (2) for all loading frequ encies, fatigue failures occurred at stress levels that mere significa ntly below the monotonic proportional limit stress of similar to 285 M Pa, and (3) pronounced internal heating occurred during fatigue, with the surface temperature of the fatigue specimens increasing by 160 K d uring 350-Hz fatigue at a peak stress of 240 MPa.