The effects of frequency and temperature on the fatigue behavior of a unidirectional titanium-matrix composite

In this study the effects of frequency and temperature on the fatigue behav ior of a unidirectional titanium-matrix composite (TMC), SCS-6/Ti-6-4, have been investigated. Fatigue tests were conducted under tension-tension, loa d-controlled, isothermal conditions. Specimens were cycled over a range of frequencies (0.01, 0.1, 1 and 10 Hz) and at different temperatures (23 degr ees C, 370 degrees C, 427 degrees C and 538 degrees C) in the laboratory en vironment. It was observed that there was no dependence on frequency below 400 degrees C, but above 400 degrees C the test frequency affected the cycl ic stress/strain response, damage mechanisms, and fatigue life. Plots of te st frequency versus cycles to failure showed that fatigue life was more cyc le-dependent at higher frequencies and more time-dependent at lower frequen cies. Comparisons of fatigue lives under different isothermal temperature e nvironments showed that these frequency effects were magnified as the tempe rature increased above 427 degrees C which was a result of the time-depende nt nature of the matrix at higher temperatures. (C) 1999 Elsevier Science L td. All rights reserved.