Abstract
The a.c. electric potential method was adopted for the crack length measurement in high temperature fatigue tests. The method was found easy to get the same relationship between the electric potential and the crack length as that in the d.c. potential method, when a constant a.c. of the relatively low frequency of 93Hz was supplied to the plate specimens of SUS304 stainless steel and titanium alloy, Ti-17, with a center crack or double edge cracks. Fatigue crack propagation tests were conducted on SUS304 at 600°C and on Ti-17 at 482°C under the trapezoidal waveforms with tension hold time in the crack center opening displacement (CCOD) control as well as the load control conditions. A creep-dominated, time-dependent relationship between the crack propagation rate, dl/dN, and the creep J-integral range, ΔJc, in the CCOD control condition was in good agreement with that in the load control condition, although the CCOD control test was a kind of ΔJc-decreasing tests. The titanium alloy, Ti-17, showed a lower bound of the available dl/dN-ΔJc data band of some heat resisting steels.
