Discussion on Crack Growth Resistance Based on Loading Frequency Dependence of Near-Threshold Fatigue Crack Growth in SUS 304 Steel at Elevated Temperature

摘要

In a previous paper fatigue crack growth tests were conducted using constant K_max test method at 550℃ and loading frequency of 30, 3 or 30-3-30 Hz. At any frequency, after the increase of K_max in the near-threshold region, crack grew in the region below the threshold value determined using conven- tional constant R test method. By the comparison of the results it was shown that loading frequency gave several influences on threshold behavior and crack growth behavior. In this study, with the comparison using the ratio of da/dNs at f=3 Hz and 30 Hz, more details of the several influences were investigated. From the comparison, it was shown that two characteristics of resistance against crack growth, i.e. frequency dependence of resistance itself and that of increasing rate of resistance lead to frequency dependence of crack growth in the region below the conventional threshold value.