Near-Threshold Fatigue Crack Growth Behavior of SUS304 Steel at High Temperatures Using Interferometric Strain/Displacement Gage : 2nd Report, Fatigue Crack Growth Behavior

Fatigue crack growth tests were conducted at 450, 550, 650 and 700(℃)using type 304 stainless steel. Crack closure level was measured using the interferometric strain/displacement gage(I.S.D.G.), described in the previous paper. Crack growth rates for stress ratio R= -0.1 plotted against stress intensity factor range, ΔK, deviated from those for R=0.5. Using the effective stress intensity factor range, ΔK_<eff> and effective J-integral range, ΔJ_<f, eff> which were calculated using crack opening ratio determined from the I.S.D.G. measurement, the crack growth behaviors for R=0.1 and 0.5 were reconciled at each test temperature. A threshold value, ΔK_<eff, th> of fatigue crack growth was determined at each temperature investigated. It was found that the threshold value reached a maximum at a temperature between 450 and 550(℃).