Near—Threshold Fatigue Crack Growth Properties for SB42 and SUS304 Steels at Elevated Temperatures : Solid-Mechanics, Strength of Materials

Abstract

Near-threshold fatigue crack growth behavior for SB 42 carbon steel and SUS 304 stainless steel was investigated at elevated temperatures of 200 and 400°C at a frequency of 50 Hz. A new test procedure was atempted in order to avoid crack closure: ΔK was decreased under increasing minimum load. A unique ΔK_th-value of about 2.8 MPa·m^1/2 was obtained independent of material and temperature by the closure-free test procedure. The crack growth rate, however, was found to be accelerated in the ΔK region higher than 4 MPa·m^1/2 for both materials at elevated temperatures. The fractographic features influenced by microstructure and environment were discussed in terms of the mechanism of crack growth.