The combined effect of frequency and load level on fatigue crack growth in stainless steel 304

The crack growth behavior in stainless steel 304 was investigated at 538°C. Compact tension specimens, 50 mm wide and 12.5 mm thick, were subjected to fatigue loading under R=0.05 load control. The combined effect of frequency (0.05 Hz≤f≤10 Hz) and load level (6 kN≤Pmax≤16 kN) on the crack growth rate was examined. Parameters ΔK and ΔJ were shown to correlate crack growth rates reasonably well. Two (f−Pmax) domains were suggested, in each of which crack growth can be characterized by a single da/dN–ΔK equation. For ΔK<25 MPa m, crack growth rates appear to be independent of f×Pmax values, except at the lowest where faster crack growth occurred because of environmental effects. For ΔK>25 MPa m, crack growth rates were found higher for larger values of f×Pmax. The mode of crack growth was transgranular for all test conditions.