Influence of Mean Stress on the Fatigue Behavior of 304L SS in Air and PWR Water

Abstract

Load-controlled experiments on 304L stainless steel were run in Air and PWR water, at 150°C and 300°C, with and without a mean stress of 100MPa. These experiments were run to determine the influence of temperature, environment, and mean stress on the 107 Cycle Fatigue Limit stress amplitude. A 100MPa mean stress was found to have different effects at the different temperatures and environments. In contrast to all the conventional models used to describe the effects of mean stress, when the testing was done at 300°C (for both air and PWR water), a 100MPa mean stress was found to raise the 107 Cycle Fatigue Limit relative to that observed without a mean stress. This was ascribed to the effect of the hardening due to the initial straining and to secondary hardening, both of which are more pronounced at 300°C than at 150°C. The increased initial and secondary hardening resulted in the development of less non-elastic strain, thereby improving the fatigue behavior. In PWR water at 150°C, a 100MPa mean stress reduced the 107 Cycle Fatigue Limit by more than that predicted by conventional mean stress models, but in air at 150°C, the decrease in the endurance limit was more in keeping with the predictions of these models. This difference was ascribed to the effect of the PWR water, in the absence of significant initial straining and secondary hardening.

Influence of strain range on fatigue life reduction of stainless steel in PWR primary water

“…In general, the environmental effect can lower the fatigue limit, and the magnitude of the effect depends on the strain range. 10 This study is aimed at investigating the detailed strain range dependency of the environmental effect in simulated Nomenclature: ΔK ε , Strain intensity factor; Δε, Strain range; a, Crack depth; dε/dt, Strain rate; f, Geometrical constant for strain intensity factor; F en , Fatigue life correction factor; N f , Fatigue life; N f(air) , Fatigue life in air; N f(pred) , Fatigue life obtained by crack growth prediction; t, Thickness of hollow specimen; V air , Crack growth rate in air; V PWR , Crack growth rate in PWR water environment coolant water of a pressurized water reactor (PWR). It has been shown that the fatigue life consists of the number of cycles for small crack initiation (hereafter, initiation life) and that for the crack growing to a critical size for specimen failure (hereafter, growth life).…”

Environmental Fatigue Behavior of a Z3CN20.09M Stainless Steel in High Temperature Water

“…As is seen, in the same loading condition, the fatigue life of the Z3CN20.09M ASS in water at 300 • C was shorter than that in air at RT [2,3,6,9,[13][14][15]. It indicates that the involvement of corrosive medium or the interactions of corrosive medium with applied load might be responsible for the decrease in the fatigue life of the Z3CN20.09M ASS [16,17]. At the same strain amplitude, the decrease in strain rate yielded a lower fatigue life [15,[18][19][20][21].…”

“…Furthermore, the difference in the fatigue life at these three strain rates became more pronounced at higher strain amplitude. It might be caused by the higher corrosion rate of the tested material at higher strain amplitude in the autoclave environments [6,[13][14][15][16][17][18][19][20][21][22][23][24][25][26][27].…”

Overview of French Proposal of Updated Austenitic SS Fatigue Curves and of a Methodology to Account for EAF

“…The second method simply consists in multiplying the strain by a weighted K e value (K e avg ), defined as follows: (10) The analyst can choose either one of the methods or even use another methodology that ensures a conservative result.…”