Mean Stress Effect on Fatigue Behavior of Austenitic Stainless Steel in Air and LWR Conditions

The mean stress effect on the fatigue life of Type 316 stainless steel was investigated at 325°C in simulated PWR primary water. It was shown that, as shown in high-temperature air environment, the fatigue life was extended by applying the mean stress under the same stress amplitude. An increase in the maximum peak stress by applying the mean stress induced additional plastic strain and this hardened the material. On the other hand, the fatigue life was shortened by the mean stress for the same strain range. The ratcheting strain caused by applying mean stress accelerated crack mouth opening and reduced fatigue life. It was also shown that the fatigue life in the simulated PWR primary water was shorter than that in air even without the mean stress. The magnitude of the reduction depended on the strain range. The reduction in fatigue life was the maximum when the strain range was 0.6%. The environmental effect disappeared when the effective strain was less than 0.4%.

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Mean Stress Effect on Fatigue Properties of Type 316 Stainless Steel in Pressurized Water Reactors Primary Water Environment

Journal of Pressure Vessel Technology ◽

10.1115/1.4043997 ◽

2019 ◽

Vol 141 (5) ◽

Author(s):

Masayuki Kamaya

Keyword(s):

Stainless Steel ◽

Fatigue Life ◽

Water Environment ◽

Stress Effect ◽

Mean Stress ◽

Pressurized Water ◽

316 Stainless Steel ◽

Mean Stress Effect ◽

Primary Water ◽

The Mean

The mean stress effect on the fatigue life of type 316 stainless steel was investigated in simulated pressurized water reactor (PWR) primary water and air at 325 °C. The tests in air environment have revealed that the fatigue life was increased with application of the positive mean stress for the same stress amplitude because the strain range was decreased by hardening of material caused by increased maximum peak stress. On the other hand, it has been shown that the fatigue life obtained in simulated PWR primary water was decreased compared with that obtained in air environment even without the mean stress. In this study, type 316 stainless steel specimens were subjected to the fatigue test with and without application of the positive mean stress in high-temperature air and PWR water environments. First, the mean stress effect was discussed for high-temperature air environment. Then, the change in fatigue life in the PWR water environment was evaluated. It was revealed that the change in the fatigue life due to application of the mean stress in the PWR water environment could be explained in the same way as for the air environment. No additional factor was induced by applying the mean stress in the PWR water environment.

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Fatigue behavior of 316L austenitic stainless steel in air and LWR environment with and without mean stress

MATEC Web of Conferences ◽

10.1051/matecconf/201816503012 ◽

2018 ◽

Vol 165 ◽

pp. 03012 ◽

Cited By ~ 2

Author(s):

Wen Chen ◽

Philippe Spätig ◽

Hans-Peter Seifert

Keyword(s):

Stainless Steel ◽

Fatigue Life ◽

Austenitic Stainless Steel ◽

Fatigue Limit ◽

Fatigue Behavior ◽

Cyclic Hardening ◽

Fatigue Tests ◽

Mean Stress ◽

Test Results ◽

316L Austenitic Stainless Steel

The fatigue life design curves in nuclear codes are generally derived from uniaxial straincontrolled fatigue test results. Evidently, the test conditions are very different from the actual components loading context, which involves much more complex thermo-mechanical loading including mean stress, static load holding time and variation in water chemistry, etc. In this work, the mean stress and environmental effects on fatigue life of 316L austenitic stainless steel in air and light water reactor (LWR) environment were studied using hollow fatigue specimens and testing under load-controlled condition. Both positive (+50 MPa) and negative (-20 MPa) mean stresses showed beneficial effect on fatigue life in LWR environment and in air. This is tentatively attributed to mean stress enhanced cyclic hardening, which leads to smaller strain response at the same loading force. -20 MPa mean stress was found to increase fatigue limit, whereas the effect of +50 MPa mean stress on fatigue limit is still unclear. The preliminary results illustrate that the environmental reduction of fatigue life is amplified in load-controlled fatigue tests with tensile mean stress.

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