scholarly journals Influence of Strain Rate and Waveshape on Environmentally-Assisted Cracking during Low-Cycle Fatigue of a 304L Austenitic Stainless Steel in a PWR Water Environment

Metals ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 197 ◽  
Author(s):  
Thibault Poulain ◽  
Laurent de Baglion ◽  
Jose Mendez ◽  
Gilbert Hénaff
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Strain Rate ◽  
Crack Growth ◽  
Growth Rates ◽  
Low Cycle Fatigue ◽  
Water Environment ◽  
Cycle Fatigue ◽  
Pressurized Water ◽  
Environmentally Assisted Cracking

In this paper, the low cycle fatigue resistance of a 304L austenitic stainless steel in a simulated pressurized water reactor (PWR) primary water environment has been investigated by paying a special attention to the interplay between environmentally-assisted cracking mechanisms, strain rate, and loading waveshape. More precisely, one of the prime interests of this research work is related to the consideration of complex waveshape signals that are more representative of solicitations encountered by real components. A detailed analysis of stress-strain relation, surface damage, and crack growth provides a preliminary ranking of the severity of complex, variable strain rate signals with respect to triangular, constant strain-rate signals associated with environmental effects in air or in PWR water. Furthermore, as the fatigue lives in PWR water environment are mainly controlled by crack propagation, the crack growth rates derived from striation spacing measurement and estimated from interrupted tests have been carefully examined and analyzed using the strain intensity factor range ΔKε. It is confirmed that the most severe signal with regards to fatigue life also induces the highest crack growth enhancement. Additionally two characteristic parameters, namely a threshold strain εth* and a time T*, corresponding to the duration of the effective exposure of the open cracks to PWR environment have been introduced. It is shown that the T* parameter properly accounts for the differences in environmentally-assisted growth rates as a function of waveshape.

Influence of the Strain Rate on the Low Cycle Fatigue Life of an Austenitic Stainless Steel with a Ground Surface Finish in Different Environments

2014 ◽  
Vol 891-892 ◽  
pp. 1320-1326 ◽  
Author(s):  
Thibault Poulain ◽  
José Mendez ◽  
Gilbert Hénaff ◽  
Laurent de Baglion
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Austenitic Stainless Steel ◽  
Strain Rate ◽  
Surface Finish ◽  
Power Plants ◽  
Low Cycle Fatigue ◽  
Total Strain Amplitude ◽  
Cycle Fatigue ◽  
Pressurized Water

This paper focuses on the influence of strain rate in Low Cycle Fatigue (LCF) of a 304L austenitic stainless steel at 300 °C in different environments (secondary vacuum, air and Pressurized Water Reactor (PWR) water environment). Moreover test samples are ground to obtain a surface finish rougher than all that could be found in nuclear power plants. Different strain rates (4x10-3, 1x10-4and 1x10-5s-1) are studied, with a triangular waveform at a total strain amplitude of ±0.6%. The influence of strain rate on cyclic stress-strain behavior and fatigue life is firstly analyzed in secondary vacuum, considered as a non-active environment. Then, interactions between stain rate and environmental effects in Air and in PWR environment are presented. In all environments, a decrease in strain rate leads to a negative strain rate dependence of the stress response and a reduction in fatigue life. Finally, SEM observations of fatigue striations in PWR environment indicate a crack propagation rate enhancement when the strain rate is decreased.

Evaluation of the Effect of Dynamic Sodium on the Low Cycle Fatigue Properties of 316L(N) Stainless Steel Base and Weld Joints

2012 ◽  
Vol 31 (3) ◽  
Author(s):  
V. Ganesan ◽  
R. Kannan ◽  
K. Mariappan ◽  
G. Sukumaran ◽  
R. Sandhya ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Strain Rate ◽  
Low Cycle Fatigue ◽  
Constant Strain Rate ◽  
Fatigue Properties ◽  
Cycle Fatigue ◽  
Weld Joints ◽  
Steel Base

AbstractLow cycle fatigue (LCF) tests on 316L(N) austenitic stainless steel base and weld joints were at 823 K and 873 K at a constant strain rate of 3

Effect of Loading Signal Shape and of Surface Finish on the Low Cycle Fatigue Behavior of 304L Stainless Steel in PWR Environment

2010 ◽  
Author(s):  
Jean Alain Le Duff ◽  
Andre´ Lefranc¸ois ◽  
Jean Philippe Vernot ◽  
Delphine Bossu
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Strain Rate ◽  
Strain Amplitude ◽  
Environmental Effects ◽  
Integral Method ◽  
Low Cycle Fatigue ◽  
Strain History ◽  
Cycle Fatigue ◽  
Penalty Factor

NUREG report CR-6909 [1] proposed in 2007 new rules for evaluating environmental effects in fatigue analyses of new reactors components. These new rules, based on simple correlations, consider that Fen penalty factors (ratio of fatigue life in air at room temperature to that in water at service temperature) are mainly function of strain rate, temperature, sulfur content and dissolved oxygen concentrations. In order to evaluate the conservatisms included in the NUREG report CR-6909, discriminating Low Cycle Fatigue (LCF) tests were performed on a 304L austenitic stainless steel in PWR environment using various modified loading signals deduced from a representative loading strain history as close as possible to actual transients. Using the strain rate integral method recommended in the NUREG/CR-6909, the expected Fen penalty factors evaluated for each modified representative loading signal was close to 6, while the experimental Fen penalty factors measured were strongly dependent of the shape of the loading signals. Experimental Fen penalty factors obtained for the various modified loading signals vary from ∼ 1.5 to ∼ 4. These discriminating LCF tests performed on polished specimens demonstrate that the detailed strain integral method cannot correctly predict the actual environmental effects for the various shapes of loading signals deduced from a representative loading strain history. Other LCF tests were also performed for various constant strain amplitudes using fully reverse triangle signals for comparison purpose with tests performed by other laboratories. It appears that, contrary to published results, environmental effects decrease when the strain amplitude decreases from 0.6% until 0.2%. In the case of the strain amplitude of 0.6%, the Fen penalty factor formulation proposed in the NUREG report CR-6909 is accurate while, for lower strain amplitude of 0.2%, the Fen penalty factor formulation is very severe. It appears that the application of the NUREG/CR-6909 including the Fen model proposed by ANL (Argonne National Laboratory) for austenitic stainless steel provides excessive margins compared to penalty factors as observed experimentally. From this experimental program, conservatisms included in the NUREG/CR-6909 methodology appear to be excessive and can lead to fatigue design issues.

Effects of Surface Finish and Loading Conditions on the Low Cycle Fatigue Behavior of Austenitic Stainless Steel in PWR Environment for Various Strain Amplitude Levels

2009 ◽  
Author(s):  
Jean Alain Le Duff ◽  
Andre´ Lefranc¸ois ◽  
Jean Philippe Vernot
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Strain Amplitude ◽  
Surface Finish ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Complex Loading ◽  
Loading Conditions ◽  
Test Results ◽  
Cycle Fatigue

In February/March 2007, The NRC issued Regulatory Guide “RG1.207” and Argonne National Laboratory issued NUREG/CR-6909 that is now applicable in the US for evaluations of PWR environmental effects in fatigue analyses of new reactor components. In order to assess the conservativeness of the application of this NUREG report, Low Cycle Fatigue (LCF) tests were performed by AREVA NP on austenitic stainless steel specimens in a PWR environment. The selected material exhibits in air environment a fatigue behavior consistent with the ANL reference “air” mean curve, as published in NUREG/CR-6909. LCF tests in a PWR environment were performed at various strain amplitude levels (± 0.6% or ± 0.3%) for two loading conditions corresponding to a simple or to a complex strain rate history. The simple loading condition is a fully reverse triangle signal (for comparison purposes with tests performed by other laboratories with the same loading conditions) and the complex signal simulates the strain variation for an actual typical PWR thermal transient. In addition, two various surface finish conditions were tested: polished and ground. This paper presents the comparisons of penalty factors, as observed experimentally, with penalty factors evaluated using ANL formulations (considering the strain integral method for complex loading), and on the other, the comparison of the actual fatigue life of the specimen with the fatigue life predicted through the NUREG report application. For the two strain amplitudes of ± 0.6% and ± 0.3%, LCF tests results obtained on austenitic stainless steel specimens in PWR environment with triangle waveforms at constant low strain rates give “Fen” penalty factors close to those estimated using the ANL formulation (NUREG/6909). However, for the lower strain amplitude level and a triangle loading signal, the ANL formulation is pessimistic compared to the AREVA NP test results obtained for polished specimens. Finally, it was observed that constant amplitude LCF test results obtained on ground specimens under complex loading simulating an actual sequence of a cold and hot thermal shock exhibits lower combined environmental and surface finish effects when compared to the penalty factors estimated on the basis of the ANL formulations. It appears that the application of the NUREG/CR-6909 in conjunction with the Fen model proposed by ANL for austenitic stainless steel provides excessive margins, whereas the current ASME approach seems sufficient to cover significant environmental effects for representative loadings and surface finish conditions of reactor components.

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