Influence of Mean Strain on Fatigue Life of Stainless Steel in PWR Water Environment

2021 ◽  
Author(s):  
Masayuki Kamaya
Keyword(s):  
Surface Roughness ◽  
Stainless Steel ◽  
Fatigue Life ◽  
Cold Working ◽  
Water Environment ◽  
Martensitic Phase ◽  
Pressurized Water ◽  
The Mean ◽  
Fatigue Life Reduction ◽  
Mean Strain

Abstract Influence of application of the mean strain on the fatigue life was investigated for Type 316 stainless steel in the simulated pressurized water rector (PWR) primary water environment. Low-cycle fatigue tests were conducted for a constant mean strain by controlling the strain range to be 1.2%. The applied strain rates were 0.4, 0.004, or 0.001%/s. The applied mean strain was 15% in nominal strain. In addition, cold worked specimens were also used for the tests without applying the mean strain. The cold working simulated the application of mean strain without increase in surface roughness due to application of plastic deformation. By inducing the cold working at low temperature, the influence of martensitic phase on the fatigue life was also examined. The PWR water environment reduced the fatigue life and the degree of the fatigue life reduction was consistent with the prediction model of the code issued by the Japan Society of Mechanical Engineers (JSME) and NUREG/CR-6909. Increases in the maximum peak stress and stress range caused by cold working did not cause any apparent change on the fatigue life. It was revealed that the 10.5 wt% martensitic phase and the increase in the surface roughness caused by application of 15% mean strain did not bring about further fatigue life reduction. The current JSME and NUREG/CR-6909 models were applicable for predicting the fatigue in the PWR water environment even when the mean strain or cold working was applied.

Influence of Mean Strain on Fatigue Life of Stainless Steel in PWR Water Environment

2018 ◽  
Author(s):  
Masayuki Kamaya
Keyword(s):  
Surface Roughness ◽  
Stainless Steel ◽  
Fatigue Life ◽  
Cold Working ◽  
Water Environment ◽  
Martensitic Phase ◽  
The Mean ◽  
Cold Worked ◽  
Fatigue Life Reduction ◽  
Mean Strain

Change in the fatigue life due to application of the mean strain was investigated for Type 316 stainless steel in simulated pressurized water rector (PWR) primary water environment. The tests were conducted by controlling the strain range to 1.2% for different strain rates of 0.4, 0.004, or 0.001%/s. The applied mean strain was 15% in nominal strain. In addition, cold worked specimens were also subjected to the tests without applying the mean strain. The tests using the cold worked specimens were regarded as the tests with the mean strain without increase in surface roughness due to application of plastic deformation. By inducing the cold working at low temperature, the effect of martensitic phase on the fatigue life was also examined. It was shown that the fatigue life of the stainless steel was reduced in the PWR water environment and the degree of the fatigue life reduction was consistent with the prediction model prescribed in the code issued by the Japan Society of Mechanical Engineers (JSME) and NUREG/CR-6909. Increases in peak stress and stress range due to cold working did not cause any apparent influence on the fatigue life. It was also shown that the 10.5 wt% martensitic phase induced by the low temperature cold working and the increase in the surface roughness caused by application of 15% mean strain did not bring about further fatigue life reduction. It was concluded that the effects of the mean strain, cold working, and martensitic phase were minor on the fatigue life in the PWR water environment. The current JSME and NUREG/CR-6909 models were applicable for predicting the reduction in fatigue due to the PWR water environment even if the mean strain or cold working was applied.

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

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.

Environmental Effect on Fatigue Crack Initiation and Growth of Stainless Steel for Flaw Tolerance Assessment

2016 ◽  
Author(s):  
Masayuki Kamaya
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Crack Initiation ◽  
Crack Growth ◽  
Correction Factor ◽  
Stress Gradient ◽  
Water Environment ◽  
Pressurized Water ◽  
Flaw Tolerance ◽  
Fatigue Life Reduction

Fatigue life can be divided into cycles of crack initiation and those in which the initiated crack grows to macroscopic size. In crack growth analysis, it is possible to consider the effect of the strain or stress gradient in the depth direction on the fatigue life. Therefore, flaw tolerance assessments allow reasonable fatigue life prediction. The fatigue life is reduced in the primary water environment of pressurized water reactor (PWR) nuclear power plants, and the correction factor Fen is used for considering the fatigue life reduction in fatigue damage assessments. To apply the flaw tolerance concept to a PWR water environment, the correction factor must be applied not to the fatigue life but to the number of cycles for crack growth. In this study, the fatigue life reduction in the PWR environment was correlated to the crack growth acceleration for a flaw tolerance assessment. The crack growth rates were obtained from fatigue life tests and crack growth tests performed in the PWR environment using Type 316 stainless steel. Then, the fatigue life was estimated by predicting the crack growth from an initial depth of 20 μm. It was concluded that a reasonable flaw tolerance assessment can be performed by using the strain intensity factor. The fatigue life reduction was successfully replaced with the crack growth acceleration.

Influence of Mean Strain on Fatigue Life of Stainless Steel (Effect of Constant and Ratcheting Mean Strain)

2014 ◽  
Author(s):  
Masayuki Kamaya
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Effective Strain ◽  
Mouth Opening ◽  
Strain Range ◽  
Fatigue Tests ◽  
Mean Stress ◽  
Crack Mouth ◽  
The Mean ◽  
Mean Strain

The influence of mean strain on fatigue life was investigated for Type 316 stainless steel at room temperature in ambient environment. Two types of mean strain were simulated in the fatigue tests: constant and increasing (ratcheting) mean strains. In order to apply the constant mean strain, prestraining was induced prior to fatigue tests. Although the stress amplitudes became larger due to the prestraining, fatigue lives were almost the same as those obtained using non-prestrained specimens for the same strain range. Change in the maximum peak stress and stress amplitude due to the prestraining had little influence on the fatigue life. It was shown that the mean strain showed little influence on the fatigue life under the same strain range. The ratcheting mean strain was observed during the fatigue tests under mean stress. The fatigue life was reduced by applying the mean stress for the same strain range. The degree of the reduction was increased with the magnitude of the ratcheting mean strain. It was deduced that the increasing mean strain enhanced the crack mouth opening and increased the effective strain range. It was concluded that the ratcheting mean strain reduced the fatigue life for the same strain range, and the reduction in fatigue life could be predicted conservatively by assuming the crack mouth was never closed during the fatigue tests.

scholarly journals Investigation of Changes in Fatigue Damage Caused by Mean Load under Block Loading Conditions

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 2738
Author(s):  
Roland Pawliczek ◽  
Tadeusz Lagoda
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Strain Curve ◽  
Mean Value ◽  
Fatigue Properties ◽  
Stress Strain ◽  
Reference Case ◽  
Block Loading ◽  
The Mean ◽  
Mean Strain

The literature in the area of material fatigue indicates that the fatigue properties may change with the number of cycles. Researchers recommend taking this into account in fatigue life calculation algorithms. The results of simulation research presented in this paper relate to an algorithm for estimating the fatigue life of specimens subjected to block loading with a nonzero mean value. The problem of block loads using a novel calculation model is presented in this paper. The model takes into account the change in stress–strain curve parameters caused by mean strain. Simulation tests were performed for generated triangular waveforms of strains, where load blocks with changed mean strain values were applied. During the analysis, the degree of fatigue damage was compared. The results of calculations obtained for standard values of stress–strain parameters (for symmetric loads) and those determined, taking into account changes in the curve parameters, are compared and presented in this paper. It is shown that by neglecting the effect of the mean strain value on the K′ and n′ parameters and by considering only the parameters of the cyclic deformation curve for εm = 0 (symmetric loads), the ratio of the total degree of fatigue damage varies from 10% for εa = 0.2% to 3.5% for εa = 0.6%. The largest differences in the calculation for ratios of the partial degrees of fatigue damage were observed in relation to the reference case for the sequence of block n3, where εm = 0.4%. The simulation results show that higher mean strains change the properties of the material, and in such cases, it is necessary to take into account the influence of the mean value on the material response under block loads.

scholarly journals Characterization of Austenitic Stainless Steels with Regard to Environmentally Assisted Fatigue in Simulated Light Water Reactor Conditions

Metals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 307
Author(s):  
Matthias Bruchhausen ◽  
Gintautas Dundulis ◽  
Alec McLennan ◽  
Sergio Arrieta ◽  
Tim Austin ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Fatigue Life ◽  
Elevated Temperature ◽  
Strain Rate ◽  
Power Plants ◽  
Research Effort ◽  
Hold Time ◽  
Strain Range ◽  
Austenitic Steels ◽  
Mean Strain

A substantial amount of research effort has been applied to the field of environmentally assisted fatigue (EAF) due to the requirement to account for the EAF behaviour of metals for existing and new build nuclear power plants. We present the results of the European project INcreasing Safety in NPPs by Covering Gaps in Environmental Fatigue Assessment (INCEFA-PLUS), during which the sensitivities of strain range, environment, surface roughness, mean strain and hold times, as well as their interactions on the fatigue life of austenitic steels has been characterized. The project included a test campaign, during which more than 250 fatigue tests were performed. The tests did not reveal a significant effect of mean strain or hold time on fatigue life. An empirical model describing the fatigue life as a function of strain rate, environment and surface roughness is developed. There is evidence for statistically significant interaction effects between surface roughness and the environment, as well as between surface roughness and strain range. However, their impact on fatigue life is so small that they are not practically relevant and can in most cases be neglected. Reducing the environmental impact on fatigue life by modifying the temperature or strain rate leads to an increase of the fatigue life in agreement with predictions based on NUREG/CR-6909. A limited sub-programme on the sensitivity of hold times at elevated temperature at zero force conditions and at elevated temperature did not show the beneficial effect on fatigue life found in another study.

Finite-Element Analysis of Crack Growth in Austenitic Stainless Steel Under Equibiaxial Loading

2018 ◽  
Author(s):  
H. Dhahri ◽  
C. Gourdin ◽  
H. Maitournam
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Austenitic Stainless Steel ◽  
Crack Growth ◽  
Power Plants ◽  
Austenitic Steels ◽  
Biaxial Test ◽  
New Device ◽  
Penalty Factor ◽  
Mean Strain

The lifetime extension of the nuclear power plants is considered as an energy challenge worldwide. That is why, the risk analysis and the study of various effects of different factors that could potentially represent a hazard to a safe long term operation are necessary. These structures, often of great dimensions, are subjected during their life to complex loading combining varying mechanical loads, multiaxial, with non-zero mean values associated with temperature fluctuations and also PWR environment. Based on more recent fatigue data (including tests at 300°C in air and PWR environment, etc...), some international codes (RCC-M [2], ASME and others [3][4][5]) have introduced a modification of the austenitic stainless steels fatigue curve combined with a calculation of an environmental penalty factor, namely Fen, which has to be multiplied by the usual fatigue usage factor [6]. Unfortunately, experimental data on this issue are rare. In order to obtain fatigue strength data under structural loading, biaxial test means with and without PWR environment were developed at LISN in collaboration with EDF and AREVA [6]. Two kinds of fatigue device have been developed. Within the same specimen geometry, structural loads can be applied in varying only the PWR environment. The first device (FABIME2) is devoted to study the effect of biaxiality and mean strain/stress on the fatigue life [9]. A second and new device called FABIME2e is for the study of the environmental effect. With these new experimental results, the PWR environment effect on the fatigue life of stainless austenitic steels will be quantified accurately on semi-structure specimen. This device combines the structural effect like equi-biaxiality and mean strain and the environmental penalty effect with the use of PWR environment during the fatigue tests. The aim of this paper is to present the numerical interpretation of the results obtained with these two devices “FABIME2” and “FABIME2e”. Two important aspects will be addressed. The first concerns the mechanical behavior of austenitic stainless steel and the capabilities of the numerical model to reproduce the hardening of the material. And the second concerns the study of the crack growth during the equibiaxial fatigue test.

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