The Modified Rate Approach Method to Evaluate Fatigue Life Under Synchronously Changing Temperature and Strain Rate in Elevated Temperature Water

2002 ◽  
Author(s):  
Kazuya Tsutsumi ◽  
Makoto Higuchi ◽  
Kunihiro Iida ◽  
Yutaka Yamamoto
Keyword(s):  
Fatigue Life ◽  
Elevated Temperature ◽  
Strain Rate ◽  
Constant Strain Rate ◽  
Environmental Water ◽  
Transient Condition ◽  
Strain Rate Change ◽  
Rate Condition ◽  
Approach Method ◽  
Temperature Water

The fatigue life of steel in elevated temperature water is strongly affected by the composition of the environmental water, temperature and strain rate. The effects of these parameters on fatigue life reduction have been investigated experimentally in these years. One problem to be discussed is the fact that the previous experiments which leaded main conclusions on the environmental effects were generally executed by keeping a set of experimental parameters constant. In the transient condition in an actual plant, however, such parameters as temperature and strain rate are not constant. In order to evaluate fatigue damage in an actual plant on the basis of experimental results under constant temperature and constant strain rate conditions, the modified rate approach method was developed. The method can be applicable to changing temperature condition and strain rate condition separately. In the present study, an additional model is proposed with considering that both temperature and strain rate change simultaneously in an actual plant. The applicability of this method is discussed and verified experimentally. The fatigue lives predicted by this method are scattered within the factor of 2 or 3 bands against test results even when several parameters changed synchronously.

The Modified Rate Approach Method to Evaluate Fatigue Life Under Synchronously Changing Temperature and Strain Rate in Elevated Temperature Water in Austenitic Stainless Steel

2004 ◽  
Author(s):  
Yuichiro Nomura ◽  
Makoto Higuchi ◽  
Yasuhide Asada ◽  
Katsumi Sakaguchi
Keyword(s):  
Fatigue Life ◽  
Elevated Temperature ◽  
Strain Rate ◽  
Constant Strain Rate ◽  
Environmental Water ◽  
Experimental Parameters ◽  
Approach Method ◽  
Increasing Temperature ◽  
Fatigue Life Reduction ◽  
Temperature Water

The fatigue life of steel of light water reactor (LWR) in elevated temperature water is affected by the composition of the environmental water, decreasing strain rate and increasing temperature. The effects of these parameters on fatigue life reduction have been investigated experimentally. One problem to be discussed is the fact that the previous studies which leaded main results on the environmental effects were generally executed by experimental parameters constant. On the other hand, in an actual plant, such parameters as temperature and strain rate are changing transient. In order to evaluate fatigue damage in an actual plant on the basis of experimental results under constant temperature and constant strain rate conditions, the modified rate approach method was developed. The study has conducted as a part of the EFT project in order to evaluate the applicability of the modified rate approach to the case that LWR environment. The applicability of a modified rate approach method to the case where temperature and strain rate varied simultaneously was discussed in the previous paper(1). In order to confine the applicability under extended condition, the tests of which conditions were different from those of the previous study were conducted. The accuracy of modified rate approach is same level of the result of previous paper.

Applicability of the Modified Rate Approach Method Under Various Conditions Simulating Actual Plant Conditions

2006 ◽  
Author(s):  
Katsumi Sakaguchi ◽  
Yuichiro Nomura ◽  
Shigeki Suzuki ◽  
Hiroshi Kanasaki
Keyword(s):  
Fatigue Life ◽  
Strain Rate ◽  
Fatigue Tests ◽  
Transient Condition ◽  
Stress Cycle ◽  
Rate Condition ◽  
Approach Method ◽  
Strain Rate Condition ◽  
Fatigue Evaluation ◽  
Fatigue Life Reduction

The fatigue life in elevated temperature water is strongly affected by water chemistry, temperature and strain rate. The effects of these parameters on fatigue life reduction have been investigated experimentally. In transient condition in an actual plant, however, such parameters as temperature and strain rate are not constant. In order to evaluate fatigue damage in actual plant on the basis of experimental results under constant temperature and strain rate condition, the modified rate approach method was developed. As a part of the EFT (Environmental Fatigue Tests) project, the study was conducted in order to evaluate the applicability of the modified rate approach to the case where temperature and strain rate varied simultaneously. It was reported in the previous papers (1,2) that the accuracy of modified rate approach is about factor of 2. Various kinds of transient have to be taken into account of in actual plant fatigue evaluation, and stress cycle of several ranges of amplitude has to be considered in assessing damage from fatigue. Generally, cumulative usage factor is applied in this type of evaluation. In this study, in order to confirm applicability of modified rate approach method together with cumulative usage factor, tests were carried out by combining stress cycle blocks of different strain amplitude levels, in which temperature changes in response to strain change in a simulated PWR environment.

Examination of Factors in the Modified Rate Approach Method Under Various Conditions

2011 ◽  
Author(s):  
Yuichi Fukuta ◽  
Seiji Asada ◽  
Yuichiro Nomura ◽  
Hiroshi Kanasaki
Keyword(s):  
Fatigue Life ◽  
Elevated Temperature ◽  
Strain Rate ◽  
Fatigue Damage ◽  
Correction Factor ◽  
Strain Range ◽  
Approach Method ◽  
Fatigue Evaluation ◽  
Response To Temperature ◽  
Temperature Water

Fatigue life in elevated-temperature water is affected by water chemistry, temperature, and strain rate. To evaluate these effects, the environmental fatigue life correction factor was established. And to evaluate fatigue damage in actual plants where factors such as temperature and strain rate are not constant, the modified rate approach method was developed. In order to confirm the applicability of these methods, several tests were carried out under a condition in which strain rate changes in response to temperature and fatigue life could be evaluated with an accuracy of a factor of 3, but conservatism was observed. In this evaluation, conservatism of environmental fatigue prediction is studied. To minimize conservatism in environmental fatigue evaluation, four factors are examined. As a result of examination, we conclude that an improvement the environmental fatigue life correction factor and application of a strain range insensitive to the environment may reduce conservatism, and that investigation into the mechanism of reduction in fatigue life is necessary for further improvement.

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.

Effects of Continuous Strain Rate Changing on Environmental Fatigue for Stainless Steels in PWR Environment

2010 ◽  
Author(s):  
Yuichiro Nomura ◽  
Seiji Asada ◽  
Takao Nakamura ◽  
Masakazu Tanaka
Keyword(s):  
Fatigue Life ◽  
Strain Rate ◽  
Water Environment ◽  
Sine Wave ◽  
Fatigue Tests ◽  
Integral Model ◽  
Strain Rates ◽  
Test Results ◽  
Approach Method ◽  
The Difference

The strain rates in actual transients of operating plants are not constant and changing momentarily. A large number of fatigue tests under stepwise strain rate changing conditions were performed to develop a method for evaluating fatigue life under varying strain rate conditions. Based on these test results, a strain base integral model known as the named the modified rate approach method was developed and verified. However it was reported recently that in the case of sine wave fatigue tests in BWR environment, the fatigue life was two to six times longer than the fatigue life predicted by the modified rate approach method. For this paper, in order to confirm whether the same tendency is observed in PWR environment, fatigue tests of sine wave were performed of SS316 in simulated PWR water environment. As the result, the difference of fatigue life by sine wave test reported in BWR environment was not observed between experimental and predicted life in PWR environment and the modified rate approach method was applicable under continuous strain rate changing condition.

Strain Rate and Loading Waveform Effects on an Energy-Based Fatigue Life Prediction for AL6061-T6

2012 ◽  
Author(s):  
Todd Letcher ◽  
M.-H. Herman Shen ◽  
Onome Scott-Emuakpor ◽  
Tommy George ◽  
Charles Cross
Keyword(s):  
Fatigue Life ◽  
Strain Rate ◽  
Constant Strain Rate ◽  
Hysteresis Loops ◽  
Sine Wave ◽  
Wave Loading ◽  
Cumulative Energy ◽  
Loading Pattern ◽  
Loading Waveform ◽  
Strain Rate Loading

The energy-based lifing method is based on the theory that the cumulative energy in all hysteresis loops of a specimens’ lifetime is equal to the energy in a monotonic tension test. Based on this theory, fatigue life can be calculated by dividing monotonic strain energy by a hysteresis energy model, which is a function of stress amplitude. Recent studies have focused on developing this method for a sine wave loading pattern — a variable strain rate. In order to remove the effects of a variable strain rate throughout the fatigue cycle, a constant strain rate triangle wave loading pattern was tested. The testing was conducted at various frequencies to evaluate the effects of multiple constant strain rates. Hysteresis loops created with sine wave loading and triangle loading were compared. The effects of variable and constant strain rate loading patterns on hysteresis loops throughout a specimens’ fatigue life are examined.

Evaluation of Environmental Effects on the Fatigue of Notched Specimen of Austenitic Stainless Steel Using Modified Rate Approach Method

2004 ◽  
Author(s):  
Katsumi Sakaguchi ◽  
Yasuhide Asada ◽  
Masao Itatani ◽  
Toshiyuki Saito
Keyword(s):  
Stainless Steel ◽  
High Temperature ◽  
Fatigue Life ◽  
Stress Concentration ◽  
Austenitic Stainless Steel ◽  
Notch Root ◽  
Notched Specimen ◽  
High Temperature Water ◽  
Approach Method ◽  
Temperature Water

Fatigue testing was conducted on notched specimens of austenitic stainless steel 316NG in high temperature water. Specimens were notched round bar with elastic stress concentration factors Kt of 1.4 and 3. For the specimen of Kt = 3, fatigue test was also performed in high temperature air. Environmental correction factor Fen recently proposed by Environmental Fatigue Tests (EFT) project in Japan Nuclear Safety Organization (JNES) was applied to the result of fatigue test to evaluate the environmental effects on fatigue life of notched specimen. Since the notch root strain varies non-proportionally to nominal strain in the elastic-plastic region, the modified rate approach method was applied to predict the fatigue life of notched specimen in the water, which was proposed to account for the environmental effect on fatigue life of nuclear component materials under varying conditions. Notch root strain and strain rate were calculated by FEM analysis. The difference between predicted and experimental fatigue lives in high temperature water was within factor of 2 for Kt = 3. The relationships between fictitious stress amplitude at notch root (= notch root strain amplitude multiplied by elastic modulus) and corrected fatigue life shows good coincidence with best fit curve for austenitic stainless steels. It is concluded that the modified rate approach method and current environmental correction factor Fen proposed by EFT project is applicable to predict fatigue life of the stress concentration when the notch root strain is adequately estimated.

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