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.

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.

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.

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.

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.

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.

Study of the Effects of Environment in the Fatigue Analysis on Existing LWR as Proposed in USNRC RG 1.207

2009 ◽  
Author(s):  
Eugene Tom ◽  
Milton Dong ◽  
Hong Ming Lee
Keyword(s):  
Fatigue Life ◽  
Correction Factor ◽  
Environmental Effects ◽  
Environmental Parameters ◽  
Computer Code ◽  
Cyclic Behavior ◽  
Simplified Approach ◽  
Asme Code ◽  
Detailed Computer ◽  
Fatigue Evaluation

US NRC Regulatory Guide 1.207 Rev. 0 provides guidance for use in determining the acceptable fatigue life of ASME pressure boundary components, with consideration of the light-water reactor (LWR) environment. Because of significant conservatism in quantifying other plant-related variables (such as cyclic behavior, including stress and loading rates) involved in cumulative fatigue life calculations, the design of the current fleet of reactors is satisfactory. For new plants under design and current operating plants considering applying for License Renewal, the environment effects may need to be considered in the design. RG 1.207 proposes using an environmental correction factor (Fen) to account for LWR environments by correcting the fatigue usage calculated with the ASME “air” curves. The Fen method is presented in NUREG/CR-6909, “Effect of LWR Coolant Environments on the Fatigue Life of Reactor Materials”. By definition, Fen is the ratio of fatigue life of the component material at room temperature air environments to its fatigue life in LWR coolant at operating temperature. To incorporate environmental effects into the fatigue evaluation, the fatigue usage is calculated using provisions set forth in Section III of the ASME Code, and is adjusted by multiplying a correction factor. The calculated Fen values are then used to incorporate environmental effects into ASME fatigue usage factor evaluation. Once the environmental correction factors have been determined, the previously calculated allowable number of cycles for each load set pair based on the current Code fatigue design curve can be adjusted to determine the new fatigue usage factors for environmental effects. This paper presents a study of the effect of the Regulatory Guide if it is to be implemented on the current fleet of LWR. A quick assessment of the sensitivity of the various environmental parameters is also included in this paper. The comparison of environmental effects between the simplified approach in this paper and the results with detailed computer analyses, such as Unisont’s propriety computer code UPIPENB (Ref. 4), will be our next research project to be presented in the future conference.

Fatigue Evaluation Under Continuous Strain Rate Changing Condition of Carbon Steel in BWR Environment

2014 ◽  
Author(s):  
Akihiko Hirano ◽  
Satoko Mizuta
Keyword(s):  
Surface Roughness ◽  
Fatigue Life ◽  
Strain Rate ◽  
Fatigue Test ◽  
Fatigue Tests ◽  
Wave Form ◽  
Strain Wave ◽  
Water Reactor ◽  
Component Size ◽  
Fatigue Evaluation

Fatigue evaluation methods have been proposed based on environmental fatigue test results regarding parameters selected for simulating Boiling Water Reactor (BWR) and Pressurized Water Reactor (PWR) conditions. The effects of strain wave form have been discussed by comparing experimental fatigue life with predicted fatigue life evaluated by modified rate approach (MRA) method. The applicability of the MRA method has been verified extensively by the environmental fatigue tests with strain rate changing conditions consisting of combined constant strain rates. However, different results have been obtained for a sine strain wave in simulated BWR and PWR conditions. More study for evaluating the applicability of MRA method was required by evaluating with continuous strain rate conditions such as a sine wave. For the purpose of verification, two approaches were applied. One is performing the environmental fatigue tests with the sine strain wave in simulated BWR condition. The other is to evaluate the low cycle thermal fatigue test performed in simulated BWR condition because the wave form of this test contains continuous strain rate changing condition. MRA method was indicated to be applicable to predict fatigue lives under these kinds of continuous strain rate changing conditions. All of the studies including this study verifying the applicability of the MRA method were performed with small specimens having the well polished surfaces in the gage length. These results indicate that the evaluation by the MRA method includes the synergistic effect between the water environment and the transient. However, the synergistic effects with the surface roughness and the component size are not known. Design margin derived by the multiplication of the sub-factors of environment, surface roughness and component size may be conservative. The evaluation of the conservatism is considered to be beneficial.

A Novel Fatigue Evaluation Approach with Direct Steady Cycle Analysis (DSCA) Based on the Linear Matching Method (LMM)

2019 ◽  
Vol 795 ◽  
pp. 383-388 ◽  
Author(s):  
Xiao Tao Zheng ◽  
Zhi Yuan Ma ◽  
Hao Feng Chen ◽  
Jun Shen
Keyword(s):  
Fatigue Life ◽  
Evaluation Method ◽  
Low Cycle Fatigue ◽  
Effective Strain ◽  
Strain Range ◽  
Matching Method ◽  
Evaluation Approach ◽  
Perfectly Plastic ◽  
Fatigue Evaluation ◽  
Linear Matching Method

The traditional Low Cycle Fatigue (LCF) evaluation method is based on elastic analysis with Neuber’s rule which is usually considered to be over conservative. However, the effective strain range at the steady cycle should be calculated by detailed cycle-by-cycle analysis for the alternative elastic-plastic method in ASME VIII-2, which is obviously time-consuming. A Direct Steady Cycle Analysis (DSCA) method within the Linear Matching Method (LMM) framework is proposed to assess the fatigue life accurately and efficiently for components with arbitrary geometries and cyclic loads. Temperature-dependent stress-strain relationships considering the strain hardening described by the Ramberg-Osgood (RO) formula are discussed and compared with those results obtained by the Elastic-Perfectly Plastic (EPP) model. Additionally, a Reversed Plasticity Domain Method (RPDM) based on the shakedown and ratchet limit analysis method and the DSCA approach within the LMM framework (LMM DSCA) is recommended to design cyclic load levels of LCF experiments with predefined fatigue life ranges.

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