scholarly journals Fatigue Crack Growth Thresholds at Negative Stress Ratio for Ferritic Steels in ASME Code Section XI

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
Kunio Hasegawa ◽  
Bohumir Strnadel ◽  
Saburo Usami ◽  
Valery Lacroix
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stress Ratio ◽  
Maximum Stress ◽  
Ferritic Steels ◽  
Intensity Factors ◽  
Asme Code ◽  
Maximum Stress Intensity ◽  
Stress Ratios

Thresholds of fatigue crack growth rates are important characteristics for fatigue crack growth assessment for the integrity of structural components. ASME Code Section XI provides fatigue crack growth thresholds for ferritic steels in air and water environments. The threshold is given as a constant value under a negative stress ratio. However, the thresholds are not clearly defined in the range of negative stress ratios. The definition seems to be maximum stress intensity factors. Besides, the thresholds expressed by the maximum stress intensity factors decrease with decreasing stress ratios. This means that the thresholds under negative stress ratios become unconservative assessments. The objective of this paper is to discuss the definition of fatigue crack growth threshold and to propose the threshold equation for the ASME Code Section XI, based on experimental data obtained from a literature survey.

Consideration on Fatigue Crack Growth Thresholds Under Negative Stress Ratio

2019 ◽  
Author(s):  
Kunio Hasegawa ◽  
Saburo Usami ◽  
Valery Lacroix
Keyword(s):  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Intensity Factor ◽  
Crack Growth ◽  
Stress Ratio ◽  
Maximum Stress ◽  
Maximum Stress Intensity ◽  
Maximum Stress Intensity Factor

Abstract Fatigue crack growth thresholds ΔKth are provided by several fitness-for-service (FFS) codes. When evaluating cracked components subjected to cyclic loading, maximum stress intensity factor Kmax and/or minimum stress intensity factor Kmin are required. However, the definitions of the thresholds ΔKth under negative stress ratio R are not clearly written, except for BS (British Standards) 7910. In addition, the ΔKth are given by constant values under negative R. Fatigue crack growth rates under negative stress ratio is recommended to use maximum stress intensity factor Kmax by ASTM (American Society of Testing and Materials) E 647, because of the Kmax being close to crack driving force. Therefore, it deems that the ΔKth under negative R seems to be Kmax. This paper shows that the Kmax converted by the ΔKth are not constant values under negative R based on the survey of experimental data. The Kmax decreases with decreasing the stress ratio R. Therefore, the ΔKth for the FFS codes are less conservative. As experimental data under negative stress ratio R were taken by Kmax – Kmin, the definition of the threshold ΔKth is benefit to use Kmax – Kmin, instead of Kmax.

Definition of Fatigue Crack Growth Thresholds for Ferritic Steels in Fitness-for-Service Codes

2018 ◽  
Author(s):  
Kunio Hasegawa ◽  
Bohumir Strnadel
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Stress Ratio ◽  
Fatigue Tests ◽  
Ferritic Steels ◽  
Stress Ratios ◽  
Definition Of ◽  
Crack Growth Rates

Fatigue crack growth rates are expressed as a function of the stress intensity factor ranges. The fatigue crack growth thresholds are important characteristics of fatigue crack growth assessment for the integrity of structural components. Almost all materials used in these fatigue tests are ferritic steels. As a result, the reference fatigue crack growth rates and the fatigue crack growth thresholds for ferritic steels were established as rules and they were provided by many fitness-for-service (FFS) codes. However, the thresholds are not well defined in the range of negative stress ratio. There are two types of thresholds under the negative stress ratio. That is, constant thresholds and increment of thresholds with decreasing stress ratios. The objective of this paper is to introduce the thresholds provided by FFS codes and to analyze the thresholds using crack closure. In addition, based on the experimental data, definition of the threshold is discussed to apply to FFS codes. Finally, threshold for ferritic steels under the entirely condition of stress ratio is proposed to the ASME Code Section XI.

An Assessment of Low Alloy Steel EAC Corrosion Fatigue Relationships for BWR Environment

2005 ◽  
Author(s):  
Hardayal Mehta ◽  
Ron Horn
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Water Chemistry ◽  
Crack Growth ◽  
Corrosion Fatigue ◽  
Growth Rates ◽  
Ferritic Steels ◽  
Asme Code ◽  
Crack Growth Rates

The fatigue crack growth rates for ferritic steels in water environments given in A-4300 of Appendix A, Section XI, ASME Code, were developed from data obtained prior to 1980. Subsequently, updated assessments by Eason, et al. and recent laboratory test results from Seifert and Ritter demonstrated that under certain conditions, ferritic steels exposed to oxygenated water environments may be susceptible to high fatigue crack growth rates that exceed the current disposition curves. In the light of ASME adopting Code Case N-643 for PWRs, there is a need for a similar Code Case for the BWR water environments (for both the normal water chemistry and hydrogen water chemistry/NobleChem) that takes into account these findings. This could mean modification of current EAC curves in the ASME Code. A joint program of EPRI and GE was developed to address this need for updated evaluations of the corrosion fatigue. The program’s first task has been to re-assess the role of rise time, environment, alloy, heat treatment and impurity levels on the established ASME codified disposition curves/methodologies. The data was then used as a basis to assess the impact of on modified cyclic curves on the disposition approaches that are currently used to evaluate postulated flaws in the BWR reactor pressure vessel or RPV head and the feed water nozzle regions. The presentation would include a discussion of the appropriate BWR plant transients and the GE process for performing evaluations. The role of the evaluations on the establishment of inspection intervals currently determined using NUREG-0619 and the latest BWROG Report would also be presented. Finally, the relationship between cyclic load and constant load behavior in these steels are discussed in the context of the mechanisms for environmentally assisted cracking.

Development of Fatigue Crack Growth Thresholds for Austenitic Stainless Steels Exposed to Air Environment for ASME Code Section XI

2018 ◽  
Vol 140 (3) ◽  
Author(s):  
Kunio Hasegawa ◽  
Saburo Usami
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stainless Steels ◽  
Stress Ratio ◽  
Austenitic Stainless Steels ◽  
Stress Intensity Factor Range ◽  
Asme Code ◽  
American Society ◽  
Growth Experiments

Fatigue crack growth thresholds ΔKth define stress intensity factor range below which cracks will not grow. The thresholds ΔKth are useful in industries to determine durability lifetime. Although massive fatigue crack growth experiments for stainless steels in air environment had been reported, the thresholds ΔKth are not codified at the American Society of Mechanical Engineers (ASME) Code Section XI, as well as other fitness-for-service (FFS) codes and standards. Based on the investigation of a few FFS codes and review of literature survey of experimental data, the thresholds ΔKth exposed to air environment have been developed for the ASME Code Section XI. A guidance of the thresholds ΔKth for austenitic stainless steels in air at room and high temperatures can be developed as a function of stress ratio R.

Statistical Analysis of Fatigue Crack Growth Threshold Based on Test Data

2011 ◽  
Vol 127 ◽  
pp. 466-470
Author(s):  
Wen Lin Liu ◽  
Guang Ming Kong ◽  
Zhi Tao Mu ◽  
Zhong Hu Jia ◽  
Da Zhao Yu
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Test Data ◽  
Stress Ratio ◽  
Least Square ◽  
Growth Speed ◽  
Fitting Method ◽  
Stress Ratios ◽  
Growth Threshold

Statistical analyses on fatigue crack growth threshold under three different stress ratios have been done. By the stratified random sampling theory and the weighted least square fitting method, the test data were analyzed based on Paris crack growth rate formulation. The statistical results of the fatigue crack growth threshold under different stress ratios were obtained by linear fitting method. The results show that the fatigue crack growth threshold is influenced by stress ratio R significantly. In the slow crack growth area near the threshold, the increase of stress ratio leads to the decrease of threshold and the increase of crack growth speed. The threshold results under different stress ratios satisfy the normal distribution.

Fatigue Crack Growth Rates for Ferritic Steels Under Negative R Ratio

2016 ◽  
Author(s):  
Kunio Hasegawa ◽  
Vratislav Mares ◽  
Yoshihito Yamaguchi ◽  
Yinsheng Li
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Closure ◽  
Growth Rates ◽  
Ferritic Steels ◽  
R Ratio ◽  
Asme Code ◽  
Reference Curves ◽  
Crack Growth Rates

Reference curves of fatigue crack growth rates for ferritic steels in air environment are provided by the ASME Code Section XI Appendix A. The fatigue crack growth rates under negative R ratio are given as da/dN vs. Kmax, It is generally well known that the growth rates decreases with decreasing R ratios. However, the da/dN as a function of Kmax are the same curves under R = 0, −1 and −2. In addition, the da/dN increases with decreasing R ratio for R < −2. This paper converts from da/dN vs. Kmax to da/dN vs. ΔKI, using crack closure U. It can be obtained that the growth rates da/dN as a function of ΔKI decrease with decreasing R ratio for −2 ≤ R < 0. It can be seen that the growth rate da/dN vs. ΔKI is better equation than da/dN vs. Kmax from the view point of stress ratio R. Furthermore, extending crack closure U to R = −5, it can be explained that the da/dN decreases with decreasing R ratio in the range of −5 ≤ R < 0. This tendency is consistent with the experimental data.

scholarly journals The stress ratio effect on plastic dissipation during fatigue crack growth

2018 ◽  
Vol 165 ◽  
pp. 13002
Author(s):  
H. Quan ◽  
R.C. Alderliesten ◽  
R. Benedictus
Keyword(s):  
Fatigue Crack ◽  
Energy Dissipation ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stress Ratio ◽  
Dissipated Energy ◽  
Plastic Energy ◽  
Plastic Dissipation ◽  
Stress Ratios ◽  
The Individual

Plastic energy dissipation is inevitable during fatigue crack growth. There have been previous attempts reported in literature to correlate the plastic dissipated energy (dW/dN) to fatigue crack growth rate (da/dN). However, at a given dW/dN, the da/dN changes with the ratio of minimum and maximum loads, known as the stress ratio. This paper describes an experimental study carried out on 2024-T3 central crack tension specimens to quantify the relation between dW/dN and da/dN. By selecting different stress ratios in the individual tests, the experiments reveal the influence of the stress ratio on this relationship. It is evident that dW/dN has no unique relationship with da/dN valid for the tested stress ratios. Instead, the relationship for each stress ratio is different. This is illustrated with the value of plastic dissipation per unit of fatigue crack growth (dW/da), representing the effective resistance to the crack increment. This value is not a constant, but changes with the stress ratios and da/dN values. Hence the plastic energy dissipation cannot be used directly for predicting crack growth.

A Review of Fatigue Crack Growth Thresholds for Metals in Fitness-for-Service Codes: On the Uncertainty of Using the Thresholds at Negative Stress Ratios

2021 ◽  
Author(s):  
Kunio Hasegawa ◽  
Bohumir Strnadel ◽  
Vratislav Mares ◽  
David Dvorak ◽  
Saburo Usami
Keyword(s):  
Stainless Steel ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stainless Steels ◽  
Ferritic Steel ◽  
Literature Survey ◽  
Ferritic Steels ◽  
Section Viii ◽  
Stress Ratios

Abstract Fatigue crack growth thresholds deltaKth for metals are provided in many fitness-for-service codes. However, fatigue thresholds at negative stress ratios are not uniform. There are two forms of thresholds at negative stress ratios: constant thresholds irrespective of stress ratios, or increasing thresholds with decreasing stress ratios. The definitions of the thresholds at negative stress ratios also take two forms: either deltaKth = Kmax - Kmin, or deltaKth = Kmax. ASME Section VIII, Section XI (ferritic steel) and IIW give constant thresholds expressed by deltaKth = Kmax. API 579 and ASME Section XI (stainless steel) give increases in thresholds with decreasing stress ratios and the thresholds are expressed by deltaKth = Kmax - Kmin. BS 7910 gives constant thresholds expressed by deltaKth = Kmax - Kmin. The fatigue thresholds differ significantly among different FFS codes. Appropriate thresholds for ferritic steels, stainless steels and aluminum alloys are demonstrated in the literature survey.

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