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.

Fatigue Properties of Casting TC4 Alloys Treated by Hot Isostatic Pressing

2011 ◽  
Vol 197-198 ◽  
pp. 1668-1673
Author(s):  
Yu Hong Yao ◽  
Xiao Feng Shangguan ◽  
Jiang Nan Liu ◽  
Zheng Pin Wang ◽  
Jian Feng Wei
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Growth Rates ◽  
Stress Ratio ◽  
Fatigue Properties ◽  
Stress Ratios ◽  
Crack Growth Rates

With the aircraft structure design criterion from traditional static strength design to damage tolerance design and with the independent research and development of new-type civil turbofan regional aircraft and the implement of the plan to develop the country's own large passenger jets in China, it is essential to do some researches on casting TC4 alloys for the lack of the data of fatigue properties. The detail fatigue rating cut-off (DFRcutoff) values of casting TC4 alloys are measured and calculated by double dots method, the thresholds in fatigue crack propagation and the fatigue crack growth rates at different stress ratios are studied and the fatigue fracture at different stress ratios are observed by scanning electron microscopy. The results show that DFRcutoff value by double-dot method is 375.83 Mpa. The thresholds of fatigue crack propagation decrease with the increase of the stress ratio, whereas the fatigue crack growth rates increase with the increment of the stress ratio and the relationship curves between fatigue crack propagation rates and the stress intensity factor range have been obtained. Moreover, SEM observations indicate that the fatigue trips become wide with the increasing of the stress ratio.

Analysis on Fatigue Crack Growth Rates Under a Wide Range of Stress Ratios

1986 ◽  
Vol 108 (2) ◽  
pp. 209-213 ◽  
Author(s):  
M. Kurihara ◽  
A. Katoh ◽  
M. Kawahara
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Stress Ratio ◽  
Crack Opening ◽  
Wide Range ◽  
Stress Ratios ◽  
Crack Opening Stress ◽  
Crack Growth Rates

In the present study, a series of fatigue crack growth tests were carried out in order to examine the effects of stress ratio R upon crack growth rates, together with the crack closure behaviors. Fatigue tests were conducted with center-notched specimens of two kinds of pressure vessel steels (500 MPa class and 800 MPa class) under cyclic axial loading in various stress ratios R ranging from −5 to +0.8. Crack opening stress levels were determined by the unloading elastic compliance method. An expression of fatigue crack growth rates under a wide range of stress ratios was proposed, taking into account the relationship between stress ratio R and crack opening stress ratio U. The crack growth behaviors near the threshold conditions were also discussed.

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.

Fatigue Crack Growth in Steels 42CrV and IR3Mo

2004 ◽  
Vol 261-263 ◽  
pp. 1179-1184 ◽  
Author(s):  
Qin Zhi Fang
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Measurement System ◽  
Growth Rates ◽  
Fatigue Tests ◽  
Intensity Factors ◽  
Growth Measurement ◽  
Crack Growth Rates

An automatic fatigue crack growth measurement system was developed, in which a special four-channel A-D acquisition board that could collect data in phase was used. The data collecting frequency is in the range of 4×(2~25600)Hz. The system is suitable for fatigue tests with the frequencies not higher than 250Hz. Eddy current transducers and standard load cell were used to measure displacement and load, respectively. The system can instantly calculate fatigue crack lengths, stress intensity factors and fatigue crack growth rates. As an application of the system, fatigue crack growth rates (FCG) and the thresholds of steels 42CrV and IR3Mo were presented.

scholarly journals Fatigue crack growth rates of 10CrNi3MoV steel welded joints considering the stress ratio

2021 ◽  
Vol 33 ◽  
pp. 802-808
Author(s):  
Wei Song ◽  
Jingjing Li ◽  
Xuesong Liu ◽  
Ping Wang ◽  
Di Wan ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Welded Joints ◽  
Stress Ratio ◽  
Crack Growth Rates

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.

Sign in / Sign up

Export Citation Format

Share Document