Reference Curve of Fatigue Crack Growth for Ferritic Steels Under Negative R Ratio Provided by ASME Code Section XI

2016 ◽  
Vol 139 (3) ◽  
Author(s):  
Kunio Hasegawa ◽  
Vratislav Mares ◽  
Yoshihito Yamaguchi
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Closure ◽  
Growth Rates ◽  
Ferritic Steels ◽  
Reference Curve ◽  
R Ratio ◽  
Asme Code ◽  
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 versus 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 versus Kmax to da/dN versus 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 versus ΔKI is better equation than da/dN versus 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.

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.

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.

Fracture and Fatigue Tolerant Steel Pressure Vessels for Gaseous Hydrogen

2010 ◽  
Author(s):  
Kevin A. Nibur ◽  
Chris San Marchi ◽  
Brian P. Somerday
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Maximum Load ◽  
Pressure Vessels ◽  
Hydrogen Gas ◽  
R Ratio ◽  
History Of ◽  
Crack Growth Rates

Fatigue crack growth rates and rising displacement fracture thresholds have been measured for a 4130X steel in 45 MPa hydrogen gas. The ratio of minimum to maximum load (R-ratio) and cyclic frequency was varied to assess the effects of these variables on fatigue crack growth rates. Decreasing frequency and increasing R were both found to increase crack growth rate, however, these variables are not independent of each other. Changing frequency from 0.1 Hz to 1 Hz reduced crack growth rates at R = 0.5, but had no effect at R = 0.1. When applied to a design life calculation for a steel pressure vessel consistent with a typical hydrogen trailer tube, the measured fatigue and fracture data predicted a re-inspection interval of nearly 29 years, consistent with the excellent service history of such vessels which have been in use for many years.

An Approach to Account for Negative R-Ratio Effects in Fatigue Crack Growth Calculations for Pressure Vessels Based on Crack Closure Concepts

1994 ◽  
Vol 116 (1) ◽  
pp. 30-35 ◽  
Author(s):  
J. M. Bloom
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Closure ◽  
Pressure Vessels ◽  
Nuclear Industry ◽  
Closure Models ◽  
R Ratio ◽  
Compressive Loads ◽  
Asme Code

Current fatigue crack growth procedures in the commercial nuclear industry do not clearly specify how compressive loads are to be handled and, therefore, regulatory agencies usually recommend a conservative approach requiring full consideration of the loads. This paper demonstrates that a more realistic approach to account for compressive loads can be formulated using crack closure concepts. Several empirical plasticity-induced crack closure models were evaluated. An approach in the Section XI ASME Code for tensile loading only has been extended and evaluated for negative R-ratios. However, the paper shows this approach to be overly conservative. The approaches using crack closure models are shown to be more accurate. An analytically based crack closure model, while more complicated, is shown to give a theoretical basis to the empirically derived crack closure models. The paper concludes with a recommendation for modifying the current ASME Code practices consistent with the crack closure models and fatigue crack growth data from negative R-ratio tests.

Analysis of the Effect of Load Ratio on Fatigue Crack Growth

2011 ◽  
Vol 181-182 ◽  
pp. 330-336 ◽  
Author(s):  
Ying Xiong
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Multiaxial Fatigue ◽  
Cyclic Plasticity ◽  
Plasticity Model ◽  
R Ratio ◽  
Crack Growth Rates ◽  
Fatigue Criterion

In this paper, fatigue test and numerical simulation are carried out for Q345 weld joint under constant amplitude loading at different R-ratio using the compact tension samples with 3.8mm thickness. The result indicates that fatigue crack growth rates in the base metal is not sensitive to R-ratio, but the fatigue crack growth rates increases in the weld zone with R-ratio increasing. The effect of R-ratio on fatigue crack growth is analyzed based on J-S cycle plasticity model and Jiang’s multiaxial fatigue criterion. The finite element method (FEM) is used for the stress-strain analysis with the implementation of an accurate J-S cyclic plasticity model. With the detailed stresses and strains, fatigue damage assessment is made using a Jiang’s multiaxial fatigue criterion.

Fatigue Crack Growth Rate Analysis in a Titanium Alloy

2008 ◽  
Vol 385-387 ◽  
pp. 5-8
Author(s):  
Alexander M. Korsunsky ◽  
Daniele Dini ◽  
Michael J. Walsh
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Complex Load ◽  
R Ratio ◽  
Lower Amplitude ◽  
Crack Growth Rates

Reliable prediction of fatigue crack growth rates in aerospace materials and components underpins the so-called defect-tolerant approach to lifing. In this methodology the presence or appearance of defects and cracks in components is accepted. However, safe operation is guaranteed by regular inspections and health monitoring, and ensuring (by means of reliable modelling) that no crack may grow far enough to reach the critical size in the interval between inspections. Under such circumstances it is clear that particular attention has to be paid to the development and validation of predictive modelling capabilities for fatigue crack propagation. The situation is complicated by the fact that it is often a challenge to represent correctly the in-service loading experienced by a cracked component. In practice, on top of the major cycles associated with each flight (LCF component), cycles of higher frequency and lower amplitude are also present (HCF component). Sensitivity to dwell at maximum load is also often observed. Furthermore, it is well established that complex load sequences involving overloads and underloads result in fluctuations of fatigue crack growth rates (retardation and acceleration) that must be accounted for in crack growth calculations. In the present study we consider the application of an approach due to Noroozi et al. [1] to the analysis of R-ratio effects in Ti-6Al-4V material, on the basis of the experimental crack growth rate data collected under the auspices of AGARD programme [2]. The approach shows promising results, and has the capacity to capture loading sequence effects.

Transient Fatigue Crack-Growth Behavior and Damage Zones in Zr-Based Bulk Metallic Glass

2003 ◽  
Vol 806 ◽  
Author(s):  
Peter A. Hess ◽  
Reinhold H. Dauskardt
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Crack Closure ◽  
Growth Rates ◽  
Fatigue Loading ◽  
Structural Applications ◽  
Crack Growth Rates

ABSTRACTFatigue crack propagation mechanisms of bulk metallic glasses (BMGs) are not well understood, limiting their use in safety-critical structural applications particularly where complex fatigue loading may occur. Accordingly, the present study examines the effects of variable amplitude fatigue loading associated with block loading and tensile overloads on fatigue crack-growth rates in a Zr-based BMG. Crack growth studies were conducted on compact tension specimens using computer control of the applied stress intensity range, ΔK. Fatigue crack closure loads, which represent the initial contact of mating crack surfaces during the unloading cycle, were continuously monitored during testing. Abrupt drops in ΔK were found to significantly decrease fatigue crack-growth rates far below equilibrium values, arresting growth completely at a ΔK twice the nominal fatigue threshold ΔKTH. Conversely, an abrupt increase in ΔK was found to accelerate fatigue crack-growth rates. The effects of roughness-induced crack closure were assessed and found to be consistent with the suppression or acceleration of growth rates. However, in order to fully explain the observed transient growth rate response, other mechanisms that may be related to the fatigue mechanism itself were also considered. Specifically, the nature of the fatigue crack tip damage zone was also investigated. As BMGs lack distributed plasticity at low temperatures, the plastic zone differs greatly from that seen in ductile crystalline materials, and its role in fatigue crack propagation mechanisms is examined.

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.

Prediction of Fatigue Crack Growth of Aged Hardening Al-Alloys under Variable Amplitude Loading

2014 ◽  
Vol 891-892 ◽  
pp. 1729-1735
Author(s):  
Mustapha Benachour ◽  
Boumedienne Zeggai ◽  
Nadjia Benachour ◽  
Mohamed Benguediab ◽  
Abdelkader Belmokhtar
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Al Alloys ◽  
Variable Amplitude Loading ◽  
Variable Amplitude ◽  
R Ratio ◽  
Single Overload ◽  
Crack Growth Rates

In this investigation, variable amplitude loading effect was studied on aged hardening Al-alloys in series 2000 and 7000. Generalised Willenborg model was used in order to show loading interaction effects (overload effects). Variable amplitude loading under different form of spectrum has affected highly the fatigue life and fatigue crack growth rates. Fatigue lives were increased and fatigue crack growth rates (FCGRs) were decreased in increasing of overload ratio in single overload case. In application of overload band, the fatigue lives and FCGRs were affected by band overload and R-ratio of them when level in FCGRs was increased.

Sign in / Sign up

Export Citation Format

Share Document