Low Cycle Fatigue: Probability and Statistical Modeling of Fatigue Life

2014 ◽  
Author(s):  
D. Gary Harlow
Keyword(s):  
Distribution Function ◽  
Fatigue Life ◽  
Damage Accumulation ◽  
Power Plants ◽  
Structural Reliability ◽  
Low Cycle Fatigue ◽  
High Reliability ◽  
Cycle Fatigue ◽  
Low Carbon ◽  
Side Body

Low cycle fatigue (LCF) induces damage accumulation in structural components used in various applications. LCF typically describes conditions for which plastic strains are larger than elastic strains. In order to certify and qualify a structural component, manufactured from a given material, that requires high reliability for operation and safety, fundamental material properties should be experimentally investigated and validated. The traditional strain–life approach serves as the underlying experimental method for most LCF investigations. Building upon that background, the purpose of this paper is to investigate the statistical variability and appropriately model that variability for life in LCF. Specifically, the variability associated with the median behavior in a strain–life graph for data is examined. The ensuing analyses are based on data for a cold-rolled, low carbon, extra deep drawing steel; ASTM A969 which is appropriate for applications where extremely severe drawing or forming is envisioned. It is frequently used in the automotive industry for components such as inner door components and side body components. For substantiation of the proposed modeling techniques, data for 9Cr-1Mo steel is also investigated. Such steel is frequently used in the construction of power plants and other structures that experience operating temperatures in excess of 500°C. The commonly used universal slopes approach for fatigue life modeling for which the strain–life computation employs the standard Coffin–Manson relationship is compared to a statistical methodology using a distribution function frequently used in structural reliability. The proposed distribution function for characterizing the fatigue life is a generalized Weibull distribution function that empirically incorporates load history and damage accumulation.

Low-Cycle Fatigue Performance of Buckling Restrained Braces and Assessment of Cumulative Damage under Severe Earthquakes

2018 ◽  
Vol 763 ◽  
pp. 867-874
Author(s):  
Yu Shu Liu ◽  
Ke Peng Chen ◽  
Guo Qiang Li ◽  
Fei Fei Sun
Keyword(s):  
Fatigue Life ◽  
Energy Dissipation ◽  
Structural Reliability ◽  
Low Cycle Fatigue ◽  
Engineering Application ◽  
Fatigue Performance ◽  
Cycle Fatigue ◽  
Variable Amplitude ◽  
Buckling Restrained Braces ◽  
Energy Dissipation Devices

Buckling Restrained Braces (BRBs) are effective energy dissipation devices. The key advantages of BRB are its comparable tensile and compressive behavior and stable energy dissipation capacity. In this paper, low-cycle fatigue performance of domestic BRBs is obtained based on collected experimental data under constant and variable amplitude loadings. The results show that the relationship between fatigue life and strain amplitude satisfies the Mason-Coffin equation. By adopting theory of structural reliability, this paper presents several allowable fatigue life curves with different confidential levels. Besides, Palmgren-Miner method was used for calculating BRB cumulative damages. An allowable damage factor with 95% confidential level is put forward for assessing damage under variable amplitude fatigue. In addition, this paper presents an empirical criterion with rain flow algorithm, which may be used to predict the fracture of BRBs under severe earthquakes and provide theory and method for their engineering application. Finally, the conclusions of the paper were vilified through precise yet conservative prediction of the fatigue failure of BRB.

Evaluation of Low-Cycle Fatigue in Simulated PWR Environment

2006 ◽  
Vol 326-328 ◽  
pp. 1011-1014 ◽  
Author(s):  
Ill Seok Jeong ◽  
Sang Jai Kim ◽  
Taek Ho Song ◽  
Sung Yull Hong
Keyword(s):  
Fatigue Life ◽  
Nuclear Power ◽  
Power Plants ◽  
Low Cycle Fatigue ◽  
Water Environment ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Fatigue Design ◽  
Number Of Cycles ◽  
Measured Length

For developing fatigue design curve of cast stainless steel that is used in piping material of nuclear power plants, a low-cycle fatigue test rig was built. It is capable of performing tests in pressurized high temperature water environment of PWR. Cylindrical solid fatigue specimens of CF8M were used for the strain-controlled environmental fatigue tests. Fatigue life was measured in terms of the number of cycles with the variation of strain amplitude at 0.04%/s strain rates. The disparity between target length and measured length of specimens was corrected by using finite element method. The corrected test results showed similar fatigue life trend with other previous results.

scholarly journals Parameters influencing the low-cycle fatigue life of materials in pressure water reactor nuclear power plants / Parametry ovlivòující únavové chování materiálù pro tlakovodní jaderné reaktory v režimu nízkocyklové únavy

2015 ◽  
Vol 59 (3) ◽  
pp. 91-98
Author(s):  
V. Šefl
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Carbon Steel ◽  
Austenitic Stainless Steel ◽  
Literature Review ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Low Cycle Fatigue ◽  
Cycle Fatigue

Abstract In this literature review we identify and quantify the parameters influencing the low-cycle fatigue life of materials commonly used in nuclear power plants. The parameters are divided into several groups and individually described. The main groups are material properties, mode of cycling and environment parameters. The groups are further divided by the material type - some parameters influence only certain kind of material, e.g. sulfur content may decreases fatigue life of carbon steel, but is not relevant for austenitic stainless steel; austenitic stainless steel is more sensitive to concentration of dissolved oxygen in the environment compared to the carbon steel. The combination of parameters i.e. conjoint action of several detrimental parameters is discussed. It is also noted that for certain parameters to decrease fatigue life, it is necessary for other parameter to reach certain threshold value. Two different approaches have been suggested in literature to describe this complex problem - the Fen factor and development of new design fatigue curves. The threshold values and examples of commonly used relationships for calculation of fatigue lives are included. This work is valuable because it provides the reader with long-term literature review with focus on real effect of environmental parameters on fatigue life of nuclear power plant materials.

The Effect of Alloy Elements on Cyclic Fatigue Behavior of Bucket Candidate Materials for USC Power Plants

2007 ◽  
Vol 26-28 ◽  
pp. 1141-1144 ◽  
Author(s):  
Kuk Cheol Kim ◽  
Byung Hoon Kim ◽  
Jin Ik Suk ◽  
Dong Soo Kim ◽  
Jeong Tae Kim
Keyword(s):  
Fatigue Life ◽  
Power Plants ◽  
Boron Content ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Cyclic Fatigue ◽  
Strengthening Effect ◽  
Cycle Fatigue ◽  
Commercial Steel ◽  
Power Plant Operation

The demand for ultra supercritical (USC) power plants has increased due to the need for high thermal efficiency and reduced CO2 emissions. For turbine materials, high-cycle and lowcycle fatigue life at USC service temperatures are needed to verify material integrity due to the heat-up and cool-down process of power plant operation and due to turbine variations during operation. In this paper, fatigue characteristics for 9~12 Cr steels as candidate USC bucket materials were investigated. First, the fatigue life between DS2B2 and COST B2 steel were compared. COST B2 is the commercial steel with improved high temperature properties by adding boron, and DS2B2 is the new steel developed by Doosan by adding Co and adjusting Mo and W based on the same Mo equivalent value (%wt. Mo + 1/2 %wt. W). DS2B2 steel was found to have longer low cycle fatigue life than COST B2. Second, the effect of boron on fatigue life for bucket materials based on COST B2 steel was investigated. At room temperature, as boron content increased, low cycle fatigue life became superior, whereas, at 593oC the fatigue life was similar. For high cycle fatigue, as boron content increased, fatigue life increased due to the strengthening effect by the addition of boron.

scholarly journals Numerical modeling of the low cycle fatigue: effect of manufacturing imperfections caused by machining process

2021 ◽  
Vol 349 ◽  
pp. 02011
Author(s):  
Ikram Abarkan ◽  
Abdellatif Khamlichi ◽  
Rabee Shamass
Keyword(s):  
Surface Roughness ◽  
Fatigue Life ◽  
Power Plants ◽  
Low Cycle Fatigue ◽  
Machining Process ◽  
Loading Conditions ◽  
Cycle Fatigue ◽  
Maximum Shear Strain ◽  
Element Analysis ◽  
The Impact

The majority of mechanical components in nuclear power plants must be designed to withstand extreme cyclic loading conditions. In fact, when these components are subjected to low cycle fatigue, machining imperfections are considered one of the most significant factors limiting their service life. In the present work, using finite element analysis, a methodology has been suggested to predict the fatigue life of cylindrical parts made of 316 SS, at ambient temperature, under nominal strain amplitude ranging from ± 0.5 to ±1.2% with various surface roughness conditions. Two different multiaxial strain-life criteria have been considered to estimate the fatigue life, namely Brown-Miller and maximum shear strain. The comparison between the predicted and the experimental fatigue lifetimes has revealed that the adopted multiaxial strain life criteria can successfully estimate the fatigue life of 316 SS grade under uniaxial loading conditions. Furthermore, it has been found that the fatigue life decreases as the surface roughness average value increases, which indicates that surface regularities have a significant impact on low cycle fatigue life. Therefore, the proposed methodology is found to be capable of assessing the impact of surface roughness on the fatigue life of this specific steel in the low cycle fatigue regime.

Effect of Temperature Changes on the Waveform of Fatigue Damage Accumulation

2014 ◽  
Vol 598 ◽  
pp. 160-167 ◽  
Author(s):  
Stanisław Mroziński ◽  
Michał Piotrowski
Keyword(s):  
Fatigue Life ◽  
Temperature Change ◽  
Damage Accumulation ◽  
Low Cycle Fatigue ◽  
Fatigue Tests ◽  
Effect Of Temperature ◽  
Cycle Fatigue ◽  
Temperature Changes ◽  
Fatigue Damage Accumulation ◽  
Two Temperatures

In this paper there have been presented the results of low-cycle fatigue tests of steel P91 samples in the conditions of isothermal fixed amplitude loads as well as loads with a temperature change. Fixed amplitude isothermal loads were conducted on five levels of full strain and in two temperatures T1=20°C and T2=600°C. In the paper there has been found a significant influence of the sequence of temperature changes on the cyclic properties after the temperature change and on the fatigue life. The conducted experimental verification of the Palmgren-Miner hypothesis proved its influence on the temperature changes during the tests.

Statistical Model of Micro Crack Growth for the Evaluation of Accumulated Fatigue in NPPs

2014 ◽  
Author(s):  
Shigeki Abe ◽  
Takao Nakamura
Keyword(s):  
Statistical Model ◽  
Crack Growth ◽  
Fatigue Failure ◽  
Structural Factor ◽  
Nuclear Power ◽  
Power Plants ◽  
Low Cycle Fatigue ◽  
High Reliability ◽  
Reduction Factor ◽  
Cycle Fatigue

In order to establish sophisticated management of aging degradation and to achieve high reliability of components in nuclear power plants (NPPs), it is required to reveal the mechanism of aging degradation and to quantify its deterioration. Present design code requires the assessment of CUF (cumulated usage factor) using design fatigue curve to prevent the occurrence of low-cycle fatigue failure in class 1 components of NPPs. This assessment of CUF prevents the low-cycle fatigue failure effectively up to the present date. However, the margins of structural factor (safety factor) and environmental fatigue reduction factor Fen need to be clarified for the quantitative assessment of aging degradation based on the mechanism of fatigue accumulation in NPPs,. Structural factor and environmental factor are defined in NUREG/CR6909, etc, but they do not clearly explain the technical basis of these factors according to the mechanism of fatigue and environmental effect. In this study, we quantify the dispersions of crack initiation and crack growth in fatigue test in a certain condition aiming at more sophisticated management of aging degradation based on the mechanism of crack growth. Applying these dispersions, we establish a statistical model of micro crack growth to predict fatigue life. We will propose the application of this prediction model of fatigue crack growth to the management of actual components degradation and establish proper maintenance program in order to achieve high reliability of components in NPPs in future.

Influence of the Strain Rate on the Low Cycle Fatigue Life of an Austenitic Stainless Steel with a Ground Surface Finish in Different Environments

2014 ◽  
Vol 891-892 ◽  
pp. 1320-1326 ◽  
Author(s):  
Thibault Poulain ◽  
José Mendez ◽  
Gilbert Hénaff ◽  
Laurent de Baglion
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Austenitic Stainless Steel ◽  
Strain Rate ◽  
Surface Finish ◽  
Power Plants ◽  
Low Cycle Fatigue ◽  
Total Strain Amplitude ◽  
Cycle Fatigue ◽  
Pressurized Water

This paper focuses on the influence of strain rate in Low Cycle Fatigue (LCF) of a 304L austenitic stainless steel at 300 °C in different environments (secondary vacuum, air and Pressurized Water Reactor (PWR) water environment). Moreover test samples are ground to obtain a surface finish rougher than all that could be found in nuclear power plants. Different strain rates (4x10-3, 1x10-4and 1x10-5s-1) are studied, with a triangular waveform at a total strain amplitude of ±0.6%. The influence of strain rate on cyclic stress-strain behavior and fatigue life is firstly analyzed in secondary vacuum, considered as a non-active environment. Then, interactions between stain rate and environmental effects in Air and in PWR environment are presented. In all environments, a decrease in strain rate leads to a negative strain rate dependence of the stress response and a reduction in fatigue life. Finally, SEM observations of fatigue striations in PWR environment indicate a crack propagation rate enhancement when the strain rate is decreased.

Damage accumulation near a hole under low cycle fatigue proceeding from measurements of local deformation response

2020 ◽  
Vol 86 (10) ◽  
pp. 46-55
Author(s):  
S. I. Eleonsky ◽  
Yu. G. Matvienko ◽  
V. S. Pisarev ◽  
A. V. Chernov
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Damage Accumulation ◽  
Stress Ratio ◽  
Low Cycle Fatigue ◽  
Accumulation Process ◽  
Stress Range ◽  
Cycle Fatigue ◽  
Deformation Response

A new destructive method for quantitative determination of the damage accumulation in the vicinity of a stress concentrator has been proposed and verified. Increase of damage degree in local area with a high level of the strain gradient was achieved through preliminary low-cycle pull-push loading of plane specimens with central open holes. The above procedure is performed for three programs at the same stress range (333.3 MPa) and different stress ratio values 0.33, – 0.66 and – 1.0, and vice versa for two programs at the same stress ratio – 0.33 and different stress range 333.3 and 233.3 MPa. This process offers a set of the objects to be considered with different degree of accumulated fatigue damages. The key point of the developed approach consists in the fact that plane specimens with open holes are tested under real operation conditions without a preliminary notching of the specimen initiating the fatigue crack growth. The measured parameters necessary for a quantitative description of the damage accumulation process were obtained by removing the local volume of the material in the form of a sequence of narrow notches at a constant level of external tensile stress. External load can be considered an amplifier enhancing a useful signal responsible for revealing the material damage. The notch is intended for assessing the level of fatigue damage, just as probe holes are used to release residual stress energy in the hole drilling method. Measurements of the deformation response caused by local removing of the material are carried out by electronic speckle-pattern interferometry at different stages of low-cycle fatigue. The transition from measured in-plane displacements to the values of the stress intensity factor (SIF) and the T-stress was carried out on the basis of the relations of linear fracture mechanics. It was shown that the normalized dependences of the stress intensity factor on the durability percentage for the first notch (constructed for four programs of cyclic loading with different parameters), reflect the effect of the stress ratio and stress range of the loading cycle on the rate of damage accumulation. The data were used to obtain the explicit form of the damage accumulation function that quantitatively describes damage accumulation process. The functions were constructed for different stress ratios and stress ranges.

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