A Study On Low Cycle Fatigue Life Assessment of Notched Specimens Made of 316LN Austenitic Stainless Steel

2021 ◽  
Author(s):  
Ikram Abarkan ◽  
Abdellatif Khamlichi ◽  
Rabee Shamass
Keyword(s):  
High Temperature ◽  
Fatigue Life ◽  
Strain Amplitude ◽  
Notch Root ◽  
Life Assessment ◽  
Root Radius ◽  
Local Strains ◽  
Analytical Approximations ◽  
Notch Root Radius ◽  
Neuber's Rule

Abstract The local strains obtained from the best known analytical approximations namely; Neuber's rule, Equivalent Strain Energy Density method, and linear rule, were compared to those resulting from finite- element analysis. It was found that apart from Neuber's rule with elastic stress concentration factor Kt, all the mentioned methods underestimate the local strains for all notch root radius, strain amplitudes level, at room temperature, and 550°C. Neuber's rule with Kt slightly overestimates the maximum strains for 1.25mm notch-root radius at high-temperature. Based on the analytically and numerically obtained notch root strains, the fatigue lives were estimated using the Coffin-Manson-Basquin equation. Besides, a numerical assessment of fatigue lives was estimated based on Brown-Miller and maximum shear strain equations. It was found that all these methods considerably underestimate the fatigue lives for all notch root radius, strain amplitude level, and under both temperature conditions. A new method was suggested, for which only the applied strain amplitude is needed to calculate the fatigue life of notched components. It was revealed that the suggested-method provides a good fatigue life prediction at a high-temperature loading state.

scholarly journals Low cycle fatigue behavior of circumferentially notched specimens made of modified 9Cr–1Mo steel at elevated temperature

2021 ◽  
Vol 13 (1) ◽  
pp. 54-62
Author(s):  
Ikram Abarkan ◽  
Abdellatif Khamlichi ◽  
Rabee Shamass
Keyword(s):  
Fatigue Life ◽  
Elevated Temperature ◽  
Applied Stress ◽  
Stress Amplitude ◽  
Low Cycle Fatigue ◽  
Notch Root ◽  
Reliable Determination ◽  
Local Strains ◽  
Analytical Approximations ◽  
Neuber's Rule

Abstract During service, notched designed components such as steam generators in the nuclear power plant usually experience fatigue damage at elevated temperatures, due to the repeated cyclic loadings during start-up and shut-down operations. Under such extreme conditions, the durability of these components is highly-affected. Besides, to assess the fatigue life of these components, a reliable determination of the local stress-strain at the notch-tips is needed. In this work, the maximum strains of circumferentially notched cylindrical specimens were calculated using the most commonly known analytical methods, namely Neuber's rule, modified Neuber's rule, Glinka's rule, and linear rule, with notch root radius of 1.25, 2.5, and 5 mm, made of modified 9Cr–1Mo steel at 550 °C, and subjected to nominal stress amplitudes of ±124.95, ±149.95, and ±174.95 MPa. The calculated local strains were compared to those obtained from Finite Element Analysis (FEA). It was found that all the analytical approximations provided unreliable local strains at the notch-tips, resulting in an overestimation or underestimation of the fatigue life. Therefore, a mathematical model that predicts the fatigue lives for 9Cr–1Mo steel at elevated temperature was proposed in terms of the applied stress amplitude and the fatigue stress concentration factor. The calculated fatigue lifetimes using the proposed model are found to be in good agreement with those obtained experimentally from the literature with relative errors, when the applied stress amplitude is ±149.95 MPa, are of 1.97%,–8.67%, and 13.54%, for notch root radii of 1.25, 2.5, and 5 mm, respectively.

scholarly journals Creep Fatigue Life Assessment of a Pipe Intersection with Dissimilar Material Joint by Linear Matching Method

2016 ◽  
Vol 853 ◽  
pp. 366-371
Author(s):  
Daniele Barbera ◽  
Hao Feng Chen ◽  
Ying Hua Liu
Keyword(s):  
High Temperature ◽  
Fatigue Life ◽  
Direct Method ◽  
Life Assessment ◽  
Dissimilar Material ◽  
Matching Method ◽  
Fatigue Life Assessment ◽  
Creep Fatigue ◽  
The Impact ◽  
Linear Matching Method

As the energy demand increases the power industry has to enhance both efficiency and environmental sustainability of power plants by increasing the operating temperature. The accurate creep fatigue life assessment is important for the safe operation and design of current and future power plant stations. This paper proposes a practical creep fatigue life assessment case of study by the Linear Matching Method (LMM) framework. The LMM for extended Direct Steady Cycle Analysis (eDSCA) has been adopted to calculate the creep fatigue responses due to the cyclic loading under high temperature conditions. A pipe intersection with dissimilar material joint, subjected to high cycling temperature and constant pressure steam, is used as an example. The closed end condition is considered at both ends of main and branch pipes. The impact of the material mismatch, transitional thermal load, and creep dwell on the failure mechanism and location within the intersection is investigated. All the results demonstrate the capability of the method, and how a direct method is able to support engineers in the assessment and design of high temperature component in a complex loading scenario.

Anomaly of Toughness Behavior with Notch-Root Radius

2009 ◽  
pp. 218-218-18
Author(s):  
KP Datta ◽  
WE Wood
Keyword(s):  
Notch Root ◽  
Root Radius ◽  
Notch Root Radius

Assessment of Fatigue Life for High-Temperature Pipeline Welds Using X-Ray Diffraction Technique

2007 ◽  
Vol 353-358 ◽  
pp. 130-133
Author(s):  
Keun Bong Yoo ◽  
Jae Hoon Kim
Keyword(s):  
High Temperature ◽  
Fatigue Life ◽  
Fatigue Damage ◽  
Power Plants ◽  
Low Cycle Fatigue ◽  
Diffraction Method ◽  
Life Assessment ◽  
Fatigue Properties ◽  
X Ray Diffraction ◽  
X Ray

The objective of this study is to examine the feasibility of the X-ray diffraction method for the fatigue life assessment of high-temperature steel pipes used for main steam pipelines, re-heater pipelines and headers etc. in power plants. In this study, X-ray diffraction tests were performed on the specimens simulated for low cycle fatigue damage, in order to estimate fatigue properties at the various stages of fatigue life. As a result of X-ray diffraction tests, it was confirmed that the full width at the half maximum (FWHM) decreased with an increase in the fatigue life ratio, and that the FWHM and the residual stress due to fatigue damage were algebraically linearly related to the fatigue life ratio. From this relationship, a direct assessment of the remaining fatigue life was feasible.

Evaluation of Environmental Effects on the Fatigue of Notched Specimen of Austenitic Stainless Steel Using Modified Rate Approach Method

2004 ◽  
Author(s):  
Katsumi Sakaguchi ◽  
Yasuhide Asada ◽  
Masao Itatani ◽  
Toshiyuki Saito
Keyword(s):  
Stainless Steel ◽  
High Temperature ◽  
Fatigue Life ◽  
Stress Concentration ◽  
Austenitic Stainless Steel ◽  
Notch Root ◽  
Notched Specimen ◽  
High Temperature Water ◽  
Approach Method ◽  
Temperature Water

Fatigue testing was conducted on notched specimens of austenitic stainless steel 316NG in high temperature water. Specimens were notched round bar with elastic stress concentration factors Kt of 1.4 and 3. For the specimen of Kt = 3, fatigue test was also performed in high temperature air. Environmental correction factor Fen recently proposed by Environmental Fatigue Tests (EFT) project in Japan Nuclear Safety Organization (JNES) was applied to the result of fatigue test to evaluate the environmental effects on fatigue life of notched specimen. Since the notch root strain varies non-proportionally to nominal strain in the elastic-plastic region, the modified rate approach method was applied to predict the fatigue life of notched specimen in the water, which was proposed to account for the environmental effect on fatigue life of nuclear component materials under varying conditions. Notch root strain and strain rate were calculated by FEM analysis. The difference between predicted and experimental fatigue lives in high temperature water was within factor of 2 for Kt = 3. The relationships between fictitious stress amplitude at notch root (= notch root strain amplitude multiplied by elastic modulus) and corrected fatigue life shows good coincidence with best fit curve for austenitic stainless steels. It is concluded that the modified rate approach method and current environmental correction factor Fen proposed by EFT project is applicable to predict fatigue life of the stress concentration when the notch root strain is adequately estimated.

A comparison between rapid expressions for evaluation of the critical J-integral in plates with U-notches under mode I loading

2011 ◽  
Vol 46 (8) ◽  
pp. 852-865 ◽  
Author(s):  
E Barati ◽  
F Berto
Keyword(s):  
Loading Condition ◽  
Control Volume ◽  
Notch Root ◽  
Critical Value ◽  
Fracture Load ◽  
Mode I ◽  
J Integral ◽  
Root Radius ◽  
Notch Root Radius ◽  
Mode I Loading

In this paper, some practical linear-elastic equations for evaluation of the critical value of the J-integral in plates with U-notches under mode I loading are presented and applied to brittle and quasi-brittle materials. The relationship between the J-integral and strain energy averaged over a well-defined control volume, depending on the static properties of the material, is applied, with the aim of obtaining the final expressions. It is found that these three proposed equations provide the same results, with any differences being negligible. By using one of these equations, one can evaluate Jcr and then predict the critical fracture load by means of the Jcr criterion. The results have shown that the critical value of the J-integral ( Jcr) is a function of the ratio of the material control radius to the notch-root radius ( Rc/ρ), the ratio of specimen width to notch depth ( w/ a), the notch acuity ( a/ρ), and the loading condition (tensile or bending loadings) in U-notches under mode I loading. However, the effect of the loading condition, a/ρ and w/ a ratios may be negligible. Therefore only the Rc/ρ ratio (i.e. the material properties and the notch-root radius of the specimen) affects Jcr.

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