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.

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.

Effect of Local Strain on Low Cycle Fatigue Measured by ESPI System

2006 ◽  
Vol 321-323 ◽  
pp. 678-683
Author(s):  
Kyung Su Kim ◽  
Ki Sung Kim ◽  
Kyung Ho Lee ◽  
Jung Min Kwon ◽  
Seong Mo Park ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Speckle Pattern ◽  
Local Strain ◽  
Material Behavior ◽  
Electronic Speckle Pattern Interferometry ◽  
Cycle Fatigue ◽  
Local Strains ◽  
Neuber's Rule

Low cycle fatigue cracks are mainly detected at discontinuous welded locations with high stresses under repeated cyclic static loads due to cargo loading and unloading. Theoretical and analytical methods have been used to estimate the local stress and strain, which affect the prediction of fatigue life, but these methods have difficulties considering stress concentration at notched locations and complicated material behavior of welded joints or heat affected zones. Electronic speckle pattern interferometry(ESPI) system is a nondestructive and non-contact measurement system, which can provide relatively accurate full field strain at critical positions such as welded zones and structurally discontinuous locations. In this study, local strain was measured by ESPI system at the welded cruciform joint, and then low cycle fatigue test was performed. Effect of local strain on low cycle fatigue life was examined by using the strain value measured by ESPI. In order to verify the relations between local strains and fatigue lives, after theoretical local strains and stresses were calculated by using Neuber’s rule, the measured local strains corresponding the experimental fatigue lives were compared with the results of Neuber’s rule and established codes of the British standard and DNV curve.

Uniaxial Ratcheting and Low-Cycle Fatigue Failure of U75V Rail Steel

2016 ◽  
Vol 853 ◽  
pp. 246-250 ◽  
Author(s):  
Tao Fang ◽  
Qian Hua Kan ◽  
Guo Zheng Kang ◽  
Wen Yi Yan
Keyword(s):  
Fatigue Life ◽  
Strain Amplitude ◽  
Stress Ratio ◽  
Stress Amplitude ◽  
Rail Steel ◽  
Low Cycle Fatigue ◽  
Mean Stress ◽  
Cycle Fatigue ◽  
Ratcheting Strain ◽  
Cyclic Straining

Experiments on U75V rail steel were carried out to investigate the cyclic feature, ratcheting behavior and low-cycle fatigue under both strain- and stress-controlled loadings at room temperature. It was found that U75V rail steel shows strain amplitude dependent cyclic softening feature, i.e., the responded stress amplitude under strain-controlled decreases with the increasing number of cycles and reaches a stable value after about 20th cycle. Ratcheting strain increases with an increasing stress amplitude and mean stress, except for stress ratio, and the ratcheting strain in failure also increases with an increasing stress amplitude, mean stress and stress ratio. The low-cycle fatigue lives under cyclic straining decrease linearly with an increasing strain amplitude, the fatigue lives under cyclic stressing decrease with an increasing mean stress except for zero mean stress, and decrease with an increasing stress amplitude. Ratcheting behavior with a high mean stress reduces fatigue life of rail steel by comparing fatigue lives under stress cycling with those under strain cycling. Research findings are helpful to evaluate fatigue life of U75V rail steel in the railways with passenger and freight traffic.

Low Cycle Fatigue Properties of FGH720Li Superalloy

2021 ◽  
Vol 1035 ◽  
pp. 292-296
Author(s):  
Zi Chao Peng ◽  
Jun Ying Sheng ◽  
Xu Qing Wang ◽  
Yue Tang
Keyword(s):  
Fatigue Life ◽  
Powder Metallurgy ◽  
Applied Stress ◽  
Low Cycle Fatigue ◽  
Influencing Factor ◽  
Fatigue Tests ◽  
Fatigue Properties ◽  
Nickel Base Superalloy ◽  
Loading Frequency ◽  
Cycle Fatigue

Low cycle fatigue (LCF) properties of a powder metallurgy(PM) nickel base superalloy FGH720Li were systematically studied in this work, including smooth LCF and notched LCF tested at various temperatures and different stress. The relationship between the fatigue life and applied stress was analyzed both for smooth fatigue and notch fatigue tests. The effects of loading frequency and stress ratio on LCF behavior were also studied. As an important influencing factor of the fatigue life in powder metallurgy superalloy, the effect of inclusions on LCF life was also investigated. The results showed that the fatigue properties of FGH720Li alloy was excellent, when tested at the temperature of 450°C and applied stress of 1230MPa, the fatigue life could exceed 5×104 cycles. When tested at 650°C and 1150MPa, the average fatigue life was still beyond 2×105 cycles.

Multiaxial Fatigue of 6061-T6 Aluminum Alloy under Corrosive Environment

2016 ◽  
Vol 853 ◽  
pp. 77-82
Author(s):  
Xu Chen ◽  
Rui Si Xing ◽  
Xiao Peng Liu
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Life ◽  
Stress Amplitude ◽  
Low Cycle Fatigue ◽  
Cyclic Hardening ◽  
Cyclic Softening ◽  
Fatigue Tests ◽  
Plastic Strain Amplitude ◽  
Multiaxial Fatigue ◽  
Corrosive Environment

Aluminium alloys are widely used in the fields of automobile, machinery and naval construction. To investigate the effect of non-proportional loadings and corrosive environment on the fatigue resistance of 6061-T6 aluminum alloy, a set of uniaxial and multiaxial low cycle fatigue tests were carried out. Firstly, the results of uniaxial tests showed that the alloy exhibited cyclic hardening then cyclic softening. With the increase of stress amplitude the cyclic softening became pronounced. The increasing of plastic deformation was basically cyclically stable with small plastic strain amplitude accumulation when the stress amplitude was lower than 200MPa ,while it was increasing rapidly when the stress amplitude was higher than 220MPa. Secondly, it was observed that non-proportional cycle additional hardening of 6061-T6 aluminum alloy was little. While the fatigue life was badly affected by the loading paths. Thirdly ,the fatigue corrosion interactions were also talked about in details by performing the tests under the same loading conditions with corrosive environment. The experiment proved that the seawater corrosion has huge impact on fatigue life under pH 3. Finally, a multi-axial fatigue life prediction model was used to predict the fatigue life with or without the corrosive environment which showed a good agreement with experimental data.

Verification of the Prediction Methods of Strain Range in Notched Specimens Made of Mod.9Cr-1Mo

2010 ◽  
Author(s):  
Masanori Ando ◽  
Yuichi Hirose ◽  
Shingo Date ◽  
Sota Watanabe ◽  
Yasuhiro Enuma ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Elevated Temperature ◽  
Low Cycle Fatigue ◽  
Strain Range ◽  
Fatigue Tests ◽  
Estimation Methods ◽  
Prediction Methods ◽  
Test Machine ◽  
Notched Specimens ◽  
Creep Fatigue

Several innovative prediction methods of strain range have been developed in order to apply to the Generation IV plants. In a component design at elevated temperature, ‘strain range’ is used to calculate the fatigue and creep-fatigue damage. Therefore, prediction of ‘strain range’ is one of the most important issues to evaluate the components’ integrity during these lifetimes. To verify the strain prediction method of discontinues structures at evaluated temperature, low cycle fatigue tests were carried out with notched specimens. All the specimens were made of Mod.9Cr-1Mo, because it is a candidate material for a primary and secondary heat transports system components of JSFR (Japanese Sodium Fast Reactor). Deformation control fatigue tests and thermal fatigue tests were performed by ordinary uni-axial push-pull test machine and equipment generating the thermal gradient in the notched plate by induction heating. Stress concentration level was changed by varying the notch radius in the both kind of tests. Crack initiation and propagation process during the fatigue test were observed by the digital micro-scope and replica method. Elastic and inelastic FEAs were also carried out to estimate the ‘strain range’ for the prediction of fatigue life. Then the ranges of several strain predictions and estimations were compared with the test results. These predictions were based on the sophisticated technique to estimate the ‘strain range’ from elastic FEA. Stress reduction locus (SRL) method, simple elastic follow-up method, Neuber’s rule method and the methods supplied by elevated temperature design standards were applied. Through these results, the applicability and conservativeness of these strain prediction and estimation methods, which is the basis of the creep-fatigue life prediction, is discussed.

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