scholarly journals Study on deformation behavior and life evaluation method for SUS304 notched plate under bending creep fatigue loading.

1990 ◽  
Vol 39 (442) ◽  
pp. 982-988
Author(s):  
Yoshio FUKUDA ◽  
Yoshimi SATOH ◽  
Kazuhiro NAKAMURA ◽  
Yukio TAKAHASHI ◽  
Kazuo KUWABARA
Keyword(s):  
Deformation Behavior ◽  
Evaluation Method ◽  
Fatigue Loading ◽  
Life Evaluation ◽  
Creep Fatigue

Change of the Effective Strength of Grain Boundaries in Alloy 617 Under Creep-Fatigue Loadings at 800°C

2019 ◽  
Author(s):  
Wataru Suzuki ◽  
Kenta Ishihara ◽  
Ryo Kikuchi ◽  
Ken Suzuki ◽  
Hideo Miura
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Evaluation Method ◽  
Accumulation Rate ◽  
Ion Beam ◽  
Fatigue Loading ◽  
Test System ◽  
Total Density ◽  
Alloy 617 ◽  
Creep Fatigue

Abstract In this study, both EBSD (Electron Back-Scatter Diffraction) analysis and a micro tensile test system with FIB (Focused Ion Beam) equipment were applied to bicrystal specimens of Alloy 617 in order to establish a quantitative theory of the lifetime evaluation method under creep-fatigue loadings. The IQ (Image Quality) value which is obtained from the diffraction pattern (Kikuchi pattern) indicates the total density of defects such as vacancies, dislocations, and local strain was used for quantitatively evaluating the crystallinity of the alloy. KAM (Kernel Average Misorientation) value was also used for density analysis of GN (Generally Necessary) dislocations. Continuous changes of microtexture of grains and grain boundaries were observed by applying an intermittent creep fatigue test. As a result, it was confirmed that the IQ value around specific grain boundaries in damaged specimen was drastically degraded compared to that of the initial specimen. Intergranular cracks always occurred when the IQ value decreased to a certain value. Therefore, there is a correlation between the IQ value and the strength of a grain boundary in this alloy. The decrease of the IQ value was attributed to the accumulation of both dislocations and vacancies around the specific grain boundaries under creep loading. The accumulation rate under the creep-fatigue loading was clearly higher than that under simple fatigue and creep loadings. Finally, it was clarified that the degradation of the crystallinity in the vicinity of a grain boundary was a criterion of an intergranular crack under creep-fatigue loadings.

Fatigue and Creep-Fatigue Life Evaluation of U-Shaped Bellows

1992 ◽  
Vol 114 (3) ◽  
pp. 280-291 ◽  
Author(s):  
K. Tsukimori ◽  
T. Yamashita ◽  
M. Kikuchi ◽  
K. Iwata ◽  
A. Imazu
Keyword(s):  
Fatigue Life ◽  
Evaluation Method ◽  
Strain Range ◽  
Creep Damage ◽  
Fatigue Tests ◽  
Reliable Operation ◽  
Life Evaluation ◽  
Creep Fatigue ◽  
Fatigue Life Evaluation ◽  
Rational Evaluation

For the reliable operation of bellows under cyclic loadings at high temperatures, a rational evaluation method of life of bellows would be needed. Authors investigated simplified analysis methods for fatigue and creep-fatigue life prediction of U-shaped bellows considering inelasticity as well as various geometrical nonuniformity such as thickness and shape of convolutions. A conservative evaluation method of the strain range is developed, introducing three strain range amplification factors for nominal elastic strain range. Creep and relaxation behaviors of bellows are studied. Consequently, a new evaluation method of creep damage fractions is proposed which depends upon the relation between primary and secondary stresses. Fatigue and creep-fatigue tests are conducted and the validity of the present methods is discussed.

Crack Growth in Stainless Steel 304 under Creep-Fatigue Loading

2007 ◽  
Vol 353-358 ◽  
pp. 485-490 ◽  
Author(s):  
Y.M. Baik ◽  
K.S. Kim
Keyword(s):  
Stress Intensity Factor ◽  
Stainless Steel ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Growth ◽  
Growth Rates ◽  
Static Loading ◽  
Fatigue Loading ◽  
Creep Fatigue ◽  
Crack Growth Rates

Crack growth in compact specimens of type 304 stainless steel is studied at 538oC. Loading conditions include pure fatigue loading, static loading and fatigue loading with hold time. Crack growth rates are correlated with the stress intensity factor. A finite element analysis is performed to understand the crack tip field under creep-fatigue loading. It is found that fatigue loading interrupts stress relaxation around the crack tip and cause stress reinstatement, thereby accelerating crack growth compared with pure static loading. An effort is made to model crack growth rates under combined influence of creep and fatigue loading. The correlation with the stress intensity factor is found better when da/dt is used instead of da/dN. Both the linear summation rule and the dominant damage rule overestimate crack growth rates under creep-fatigue loading. A model is proposed to better correlate crack growth rates under creep-fatigue loading: 1 c f da da da dt dt dt Ψ −Ψ     =         , where Ψ is an exponent determined from damage under pure fatigue loading and pure creep loading. This model correlates crack growth rates for relatively small loads and low stress intensity factors. However, correlation becomes poor as the crack growth rate becomes large under a high level of load.

On the Evaluation and Consideration of Fracture Mechanical Notch Support Within a Creep Fatigue Lifetime Assessment

2018 ◽  
Author(s):  
Christian Kontermann ◽  
Henning Almstedt ◽  
Falk Müller ◽  
Matthias Oechsner
Keyword(s):  
Fatigue Loading ◽  
Experimental Program ◽  
Energy Market ◽  
Steam Turbines ◽  
Fatigue Lifetime ◽  
Global Strain ◽  
Creep Fatigue ◽  
Main Components ◽  
Flexible Operation ◽  
The Impact

Changes within the global energy market and a demand for a more flexible operation of gas- and steam-turbines leads to higher utilization of main components and raises the question how to deal with this challenge. One strategy to encounter this is to increase the accuracy of the lifetime assessment by quantifying and reducing conservatisms. At first the impact of considering a fracture mechanical notch support under creep-fatigue loading is studied by discussing the results of an extensive experimental program performed on notched round-bars under global strain control. A proposal how to consider this fracture mechanical notch support within a lifetime assessment is part of the discussion of the second part. Here, a theoretical FEM-based concept is introduced and validated by comparing the theoretical prediction with the results of the previously mentioned experimental study. Finally, the applicability of the developed and validated FEM-based procedure is demonstrated.

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