Long-Term Creep Modeling of Modified 9Cr-1Mo Steel for a Sodium Cooled Fast Reactor

2010 ◽  
Author(s):  
Woo-Gon Kim ◽  
Jae-Young Park ◽  
Sung-Ho Kim ◽  
Chan-Bock Lee
Keyword(s):  
Constant Load ◽  
Primary Creep ◽  
Least Square ◽  
Creep Data ◽  
Creep Tests ◽  
Omega Method ◽  
Creep Curves ◽  
The Individual ◽  
Term Creep

This paper focused on long-term creep modeling for describing total creep curves of up to rupture for modified 9Cr-1Mo steel (G91). Creep data was obtained by a series of constant-load creep tests at 600°C. Three modified constitutive equations of modified power-law method (MPM), modified theta method (MTM) and modified omega method (MOM), described as a sum of a decaying primary creep and an accelerating tertiary creep, were proposed. A nonlinear least square fitting (NLSF) analysis was carried out on the basis of the creep data so that they provide the best fit to experimental data in optimizing parameter constants of the individual equation. Results of the NLSF analysis showed that in the lower stress regions of 160MPa (σ/σys<0.65), the MTM matched well with the experimental creep data compared with the MPM and MOM, but that in the higher stress regions of 160MPa (σ/σy > 0.65), the MPM revealed better agreement than the MTM and MOM. It was found that the MTM was superior in the modeling of long-term creep curves to the MPM and MOM. Long-term creep curves for the G91 steel were numerically modeled and its creep life was predicted by the MTM.

Creep Model Based on Theta Projection and Omega Method for Predicting the Creep Behavior of Alloy

2007 ◽  
Vol 353-358 ◽  
pp. 533-536
Author(s):  
Bong Min Song ◽  
Jong Yup Kim ◽  
Joon Hyun Lee
Keyword(s):  
Creep Behavior ◽  
Constant Load ◽  
Control Mode ◽  
Creep Model ◽  
Test Results ◽  
Creep Data ◽  
Creep Tests ◽  
Omega Method ◽  
Improved Model ◽  
Term Creep

Creep testing of Alloy 718 has been carried out at various loads in the temperature range near 650°C in constant load control mode in order to understand how to predict the creep behavior including tertiary creep. The test results have been used for evaluating the existed models, such as Theta projection and Omega method that have been widely used for predicting long term creep strain and rupture time. After determining variables and material parameters of each method with the test results, estimated creep data from each model have been compared with the each measured creep data from the creep tests. The root cause of the discrepancy between estimated and measured data has been analyzed in order to improve the existed methods. The reliability of the improved model has been evaluated in relation to creep data.

Modeling of a Long-Term Creep Curve of Alloy 617 for a High Temperature Gas-Cooled Reactor

2008 ◽  
Vol 385-387 ◽  
pp. 693-696 ◽  
Author(s):  
Woo Gon Kim ◽  
Song Nan Yin ◽  
Ik Hee Jung ◽  
Yong Wan Kim
Keyword(s):  
Least Square ◽  
Short Term ◽  
Creep Tests ◽  
Least Square Fitting ◽  
Creep Curves ◽  
Term Creep ◽  
Good Agreement ◽  
Short Term Creep ◽  
Stress Dependency

This study aimed to model the long-term creep curves above 105 hours by implementing a nonlinear least square fitting (NLSF) of the Kachanov-Rabotnov (K-R) model. For this purpose, the short-term creep curves obtained from a series of creep tests at 950oC were used. In the NLSF of their full creep curves, the K-R model represented a poor match to the experimental curves, but the modified K-R one revealed a good agreement to them. The Monkman-Grant (M-G) strain represented the behavior of a stress dependency, but the 􀁏 parameter was constant with a stress independency. The 􀁏 value in the modified K-R model was 2.78. Long-term creep curves above 105 hours from short-term creep data were modeled by the modified K-R model.

Microstructures of Grade 91 Steels Under Long-Term Creep Conditions

2018 ◽  
Author(s):  
Kenji Kako ◽  
Susumu Yamada ◽  
Masatsugu Yaguchi ◽  
Yusuke Minami
Keyword(s):  
Remaining Life ◽  
Martensitic Steels ◽  
Creep Data ◽  
Creep Life ◽  
Creep Tests ◽  
Microstructural Observation ◽  
Type Iv ◽  
Grade 91 ◽  
Term Creep

Type IV damage has been found at several ultra-supercritical (USC) plants that used high-chromium martensitic steels in Japan, and the assessment of the remaining life of the steels is important for electric power companies. The assessment of the remaining life needs long-term creep data for over 10 years, but such data are limited. We have attempted to assess the remaining life by creep tests and by microstructural observation of Grade 91 steels welded pipes which were used in USC plants for over 10 years. Following the results of microstructural observation of USC plant pipes, we find that microstructures, especially distribution of MX precipitates, have large effect on the creep life of Grade 91 steels.

Long Term Creep Life Prediction of New and Service Exposed P91 Steel

2018 ◽  
Author(s):  
Muneeb Ejaz ◽  
Norhaida Ab Razak ◽  
Andrew Morris ◽  
Scott Lockyer ◽  
Catrin M. Davies
Keyword(s):  
Tensile Strength ◽  
Creep Behaviour ◽  
Equivalent Stress ◽  
Practical Reasons ◽  
Creep Data ◽  
Short Term ◽  
Creep Tests ◽  
High Temperature Components ◽  
Term Creep

P91 steels are widely used in high temperature components for power generation. Creep data is often generated through accelerated short term creep tests, for practical reasons, via increasing stress or temperature though this may alter the creep behaviour. Through normalising the creep test stress by tensile strength the Wilshire models reduce the batch to batch scatter in the creep data and enable the prediction of long term creep data from relatively short term test results. In this work it is shown that the Wilshire models fitted to uniaxial creep rupture data can be used to predict failure in both as cast and service exposed multiaxial tests. This is provided that the equivalent stress is the rupture controlling stress, as is the case for the P91 tests examined, and the tensile strength is measured as part of the test programme.

Creep Characterization of Ni-Based Superalloy IN-792 Using the 4- and 6-θ Projection Method

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
S. A. Sajjadi ◽  
M. Berahmand ◽  
A. Rezaee-Bazzaz
Keyword(s):  
Projection Method ◽  
High Strain ◽  
Operating Temperature ◽  
Constant Load ◽  
Least Square ◽  
Creep Tests ◽  
Wide Range ◽  
Creep Curves ◽  
Projection Techniques

This paper studies the accuracy of a technique which is capable of predicting and modeling a wide range of creep life in Ni-based superalloys. The θ-projection method was applied to characterize the creep behavior of the Ni-based superalloy IN-792 at 800 °C. Constant load creep tests have been carried out over a wide range of loads at the constant operating temperature. Creep curves were fitted using either 4-θ or 6-θ equation by the use of a nonlinear least-square technique. The results showed that both 4- and 6-θ projection parameters revealed a good linearity as a function of stress. Comparison of experimental creep curves with those predicted using both of the utilized θ-projection techniques showed that the techniques fit the experimental data at high strain values very well while the 6-θ approach describes much better the creep curves at low strain region.

Effect of Long-Term Aging and Creep Exposure on the Microstructure of TiAl-Based Alloy for Industrial Applications

2004 ◽  
Vol 842 ◽  
Author(s):  
Juraj Lapin ◽  
Mohamed Nazmy ◽  
Marc Staubli
Keyword(s):  
Chemical Composition ◽  
Constant Load ◽  
Industrial Applications ◽  
Tensile Creep ◽  
Creep Tests ◽  
Fine Needle ◽  
Term Creep ◽  
Applied Stresses ◽  
Creep Exposure

ABSTRACTThe effect of long-term aging and creep exposure on the microstructure of a cast TiAl-based alloy with nominal chemical composition Ti-46Al-2W-0.5Si (at.%) was studied. The aging experiments were performed at temperatures between 973 and 1073 K for various times ranging from 10 to 14000 h in air. Constant load tensile creep tests were performed at applied stresses ranging from 150 to 400 MPa and at temperatures between 973 and 1123 K up to 25677 h. During aging and creep testing the α2(Ti3Al)-phase in the lamellar and feathery regions transforms to the γ(TiAl)-phase and fine needle-like B2 precipitates. Microstructural instabilities lead to a softening of the alloy. The effect of this softening on long-term creep resistance is negligible at temperatures of 973 and 1023 K.

Viscoplasticity Based on Total Strain. The Modelling of Creep With Special Considerations of Initial Strain and Aging

1979 ◽  
Vol 101 (4) ◽  
pp. 380-386 ◽  
Author(s):  
Erhard Krempl
Keyword(s):  
Strain Relaxation ◽  
Stress Test ◽  
Time Derivative ◽  
Constant Load ◽  
Primary Creep ◽  
True Stress ◽  
Initial Strain ◽  
304 Stainless Steel ◽  
Creep Tests ◽  
Creep Curves

A previously proposed theory is specialized for the uniaxial state of stress and its prediction for creep and relaxation is analyzed in detail. Constant true stress and constant load creep tests are simulated in the presence and absence of thermal aging together with the constant strain relaxation test. The signs of the creep rate and its time derivative as well as the relaxation rate and its time derivative are introduced as criteria. The constant load creep test can reproduce the normal creep curves and nonclassical creep curves (ε˙ > 0; ε¨ > 0 for all ε and for σ0 > 0). The capabilities of the constant true stress test are limited to primary creep if the work-hardening slope is positive. When aging is introduced almost any creep curve can be reproduced in both tests. The importance of initial strain is discussed and demonstrated by room temperature creep tests on Type 304 Stainless Steel. It is suggested that the initial strains together with the creep curves be reported in the future. Poisson’s ratio in creep needs to be measured and tests are proposed which will enable a quantitative assessment of aging.

The Effect of Long Term Loading on Epoxy-Based Adhesive Reinforced with Nano-Particles for In Situ Timber Bonding

2012 ◽  
Vol 545 ◽  
pp. 111-118 ◽  
Author(s):  
Zakiah Ahmad ◽  
Martin P. Ansell ◽  
Dave Smedley ◽  
Paridah Md Tahir
Keyword(s):  
Constant Load ◽  
Nano Particles ◽  
Design Stage ◽  
Creep Tests ◽  
Link Density ◽  
Cross Link Density ◽  
Term Creep ◽  
Adhesive Materials

The mechanical properties of adhesive materials change over time, especially when they are subjected to long-term loading regimes. The significance of this is often overlooked at the design stage. When adhesives are subjected to a constant load, they may deform continuously, depending on temperature, humidity and cross-link density. This progressive deformation is called creep and will continue until rupture or yielding causes failure. It is imperative that reliable accelerated tests be developed to determine the long-term time-dependent performance of adhesives under different environmental conditions. The long-term creep behaviors of thixotropic and room temperature cure epoxy based adhesives reinforced with nano-particles specially formulated for in-situ bonding of pultruded rod into timber for repair and strengthening of timber structures were investigated. In this study two epoxy-based adhesives with nano-particles (silica fume and rubber) addition were subjected to bending creep tests, in accelerated environments. Experimental data showed that the adhesives reinforced with nano-rubber particles showed less creep deformation than the unreinforced adhesives.

An Extrapolation Procedure of Creep Data for St Determination: With Special Reference to Cr-Mo-V Steel

1987 ◽  
Vol 109 (1) ◽  
pp. 142-146 ◽  
Author(s):  
K. Maruyama ◽  
H. Oikawa
Keyword(s):  
Special Reference ◽  
Creep Curve ◽  
Creep Data ◽  
Extrapolation Procedure ◽  
Creep Curves ◽  
Asme Code ◽  
Term Creep ◽  
Predictive Rule

A predictive rule for long-term creep data, necessary to determine St of the ASME Code, was proposed with special reference to a Cr-Mo-V steel. This rule can predict long-term creep curves as well as rupture lives. A creep curve three hundred times longer than the longest test was estimated without unreasonable extrapolation.

The behaviour of friction piles in ice and ice-rich soils

1980 ◽  
Vol 17 (3) ◽  
pp. 405-415 ◽  
Author(s):  
N. R. Morgenstern ◽  
W. D. Roggensack ◽  
J. S. Weaver
Keyword(s):  
Test Data ◽  
Upper Bound ◽  
Creep Data ◽  
Creep Tests ◽  
Comprehensive Review ◽  
Flow Law ◽  
Term Creep ◽  
Good Agreement

A comprehensive review of long-term creep tests on ice has been undertaken and a flow law for ice has been proposed. Creep tests on ice-rich soils have also been reviewed, and it is concluded that the flow law for ice constitutes an upper bound to these test data. Using this flow law, pile velocities in ice and ice-rich soils have been predicted and the predictions are shown to be in good agreement with available long-term creep data for piles in ice and ice-rich soils.

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