Application of Shakedown Analysis to Evaluation of Creep-Fatigue Limits

2012 ◽  
Author(s):  
Peter Carter ◽  
R. I. Jetter ◽  
T.-L. (Sam) Sham
Keyword(s):  
Plastic Material ◽  
Full Range ◽  
Strain Range ◽  
Creep Damage ◽  
Local Strain ◽  
Cyclic Creep ◽  
Equivalent Strain ◽  
Shakedown Analysis ◽  
Perfectly Plastic ◽  
Creep Fatigue

Shakedown analysis may be used to provide a conservative estimate of local rupture and hence cyclic creep damage for use in a creep-fatigue assessment. The shakedown analysis is based on an elastic-perfectly plastic material with a temperature-dependent pseudo yield stress defined to guarantee that a shakedown solution exists, which does not exceed rupture stress and temperature for a defined life. The ratio of design life to the estimated cyclic life is the shakedown creep damage. Fatigue damage may be calculated from the local strain values in the shakedown analysis using the existing procedures in Appendix T of Subsection NH for equivalent strain range. The methodology does not require stress classification and is also applicable to cycles over the full range of temperature above and below the creep regime.

Notch Behavior of Components Under the Stress-Controlled Creep–Fatigue Condition: Weakening or Strengthening?

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Jian-Guo Gong ◽  
Fu-Zhen Xuan
Keyword(s):  
Stress Ratio ◽  
Maximum Stress ◽  
Strain Range ◽  
Creep Damage ◽  
Equivalent Strain ◽  
Holding Time ◽  
Damage Analysis ◽  
Strengthening Effect ◽  
Creep Fatigue ◽  
The Difference

Notch-related weakening and strengthening behavior under creep–fatigue conditions was studied in terms of the elastic–viscoplasticity finite-element method (FEM). A coupled damage analysis, i.e., the skeletal point method for creep damage evaluation coupled with the equivalent strain range method for fatigue damage, was employed in the notch effect evaluation. The results revealed that, under the short holding time condition, a weakening behavior was observed for the notch, while a strengthening effect was detected with the increase of holding time. The difference could be ascribed to the creep damage contribution in the holding stage. The influence of stress concentration factor (SCF), stress ratio, and the maximum stress was strongly dependent on the competition of creep and fatigue mechanism.

scholarly journals The Role of Material Modeling on Strain Range Estimation for Elevated Temperature Cyclic Life Evaluation

2018 ◽  
Author(s):  
M. C. Messner ◽  
R. I. Jetter ◽  
T.-L. Sham ◽  
Yanli Wang
Keyword(s):  
Strain Range ◽  
Creep Damage ◽  
Strain History ◽  
Stress And Strain ◽  
Interaction Diagram ◽  
Perfectly Plastic ◽  
Inelastic Analysis ◽  
Creep Fatigue ◽  
Elastic Perfectly Plastic ◽  
Simplified Procedure

High temperature nuclear reactors operating in the creep regime are designed to withstand numerous cyclic events. Current ASME code rules provide two basic paths for evaluating creep fatigue and ratcheting under these conditions; one based on full inelastic analysis intended to provide a representative stress and strain history and the other based on elastic material models with adjustments of varying complexity to account for inelastic stress and strain redistribution. More recent developments have used elastic-perfectly plastic analysis to bound the effects of cyclic service. However, these methods still rely on the separate evaluation of fatigue and creep damage utilizing a damage interaction diagram. There is a procedure under current development that uses creep-fatigue data from key feature test articles directly without the use of the damage interaction diagram. However, it requires a reasonable representation of the strain range in a structure as an input. This work develops a simplified procedure based on elastic perfectly-plasticity analysis that can be used to represent the strain range in a structure in the steady state under cyclic loading conditions.

Overview of Proposed High Temperature Design Code Cases

2016 ◽  
Author(s):  
Peter Carter ◽  
T.-L. (Sam) Sham ◽  
Robert I. Jetter
Keyword(s):  
High Temperature ◽  
Yield Stress ◽  
Creep Damage ◽  
Cyclic Strain ◽  
Inelastic Strain ◽  
Cyclic Creep ◽  
Strain Accumulation ◽  
Temperature Dependent ◽  
Common Basis ◽  
Creep Fatigue

Proposals for high temperature design methods have been developed for primary loads, creep-fatigue and strain limits. The methodologies rely on a common basis and assumption, that elastic, perfectly plastic analysis based on appropriate properties reflects the ability of loads and stress to redistribute for steady and cyclic loading for high temperature as well as for conventional design. The cyclic load design analyses rely on a further key property, that a cyclic elastic-plastic solution provides an upper bound to displacements, strains and local damage rates. The primary load analysis ensures that the design load is in equilibrium with the code allowable stress, taking into account: i) The stress state dependent (multi-axial) rupture criterion, ii) The limit to stress re-distribution defined by the material creep law. The creep-fatigue analysis is focused on the cyclic creep damage calculation, and uses conventional fatigue and creep-fatigue damage calculations. It uses a temperature-dependent pseudo “yield” stress defined by the material yield and rupture data to identify cycles which will not cause creep damage > 1 for the selected life. Similarly the strain limits analysis bounds cyclic strain accumulation. It also uses a temperature-dependent pseudo “yield” stress defined by the material yield and creep strain accumulation data to identify cycles which will not cause average (membrane) inelastic strain > 1% for the design life. The paper gives an overview of the background and justification of these statements, and examples.

Creep Fatigue Interactions in a 1 CrMo V Steel

1976 ◽  
Vol 190 (1) ◽  
pp. 319-330 ◽  
Author(s):  
E.G. Ellison ◽  
A.J.F. Paterson
Keyword(s):  
Plastic Strain ◽  
High Strain ◽  
Creep Behaviour ◽  
Creep Damage ◽  
Cyclic Creep ◽  
Creep Data ◽  
Creep Tests ◽  
Brittle Transition ◽  
Creep Fatigue ◽  
Cyclic Plastic Strain

Static and cyclic creep tests have been carried out on a 1 Cr Mo V steel at 565 °C. In addition, the effects of prior high strain fatigue on subsequent creep behaviour has been studied. A well defined ductile/brittle transition was noted which was unaffected by the type of load controlled cycle. The material softened under cyclic plastic strain and no experimental evidence was obtained which indicated that fatigue and creep damage interacted in a load controlled test to give rise to unexpectedly short lives. The conclusion derived is that “softened creep” data should be used in predictions of deformation and rupture behaviour, and that the use of virgin creep data can give rise to substantial errors.

Systematic Evaluation of Creep-Fatigue Life Prediction Methods for Various Alloys

2009 ◽  
Author(s):  
Yukio Takahashi ◽  
Bilal Dogan ◽  
David Gandy
Keyword(s):  
Power Generation ◽  
Nuclear Power ◽  
Power Plants ◽  
Strain Range ◽  
Creep Damage ◽  
Small Strain ◽  
Systematic Evaluation ◽  
Wide Range ◽  
Creep Fatigue ◽  
Different Temperatures

Failure under creep-fatigue interaction is receiving increasing interest due to an increased number of start-up and shut-down in fossil power generation plants as well as development of newer nuclear power plants employing low-pressure coolant. These situations have promoted the development of various approaches for evaluating its significance. However, most of them are fragment and rather limited in terms of materials and test conditions they covered. Therefore applicability of the proposed approaches to different materials or even different temperatures is uncertain in many cases. The present work was conducted in order to evaluate and compare the representative approaches used in the prediction of failure life under creep-fatigue conditions as well as their modifications, by systematically applying them to available test data on a wide range of materials which have been used or are planned to be used in various types of power generation plants. The following observations have been made from this exercise. (i) Time fraction model has a tendency to be unconservative in general, especially at low temperature and small strain range. Because of the large scatter of the total damage, this shortcoming would be difficult to cover by the consideration of creep-fatigue interaction in a fixed manner. (ii) Classical ductility exhaustion model showed a common tendency to be overly conservative in many situations, especially at small strain ranges. (iii) The modified ductility exhaustion model based on the re-definition of creep damage showed improved predictability with a slightly unconservative tendency. (iv) Energy-based ductility exhaustion model developed in this study seems to show the best predictability among the four procedures in an overall sense although some dependency on strain range and materials was observed.

Creep-Fatigue Fracture of Dissimilar Metal Electron Beam Welded Joints at Elevated Temperature

1988 ◽  
Vol 110 (3) ◽  
pp. 212-218 ◽  
Author(s):  
M. Okazaki ◽  
Y. Mutoh ◽  
M. Yamaguchi
Keyword(s):  
Electron Beam ◽  
Fatigue Life ◽  
Welded Joints ◽  
Prediction Method ◽  
Strain Range ◽  
Local Strain ◽  
Base Metals ◽  
Dissimilar Metal ◽  
Creep Fatigue ◽  
Metal Electron

Creep-fatigue tests of dissimilar-metal electron beam welded joints between A387 Gr.22 ferritic low-alloy steel and AISI 405 ferritic stainless steel were carried out under strain-controlled cycling at a temperature of 873 K. It was found that the creep-fatigue life of a dissimilar metal welded joint was significantly shorter than those of its base metals. This resulted from the strain concentration on the AISI 405 side (with the lower deformation resistance.) It was also found that the hardness distribution was one of the important measures by which the local strain distribution was reflected. Furthermore, a simple prediction method for the creep-fatigue life of dissimilar metal welded joints was proposed based on the creep-fatigue life properties of its base metals by applying the strain range partitioning approach. The predicted lives were in good agreement with the experimental results.

Lower Bound Methods in Elastic-Plastic Shakedown Analysis

2010 ◽  
Author(s):  
Wolf Reinhardt ◽  
Reza Adibi-Asl
Keyword(s):  
Lower Bound ◽  
Plastic Material ◽  
Shakedown Analysis ◽  
Elastic Plastic ◽  
Perfectly Plastic ◽  
Efficient Calculation ◽  
Asme Code ◽  
Elastic Shakedown ◽  
Plastic Shakedown

Several methods were proposed in recent years that allow the efficient calculation of elastic and elastic-plastic shakedown limits. This paper establishes a uniform framework for such methods that are based on perfectly-plastic material behavour, and demonstrates the connection to Melan’s theorem of elastic shakedown. The paper discusses implications for simplified methods of establishing shakedown, such as those used in the ASME Code. The framework allows a clearer assessment of the limitations of such simplified approaches. Application examples are given.

Simplified Inelastic Analysis in Helical Coil Heat Exchanger Design

1980 ◽  
Vol 102 (3) ◽  
pp. 558-562
Author(s):  
C. E. Richard
Keyword(s):  
Creep Damage ◽  
Cyclic Creep ◽  
Helical Coil ◽  
Heat Exchanger Design ◽  
Inelastic Analysis ◽  
Allowable Stresses ◽  
Creep Fatigue ◽  
Time Test ◽  
Coil Heat Exchanger ◽  
Short Time

A simplified, inelastic analysis of helical coil tubing for high-temperature applications is described. Elastically calculated operating stresses are compared with inelastic estimates of allowable cyclic creep/fatigue stresses. The technique of simplifying and analyzing the operating cycles to determine acceptable creep damage levels has general application. The allowable stresses represent the greatest uncertainty in the method, and tests are required to improve their accuracy. A method of utilizing short-time test data to determine allowable stresses for reactor lifetimes of 30 to 40 years is proposed.

The Creep-Fatigue Evaluation Method for Intermediate Hold Conditions: Proposal and Validation

2011 ◽  
Author(s):  
Satoshi Okajima ◽  
Nobuchika Kawasaki ◽  
Shoichi Kato ◽  
Naoto Kasahara
Keyword(s):  
Initial Stress ◽  
Fatigue Damage ◽  
Evaluation Method ◽  
Strain Range ◽  
Creep Damage ◽  
Fatigue Tests ◽  
Reactor Vessel ◽  
Liquid Sodium ◽  
Improved Method ◽  
Creep Fatigue

In this paper, for the application to the Japan Sodium-cooled Fast Reactor, JSFR, the creep-fatigue damage evaluation method is improved to consider the intermediate holding condition. The improved method is validated through both of the uni-axial and the structure model creep-fatigue tests. In these validations, the target material is 316FR steel, which is planned to use for the reactor vessel. The reactor vessel portion near the liquid sodium surface is one of the most probable points where the creep-fatigue damage is considerable. Because of the relaxation of the temperature gradient, the steady operation stress on the portion near the liquid sodium surface is less than the maximum stress in the transient. In the conventional method, in order to evaluate the creep damage conservatively, the maximum tensile value in the thermal stress transient cycle is used as the initial stress. The improved method evaluates the creep damage using the lower initial stress than the conventional method, while it has the rational margin. For the validation of the improved method, uni-axial creep-fatigue tests and structure model tests are carried out. A series of uni-axial creep-fatigue tests was carried out in the following conditions: 600 degree C testing temperature, 1% total strain range, 1 hour holding time, vacuum or air environments, and the various holding position. While the test environment affects the fatigue damage, it didn’t have significant effect on the creep damage. In the cases with high holding position, the creep damages were evaluated based on the given initial stress with high precision. In the other cases, by the assumption of the steady-stress existence, the rational margin is given for the evaluation. Furthermore, in the design stage, the evaluated creep-fatigue damage has enough margins derived from the conservative evaluation of the initial stress. The structural tests modeled the movement of the liquid sodium surface in the start-up and the shut-down stages, and the relaxation of the temperature gradient in the operation stage. In these tests, the temperature distribution was given by coolant water and an external high-frequency heating coil for the cylindrical specimen, and moved in the axial direction. In addition, the primary stress, which was caused by the weight of the reactor vessel, was given by the screw jack. As a result, using the strain range evaluated by the elastic analysis, the improved method evaluated the crack initiation life due to the creep-fatigue damage with the sufficient safety margin. In the case when the strain range was evaluated by the elastic-plastic analysis, the method predicted the crack initiation life with the good precision. While the evaluation of the crack penetration life was possible, further examination was desired for the precision improvement.

Fatigue Analysis in Pressure Vessel Design by Local Strain Approach: Methods and Software Requirements

2005 ◽  
Vol 128 (1) ◽  
pp. 2-7 ◽  
Author(s):  
Arturs Kalnins
Keyword(s):  
Pressure Vessel ◽  
Kinematic Hardening ◽  
Strain Range ◽  
Local Strain ◽  
Equivalent Strain ◽  
Software Requirements ◽  
Cyclic Plasticity ◽  
Half Cycle ◽  
Fatigue Evaluation ◽  
Cyclic Plasticity Model

The purpose, methods for the analysis, software requirements, and meaning of the results of the local strain approach are discussed for fatigue evaluation of a pressure vessel or its component designed for cyclic service. Three methods that are consistent with the approach are evaluated: the cycle-by-cycle method and two half-cycle methods, twice-yield and Seeger’s. For the cycle-by-cycle method, the linear kinematic hardening model is identified as the cyclic plasticity model that produces results consistent with the local strain approach. A total equivalent strain range, which is entered on a material strain-life curve to read cycles, is defined for multiaxial stress situations

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