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.

Simplified Methods for Elevated Temperature Structural Design: An Overview of Some Current Activities

2014 ◽  
Author(s):  
Robert I. Jetter ◽  
Yanli Wang ◽  
Peter Carter ◽  
T.-L. (Sam) Sham
Keyword(s):  
Elevated Temperature ◽  
Fatigue Damage ◽  
Temperature Regime ◽  
Structural Integrity ◽  
Stress And Strain ◽  
Damage Evaluation ◽  
Real Component ◽  
Perfectly Plastic ◽  
Inelastic Analysis ◽  
Creep Fatigue

Elevated temperature design criteria for Class 1 nuclear components employ two fundamental approaches for evaluation of structural integrity in the temperature regime where creep effects are significant: full inelastic analysis to predict the actual stress and strain resulting from time dependent loading conditions and simplified methods which bound the actual response with, conceptually, simpler material models and analytical procedures. However, the current simplified methods have been found to be more complex for real component design applications than originally envisioned. There is an added complication that the current simplified methods are considered inappropriate in the very high temperature regime where there is no distinction between plasticity and creep. Recently, some improved, less complex methods have been proposed which would overcome these objections. One set of criteria are based on elastic-perfectly plastic (E-PP) analysis methods. Draft code cases have been prepared which address the use of the E-PP methodology to primary loading, strain limits and creep-fatigue damage evaluation. Another proposed criterion is based on the use of test specimens which include the effects of stress and strain redistribution due to plasticity and creep to develop creep-fatigue damage evaluation design curves. An overview of the key features, associated analytical and experimental verification, status and path forward are presented. Although targeted to nuclear components, these criteria also have potential application to non-nuclear components and operating temperatures below the creep regime. Paper published with permission.

A High Temperature Primary Load Design Method Based on Elastic Perfectly-Plastic and Simplified Inelastic Analysis

2020 ◽  
Author(s):  
M. C. Messner ◽  
R. I. Jetter ◽  
T.-L. Sham
Keyword(s):  
Finite Element ◽  
High Temperature ◽  
Creep Damage ◽  
Elastic Analysis ◽  
Allowable Stress ◽  
Perfectly Plastic ◽  
Inelastic Analysis ◽  
Stress Classification ◽  
Elastic Perfectly Plastic ◽  
Primary Load

Abstract The current primary load design provisions of Section III, Division 5 of the ASME Boiler and Pressure Vessel Code, covering high temperature nuclear components, represent an allowable stress methodology using elastic analysis and stress classification procedures to approximate stress redistribution caused by creep and plasticity. This process is difficult to implement and automate in modern finite element frameworks. This paper describes an alternate primary load design approach that uses elastic perfectly-plastic analysis in conjunction with the reference stress concept to eliminate stress classification while retaining a link to the existing Section III, Division 5 allowable stresses. This global, structural allowable stress check is supplemented with a local check to guard against the initiation of creep damage at local stress discontinuities like headers, nozzles, and other stress concentrations. This check is based on a simple elastic-creep analysis with creep damage calculated with the time-fraction approach, using the current ASME minimum-stress-to-rupture values already provided in the current Code. Both the global and local checks are easily implemented in modern finite element analysis software and greatly simplify Section III, Division 5 primary load design when compared to the current design-by-elastic-analysis method. Several examples demonstrate the utility of the new approach and its potential to reduce over-conservatism.

Elevated Temperature Cyclic Service Evaluation Based on Elastic-Perfectly Plastic Analysis and Integrated Creep-Fatigue Damage

2016 ◽  
Author(s):  
T.-L. (Sam) Sham ◽  
Robert I. Jetter ◽  
Yanli Wang
Keyword(s):  
Elevated Temperature ◽  
Fatigue Damage ◽  
Stress And Strain ◽  
Damage Evaluation ◽  
Perfectly Plastic ◽  
Stress Classification ◽  
Plastic Analysis ◽  
Creep Fatigue ◽  
Cyclic Service ◽  
Elastic Perfectly Plastic

The goal of the Elastic-Perfectly Plastic (EPP) combined integrated creep-fatigue damage evaluation approach is to incorporate a Simplified Model Test (SMT) data based approach for creep-fatigue damage evaluation into the EPP methodology to avoid the separate evaluation of creep and fatigue damage and eliminate the requirement for stress classification in current methods; thus greatly simplifying evaluation of elevated temperature cyclic service. The EPP methodology is based on the idea that creep damage and strain accumulation can be bounded by a properly chosen “pseudo” yield strength used in an elastic-perfectly plastic analysis, thus avoiding the need for stress classification. The original SMT approach is based on the use of elastic analysis. The experimental data, cycles to failure, is correlated using the elastically calculated strain range in the test specimen and the corresponding component strain is also calculated elastically. The advantage of this approach is that it is no longer necessary to use the damage interaction, or D-diagram, because the damage due to the combined effects of creep and fatigue are accounted in the test data by means of a specimen that is designed to replicate or bound the stress and strain redistribution that occurs in actual components when loaded in the creep regime. The reference approach to combining the two methodologies and the corresponding uncertainties and validation plans are presented. Results from recent key feature tests are discussed to illustrate the applicability of the EPP methodology and the behavior of materials at elevated temperature when undergoing stress and strain redistribution due to plasticity and creep.

Verification of Elastic-Perfectly Plastic Methods for Evaluation of Strain Limits: Analytical Comparisons

2014 ◽  
Author(s):  
Peter Carter ◽  
R. I. Jetter ◽  
T.-L. (Sam) Sham
Keyword(s):  
Fatigue Damage ◽  
Plastic Material ◽  
Material Model ◽  
Alloy 617 ◽  
Perfectly Plastic ◽  
Inelastic Analysis ◽  
Accumulated Strain ◽  
Creep Fatigue ◽  
Verification Process ◽  
Elastic Perfectly Plastic

The current rules in Subsection NH for the evaluation of strain limits and creep-fatigue damage using simplified methods based on elastic analysis have been deemed inappropriate for Alloy 617 at temperatures above 1200°F (650°C) because, at higher temperatures, it is not feasible to decouple plasticity and creep; which is the basis for the current simplified rules. To address this issue, proposed code rules have been developed which are based on the use of elastic-perfectly plastic analysis methods and which are expected to be applicable to very high temperatures. The proposed rules are based on the use of an elastic-perfectly plastic material model with a pseudo yield strength selected to ensure that the accumulated strain and creep-fatigue damage with meeting the currently specified limits in Subsection NH. For this phase of the verification process, the proposed rules have been compared using simplified example problems to the results obtained from application of the current Subjection NH rules for both simplified methods and full inelastic analysis. The Subsection NH 316 stainless steel properties data are used for these comparisons. Results of calculations for a testing program underway on Alloy 617 at 950C are given.

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.

Pathway to Evaluate Printed Circuit Heat Exchanger Based on Simplified Elastic-Perfectly Plastic Analysis Methodology for High Temperature Nuclear Service

2019 ◽  
Author(s):  
Urmi Devi ◽  
Machel Morrison ◽  
Tasnim Hassan
Keyword(s):  
High Temperature ◽  
Fatigue Damage ◽  
Analysis Method ◽  
Printed Circuit ◽  
Perfectly Plastic ◽  
Analysis Methodology ◽  
Inelastic Analysis ◽  
Creep Fatigue ◽  
Asme Code ◽  
Elastic Perfectly Plastic

Abstract Printed Circuit Heat Exchangers (PCHEs) are well-suited for Very High Temperature Reactors (VHTRs) due to high compactness and efficiency for heat transfer. The design of PCHE must be robust enough to withstand possible failure caused by cyclic loading during high temperature operation. The current rules in ASME Code Section III Division 5 to evaluate strain limits and creep-fatigue damage based on elastic analysis method have been deemed infeasible at temperatures above 650°C. Hence, these rules are inapplicable for temperatures ranging from 760–950°C for VHTRs. A full inelastic analysis method with complex constitutive material description as an alternative, on the other hand, is time consuming; hence impracticable. Therefore, the simplified Elastic-Perfectly Plastic (EPP) analysis methodology is used as a solution in ASME Code Section III Division 5. The current literature, however, lacks any study on the performance evaluation of PCHE through EPP analysis. To address these issues, this study initiates the pathway of EPP evaluation of an actual size PCHE starting with elastic orthotropic analysis in the global scale. Subsequently, preliminary planning for analyzing intermediate and local submodels are provided to determine channel level responses to evaluate PCHE performance against strain limits and creep-fatigue damage using Code Case-N861 and N862 respectively.

scholarly journals Determination of the Creep-Fatigue Interaction Diagram for Alloy 617

2016 ◽  
Author(s):  
J. K. Wright ◽  
L. J. Carroll ◽  
T.-L. Sham ◽  
N. J. Lybeck ◽  
R. N. Wright
Keyword(s):  
Fatigue Testing ◽  
Hold Time ◽  
Strain Range ◽  
Fatigue Tests ◽  
Alloy 617 ◽  
Interaction Diagram ◽  
Creep Fatigue ◽  
Intermediate Heat Exchanger ◽  
Cycles To Failure

Alloy 617 is the leading candidate material for an intermediate heat exchanger for the very high temperature reactor (VHTR). As part of evaluating the behavior of this material in the expected service conditions, creep–fatigue testing was performed. The cycles to failure decreased compared to fatigue values when a hold time was added at peak tensile strain. At 850°C, increasing the tensile hold duration continued to degrade the creep–fatigue resistance, at least to the investigated strain–controlled hold time of up to 60 minutes at the 0.3% strain range and 240 minutes at the 1.0% strain range. At 950°C, the creep–fatigue cycles to failure are not further reduced with increasing hold duration, indicating saturation occurs at relatively short hold times. The creep and fatigue damage fractions have been calculated and plotted on a creep–fatigue interaction D–diagram. Test data from creep–fatigue tests at 800 and 1000°C on an additional heat of Alloy 617 are also plotted on the D–diagram.

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.

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.

Evaluating Plastic Loads in Torispherical Heads Using a New Criterion of Collapse

2006 ◽  
Author(s):  
Duncan Camilleri ◽  
Donald Mackenzie ◽  
Robert Hamilton
Keyword(s):  
Pressure Vessels ◽  
Plastic Collapse ◽  
Total Work ◽  
Medium Thickness ◽  
Material Models ◽  
Hardening Material ◽  
Perfectly Plastic ◽  
Inelastic Analysis ◽  
Elastic Perfectly Plastic ◽  
New Criterion

In ASME Design by Analysis, the plastic load of pressure vessels is established using the Twice Elastic Slope criterion of plastic collapse. This is based on a characteristic load-deformation plot obtained by inelastic analysis. This study investigates an alternative plastic criteria based on plastic work dissipation where the ratio of plastic to total work is monitored. Two sample analyses of medium thickness torispherical pressure vessels are presented. Elastic-perfectly plastic and strain hardening material models are considered in both small and large deformation analyses. The calculated plastic loads are assessed in comparison with experimental results from the literature.

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