Pressurized Creep-Fatigue Testing of Alloy 617 Using Simplified Model Test Method

2017 ◽  
Author(s):  
Yanli Wang ◽  
Robert I. Jetter ◽  
T.-L. Sham
Keyword(s):  
Elevated Temperature ◽  
Hysteresis Loop ◽  
Fatigue Damage ◽  
Model Test ◽  
Test Method ◽  
Simplified Model ◽  
Damage Evaluation ◽  
Primary Stress ◽  
Creep Fatigue ◽  
Cyclic Damage

The Simplified Model Test (SMT) is an alternative approach to determine cyclic life at elevated temperature and avoids parsing the damage into creep and fatigue components. The Elastic-Perfectly Plastic (EPP) combined integrated creep-fatigue damage evaluation approach incorporates the SMT data based approach for creep-fatigue damage evaluation into the EPP methodology to avoid the separate evaluation of creep and fatigue damage and to eliminate the requirement for stress classification as in current methods; thus greatly simplifying evaluation of elevated temperature cyclic service. The conceptual basis of the SMT approach is that if the effects of plasticity, creep and strain redistribution in the SMT specimen result in a stress-strain hysteresis loop that envelopes the hysteresis loop at the peak strain location in the component, then the SMT results can be used to assess the cyclic damage in the component. The original SMT concept (Jetter, 1998) considered that the effects of sustained primary stress loading could be safely neglected because the allowable local stress and strain levels were much higher than the allowable sustained primary stress levels. This key assumption requires experimental verification. The influence of the internal pressure on SMT creep-fatigue life is demonstrated and the effect of primary load on the SMT design approach is discussed.

scholarly journals Effect of Internal Pressurization on the Creep-Fatigue Performance of Alloy 617 Based on Simplified Model Test Method

2019 ◽  
Author(s):  
Y. Wang ◽  
B. Jetter ◽  
T.-L. Sham
Keyword(s):  
Model Test ◽  
Design Method ◽  
Local Stress ◽  
Fatigue Loading ◽  
Test Method ◽  
Simplified Model ◽  
Alloy 617 ◽  
Primary Stress ◽  
Creep Fatigue ◽  
The Impact

Abstract The Simplified Model Test (SMT) is an alternative approach to determine cyclic life at elevated temperature and avoids parsing the damage into creep and fatigue components. The original SMT concept [1] considered that the effects of sustained primary stress loading could be safely neglected because the allowable local stress and strain levels were much higher than the allowable sustained primary stress levels. This key assumption is critically evaluated on Alloy 617 using internal pressurized cylindrical SMT specimens at 950 °C. The impact of combined internal pressurization and displacement-controlled creep-fatigue loading on the SMT cycle life is demonstrated at different strain ranges. The effect of primary load on the SMT design method is discussed.

scholarly journals Evaluation of Creep-Fatigue Damage Based on Simplified Model Test Approach

2013 ◽  
Author(s):  
Yanli Wang ◽  
Tianlei Li ◽  
T.-L. (Sam) Sham ◽  
Robert I. Jetter
Keyword(s):  
Fatigue Damage ◽  
High Temperatures ◽  
Test Data ◽  
Model Test ◽  
Hold Time ◽  
Simplified Model ◽  
Creep Fatigue ◽  
Asme Code ◽  
Cyclic Damage ◽  
Very High

Current methods used in the ASME Code, Subsection NH for the evaluation of creep-fatigue damage are based on the separation of elevated temperature cyclic damage into two parts, creep damage and fatigue damage. This presents difficulties in both evaluation of test data and determination of cyclic damage in design. To avoid these difficulties, an alternative approach was identified, called the Simplified Model Test or SMT approach based on the use of creep-fatigue hold time test data from test specimens with elastic follow-up conservatively designed to bound the response of general structural components of interest. A key feature of the methodology is the use of the results of elastic analysis directly in design evaluation similar to current methods in the ASME Code, Subsection NB. Although originally developed for current material included in Subsection NH, recent interest in the application of Alloy 617 for components operating at very high temperatures has caused renewed interest in the SMT approach because it provides an alternative to the proposed restriction on the use of current Subsection NH simplified methods at very high temperatures. A comprehensive review and assessment of five representative simplified methods for creep-fatigue damage evaluation is presented in Asayama [1]. In this review the SMT methodology was identified as the best long term approach but the need for test data precluded its near term implementation. Asayama and Jetter [2] is a summary of the more comprehensive report by Asayama [1] with a summary of the SMT approach presented by Jetter [3]. In this paper, the previously documented development of the SMT approach and applicable restrictions are discussed and reviewed; the design of the SMT specimen, measurement issues and constraints are presented; the test apparatus and measurement system is described; initial test results and their application to a prototypic design curve are presented; and further testing and analysis for ASME Code incorporation are discussed.

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.

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.

scholarly journals Evaluation of Primary-Load Effects on Creep-Fatigue Life of Alloy 617 Using Simplified Model Test Method

2021 ◽  
Author(s):  
Yanli Wang ◽  
Peijun Hou ◽  
Robert I. Jetter ◽  
T.-L. Sham
Keyword(s):  
Fatigue Life ◽  
Internal Pressure ◽  
Model Test ◽  
Test Method ◽  
Simplified Model ◽  
Evaluation Procedure ◽  
Alloy 617 ◽  
Creep Fatigue ◽  
Fatigue Evaluation ◽  
Primary Load

Abstract Current creep-fatigue evaluation approaches based on the creep-fatigue Damage-diagram are complex and very conservative. Simplified Model Test (SMT) method is an alternative approach to determine cyclic life at elevated temperatures. The SMT-based creep-fatigue evaluation methodology avoids parsing the damage into creep and fatigue components and greatly simplifies the evaluation procedure for elevated-temperature cyclic service. In this study, the effects of sustained primary-stress loading are evaluated in support of the development of SMT-based creep-fatigue design curves for Alloy 617. Experiments were designed and performed using internal pressurized tubular specimens at 950 °C on Alloy 617. The sustained primary-load was introduced by the internal pressure. A newly developed SMT technique, single-bar SMT, was extended to these tests and SMT creep-fatigue test data were generated with various elastic follow-ups, internal pressures and strain ranges. The test results from this study along with the original SMT data on Alloy 617 demonstrate that, although internal pressure is within the allowable stress limit per ASME Section III Division 5 Code Case N-898, the SMT creep-fatigue cycles to failure were reduced for the cases tested with primary-pressure load. The reduction of SMT creep-fatigue life due to primary-load was found to be dependent on strain ranges and elastic follow up. Approaches to handle the primary-load effect on SMT design curves are discussed.

Estimation of Creep-Fatigue Damage Through Indentation Test Method

2011 ◽  
Author(s):  
Raghu V. Prakash
Keyword(s):  
Tensile Properties ◽  
Fatigue Damage ◽  
Indentation Test ◽  
Creep Damage ◽  
Test Method ◽  
Specimen Preparation ◽  
Creep Fatigue ◽  
Critical Components ◽  
The Cost

Creep, creep-fatigue damage is often estimated through in-situ metallography, tensile testing of specimens. However, these methods require specimen preparation which includes specimen extraction from critical components. Automated ball indentation testing has been used as an effective tool to determine the mechanical properties of metallic materials. In this work, the tensile properties of materials subjected to controlled levels of damage in creep, creep-fatigue is studied. It is found that the tensile properties such as yield strength and UTS deteriorates with creep damage, whereas the same specimens show an improved UTS values (at the cost of ductility) when subjected to creep-fatigue interactions.

Structural Evaluation With Elastic and Inelastic Analysis Methods on a High Temperature Storage Tank Subjected to Static and Dynamic Loadings

2020 ◽  
Author(s):  
Wen Wang ◽  
Xiaochun Zhang ◽  
Xiaoyan Wang ◽  
Maoyuan Cai
Keyword(s):  
High Temperature ◽  
Elevated Temperature ◽  
Molten Salt ◽  
Fatigue Damage ◽  
Storage Tank ◽  
Power Plants ◽  
Elastic Analysis ◽  
Inelastic Analysis ◽  
Analysis Methods ◽  
Creep Fatigue

Abstract The structural integrity of reactor components is very essential for the reliable operation of all types of power plants, especially for components operating at elevated temperature where creep effects are significant and where components are subjected to high-temperature alteration and seismic transient loading conditions. In this article, a molten salt storage tank in high temperature thorium molten salt reactor (TMSR) is evaluated according to ASME-III-5-HBB high temperature reactor code. The evaluation based on 3D finite element analyses includes the load-controlled stress, the effects of ratcheting, and the interaction of creep and fatigue. The thermal and structural analysis and the application procedures of ASME-HBB rules are described in detail. Some structural modifications have been made on this molten salt storage tank to enhance the strength and reduce thermal stress. The effects of ratcheting and creep-fatigue damage under elevated temperature are investigated using elastic analysis and inelastic analysis methods for a defined representative load cycle. In addition, the strain range and the stress relaxation history calculated by elastic and inelastic methods are compared and discussed. The numerical results indicate that the elastic analysis is conservative for design and a full inelastic analysis method for estimating input for creep-fatigue damage evaluation need to be developed.

Proposals of Improvements of RCC-MR Creep-Fatigue Rules

2007 ◽  
Author(s):  
Marie-Noe¨l Berton ◽  
Olivier Ancelet ◽  
Marie The´re`se Cabrillat ◽  
Ste´phane Chapuliot
Keyword(s):  
Stress Relaxation ◽  
Fatigue Damage ◽  
High Temperatures ◽  
Dwell Time ◽  
Damage Evaluation ◽  
Fast Reactors ◽  
Creep Fatigue ◽  
Sodium Fast Reactors ◽  
Gen Iv ◽  
Current Rule

The RCC-MR creep-fatigue rules were developed and written in the framework of studies for the first SFR (Sodium Fast Reactors). These reactors were characterized by low primary loads and moderately high temperatures. The rule thus has to be improved with the aim of decreasing its conservatisms in case of higher temperatures and/or higher pressures (for GEN IV Gas Cooled Reactors). Studies were realized to improve the rule on the following points: - the position of the temperature dwell time in the cycle : the current rule always considers that the dwell time is located at one of the extremes of the cycle, what can be very conservative in some cases, - the symmetrisation effect of the stabilized cycle, - the case where the primary loads vary during the cycle, - the primary and secondary stresses combination during the temperature dwell time for the evaluation of the stress relaxation. These works are based on viscoelastoplastic calculations of stabilized cycles and the new proposals are applied on different tests. The consequences on creep-fatigue damage evaluation can be very significant.

scholarly journals Development of Simplified Model Test Methods for Creep-Fatigue Evaluation

2019 ◽  
Author(s):  
Y. Wang ◽  
B. Jetter ◽  
M. C. Messner ◽  
T.-L. Sham
Keyword(s):  
Model Test ◽  
Evaluation Method ◽  
Test Methods ◽  
Simplified Model ◽  
Test Results ◽  
Interaction Diagram ◽  
Creep Fatigue ◽  
Fatigue Evaluation ◽  
Creep Regime ◽  
Further Development

Abstract The Simplified Model Test (SMT) approach is an alternative creep-fatigue evaluation method that no longer requires the use of the damage interaction diagram, or D-diagram. The reason is that the combined effects of creep and fatigue are accounted for in the test data by means of a SMT specimen that is designed to replicate or bound the stress and strain redistribution that occurs in actual components when loaded in the creep regime. However, creep-fatigue experiments on SMT key feature articles are specialized and difficult to perform by the general research community. In this paper, two innovative SMT based creep-fatigue experimental methods are developed and implemented. These newly-developed SMT test methods have resolved all the critical challenges in the SMT key feature article testing and enable the potential of further development of the SMT based creep-fatigue evaluation method into a standard testing method. Scoping test results on Alloy 617 and SS 316H using the newly developed SMT methods are summarized and discussed. The concepts of the SMT methodology for creep-fatigue evaluation are explained.

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