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.

Development of 2012 Edition of JSME Code for Design and Construction of Fast Reactors: (4) Creep–Fatigue Evaluation Method for Modified 9Cr–1Mo Steel

2013 ◽  
Author(s):  
Shigeru Takaya ◽  
Yuji Nagae ◽  
Tai Asayama
Keyword(s):  
Evaluation Method ◽  
Time To Failure ◽  
Test Results ◽  
Fast Reactors ◽  
Material Test ◽  
Creep Fatigue ◽  
Summation Rule ◽  
Fatigue Evaluation ◽  
Failure Life ◽  
Design And Construction

This paper describes a creep–fatigue evaluation method for modified 9Cr–1Mo steel, which has been newly included in the 2012 edition of the JSME code for design and construction of fast reactors. In this method, creep and fatigue damages are evaluated on the basis of Miner’s rule and the time fraction rule, respectively, and the linear summation rule is employed as the failure criterion. Investigations using material test results are conducted, which show that the time fraction approach can conservatively predict failure life if margins on the initial stress of relaxation and the stress relaxation rate are embedded. In addition, the conservatism of prediction tends to increase with time to failure. Comparison with the modified ductility exhaustion method, which is known to have good failure life predictability in material test results, shows that the time fraction approach predicts failure lives to be shorter in long-term strain hold conditions, where material test data is hardly obtained. These results confirm that the creep–fatigue evaluation method in the code has implicit conservatism.

Development of Creep-Fatigue Evaluation Method for Modified 9Cr-1Mo Steel

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
Shigeru Takaya ◽  
Yuji Nagae ◽  
Tai Asayama
Keyword(s):  
Evaluation Method ◽  
Time To Failure ◽  
Test Results ◽  
Design Factor ◽  
Design Procedures ◽  
Material Test ◽  
Creep Fatigue ◽  
Summation Rule ◽  
Fatigue Evaluation ◽  
Failure Life

This paper describes a creep–fatigue evaluation method for modified 9Cr-1Mo steel, which has been newly included in the 2012 edition of the Japan Society of Mechanical Engineers code for design and construction of fast reactors (JSME FRs code). In this method, creep and fatigue damages are evaluated on the basis of Miner's rule and the time fraction rule, respectively, and the linear summation rule is employed as the failure criterion. The conservativeness of this method without design factors was investigated using material test results, and it was shown that the time fraction approach can conservatively predict failure life if margins on the initial stress of relaxation and the stress relaxation rate are embedded. In addition, the conservatism of prediction tends to increase with time to failure. Comparison with the modified ductility exhaustion method, which is known to have good failure life predictability in material test results, shows that the time fraction approach predicts failure lives to be shorter in long-term strain hold conditions, where material test data are hardly obtained. These results confirm that the creep–fatigue evaluation method in the JSME FRs code has implicit conservatism in addition to explicit margins in the design procedures such as design factor.

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.

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.

Development of New Design Fatigue Curves in Japan: Discussion of Effect of Surface Finish on Fatigue Strength of Nuclear Component Materials

2019 ◽  
Author(s):  
Motoki Nakane ◽  
Yun Wang ◽  
Hisamitsu Hatoh ◽  
Masato Yamamoto ◽  
Akihiko Hirano ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Fatigue Strength ◽  
Carbon Steel ◽  
Fatigue Test ◽  
Surface Finish ◽  
Evaluation Method ◽  
Maximum Height ◽  
Test Results ◽  
Nuclear Component ◽  
Fatigue Evaluation

Abstract Based on the world wide fatigue test database, The Design Fatigue Curve (DFC) Phase 1 and 2 subcommittees established in The Japan Welding Engineering Society (JWES) have been developed new design fatigue curves which are applied for the nuclear component materials, in air environment. The effects of the design factor, such as mean stress, size effect and surface finish, etc. on the fatigue curves are also discussed with the fatigue database in order to construct fatigue evaluation method for the new design fatigue curves. The subcommittees also have studied the applicability of newly developed fatigue evaluation method to the nuclear component materials. This paper reports the fatigue test results of machined finished small-scale test specimens which are used for the verification of proposed fatigue evaluation method. The materials subjected to the fatigue tests are austenitic stainless steel SUS316LTP, low-alloy steels SQV2A and SCM435H, and carbon steel STPT370. Specimens finished with lathe machining are subjected to the tests. The planed maximum height roughness of the specimen are 25 and 100 μm. The fatigue test results show that the surface finish effect on the fatigue strength in the high cycle region of the austenitic stainless steel can be negligible. On the other hand, fatigue strength of the carbon steel and low alloy steel is decreased as increasing the surface roughness of the specimen. Especially, decrease of fatigue strength for the specimens with more than 100 μm maximum height roughness is larger than that of conventional estimation. It is presumed that severe roughness introduced by lathe machining tends to behave as notches and increase the stress concentration at the specimen surface, and resulted in unexpected decrease of fatigue strength.

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.

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