Development of Simplified Model Test Methods for Creep-Fatigue Evaluation

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.

Initial development of an in-situ, passive material surveillance test article for monitoring high temperature reactor structural components

“…The thermal cycle used in this optimization calculation is representative of a component thermal cycle -not an accelerated furnace test. For reference, a typical test specimen might have a stable strain range of 1% and a follow up factor of 1 to 10[8]. A structural component will have a much lower strain range, likely less than 0.3% for a long design life, and a follow up factor between 1 and 4.…”

Support of the Development of EPP Plus SMT Design Method (FY2020 Test Results)

“…A detailed plan has been developed and revised for the development of this EPP+SMT methodology (Wang et al, 2016a, 2016b, 2017a, 2019. The development of SMT-based design curves requires experimental data, and the parameters to be considered include elastic follow-up factor, strain range, loading rate, test temperature, hold time, and primary load.…”

“…Recently, major progress was made in developing SMT experimental techniques by Wang et al (2018Wang et al ( , 2019. In particular, the newly developed single-bar SMT (SBSMT) test method and test protocol overcome many challenges associated with conducting SMT key feature experiments and enable the evaluation of the effect of elastic follow-up using a standard CF specimen without the need for specialized instrumentation and specimen design.…”

“…In particular, the newly developed single-bar SMT (SBSMT) test method and test protocol overcome many challenges associated with conducting SMT key feature experiments and enable the evaluation of the effect of elastic follow-up using a standard CF specimen without the need for specialized instrumentation and specimen design. In FY 2019, Wang et al (2019) demonstrated the SBSMT method on Alloy 617, SS316H, and Gr.91 by testing at high temperatures and successfully showed the flexibility of generating SMT-based failure data with a wide range of elastic follow-up values from 1 to 12. It was shown that the SBSMT test method significantly simplifies the procedure for generating SMT test data and enables the development of a SMT-based design method to advance at a rapid pace.…”

“…It was shown that the SBSMT test method significantly simplifies the procedure for generating SMT test data and enables the development of a SMT-based design method to advance at a rapid pace. Messner et al (2019) demonstrated through analysis that the effect of elastic follow-up, characterized by the factor q, on CF life can be simplified by imposing a reduction factor of (1/q) to the standard CF data at the same temperature, strain range and hold time. Preliminary evaluation of the previous SMT data generated at ORNL showed promising results, although more detailed analysis and test data are needed for further verification.…”