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

Abstract

Effect of Internal Pressure on SBSMT with an Elastic Follow-up of 3.5 at 950 o C ....... 6 3.2.2 Effect of Internal Pressure on SBSMT with an Elastic Follow up of 2 at 950 o C ........ 3.2.3 SBSMT with an Elastic Follow-up of 6 at 950 o C .

Draft Rules for Alloy 617 Creep-Fatigue Design Using an EPP+SMT Approach

“…Previous work [2,[6][7][8][9][10][11][12] developed the SMT methodology to quantify the effect follow up effect on creep-fatigue life directly from experiments. Details of several different types of SMT specimens can be found in previous ART sponsored work [6][7][8][9][10][11][12].…”

“…Previous work [2,[6][7][8][9][10][11][12] developed the SMT methodology to quantify the effect follow up effect on creep-fatigue life directly from experiments. Details of several different types of SMT specimens can be found in previous ART sponsored work [6][7][8][9][10][11][12]. In summary, the SMT specimens are designed to apply a global elastic follow up to a test section using either a stiffer driver section or an artificial control system while the whole system is subjected to a strain-controlled creep-fatigue loading.…”

“…Primary load can also accelerate the creep-fatigue damage accumulation, especially when it is above a threshold value [31]. For a fixed secondary load, increasing the primary load is found to decrease the component cyclic life [10]. The EPP+SMT creep-fatigue design method therefore must capture this "primary load effect".…”

“…This section provides validation for the draft design rules and design charts developed in Section 4.5 using the failure data gathered from p-SMT tests in previous ART sponsored works [8,10]. The applied loading in the standard creep-fatigue tests and the SMT tests are purely secondary, while the loading in p-SMT tests include both the primary and secondary loads.…”

“…A third advantage of the EPP+SMT method is it explicitly accounts for the effect of elastic follow up in the creep-fatigue design procedure. It uses the results of SMT tests, developed through extensive research and development work [2,[6][7][8][9][10][11][12][13], to evaluate the elastic follow up on cyclic creepfatigue life. Elastic follow up is a reduction in the rate of stress relaxation, compared to fullystrain controlled relaxation, caused by stored elastic energy elsewhere in the mechanical system that tends to increase the development of creep-fatigue damage and decrease the component cyclic life.…”