An improved life prediction strategy at elevated temperature based on pure creep and fatigue data: Classical strain controlled and hybrid stress–strain controlled creep-fatigue test

Song, Kai; Wang, Dong; Zhao, Lei; Xu, Longhua; Han, Yongdian

doi:10.1016/j.engfracmech.2023.109412

Cited by 2 publications

(2 citation statements)

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“…Inelastic strain energy per unit volume accumulated or consumed until rupture might be a more appropriate parameter for characterizing the deformation capability of the material. Actually, several creep-fatigue life evaluation methods based on inelastic strain energy have been developed [18][19][20][21][22][23][24][25][26][27]. Here, a similar treatment as made in the modified ductility exhaustion approach led to the following equation [19]:…”

Section: Energy-based Approachmentioning

confidence: 99%

“…In recent years, these strain energy-based evaluation methods have been further developed to account for average stress [22,23] and damage due to oxidation [23,24]. Additionally, improvements have been made to apply them to complex loading conditions, such as a combination of large and small strain variations [25] and a combination of straincontrolled and stress-controlled loading [26,27]. Furthermore, a hybrid approach has been also suggested, which considers the critical inelastic strain energy density to be dominated by the inelastic strain rate [28,29].…”

Section: Introductionmentioning

confidence: 99%

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Creep-Fatigue Life Evaluation for Grade 91 Steels with Various Origins and Service Histories

Shigeyama,

Takahashi,

Siefert

et al. 2024

Metals

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Grade 91 steel is widely used in the boilers and piping of thermal power plants. There has been significant research interest in understanding the variations in creep characteristics among different heats of this steel for effective plant management. In recent years, thermal power plants have been subjected to frequent load changes and startup/shutdown to adjust power supply and demand and stabilize frequencies. These operational shifts have raised concerns regarding the potential for creep-fatigue damage in high-temperature components. Therefore, this research focuses on creep-fatigue properties of Grade 91 steel and their predictability. Tensile, creep, strain-controlled fatigue, and strain-controlled creep-fatigue tests were performed on six Grade 91 steels with different heats and/or histories, and the characteristics in each test were compared. As a result, the variations in creep-fatigue life among the materials were found to be correlated with the difference in creep characteristics and stress level during stress relaxation. Furthermore, the study involved a comparative assessment of the predictive performance of creep-fatigue life using five different approaches: time fraction, classical ductility exhaustion, modified ductility exhaustion, energy-based, and hybrid approaches. Among these approaches, the hybrid approach, based on inelastic strain energy density at fracture formulated as a function of inelastic strain rate, exhibited the most accurate predictive performance.

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