A New 3D Creep-Fatigue-Elasticity Damage Interaction Diagram Based on the Total Tensile Strain Energy Density Model

Abstract

Fatigue damage, creep damage, and their interactions are the critical factors in degrading the integrity of most high-temperature engineering structures. A reliable creep-fatigue damage interaction diagram is a crucial issue for the design and assessment of high-temperature components used in power plants. In this paper, a new three-dimensional creep-fatigue-elasticity damage interaction diagram was constructed based on a developed life prediction model for both high-temperature fatigue and creep fatigue. The total tensile strain energy density concept is adopted as a damage parameter for life prediction by using the elastic strain energy density and mean stress concepts. The model was validated by a great deal of data such as P91 steel at 550 °C, Haynes 230 at 850 °C, Alloy 617 at 850 and 950 °C, and Inconel 625 at 815 °C. The estimation values have very high accuracy since nearly all the test data fell into the scatter band of 2.0.

An efficient fatigue and creep‐fatigue life prediction method by using the hysteresis energy density rate concept

“…Figure 9 depicts the relation between CFED and applied stress of Alloy 617 at 850°C, 46 a liner relationship is observed. In this paper, the CFED is also assumed to be a linear function of the applied stress 40 . Figure 9 also shows the fitting curve for Alloy 617 at 850°C, the proportionality constant is 1.1502.…”

“…The hysteresis energy absorbed in the material can be divided into two parts, that is, the heat dissipation part and the effective part, and only the effective part contributes to the fatigue failure. In this study, the fatigue damage stress 40 is introduced to account for the above phenomenon, and it assumes that the fatigue damage occurs only when the applied stress is above the fatigue damage stress. The shadow area in Figure 1 are considered as the effective hysteresis energy density (EHED).…”

“…The mean stress concept is adopted to determine the value of fatigue damage stress, and the tensile mean stress is generated when a compressive hold is incorporated, whereas the compressive mean stress is introduced under tensile hold periods. The fatigue damage stress is defined as follows 40 : where σ d is the fatigue damage stress, γ is a material constant and the value of γ can be a positive or negative. σ d can be set as zero for simplification under fully reversed strain‐controlled LCF conditions.…”

“…The accumulated creep damage is obtained by 40 where D c is the accumulated creep damage, is the creep component of the EHED and W c is the creep failure energy density (CFED).…”

“…W c in Eq. 17 can be determined using the creep test data conducted at the same temperature, and W c can be simply calculated as following 40 : where σ a is the applied stress in creep tests, ε r is the creep rupture elongation or area reduction.…”