Normalized creep–fatigue life prediction model based on the energy dissipation during hold time

Abstract

A new life function based on a model for the creep–fatigue life prediction in terms of stress relaxation during hold time has been proposed. From the concept that the reduction of fatigue life with hold time is due to the creep effect of stress relaxation that results in the additional energy dissipation in the hysteresis loop, the relaxed stress range is suggested to be a creep–fatigue damage function. The plastic strain range (Δ ɛ p) exhibiting a functional correlation of both strain and time requires experimental efforts following Coffin–Manson relationship [L.F. Coffin Jr., Trans. ASME 76 (1954) 931–950; S.S. Manson, NASA Technical Note 2933, NASA Research Center, Cleveland, OH, 1954] upon applied creep–fatigue conditions. After the new concept was applied to the relationship, all the Coffin–Manson plots at the various levels of hold time under strain-controlled fatigue tests were identified as a linear relationship with relaxed stress range (Δ σ) and fatigue life ( N f). The normalized creep–fatigue life prediction model, which can be applied to high temperature materials regardless of the fracture morphology is presented in view of a real situation.