High temperature low-cycle fatigue crack propagation behaviour of SUS 304 stainless steel under typical four types of reversed loading patterns (P-P, P-C, C-P and C-C type) was investigated, and the results were discussed in the light of fracture mechanics and electron fractography. The stress intensity factor range Δ
K failed to describe the crack propagation behaviour adequately. In the case of loading with tension hold (i.e. C-P and C-C type), the crack propagation rate was successfully correlated with the modified J-integral
J and agreed with the static creep crack propagation rate. The crack propagation rate for all of the four types of loading was successfully correlated in terms of the cyclic J-integral range Δ
J, and it was unnecessary to separate Δ
J into Δ
Jf and Δ
Jc. The crack propagation rate for the types of loading without tension hold or with short tension hold time (i.e. P-P and P-C type, and C-P and C-C type with comparatively short tension hold time) was successfully correlated with Δ
Jf, and that long tension hold time (i.e. C-P and C-C type with comparatively long tension hold time) was successfully correlated with Δ
Jc. The fracture surfaces of the case where the crack propagation rate was correlated with Δ
Jf were predominantly transgranular fatigue type, that is, fracture morphology and correlating fracture mechanics parameter (Δ
Jf) were of the same type (fatigue type). On the other hand, those of the case where crack propagation rate was correlated with Δ
Jc were transgranular fatigue type or intergranular creep type or mixed type depending on the condition, that is, fracture morphology and correlating fracture mechanics parameter (Δ
Jc) were of different type in some cases.
There was no significant effect of creep-fatigue interaction on the crack propagation under the combined creep and fatigue conditions, and crack propagation may be assessed by a simple summation of fatigue component and creep component.
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