In order to investigate the fracture mechanics law of macroscopic crack propagation in thermal fatigue, strain-controlled thermal fatigue tests on Cr-Mo-V rotor steel and SUS304 stainless steel were carried out by using a notched specimen. A smooth specimen was also employed for thermal fatigue tests under the same conditions as the crack propagation tests to discuss the applicability of the fatigue life law (
i.e., the strain-energy-parameter approach) derived from the macroscopic crack propagation law to thermal fatigue life evaluation.
The results obtained were summarized as follows:
(1) The characteristics of thermal fatigue crack propagation could be classified into two types (
i.e., cycle-dependent and time-dependent) by applying the transition criterion between the types.
(2) The fracture modes in the cycle-and time-dependent thermal fatigue were of transgranular and intergranular types, respectively.
(3) The fatigue
J-integral range, Δ
Jf, was a fracture mechanics parameter controlling the crack propagation rate,
dl/dN, in the cycle-dependent thermal fatigue, while the creep
J-integral range, Δ
Jc, in the time-dependent thermal fatigue. In this case, rapid straining could be successfully applied to the partition of the inelastic strain into plastic and creep components for evaluating the Δ
Jc-value. The crack propagation law (
i.e., the
dl/dN-Δ
Jf and
dl/dN-Δ
Jc relations) in thermal fatigue was identical with that obtained in isothermal fatigue.
(4) The thermal fatigue failure life of the smooth specimen was correlated with the strain-energy parameter, and the correlation agreed with that in isothermal fatigue. Also, it could be predicted from the crack propagation characteristics obtained by using the notched specimen.
抄録全体を表示