Abstract
The effect of mechanical degradation in a long-term-operated component on the creep- and fatigue-crack growth rates was studied. Creep-crack-growth tests and fatigue-crack growth tests were performed on creep-pre-strained and cyclic-strained CrMoV rotor-steel specimens.
It was found that under constant load, creep-crack growth rates, da/dt, of the creep-pre-damaged specimens were higher than those of virgin specimens. It was also found that under the same stress intensity factor K, da/dt in the case of about 10%-crept and creep-void-induced specimens was increased 5 times, while in the case of 0.8%- and 2.8%-crept specimens, it only increased a little. However, all the data fall in a narrow scatter band in the relationship between creep J integral C* and da/dt.
Another result showed that fatigue-crack growth rates, da/dN, of creep- and fatigue-pre-damaged specimens were higher than those of virgin specimens. Under the same stress intensity factor range ΔK, da/dN in an about 10%-crept specimen was increased 20 times. And da/dN in fatigue-pre-damaged specimens were accelerated 10 times. However, the results of the strain-controlled crack growth test fall in a narrow scatter band in the relationship between J integral range ΔJ and da/dN.
These results suggest that the creep remaining lives and fatigue remaining lives of the mechanically damaged CrMoV rotor steel can be estimated by using C* & ΔJ of the damaged material and the da/dt and da/dN values of the virgin material.
