High-Temperature Low Cycle Fatigue Crack Propagation and Life Laws of Smooth Specimens Derived from the Crack Propagation Laws

The crack propagation properties for ultrafine-grained Zn -22 wt % Al alloy during low cycle fatigue (LCF) in the superplastic region and the non-superplastic region were investigated and compared with the corresponding results for several other materials. With the Zn - 22 wt % Al alloy, it was possible to conduct LCF tests even at high strain amplitudes of more than ±5%, and the alloy appeared to exhibit a longer LCF lifetime than the other materials examined. The fatigue life is higher in the superplastic region than in the non-superplastic region. The rate of fatigue crack propagation in the superplastic region is lower than that in the other materials in the high J-integral range. In addition, the formation of cavities and crack branching were observed around a crack tip in the supereplastic region. We therefore conclude that the formation of cavities and secondary cracks as a result of the relaxation of stress concentration around the crack tip results in a reduction in the rate of fatigue crack propagation and results in a longer fatigue lifetime.

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Research on High Temperature Low Cycle Fatigue Crack Propagation of 2.25Cr-lMo Steel under Complex Stress State

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.361-363.1422 ◽

2011 ◽

Vol 361-363 ◽

pp. 1422-1425

Author(s):

Wen Xiao Zhang ◽

Guo Dong Gao ◽

Guang Yu Mu

Keyword(s):

Fatigue Crack ◽

High Temperature ◽

Stress State ◽

Crack Propagation ◽

Low Cycle Fatigue ◽

Complex Stress ◽

Complex Stress State ◽

J Integral ◽

Cycle Fatigue ◽

Propagation Law

The crack propagation law of 2.25Cr-1Mo steel with notched cylinder was researched under high temperature low cycle fatigue. The crack propagation life was viewed by fatigue experiment and the equivalent stress-strain on the crack tip was calculated by the ANSYS. The equivalent J-integral range which was computed by equivalent elastic and plastic strain ranges were employed to denote the fatigue crack propagation rate. The results showed that crack propagation law of this material under complex stress state can be characterized by equivalent J-integral ranges and the relation between da/dN and ΔJf is not influenced by the type of notch and the load strain range.

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The Fatigue and Fracture Analysis of Steam Turbine Rotor Shafts Containing Defects

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.795.254 ◽

2019 ◽

Vol 795 ◽

pp. 254-261

Author(s):

Shang Wang ◽

Wei Qiang Wang ◽

Ming Da Song ◽

Hao Zhang

Keyword(s):

Fatigue Crack ◽

Crack Propagation ◽

Steam Turbine ◽

Fatigue Crack Propagation ◽

Low Cycle Fatigue ◽

Turbine Rotor ◽

Initial Surface ◽

Cycle Fatigue ◽

Steam Turbine Rotor ◽

Fatigue Crack Propagation Life

In this study, the assessment and calculation methods for the crack propagation life of steam turbine rotor shafts containing defects are presented. The analytic methods for estimating the average stress and the alternating stress amplitude of the steam turbine rotor shafts are introduced. The defects on/in the rotor shafts were regularized by the method of fracture mechanics, and the high cycle fatigue crack propagation life and low cycle fatigue crack propagation life of the rotor shafts are estimated from Paris formula. Taking the 60MW turbine rotor shafts containing an initial surface defect and an initial internal defect as the examples respectively, the crack propagation life of them were calculated. The results indicated that the assessment method for the crack propagation life can preliminarily be both used to estimate the safety-operating life and to analyze the fracture reason of a steam turbine rotor shaft containing defects. This paper can provide reference for periodic maintenance and safety evaluation of turbine rotor shafts.

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