Low Cycle Fatigue Crack Propagation Characteristics of High Strength Steels

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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Fatigue Crack Propagation Limit Curves for S690QL and S960M High Strength Steels and their Welded Joints

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1146.44 ◽

2018 ◽

Vol 1146 ◽

pp. 44-56 ◽

Cited By ~ 3

Author(s):

János Lukács ◽

Ádám Dobosy ◽

Marcell Gáspár

Keyword(s):

Fatigue Crack ◽

Fatigue Crack Growth ◽

Crack Propagation ◽

Crack Growth ◽

Fatigue Crack Propagation ◽

Welded Joints ◽

High Strength Steels ◽

High Strength ◽

Base Materials ◽

Propagation Limit

The objective of the paper is to present the newest results of our complex research work. In order to determination and comparison of the fatigue resistance, fatigue crack growth tests were performed on different grades of S690QL quenched and tempered, and S960TM thermomechanically rolled high strength steels.15 mmand30 mmthick base materials were used for our investigations. Welded joints were made from these base materials, using gas metal arc welding with matching, overmatching, and undermatching filler metals. In the paper, the performance of the welding experiments will be presented, especially with the difficulties of the filler material selection; along with the results of the fatigue crack growth examinations executed on the base materials and its welded joints. Statistical aspects were applied both for the presenting of the possible locations of the cracks in the base materials and the welded joints and for the processing of the measured data. Furthermore, the results will be compared with each other, and the possibility of derivation of fatigue crack propagation limit curves will be referred.

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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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