期刊
INTERNATIONAL JOURNAL OF FATIGUE
卷 124, 期 -, 页码 34-41出版社
ELSEVIER SCI LTD
DOI: 10.1016/j.ijfatigue.2019.02.034
关键词
Gas turbine; Disc alloy; Shot peening; Fatigue; Mean stress; Life prediction
资金
- European Union's Horizon 2020 research and innovation programme [653941]
- H2020 Societal Challenges Programme [653941] Funding Source: H2020 Societal Challenges Programme
Turbine disks in gas turbines are subjected to cyclic load at high temperature, making, especially the fir tree type blade attachments, susceptible to fatigue. Shot peening of the fir tree attachments may be used to increase the fatigue life by introducing compressive residual stresses. In the current study, both polished and shot peened notched specimens made from alloy 718 were subjected to low cycle fatigue at 450-550 degrees C. The shot peening generally increased the fatigue life, although the effect diminished for high loads. It was shown that the effect of shot peening could be handled as mean stress effects in a life model based on a Smith-Watson-Topper (SWT) type parameter, sigma(max)Delta epsilon/2. A material model which captured the mean stress was set up to get the SWT parameter at the notch root. It was shown that thermal relaxation of residual stresses and initial strain hardening from cold work could be excluded from the finite element analysis used to establish the mean stress; this since the plasticity in the first cycle dominated the plastic deformation of the specimen. Overall, the SWT-based life model worked satisfactorily. However, the prediction of correct mean stresses at 550 degrees C proved somewhat difficult as the degree of mean stress relaxation at this temperature varies widely in available literature data.
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