Paper
Creep-fatigue Design Based on the Analyses of Thermal Stress-strain Concentration for Simplified Turbine Casing Models
- Authors:
- Kazunari Fujiyama
- Abstract
- The methodology was presented for evaluating creep-fatigue damage and for optimizing the shape of stress concentration in high temperature components under start-up cycles and steady state operations. Relatively simplified steam turbine casing models were employed by assigning shape parameters such as wall thickness t, fillet height ts and fillet corner root radius R. Total 27 cases were investigated by FE(finite element) elastic thermal stress and pressure stress analysis for different sets of shape parameters. Elastic stress concentration factors were formulated by the shape parameters and by the reference plate stress under ramp temperature change for thermal stress and also by the internally pressurized cylinder stress under steady state conditions. Neuber’s rule and cyclic stress-strain response were introduced and elastic-plastic strain ranges were obtained numerically. Fatigue life Nf was calculated by the material’s low cycle fatigue properties for the elastic-plastic total strain range and creep rupture life tr was calculated by the material’s creep rupture properties for pressure stresses. The shape optimization was realized to set the corner radius as the object parameter by attaining the optimum sets of fatigue damage as the cycle fraction and creep damage as the time fraction to meet the non-linear creep-fatigue cumulative damage curve. This method was proved to be effective for shape optimization procedure even when non-linear material behaviours were exhibited.
- Keywords
- Creep-fatigue; Damage; Thermal Stress; Stress Concentration; Steam Turbine; Casing; Shape Optimization
- StartPage
- 8
- EndPage
- 26
- Doi