Numerical Investigation of Creep–Fatigue Behavior in a Steam Turbine Inlet Valve Under Cyclic Thermomechanical Loading

The aim of this study was to investigate the cyclic creep–fatigue interaction behavior in a steam turbine inlet valve under cyclic thermomechanical loading conditions. Three years and nine iterations of idealized startup–steady-state operation–shutdown process were chosen. The Ramberg–Osgood model, the Norton–Bailey law, and continuum damage mechanics were applied to describe the stress–strain behavior and calculate the damage. The strength of the steam valve revealed that significant stress variation mainly occurred at the joint parts between the valve diffuser and the adjust valve body, due to the combination of the enhanced turbulent flow and assembly force at these areas. The contact stress at the region of component assembly was sensitive to the cyclic loading at the initial iterations. The maximum decrease amplitude in the normalized contact stress between the second and the fourth iterations reached 0.12. The damage analysis disclosed that the notch of the deflector in the adjust valve had the maximum damage due to the stress concentration.

A Unified Shakedown Assessment Method for Butt Welded Joints With Various Weld Groove Shapes

A unified shakedown assessment approach for butt welded pipes or cylindrical pressure vessels with common circumferential butt welded joints for U-groove, V-groove, X-groove, double U-groove (DU-groove), UV-groove, and single-side welding was established under cyclic thermomechanical loadings based on the simplified finite element method. Individual effects of material properties of weld metal (WM), heat affected zone (HAZ), and parent material (PM), the ratio of inner radius, and wall thickness were further considered. Results showed that the proposed method has a high accuracy for shakedown evaluation of weld pipes with various weld groove shapes. Moreover, U-groove is fit for weld pipes to improve the load-carrying capacity of thick-walled cylinders under cyclic thermomechanical loading. Furthermore, the ratio of the yield stress between WM and PM should be greater than the transition point for weld pipes with various weld groove shapes to avoid ratchet first occurs in the WM region.

Deformation Modeling and Lifetime Prediction of Ni-Base Gas Turbine Blade Alloys Under TMF-Conditions

Under cyclic thermomechanical loading conditions, various effects such as strain accumulation, creep damage, ageing, fatigue etc. may occur in the material of a gas turbine blade. Depending on the loading conditions, all these effects contribute to reduce the lifetime of the component. Subject of the present work is the development of a lifetime model able to discriminate between the different damage mechanisms, as well as the development of a material model to describe the mentioned effects and thus providing the input data for lifetime prediction.