Evaluation of Creep Damage due to Void Growth under Triaxial Stress States in the Design of Steam Turbine Components

Abstract

The application of creep damage evaluation in the design process of steam turbine components at elevated temperatures is discussed. The focus is on micromechanical methods accounting for the void growth in the creep range of ferritic steels (e. g. 1%-Cr steel). The main emphasis is on the change of void growth rate under multi-axial hydrostatic tension stress states. A commonly used calculation method, accounting for the degradation of deformation capacity due to void growth, is based on the work of Cocks and Ashby⁽¹⁾. The foundations and assumptions of this method will be discussed and the application in the design process will be shown. Based on this, an outline for a modified procedure will be presented. The comparison to experimental results shows the applicability of the modified method. A proposal for a calculation procedure using the basic evolution laws of void growth and strain rate shows the possibility of future development.