Calculation of the life of long steam turbine blades with small cracks
摘要
A computational model to determine the residual life of a long steam turbine blade containing a short corrosion-fatigue defect (crack) is proposed. The blade is subjected to longitudinal tensile loading due to centrifugal force and cyclic bending in the plane of the disk. The computational model is formulated in terms of the crack-tip opening displacement δ, enabling the study of microdefects in quasi-plastic materials. Based on available experimental data and the proposed analytical transformation, fatigue fracture kinetics diagrams for the 20Kh13 steel are constructed in the da/dN ∼ δt coordinate system. The residual life of the 20Kh13 steel blade is calculated. The influence of bending stresses induced by variable steam pressure at the nozzle exit, as well as the localization and initial size of the crack, on the blade’s residual life is evaluated.