Calculation of endurance of turbine rotors

Abstract

1. The kinetics of cyclic deformation depends to a considerable extent on the level of strength, i.e., the coefficients k1, k2, but endurance in the coordinate Δɛ — N depends weakly on this indicator, of course, if the level of ductility of the steel does not change. 2. In evaluating the endurance of parts by calculation or by measurement, the values of full deformation are usually obtained and it is, therefore, expedient to use the low-cycle fatigue curves in coordinates full deformation Δɛ vs the number of cycles to failure Np. The circumstance that these curves depend only weakly on the level of strength makes it possible to use them for materials belonging to different strength categories. 3. For evaluating the durability of turbine parts it is possible to use a calculation procedure based on summing cyclic and static damage by formula (3), and the evaluation of damage may be carried out according to data of ordinary isothermal low-cycle fatigue tests. The effect of additional factors (nonisothermy, etc.) may be taken into account by introducing a safety factor according to the number of cycles ⩽2.