Fir tree fastening of turbomachinery blades—I: Deflection analysis

Abstract

Fir tree root fastenings are widely used for securing steam turbine blades onto the disc. The existing experimental and theoretical approaches for the stress analysis, treat the root as a whole, thus giving the stress distribution for that particular root only. The root is made up of several steps and in each step various geometrical parameters are involved. For proper understanding the designer must know the effect of variation of different parameters on the loads carried by each step. The new design approach suggested is to treat the root as an assembly of steps. The study of the stiffness of a generalised step is presented here, while the assembly of the steps is the subject matter of Part II.