A novel calculation method for torsional stiffness of flange-spigot structure in aeroengine rotors

In this paper, a theoretical model to calculate the torsional stiffness of flange-spigot structure is established. Specifically, this model comprehensively considers the non-uniform contact pressure distribution and multi-scale features of rough surface. First, FEM and modified thick-walled cylinder theory are employed to calculate the pressure distribution accurately and different sub-regions are divided based on the same pressure. This idea can address the difficulty of non-uniform pressure distribution of rotor contact interface. Second, semi-analytical method is developed to calculate the dimensionless contact area of rough surface subjected to elastic-plastic deformation, based on which the total tangential contact stiffness of sub-region can be obtained using fractal contact theory. Third, the torsional contact stiffness of flange-spigot structure is calculated by discrete Iwan model. Subsequently, the effects of bolt preload, magnitude of interference, fractal parameters, and friction coefficient on torsional stiffness of flange-spigot structure are discussed. Finally, a three-layer lap joint structure is designed and machined to validate the effectiveness of the proposed theoretical model by comparing the first 4-order natural frequencies obtained by experiment and simulation. The proposed model for torsional stiffness of flange-spigot structure is helpful to analyze the change of dynamic characteristics of high-pressure rotors in the future.