Contact Stiffness Of Bolt Joint And Its Effect On Rotor-dynamics

There are many bolt joint structures in the rotor and stator structures of aero-engine,because of contact,friction,slip and fretting,the bolt joint structures are non-linear and uncertain,and their dynamic characteristics are very complex.Considering the details of bolt joint will significantly increase the computational effort,while ignoring the influence of bolts will cause some errors.Therefore,a simplified and high-precision bolt joint structure model is needed to meet the needs of engineering calculation.In this paper,the contact stiffness model of rough surface in bolt joint structure is established by theory,simulation and experimental method.The rough surface contact stiffness between two connectors under different bolt preloads is calculated and used to analyze the dynamic characteristics of typical aero-engine drum rotor system.The details are as follows:1.For theoretical calculation,analytical model of pure elastic contact stiffness of rough surface based on statistics is analyzed.The machined gasket morphology is measured and analyzed,and the contact stiffness is calculated.The results show that the contact stiffness of rough surface calculated at different positions of the same gasket fluctuates due to the machining deviation.Under the same bolt pretension,the contact stiffness decreases with the increase of roughness.2.In the aspect of simulation calculation,the two-dimensional finite element model of real shape is established,the influence of preload force on contact stiffness was obtained by contact simulation.The contact stiffness of the first loading and the second loading is compared and analyzed.The results show that the pure elastic contact theory should be adopted for the contact simulation of the second or multiple loading surfaces.Then a three-dimensional finite element model of the rough surface is established based on the fractal theory,and the contact stiffness of the rough surface under different preload force is obtained by using the Ansys non-linear contact algorithm.3.In the aspect of experimental research,the natural frequencies of bolt joint structures under different preloads are tested,and the results are compared with the finite element simulation results based on thin-layer elements method.The contact stiffness of bolt joint structures under different preloads is obtained based on modal strain energy/energy identification,and the accuracy of contact stiffness identification is improved.By comparing the results of theory,simulation and experiment,the characteristics of various methods/models and the causes of errors are analyzed,and the accurate contact stiffness of rough surfaces is determined.4.In terms of application,according to the relationship curve between contact stiffness of rough surface and preload,the dynamic characteristics of multi-bolted aero-engine Disk-Drum rotor system are studied.The results show that the contact stiffness of bolt joint has a certain influence on the modal frequency of Disk-Drum rotor,and the increase of contact stiffness will lead frequency shift phenomenon,and restrain the response amplitude to some extent.Finally,the natural frequencies of the free modes obtained from the simulation are compared with the experimental results,and the two coincide well.5.The research results provide an idea for accurate modeling and engineering simplification of bolt joint structure,and provide a reference for structural design,dynamic analysis and vibration control of bolt joint in aeroengine.