Theoretical Modeling Research On Contact Stiffness And Damping Of Bolt Joint Surface

The bolt joint surface is the most typical joint surface in the machine tool,which plays an important role in transmitting movement,load and energy during the operation of the machine tool.At the same time,the continuity of the system is destroyed,which greatly affects the performance of the whole machine.This dissertation takes the bolt joint interface as the research object,focusing on three aspects: the micro contact modeling research of the bolt joint surface,the joint surface contact mechanics model,and the joint surface dynamic response model.It aims to accurately predict and improve the dynamic performance of mechanical equipment.The dynamic service performance of mechanical equipment provides a theoretical basis and basis for improving the reliability of mechanical equipment.The specific research content is as follows:(1)For the research of rough surface micro-contact modeling,accurately simulate the rough surface topography to obtain surface topography parameters.Furthermore,a microscopic contact model with continuous smooth contact characteristics is analyzed and constructed.The research work of rough surface micro-contact modeling is first to characterize the rough surface micro-morphology by fractal.The structure function method and the surface spectral moment of the Weierstrass-Mandelbrot function are combined to determine the rough profile parameters.Furthermore,the interpolation process of the Hermite polynomial function is improved to correct the discontinuity of the Brake model when modeling the contact stiffness.The idea that the contact parameters of the asperities change continuously and smoothly during the contact deformation process is continued,and a microscopic contact model with continuous and smooth contact characteristics is established.(2)A more accurate and effective bolt joint surface contact stiffness model is established by considering the influence of substrate deformation and asperity interactions.First,a single asperity-substrate system model and a contact model of multiple asperities are established to analyzed the interaction mechanism of substrate deformation and asperity interactions,respectively.Then,the influence of substrate deformation and asperity interaction can be extended to the entire rough surface through multi-scale theory and mathematical statistics,and then their corresponding joint surface stiffness models can be established.Finally,a new contact stiffness model of the bolt joint surface is established by linking the influence of substrate deformation and asperity interactions.(3)Aiming at the hysteresis nonlinear mechanics problem of the bolt joint surface,a mechanical modeling method of modifying the Iwan model is proposed,which makes the physical meaning of the parameters of the traditional phenomenological Iwan model clearer.Firstly,the traditional Iwan model is improved by considering the different static and static friction coefficients,and a new tangential response model of bolt joint surface is proposed.Then,through the Coulomb’s law of friction,the modified Iwan phenomenological model is connected with the normal contact model of the joint surface with continuous smooth contact characteristics,and the constitutive relation of tangential displacement load is deduced.Finally,the equivalent viscous damping and hysteresis curves of the joint surface are obtained,and the effects of loading conditions,plasticity index and the ratio of dynamic and static friction coefficients on the contact characteristics of the joint surface are explored.