Normal Dynamic Contact Modeling And Research On Vibration Characteristics Of Bolted Joints With Rough Interfaces

Bolted joints are widely used in mechanical systems,mainly responsible for transmitting motion,load,and energy.Under actual working conditions,the nonlinear dynamic characteristics of bolted joints can have a certain impact on the entire mechanical system.While considering the surface topography parameters and material properties,the dynamics characteristics of the bolted joint will be more complex.In this paper,the bolted joints with micro rough morphology are taken as the research object.Firstly,the dynamic displacement of joint surface is introduced to establish a normal dynamic contact model of bolted joints.On this basis,a universal,accurate,and reliable dynamic response model of bolted joints is established.Finally,qualitative verification of the theoretical results was conducted through experiments,which providing reference for accurate prediction of the theoretical dynamics model,and contributing to improvement and optimization of the actual assembly process of the bolted joints.The specific research content is as follows:(1)A normal dynamic contact model of bolted joint rough interface considering dynamic displacement was proposed and established,and the effects of material properties,surface morphology parameters,and plasticity index on contact characteristics of bolted joints were analyzed.The research shows that in the dynamic contact process,the contact force of the system presents a nonlinear law,in which energy dissipation exists.And the dynamic contact force will increase to about 50 times of the static force when the displacement of the interface changes by several microns.The larger the surface roughness is,the greater the contact force during the loading process is,but the lower the contact force during the later unloading stage is.Increasing the elastic modulus of a material will exacerbate energy dissipation.Increasing the plasticity index will increase the contact force of the joint surface,and the maximum contact force is linearly proportional to the plasticity index.(2)Based on the modified normal dynamic contact model of bolted joint,a vibration response model of bolted joint was established,and the effects of surface morphology parameters and plasticity index on the nonlinear characteristics of bolted joints were studied.Research has shown that bolted systems is always in a quasi-periodic motion state with fixed system parameters.By increasing the excitation frequency,the system will gradually approach the single cycle motion state.When the excitation frequency increases from 1Hz to 200 Hz,the dimensionless displacement amplitude of the system will decrease from about 2 to 0.6.Increasing the plasticity index of the bonding surface will make the nonlinear characteristics of the system more pronounced.The rougher the joint surface is,the more obvious the nonlinear characteristics of the system is.When the excitation frequency is smaller,the influences of surface morphology and plasticity index are more obvious.(3)The normal contact vibration experiments on the rough interface of bolted joints are conducted,and the vibration response characteristics of bolted joints are further analyzed.The correctness of the theoretical calculation results are qualitatively verified in the paper.The experimental results indicate that there are significant differences in the response law in the three stages where the preload is less than,equal to,and greater than the excitation amplitude.When the preload is less than the excitation amplitude,the system will reach a resonance state between the joint surfaces after stability;when the preload is equal to the excitation amplitude,the displacement amplitude of the specimen will gradually increase until it reaches a fixed value,but resonance will not occur;when the preload is greater than the excitation amplitude,the fitting relationship between the displacement amplitude of the specimen and the preload meets the exponential function after the system reaches steady state.The excitation amplitude mainly affects the number of cycles required for the system to reach steady state,as well as the amplitude of the system response when the preload is greater than the excitation amplitude.The larger the excitation amplitude is,the greater the displacement amplitude is.The excitation frequency mainly affects the system response amplitude in the first two cases,the higher frequencies lead to the smaller amplitudes.When the elastic modulus of the material is smaller,that is,the surface plasticity index is higher,the nonlinear characteristics of the system are more obvious.The joint surface with higher roughness is more difficult to reach the steady-state of the system,and increasing the elastic modulus of the material will make the impact of surface morphology more significant.These laws can qualitatively verify the accuracy of the theoretical model for vibration response of bolted joints.