A Research On The Contact Characteristic Of Joint Considering The Contact Angle Distribution Between Asperities

In the whole machine analysis,modeling an accurate contact model is beneficial to study the contact characteristics of joint,and is of great significance to further analyze and predict the real contact characteristics of the whole machine.In the previous fractal models for studying the lateral contact between asperities,the distribution law of contact angle and adjacent asperities interaction were often ignored,which led to large calculation results of the real contact area and contact stiffness of joint.For the above problems,this paper starts with the micro profile of the contact surface,and studies the distribution law of horizontal distance and height difference of peaks between adjacent asperities.According to the discovered fractal law,this paper derives the distribution function of contact angle when two asperities contact with each other,which solves the problem of unclear source of contact angle for the first time,then a lateral contact model of joint is established by using the fractal theory,side contact theory and elastic-plastic deformation theory.Based on the models in this paper,the effects of morphology parameters,material properties and interaction on the normal and tangential contact stiffness of joint are studied and compared with other fractal models,then modal experiment and finite element analysis are carried out,the accuracy of the new model is verified by comparing and analyzing the relative errors of experimental and simulation results.The main study contents are as follows.1.The profiles of the contact surfaces are collected by the profile microscope,and the surface profiles are modeled by the three-point peak method to obtain the horizontal distance and peak height difference between adjacent asperities,the profile data of horizontal distance and height difference of peaks with different sampling intervals are analyzed by using the power spectral density method,and both are found to have fractal laws,then the W-M function is used to simulate the distance profile in the horizontal direction and the peak profile in the height direction respectively,the distribution function of contact angle is derived according to the angle relationship of side contact.The results indicate that,as the contact angle of joint increases,the value of the contact angle function gradually decreases.When the joint is loaded to a certain number of times,the trend of contact angle changes very slowly,which means that the number of loading times of rough surface will affect the change law of contact angle.2.A continuous deformation model for single pair of asperities in contact is established,the fractal models of normal and tangential contact stiffness of joint are established based on the side contact theory and distribution law of contact angle,then the effect of fractal parameters,plastic index,normal load and normal load coefficient on the contact stiffness of joint are studied.The research suggests that the smaller the fractal dimension parameter of rough surfaces,the greater the contact stiffness of joint.Choosing materials with high plasticity index will significantly increase the contact stiffness of joint,the contact stiffness of joint can be improved by changing the normal load coefficient.3.Firstly,the mechanism of the interaction between asperities is analyzed,and a normal contact stiffness model of joint considering the asperities interaction and contact angle distribution is constructed,then under the coupling effect of normal and tangential loads,the functional relationship between contact load,stiffness,and true displacement when asperities interact with each other is derived,then the normal and tangential contact stiffness models of joint are established,finally the change laws of the interface parameters,contact types,and the presence or absence of interaction with contact stiffness of joint are analyzed.According to the analysis results,it can be seen that increasing the fractal dimension,plasticity index and tangential load coefficient of joint can obtain a larger normal and tangential contact stiffness of joint.The tangential contact stiffness of joint can be improved when the friction coefficient,fractal roughness parameter and tangential load of contact surface are lesser.The contact stiffness of joint is significantly higher when ignoring the effect of side contact and interaction.4.For the new model in this paper and other control models,the accuracy of the proposed model is verified by comparing experimental and finite element methods.Firstly,the whole rings experimental platform is designed,and the modal parameters of the experimental device under different normal contact pressures are obtained based on the principle of modal extraction,secondly,the calculation results of the theoretical models are imported into the virtual layer of finite element by using the virtual material method,and modal analysis is carried out to obtain the mode shapes and natural frequencies of the finite element models,finally,the relative errors between the theoretical models and experimental results are compared based on the principle of mode shape matching.The results show that the absolute value of the maximum relative error is 3.50% between the new model results and experimental results,which is the highest accuracy compared with other models.And it shows that the new model proposed in this paper is in good agreement with the actual working conditions,and the side contact theory studied in this paper can be used to predict the real contact characteristics of joint.