Research On Theoretical Calculation Model Of Tangential Contact Damping Of Mechanical Joints

The mechanical joints is prevalent in the mechanical structure.For mechanical components such as power machines,machine tools and other rigid parts,more than 90% of the total damping values are derived from the joint damping.The combined damping contains normal damping and tangential damping,which have an important effect on the dynamic response and vibration performance of the mechanical structure system.Therefore,studying the damping of the joint surface is important to research the overall damping of the mechanical structure,and also provide a means for passive control of the mechanical structure vibration by using the joint damping.In the past,most people have used experimental methods to study,although in recent years,some progress in theoretical research,but are based on the equivalent rough surface contact assumptions.Based around the theoretical calculation of the tangential contact damping of the mechanical joint surface,considered the combination of normal and tangential loads,on the basis of the basic micro-contact model,established tangential damping theory calculation model of single rough surface contact,double rough surface contact and the double rough surface contact of the asperity interaction.The main research results and innovative contributions are as follows.(1) On the assumption of single rough surface,a model of tangential contact damping of joint surface is established based on the asperity normal elastic, elastic-plastic and plastic deformation mechanism and joint surface slip and friction behavior.Based on equivalent rough surface contact hypothesis,combined with Mindlin and Fujimoto theory,the energy dissipation of the asperity in different vibration periods is deduced,then, the contact damping model is established by using the probability statistic theory,the influence of the normal load, the tangential excitation frequency, the tangential dynamic displacement amplitude, the friction coefficient, the hardness and the roughness on the tangential contact damping of the joint surface are analyzed by MATLAB simulation.The results show that there is a significant nonlinear relationship between the tangential contact damping of the joint surface and the normal load,the excitation frequency,the dynamic relative displacement amplitude,the hardness and the roughness,and there is an approximately linear relationship with the friction coefficient.The contact damping of the joint surface increases with the increase of the normal load;At the low frequency and small amplitude,the tangential contact damping decreases with the increase of the dynamic displacement amplitude and the excitation frequency,under the high frequency and large amplitude,the tangential contact damping is almost independent of the dynamic displacement amplitude and the excitation frequency ;The tangential contact damping increases with the increase of the friction coefficient and decreases with the increase of the hardness;When the roughness is small,the tangential contact damping increases rapidly with the increase of the roughness,when the roughness is large,the tangential contact damping increase the range of change smaller with the increase of the roughness.(2) Based on the tangential contact damping model of the single rough joint, the tangential contact damping model of the double rough joint is proposed by considering shoulder-shoulder contact of two asperities.The inclination angle is introduced to derive the energy dissipation in the tangential surface of the asperity contact surface,a small dynamic relative displacement is introduced to derive the energy dissipation in the normal surface of the asperity contact surface,so,the calculation model of tangential contact damping under double rough surface is established.The simulation results are compared with the contact damping model assumed by single rough surface.considered the influence of contact damping on the shoulder-shoulder contact of two asperities.Considered shoulder-shoulder contact of two asperities,the results show that the influence of the normal load on the tangential contact damping is in agreement with the tangential contact damping model of the single rough joint,with the increase of the normal load,the tangential contact damping of the double rough joint is gradually larger than that of the single rough;The influence of excitation frequency,dynamic relative displacement amplitude,hardness,friction coefficient and roughness on tangential contact damping is consistent with that of single rough joint surface tangential contact damping model,but only the contact damping value slightly higher than a single rough surface.(3) Based on the tangential damping model of double rough surface, a tangential contact damping model of double rough surface contact of the asperity interaction is proposed.The asperity interaction is introduced into the basic micro-contact model,and the tangential contact damping model of the double rough surface considering the asperity interaction is established,the numerical iterative method is used to solve the model,the simulation results are compared with the tangential contact damping model of single rough surface and double rough surface,the influence of the asperity interaction on the contact damping is analyzed.The results show that the influence of the normal load,the excitation frequency,the dynamic relative displacement amplitude,the hardness,the friction coefficient and the roughness on the tangential contact damping is the same as that of the single rough surface and the double rough surface,but the contact damping value between the two.(4) On the experimental platform of the basic parameters of the joint surface,the tangential dynamic experiments were carried out on the mating surface of cast iron HT300,The experimental rules between tangential contact damping and normal preload,tangential excitation frequency and tangential dynamic relative displacement amplitude are obtained,and the results are compared with the theoretical model.The results show that the tangential contact damping model of single rough surface contact,double rough surface contact and double rough surface contact of the asperity interaction are the same as the experimental result,the tangential contact damping of single rough surface and double rough surface deviates greatly with the experimental results,and the tangential contact damping of double rough surface contact of the asperity interaction is considered to be closer to the experimental results,which verifies the accuracy and effectiveness of the tangential contact damping model of the double rough contact surface considering the asperity interaction.