Research Of Theoretical Models On Contact Stiffness And Damping For The Mechanical Joint Surface

The stiffness of mechanical joint surface is about 60%of stiffness for a machine,and the damping almost reaches to 90%above.(The specific degree of influence varies with the number,property,contact state of mechanical joint surfaces.)However,the analysis and the design of a mechanical system lack the complete contact stiffness and damping parameters of the joint surfaceat present,which greatly restricted the level improvement of the design and analysis.In early,experimental method was the common method to obtain the parameters of the joint surface,but since the large amount of experimental work,restriction of experimental conditions,incomplete data and so on,experimental method can't satisfy the demand of the engineering analysis and design.In nearly a decade year,people try to directly calculate the parameters of the joint surface in theory.However when two rough surfaces are contacting the existing researches neglect the effects of the asperity lateral contact,asperity interaction and interfacial anisotropy.Furthermore,the contact stiffness and damping of joints in dynamic are rarely studied,thus obtaining closer to the actual conditions parameters of the dynamic contact stiffness and damping of joint surface are still an unsolved and open worldwide scientific problems.This paper aimed at the problems of the existing researches,starting with surface micromorphology of machined surface and considering the contact mechanism at the micro level,the theoretical models of the contact stiffness and damping are studied by a systematic,deep,innovative method when two rough surfaces are contacting under the static\dynamic normal and tangential forces.1.The normal\tangential contact stiffness and damping models of joint surface is proposed and built,which considers the effect of asperity lateral contact.Furthermore,the influence law of the normal pressure,vibration frequency and amplitude on the static\dynamic normal and tangential contact stiffness and damping are revealed.The research results are shown as follows.Increasing the normal pressure can improve the normal\tangential contact stiffness and damping of the joint surface.Changing the magnitude of the deformation\displacement of the joint surface can not significantly change the normal\tangential contact stiffness and damping of the joint surface.The normal\tangential contact stiffness can not be changed by adjusting the vibration frequency,but the normal\tangential contact damping can be increased by reducing the vibration frequency.2.The normal\tangential contact stiffness and damping models of j oint surface is proposed and built,which both considers the effect of asperity lateral contact and the effect of adjacent asperity interaction.Moreover,the effect of asperity interaction on the normal\tangential contact stiffness and damping are analyzed,respectively.The research shows that:The interface with lower elastic modulus can obtain larger normal\tangential contact stiffness and higher tangential contact damping.The higher the hardness of the interface is,the greater the normal\tangential contact stiffness and tangential contact damping of the joint surface.The normal\tangential contact stiffness and tangential contact damping of the joint surface can be improved by reducing the roughness of the contact surface.3.For the situation of a surface morphology being anisotropy,considering the asperity lateral contact and interaction,the static\dynamic normal and tangential contact stiffness and damping models of the anisotropic joint surface is proposed and built.The effects of the anisotropic and isotropic joint surfaces on the static\dynamic normal and tangential contact stiffness and damping are contrasted,respectively.The research shows that:The matching degree of the contact surface has a great influence on the joint stiffness and the tangential stiffness and the damping of the contact surface.The improvement of the contact matching degree can improve the normal\tangential contact stiffness.The closer to the anisotropic joint surface,the smaller the normal\tangential contact stiffness is.The more isotropic,the smaller the tangential contact damping is,and the greater the normal contact damping is.4.The presented model and the other models are contrasted and analyzed by experiment.The effects of asperity lateral contact,interaction,and anisotropy on the normal\tangential contact stiffness and damping are proved,and the theoretical model of closer to the experimental results is obtained.Finally,the correctness and the effectiveness of the proposed model of this paper are validated.