Effect Of Micro Contact Damping And Macro Surface Profile On Joint

The mechanical joints have studied in this paper through experiments and finite element methods.It contains the dry contact damping mechanism of micro joints and the influence of the macro contact surface flatness information on joint properties.The study mainly includes the following three aspects:1.The micro dry contact experiments of steel 45: there is a constant phase lag angle in the stable stage under the sinusoidal exciting force which shows the existence of the contact damping.Under step load,there is also dynamic hysteresis between displacement and force.The deformation curves are not rectangular,but nonlinear,which shows the existence of the energy dissipation and it is related to the stress amplitude.According to the steel 45 tension test,it can be concluded that the viscosity is a property of steel 45 which is not obvious when stress value is low,and obvious when stress value is high.It is the source of the normal dry contact damping.According to macro contact experiments of steel 45,the first three natural frequencies and modal shapes of samples whose size is the machine tool guideway scaling can be obtained by hammering experiments.2.Based on the viscoelastic model,the normal contact damping mechanism of steel 45 is described by using the four element model.According to tension tests and theoretical derivation,The parameter functions are obtained which are used to describe the material properties under different stresses,in other words,the material can express different viscosity under different stresses.Under the macro scale,the joint stiffness is introduced into the contact algorithm,and the hammering test is introduced into the finite element model,so the modal calculation can be conducted in another aspect.3.The 2-D contact model containing detail information of surface is built.According to the contact calculations based on the viscoelastic material,the strain-time curves under different stress value can be obtained.Compared the finite element results with the experiments,the good agreement proves the existence of viscoelasticity and the effectiveness of the method.The 3-D contact modal contains macro surface flatness information is built.According to the single point exciting method in finite element model,the first three natural frequencies and modal shapes can be obtained.Compared the results from FEM with the experiments,it shows that the reasonable model should contain special surface flatness information,its calculation results are more accurate.