| Since a large number of different types of joint surfaces exist on the precision components of CNC machine tools,the contact characteristics directly affect the dynamic characteristics of the components.Therefore,researching the theoretical modeling of the contact characteristics of the joint surface,have very important theoretical value and practical significance for establishing an accurate structural dynamic model and evaluating its dynamic response characteristics of the whole machine.The research of mechanical joint interface is actually the research on the contact characteristics models of rough surfaces.In this paper,the contact characteristics models of a single asperity in different contact deformation stages are modeled and analyzed at the micro-level,the contact characteristics models of rough surfaces based on fractal theory are establishing and analyzing at the macro-level,the experimental modal analysis and modal parameter identification of the linear rail sliding table containing the joint interface are carried out.Finally,the correctness and effectiveness of theoretical modeling are verified.The main contents and innovative results in the paper are as follows:1.A new contact characteristic model based on continuous smooth exponential function for asperity contact during elastoplastic deformation is proposed.Using the Hertz elastic contact theory in the fully elastic deformation phase and the AF plastic contact characteristic model in the fully plastic deformation phase,aiming at the deficiency or defect of the contact model in the elastoplastic deformation phase,the conditions under which the relationship between the contact area,the contact load,the average contact pressure,and the contact deformation amount of the asperity should be satisfied are proposed.With the help of step response function of first-order system,a new asperity elastoplastic contact mechanics model based on continuous smooth exponential function is proposed.The simulation results show that the model is correct and effective.The model is continuous,smooth and monotonous,which is more in line with the results of finite element analysis and practice,and which provides an accurate mechanical model for the contact characteristics analysis of rough surfaces.2.A new normal contact stiffness model of joint interface considering the elastoplastic deformation phase is established.Using the typical piecewise KE contact models in asperity elastoplastic phase and the approximate exponential asperity elastoplastic contact analytical models proposed in this paper,the analytical models based on piecewise KE model and the approximate exponential model on the asperity are established respectively.The influence of parameters such as fractal dimension,fractal scale parameter and plastic index on the normal contact characteristics of joint surface are analyzed numerically.The results of experimental mode and theoretical mode of the dumbbell structure are compared and analyzed,the correctness of the two models is verified.The results show that the accuracy of the normal contact stiffness model based on the continuous smooth exponential function is higher,which provides an important foundation for further studying the law that the contact characteristic parameters affect the overall dynamic characteristics of mechanical structures.3.A new normal contact damping fractal model of joint interface considering elastoplastic phase based on energy "separation" is established.The calculation of normal contact damping of joint interface is based on the energy loss theory.In the fully elastic deformation phase,it is a storage of energy.In the completely plastic deformation phase,it is a loss of energy.In the elastoplastic deformation phase,there is both energy storage and energy loss.After analyzing the characteristics of the exponential model in the asperity elastoplastic phase,the “separation” method of the elastic load and the plastic load in the normal contact elastoplastic deformation phase of asperity is established.The fractal model for the normal contact damping of the joint interface considering the elastoplastic phase is first established.The influence of fractal dimension,fractal scale parameter and plasticity index on the normal contact damping of joint interface are analyzed numerically,and compared with the relevant models.The results show that the model established in this paper is more accurate in describing the contact characteristic mechanism and more in line with the reality,which provides important support for further research on the law of the influence of contact characteristic parameters on the overall dynamic characteristics of mechanical structures.4.The correctness of the model is verified by comparing the theoretical modal analysis with the experimental modal analysis of the linear rail sliding table.Based on the model established in this paper,the contact characteristic parameters of the linear rail sliding table are determined,and the calculation results are assigned to the contact element parameters of the simplified finite element model of the linear rail sliding table.The theoretical mode of the linear rail sliding table is obtained by theoretical modal analysis.The program of time-domain and frequency-domain modal parameter identification method based on MATLAB is compiled to identify the modal parameters of the linear rail sliding table.The MDOF method is used to carry out the experimental modal analysis of the linear rail sliding table,and the modal parameters of the linear rail sliding table are obtained,and the modal verification is carried out.By comparing the theoretical mode with the experimental mode,the correctness of the fractal model of normal contact stiffness and contact damping of joint interface based on the elasticplastic continuous smooth exponential function is verifiedThe research in this paper is of great significance to establish a more accurate dynamic model of mechanical structure and to analyze,predict and evaluate its dynamic characteristics. |
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