Condensation Modeling Of Nonlinear Dynamics In The Contact Region Of Bolted Joint

With the continuous development of aerospace,micro nano manufacturing,semiconductor manufacturing and other industrial production,the demand for high-speed ultra precision machine tools is rapidly improving.However,because of the structural complexity of precision machine tools,especially the diversity of the machine tool combination,the design theory,performance prediction and optimization calculation methods of the traditional machine tool virtual prototype have been difficult to meet the actual needs.In the machine tool combination part,the bolted joint is one of the most common and most used types in the machine tool assembly process.But so far,many methods,including the Iwan model and the equivalent layer,are used to simplify bolted joint to the analytical or numerical form.However,the method of accurately describing the dynamic characteristics of bolted joint is still not constructed.So,how to predict the dynamic characteristics of bolted joint more efficiently under the condition of ensuring the precision of the design is the key problem to be solved urgently in the design of machine tool virtual prototype.Therefore,on the basis of previous research,a new modeling method of nonlinear dynamic characteristics of contact area of bolted joint is proposed in this paper,in order to lay the foundation for predicting the dynamic characteristics and performance evaluation of bolted joint with high efficiency and precision.In order to study the influence of the nonlinear contact force of bolted joint on the dynamic characteristics,the model with bolted joint is divided into two substructure models based on the component modal synthesis technology.And the finite element model of substructure is established according to the geometric size of the model and the standard material parameters.Because of the uncertainty of the material parameters,the multi-objective genetic algorithm(MOGA)is used to optimize the material parameters to ensure the accuracy of the substructure.It lays the foundation for establishing accurate bolted joint.Based on the hybrid mode coordinate reduction technique,the eigenmodes of the linear degree of freedom in bolted joint are truncated,while the physical freedoms of the contact area characterizing the nonlinear dynamic characteristics are all retained.On this basis,based on the mixed modal coordinate reduction transformation matrix,the reduced model of substructure with mixed modal coordinate is constructed.and the efficiency of calculation and analysis can be greatly improved on the premise of ensuring the calculation precision.Under the premise of guaranteeing the accuracy of calculation,the computation efficiency is greatly improved.In order to facilitate the solution of the nonlinear dynamic characteristics of bolted joint,this paper introduces the contact coupling condensation point which can equivalently characterize the nonlinear characteristics.And the nonlinear contact force of the coupling surface can be condensed to the condensation point by the coordinate transformation.Thus,the nonlinear coupling joint is effectively reduced on the premise of ensuring the calculation precision.And it saves the computing resources.By comparing the frequency response of theoretical calculation with the modal experiment,the validity and feasibility of the nonlinear dynamic characteristic coagulation modeling method for the contact area of bolted joint is verified,which will lay the foundation for the accurate and efficient prediction of the dynamic characteristics and performance evaluation of the machine tool virtual prototype.