Investigation On Equivalent Modeling And Parameter Identification Method Of Dynamic Characteristics Of Bolted Joint

Because of the advantages of strong reliability and convenience in assembling and disassembling,bolted joint plays an irreplaceable role in the assembly process of aerospace,military and high-end manufacturing equipment.The bolted joint,whose existence results in the discontinuity of mechanical system characteristics,becomes the transition area of the inherent performance of the whole system.Whether the local stiffness decrease or the damping increase of bolted joint,the dynamic performance of the whole bolted structures will change.The basic works to study the dynamic performance of a bolted structure are to build a reasonable equivalent model and accurately identify the characteristic parameters of the joint in the model.Therefore,it has important theoretical significance and engineering practical value to study the dynamic characteristic equivalent modeling method of bolted joint and the accurate identification of model parameters.In this paper,aiming at the joint problems in spring element model and virtual material model,two aspects of model improvement and parameter identification are studied.The main research works are as follows:Based on the combination of modal experiment,finite element analysis and optimization algorithm,the reverse identification method of material property parameters is proposed.The dynamic characteristic parameters of the structure are obtained through the finite element simulation analysis and modal experiment method.Then the minimize difference between them is taken as the optimization objective,and the material property parameters to be identified are used as the optimization design variables to build the optimization function.When the simulation results of the structure keep approaching the actual state of the physical model,the solution of the parameters to be identified in the theoretical model is obtained.Using the proposed reverse parameter identification method,the inverse identification and correction of the material property parameters of specimen are successfully realized,which solves the possible uncertainty of the material property parameters of different batches of test piecesA spring element improved model of joint which is characterized by the equivalent pressure circle diameter is proposed.The equivalent spring element stiffness in the influence area is used to replace the equivalent spring element stiffness in the whole contact surface.The independent modeling of bolt stiffness and joint interface stiffness is realized,which improves the prediction accuracy of the dynamic characteristics of the spring element model of bolted joint.Aiming at the bolted connections with small-scale contact surface,the theoretical calculation formulas for the stiffness parameters of the joint interface is obtained according to Hertz contact theory.Through the simulation analysis of the joint contact area under different bolt preloads,bolt diameters and the thicknesses of connected parts,variation rules of the bolt affected region is obtained.And the validity of the improved model is verified using the dynamic characteristic experiment and simulation analysis of the single bolted platesAn inverse identification method of self iteration of joint stiffness characterization parameters based on spring element is proposed.According to the reverse parameter identification method associated with the improved joint model based on spring element,the joint stiffness characterization parameters of spring element are taken as the optimal design variables to identify and optimize the parameters using iterative operation.The identification model of joint parameters for the double bolted plates is established,and the identification of the joint stiffness parameters is completed by iterative optimization with the help of the experimental modal parameters obtained from the dynamic characteristics test.The results show that the reverse identification method of joint stiffness parameters can more accurately describe the actual joint state,and effectively improve the prediction accuracy of dynamic characteristics of bolted structures with large-scale contact surfaceA reverse identification method for the virtual material parameters of joint is proposed The joint is characterized by a layer of virtual material,and the modal parameters obtained from the virtual material simulation model and dynamic characteristics experiment are used to reverse identify and optimize the virtual material parameters of joint.Compared with the forward analysis method based on analytic method,this method effectively avoids the problem of repeated testing of many parameters in empirical formulas.The dumbbell bolted specimen is taken as an example in this paper.The equivalent strain energy principle and the reverse parameter identification method are used to calculate its virtual material parameters of joint in the simulation model.The comparison between the natural frequencies obtained from the two analysis processes and the experimental ones shows that the proposed parameter reverse identification method can effectively improve the characteristic accuracy of dynamic performances of the virtual material equivalent model of joint.A virtual material improvement model based on the offset layer element is proposed.In this model,the offset layer virtual material element is used to replace the single whole virtual material element,which can effectively reduce the number of degrees of freedom and save computing resources on the premise of realizing the local stiffness weakening representation of bolted joint.The virtual material joint models based on the offset layer element for the dumbbell bolted specimen and the multi-bolted plates are established,and the parameters of offset layer virtual material are realized successfully.The results of the examples show that the offset layer virtual material model can predict the dynamic characteristics of bolted joint more accurately and reliably,which provides a simple and effective way for the equivalent modeling and dynamic characteristic analysis of bolted joint in large and complex mechanical equipment.