Equivalent Dynamics Modelling And Experimental Study Of Bolted Beam Structures

The presence of joint surfaces in bolted structures brings additional energy dissipation and strong nonlinear characteristics,which may have adverse effects on the work of the structure because the bolts are often in a more complex use environment,so the dynamic modeling of the contact interface of bolted structures is essential to ensure the performance of the structure.This paper presents an equivalent modeling method for simulating the relative rotation of the contact interface in a bolted beam structure.The transverse vibration of the studied structure is closely related to the relative rotation of the joint,which is different from previous studies that focused more on the tangential slip of the joint interface and the bolts used under clearance-free conditions.(1)In this paper,the six-parameter Bouc-wen model and the four-parameter Valanis model are used as nonlinear hysteresis springs,respectively,to establish an equivalent dynamics model of a two-degree-of-freedom system,and the response of the system is solved numerically by using the ode45 solver based on the Longacurta method in Matlab software.The nonlinear characteristics of the response at different excitation amplitudes and excitation frequencies were investigated using swept frequency excitation and simple harmonic excitation.In addition,the effects of the parameters of the Bouc-wen and Valanis models on the shape of their hysteresis curves in the two-degree-of-freedom system were analyzed.The genetic algorithm toolbox in Matlab software was used to identify the parameters of the two models.The results of the identification show that the genetic algorithm can accurately identify the model parameters in the system with nonlinear springs,but the use of the genetic algorithm requires more computational cost for the Bouc-wen model.Therefore,in the equivalent modeling of the bolted connection beam,the Valanis model was chosen to simulate the relative rotation of the bond surface at the bolts.(2)A three-dimensional contact finite element model was established,and static numerical experiments were conducted to study the physical quantities of normal stress,transverse strain and transverse displacement at the contact interface;quasi-static numerical experiments were used to study the reaction-displacement curves and the method of extracting the moment-turn angle curves for different preload levels;dynamic numerical experiments were used to study the effects of different friction coefficients and preload forces on the characteristics of the contact interface.(3)The relative rotation of the bond surface is simulated using the Valanis model,and the deformation of the beam unit is simulated using the Timoshenko beam unit,and a dynamic equivalent model of the cantilever bolt connection beam is established,the parameters of which are determined by fitting a series of hysteresis curves obtained from the transient nonlinear analysis of the three-dimensional contact finite element model.The validation results show that the proposed equivalent modeling method can accurately simulate the dynamic response and energy dissipation of the bolted connection beam structure,and the computational efficiency is significantly improved compared with the finite element numerical calculation,with the maximum errors of 5.5% and 8.3% for the dynamic response amplitude and energy dissipation,respectively.(4)The time-domain response of the bolted beam structure under transverse excitation was analyzed by dynamic experiments.The results showed that in the actual bolted structure,the structure is a relatively ideal viscous damping system with an elliptical excitation force displacement curve when the excitation displacement amplitude is small,and an obvious softening of stiffness and relative slip rotation between the beams can be observed as the excitation displacement increases.