Research On Static Modeling Method And Hysteresis Characteristics Of Bolted Joint

Bolted joint is used in almost every mechanical equipment.Its main function is to connect two components together and to ensure a certain strength and stiffness of the joint structure by bolt preload.In general,the joint area of the members and the bolted joint are collectively referred to as the joint part of the bolted joint structure.In mechanical equipment,the joint strength of the joint part is the weakest link in the whole machine,and it is also the main source of damping during the operation of the whole machine.In order to study the stiffness and damping parameters of the joint part,this paper takes single-bolt and multi-bolt lapped beams as the research object,and studies the modeling method and hysteresis characteristics of bolted joints with bolts under different preload and different tangential loads.The specific research content is divided into the following four parts:(1)The single-bolt and multi-bolt lapped beams were used as the research objects to test the hysteresis behavior of the bolt joint and identify the joint parameters.Firstly,the quasi-static tensile test of the bolt structure is carried out by using the Shimadzu fatigue testing machine.The hysteresis characteristic curves under different conditions were obtained by changing the order of preload and the amplitude of the quasi-static tensile load displacement.Then,a method is proposed to identify the stiffness and damping of the joint part by using hysteresis curve,and the formulas derived were applied to identify the stiffness and damping parameters of the joint obtained by experiment,and then the influence law of different external factors on the stiffness and damping of the joint was obtained.(2)In order to prove the correctness of the joint stiffness and damping parameters obtained by the experimental conditions in the previous part,this part firstly uses ANSYS software to carry out three-dimensional finite element modeling of the bolt lap joint structure to simulate the state change of the bolt joint under the same conditions.In the process of the joint modeling,the influence of different parameters on the joint surface interaction is considered in order to obtain the variation of the stress state consistent with the real state.Then,the parameters in the finite element model are obtained by using the method of parameter identification.Finally,the joint stiffness and loss factor obtained by experimental conditions and finite element method are compared to prove the effectiveness of the experimental and finite element modeling methods.(3)In order to obtain the stress state of the bolt joint subject to the change of tangential displacement load and the influence of the joint parameters on the load displacement curve,a spring-mass unit analysis model of the bolt lap joint structure is proposed.In this model,the bolt structure is equivalent to the bolt a fixed mass and spring series-parallel connection,and obtains the mass and stiffness by analytical calculation.According to the force situation,the static equations of the system are listed,and then the stiffness matrix and force vector of the system can be obtained.At the same time,the bolt lap beam model can be efficiently established by this method,and the calculation speed is much higher than that of the finite element modeling method,so that the desired calculation result can be obtained with a small calculation cost.(4)In order to be able to establish the nonlinear behavior of the joint and the hysteresis behavior of the bolt joint,it is necessary to introduce a nonlinear element into the established model.Therefore,this section proposes a simplified analysis model based on the springdamping Iwan model to establish the bolted joint.Through the simplified analysis model,the simpler bolt hysteresis characteristics and the establishment method of nonlinear model can be obtained.At the same time,the mechanism of action between the joint surfaces and the nonlinear behavior of the joints can be analyzed more accurately and clearly by this way,which lays a foundation for the subsequent mechanical analysis.The research content of the bolt joint modeling method and hysteresis characteristic can provide a certain theoretical basis for the subsequent dynamics of the bolt joint,and also provide some theoretical guidance for the assembly with bolt joints.