Research On Dynamic Characteristics Of Bolted Flange Connection Structure Considering Connection Status

Bolted connection is widely used in civil engineering,mechanical engineering,aerospace engineering and other fields due to its advantages of simple construction,good stress performance,repeatable disassembly and assembly.However,because of the need to withstand cyclic loads or impact loads,bolted connections are prone to loosening or fracture failure,which will cause very serious consequences eventually.This makes the principle of bolted connection failure and connection state detection technology become the current research hotspots and key issues.In the past few decades,the connection state detection technology based on vibration measurement has received extensive attention for its advantages of being easy to measure and accurately reflecting the connection state of the structure.But so far,due to the non-linear factors existing in the connection interface,the classical Iwan model,Dahl model,and simplified to equivalent layers or spring elements have not been able to describe the dynamic characteristics of the assembly structure accurately.Therefore,how to describe the dynamic characteristics of the assembly structure accurately under the influence of nonlinear factors is still a very important issue.Based on this,this paper proposes a simplified dynamic model of bolted connection structure in order to provide a reference for the efficient and accurate study of the dynamic characteristics of bolted connection structure.Aiming at the problem of non-linear factor existing in the joint surface,and considering factors such as the distribution position and quantity of bolts,a simplified dynamic model of XYZ three-direction springs based on equivalent connection stiffness is proposed,and the motion differential equation of this multi-degree-of-freedom system is calculated.Considering the low efficiency of solving the finite element dynamic equations,the Craig-Bampton reduction method is used to reduce the redundant degrees of freedom of the two flange structures,which greatly reduces the calculation time.Considering the bolted connection structure is a whole including bolts,nuts and connected parts,the changes in the stiffness of each component will have a significant impact on the dynamic characteristics of the system,and the three-direction spring dynamics model proposed is elaborated detailly.This paper analyses the transmission path of the internal force of the bolted connection structure,respectively calculates the stiffness of the connected part,thread,bolt,contact surface and angular stiffness caused by external force inclination,etc.,and establishes the equivalent stiffness model of the bolt connection.Based on this,this paper gives the nonlinear change laws of axial stiffness and tangential stiffness.According to the proposed three-direction spring model,through solving the dynamic equation and using the finite element software Ansys Workbench for modal analysis,the dynamic response analysis of the loose installation condition and the inclined installation condition of the bolted flange connection structure is carried out.Combining with the modal test experiment,the feasibility and effectiveness of the proposed model are verified,which provides a reliable basis for predicting the bolt connection state accurately.