Research On Damage Identification Of Bolted Joints Based On Wavelet Energy Change Rate

Bolted connection has incomparable advantages in civil engineering,mechanical structure,aerospace,ship and transportation due to its advantages of convenient operation,simple disassembly and cost advantage.The main function of the bolt is to connect the scattered components together,so bolts are crucial to the whole structure.But in the process of using it,often exposed to complex natural environment,the loads such as wind,snow,earthquake,combined with the structure itself material aging,thus resulting in a decline in bolt pre-tightening force,namely the bolt looseness,at the beginning,the tensile stress in the bolt is gradually increasing,when exceed the material yield strength,bolt occurred plastic deformation,does not affect the normal use of structure,but as the pre-tightening force,The continuous drop of the bolts loosens,the connecting parts fail,and eventually the whole structure becomes unstable.Therefore,monitoring the loosening of bolts is very important.Aiming at this problem,this thesis mainly studies bolted joint adopts,the wavelet energy correlation theory as the main research method,through three research means to study the bolt loosening detection,the main work is as follows:(1)First,this thesis studied the bolt loosening theory;second,the bolt loosening mechanism and the factors affecting bolt loosening under different load types are explained in detail;third,in this thesis,the identification method of bolt looseness is studied theoretically,and the process of damage identification is introduced,which provides reference for subsequent damage identification.(2)A simplified model of bolted beam structure is established,and the principle and flow of nonlinear detection are summarized.In order to detect the nonlinear characteristics caused by bolt looseness,harmonic distortion test and frequency response function test are used to detect the nonlinear characteristics of bolted beam structure.(3)Using finite element simulation of the steel column under different damage states bolt connection model,based on loose bolts not state,put forward new damage identification method based on wavelet energy rate.Based on the dynamic response signal,this method performs discrete wavelet changes on the dynamic response signal,calculates the wavelet energy at different scales through wavelet coefficients,and finally solves the wavelet total energy change rate of each node.In addition,this method analyzes the factors affecting damage identification such as wavelet type,decomposition scale,signal type,etc.Meanwhile,the Lipschitz index is used as an index for identifying the degree of damage to identify the degree of bolt damage.(4)A bolt loosening test device was set up,and the model test of bolt connection looseness of steel frame based on shaking table is carried out.The dynamic response signals of bolted joints were collected,and damage identification of structures under different damage conditions verifies the effectiveness of the proposed method.