Welding Fatigue Measurement And Analysis Based On DIC

Fatigue failure is a common failure in engineering,especially in the automotive,aerospace,marine and other industries.It is essential to perform fatigue analysis on the above components.These components are often connected to the nodes by welding.Under the effect of fatigue load,Fatigue damage is prone to occur at the welds of components.The residual stress existing in the weld will reduce the vibration fatigue life of the component and the safety performance of the component.Comparing the test pieces with different welding residual stresses,we can study the strain changes of the weld zone of different test pieces during the vibration fatigue process,and analyze the influence of the welding residual stress on the fatigue life of the welded test pieces,which has practical significance for improving China's industrial technology level.In order to study the fatigue characteristics of the test piece with weld seam,this study used a three-dimensional optical full-field strain measurement system to obtain the image of the test piece during the welding test and fatigue vibration test process,and used the three-dimensional digital image correlation method to calculate the main strain of the test piece during the welding process.Changes,and strain changes in the weld zone during vibration fatigue,and the structural analysis software is used to simulate the residual stress of the test piece,and the fatigue analysis software is used to calculate the fatigue life of the test piece,and the simulation results are compared with the test results.The main work of the thesis includes:We conducted welding experiments and designed two kinds of welding specimens with different widths.By adjusting the speed of laser welding,we obtained specimens with different residual stresses.And by laser marking,the digital speckle image is produced on the surface of the test piece,and the residual stress generated by the laser welding of the test piece is measured using digital image correlation methods.The experimental results show that the faster the laser welding speed,the smaller the residual strain of the specimen.A vibration fatigue test system is established.The vibration fatigue test system consists of a fatigue loading system and a data acquisition system.The fatigue loading system includes supports,vibration exciters,NI control equipment,power amplifiers,sensors,etc.The data acquisition system includes NI acquisition equipment,sensors,high-speed cameras,CCD controllers,image acquisition,and analysis software.Overview and analysis of vibration fatigue test.First,the natural vibration frequency of each specimen is measured by the three-dimensional digital image correlation method,and then the vibration fatigue analysis is performed on the specimen with different residual stress under the same working conditions.During the test,the three-dimensional digital image correlation method is used to measure each the displacement of the weld zone of the test piece and the change of the strain field can be concluded by comparing the strain distribution law of the weld zone and the fatigue failure time of the test piece during the test.When the width of the test piece is the same,the test piece The greater the welding residual stress,the greater the fatigue damage in the weld zone,and the shorter the vibration fatigue life of the specimen.Finite element software analysis.Using sequential coupling to simulate welding residual stress,select Gaussian attenuation heat source to simulate laser welding,obtain the temperature field and thermal cycle curve of each specimen,and calculate the welding residual stress of each specimen.Then perform modal analysis on the specimen to obtain the natural frequency of the specimen.Finally,the analysis results of abaqus software are imported into fe-safe software to calculate the vibration fatigue life of each test piece under different welding residual stresses.