Research On Full Field High Temperature Strain Visulization Characterization Of Welding Based On Digital Image Correlation

Welding deformation is an important factor which affecting the quality of welding.In the welding process,uneven temperature transmission will cause uneven thermal stress distribution.When the thermal strain exceeds the yield limit of the material,irreversible plastic deformation will come into being.Welding stress and strain will not only cause process defects,but also affect the service life and safety of workpiece.Welding residual stress in the workpiece and external conditions will cause further deformation of workpiece,which will result in the risk of security.So it is an urgent problem to evaluate the stress and strain of the welding process reasonably and eliminate it in a reasonable way.Digital image correlation method,a modern optical measurement technology,is a non-contact,full-field measurement which is very suitable for welding in the measurement of strain.This article combine the digital image correlation method with finite element method to evaluate and analyse the stress and strain in GTAW.Firstly,a set of welding strain acquisition sensor system based on auxiliary light source is developed.By synchronously triggering the camera and light source through the external control panel and the filter system,the high quality of speckle image of weld heat affected zone can be acquired.Secondly,A speckle image processing software called DICORR which based on image gray level interpolation,image subfield template matching and full field iteration is developed.This paper optimizes its calculation speed while ensures its accuracy.A speckle pattern generationalgorithm is developed.The system error of the DICORR software is evaluated by the speckle pattern.And the best parameters of the speckle pattern are obtained.Finally,the stainless steel with speckle is prepared for the later GTAW experiment.Lastly,Before the GTAW experiment,Using the DIC historical data and temperature field data to simulate the finite element.Lately,out-of-plane displacement error verification are carried out to obtain the final reasonable strain value.And then the plate strain at different welding positions or different currency is analyzed.Finally,thermal strain and mechanical strain are separated according to the temperature field change.