An image measurement method of whole field deformation during thin plate welding process

It is hard to measure the deformation due to the high temperature and highlight during the welding process. To solve this problem, a method based on the modified digital image correlation and binocular stereovision technology were used in the thin plate welding whole field deformation. The solution to match images of poor correlation and the algorithm of digital image correlation were analyzed, and both the noise disposal and step benchmark were adopted to ensure that the images of poor correlation could be matched correctly. Firstly, Gaussian smoothing was used to deal with the noise of original image; then a method of setting up the piecewise benchmarks was adopted to overcome the matching difficulties which were caused by eliminate the effect of welding light, and the weak speckle performance around the solder joint. In order to improve the speed of correlation calculation, the second order gradient matrix was simplified by Newton-Raphson algorithm. After the metal surface pretreatment and speckle preparation, some photos of tungsten insert gas (TIG) arc welding and cooling process were taken by the high speed cameras during the whole states of deforming in the experiment. Eventually, the displacements of deformation points in all images could be calculated so that the data of whole field dynamic deformation on the thin plate especially the welding zone could be obtained. The results show that this method can get the strain curves of arbitrary points in the whole welding process, and the accurate deformation trend of the high temperature welding area can also be obtained. The measuring results can be used to analyze the influence factors of welding deformation, control the welding deformation and verify the welding numerical simulation.