Full-field time-series measurement for three-dimensional deformation under welding

Abstract

Displacement during welding provides important information to understand the mechanisms of welding deformation and residual stress. In particular, if welding deformation can be measured sequentially and the displacement distribution over full field can be measured such as the results obtained by finite element analysis, they can be valuable information. Therefore, in this study, a 3-dimensional (3D) deformation (in-plane and out-of-plane deformation) measurement method is developed using a digital camera, which requires no special equipment. This method is a non-contact method and it can sequentially measure over the entire photographed image. Furthermore, since image analysis is based on the technique of image matching, the method is applicable even when measuring deformation is large. In addition, since it is possible to use all pixels as measuring points, the number of available measuring points at one time is the same as the number of effective pixels of the camera. This is currently more than 15 million points, and the measuring precision is expected to increase as the camera pixel resolution continues to increase. Therefore, this method is expected to have future potential. In this study, the proposed method is applied to the sequential measurement of displacement under the strong lighting levels in arc welding. By comparing the time history of transverse shrinkage, longitudinal shrinkage and angular distortion with the results of FEM thermal elastic-plastic analysis, the qualitative validity of the proposed method is verified. To investigate the measurement precision and usefulness of the method, a 3D shape measurement system (LAT-3D) using a laser displacement gauge and digital caliper are used. The distributions of residual transverse shrinkage and residual angular distortion are measured by the proposed method, LAT-3D and digital caliper. Through the comparison of the results measured by these methods, quantitative validity of the proposed method is also verified.