Measurement of full-field deformations in metal sheet welding processes by image correlation method

A new three-dimensional deformation measurement method was proposed based on digital image correlation and binocular stereovision to measure the full-field deformation in metal sheet welding processes.Firstly,an algorithm based on a seed point was proposed to provide a reliable initial value for the least-square nonlinear optimization in the correlation matching.Then,the algorithms for three-dimensional coordinate reconstruction,three-dimensional displacement and the strain calculation were discussed separately.Finally,based on these algorithms and the VC++6.0 platform,a welding deformation measurement system was developed for the full-field deformation of metal sheet welding.With self-developed image acquisition devices and a standard material testing machine,a steel standard tensile test and a welding deformation measurement test were conducted to validate the performance of proposed mthod.Experimental results demonstrate that the accuracy of strain measurement is not lower than 0.5%,which is very close to that of a extensometer and the measured 3-D displacement time history is reasonable.It concludes that the proposed method can satisfy the requirements of non-contact,higher precision,and it is a more intuitive way for full-field deformation measurement during metal sheet welding processes.