Abstract: A sheet metal forming limit strain measurement system—BOSAS (binocular strain analysis measurement system) is designed and implemented, which is based on binocular stereo vision and digital image correlation method. The key techniques concerned are discussed in detail. The proposed method can break the limitations of the classical coordinate grid analysis method, such as difficult dynamic tracking of deformation process and low level automation, and can calculate whole-field strain distribution and reconstruct three-dimensional (3D) shape of the specimen’s surface in every stage during the whole deformation process. Limit strain is able to be calculated by the combination of the fractionized displacement transfer (FDT) algorithm and the finite strain theory. Strain measurement results of material varieties such as deep drawing aluminum sheet 6016,and aeronautical aluminum sheet 2A12-T4,2A12-O and 7B04-O demonstrate that the proposed method is applicable to the measurement of 3D deformation and limit strain of the sheet metal forming. Comparison of strain data obtained by BOSAS and by coordinate grid analysis method shows that the suggested method is accurate and reliable.

Key words: stereo vision, forming limit diagram, strain, digital image correlation, large deformation