A new mark shearing technique for strain measurement using digital image correlation method.

The digital image correlation (DIC) method is a noncontact, full-field surface deformation measuring method, which is widely used in experimental mechanics. Although the DIC method has a high precision in displacement measurement, its precision in strain determination is a bit low. In this paper, a new mark shearing technique is proposed to improve the accuracy of the strain measurement of the DIC method. A wedge mirror is used to introduce a shearing distance of the marks, which are made on the specimen to calculate the strain. The measurement principle of the mark shearing technique is described in detail. From the analysis, it can be concluded that this method is suitable for both large-scaled and small-scaled specimens, and thus has a wider adaptability than the common DIC method. Using this method, the maximum gauge length is 80 mm, and the accuracy of strain measurement can reach 4 microm strains. A tensile experiment with aluminum sample was conducted, and the successful results demonstrated the feasibility of this method.