New non-contact measurement method of deformation at tensile test of thin film via digital image correlation technique

Abstract

Digital image correlation technique has been widely and effectively applied in the measurement of material properties. This paper presents a new method named Stride-Crawl Approaching Method by combining the steepest descent method and the Levenberg-Marquardt method. It is no longer necessary to provide initial guess of deformation by applying this method. And, the result can always converge to the absolute optimum. Moreover, regardless of the deformations are large or small, this method can always be applied directly. Therefore, this method is more suitable and has great advantages compared to other conventional methods. The proposed method was tested two different simple deformation forms including the rigid body translation, and the uniform tensile elongation by comparing the experimental values with the theoretical values. The images for the verification were generated by numerical simulation. And then the errors were analyzed and it turned out that the error of the displacements was about pixels and the error of displacement gradients was usually limited in 3%. Finally, the stress-strain curves of BeCu was drawn using the output data of the proposed method. And then the tensile properties of BeCu including the elastic modulus, 0.2% yield strength, ultimate tensile strength, and fracture strain were obtained from the stress-strain curves.