Digital Image Correlation Method And Its Application

Digital image correlation technique is a new non-contact optical measuring technique. It has been developed rapidly since the method was originally developed in the 1980's of last century, and it has been used in many disciplinary fields because of its special advantage. Digital image correlation can make up for the deficiency of the existing measurement methods in civil engineering, and also can solve some problems in structural experiment. In this paper, an improved sub-pixel measurement algorithm of digital image correlation method is proposed to improve the computational accuracy and efficiency, based on the characteristics of civil engineering and around the two key issues—the precision and efficiency of digital image correlation method. The application of digital image correlation method in civil engineering is extended.There are many current methods of displacement and strain measurement, but non-contact measurement method is rare. This paper summarizes the current displacement and strain measurement method and analyzes the advantages and disadvantages of these methods. By analyzing the application status of digital image correlation method in civil engineering at home and abroad, this paper summed up the advantages and problems of digital image correlation method applied to civil engineering.This study focuses on how to improve the precision and efficiency of digital image correlation method. For this purpose, a detailed analysis of its basic principles,measurement systems, displacement and strain calculation methods is given. Each process is adopt the best approach as possible to improve the precision and efficiency. This article also presents a new method how to convert pixel displacement to actual displacement based on digital image correlation method. It makes the actual displacement calculate by digital image correlation method with higher accuracy.The sub-pixel displacement measurement is the most important factor affecting the precision and efficiency of digital image correlation method. In this paper, the precision and efficiency of three common sub-pixel measurement methods (surface fitting, Newton-Raphson and gradient method) has been analyzed and compared. On this basis, an improved surface fitting method is proposed. Digital simulation experiments and practical experiments show that this method has advantages of calculation precision, efficiency and anti-noise ability. In addition, a set of computer program about digital image correlation is written with matlab, which has friendly GUI,can complete interactive operation to control the process of computation and achieve all kinds of tasks about digital image correlation.Several aspects'application of digital image correlation in civil engineering is studied in this paper, which are listed as following: (1) an improved method of searching path is proposed to improve the computational efficiency based on the unidirectivity of the displacement features of structural. This method is used in three-point bending experiments of model beam and bridge static load test; (2) a method is proposed which using "weighted intensity correlation coefficient" to measure the plastic deformation of the metal's surface; (3) digital image correlation method was applied to measure the dynamic displacement and modal parameter identification experiments; (4) distance measurement method using digital image correlation method is discussed.