Digital image correlation

The image correlation or Digital Image Correlation (English: digital image correlation DIC or short ) is a camera- based method for non-contact deformation measurement. It is mainly used for material testing and mechanical unit tests.

Principle of operation

During the deformation of the component images having one or more industrial cameras are recorded. With a camera is measured on flat components and there are displacements and strains detected in the device level. With two cameras, 3D displacements and strains can be measured on any object geometries.

The object to be measured surface is provided with a random dot pattern. The dot pattern is generated either from the natural structure of the sample surface or applied by various methods.

The image correlation algorithms work like pattern recognition methods and identify the screen shifted and deformed pattern in the recorded camera images. From the measured pixel coordinates of the pattern displacements and strains in the component surface, are calculated areally and with high precision.

The image correlation determined from the observed flow patterns at the measuring points the "true" or logarithmic strain. Measurement procedures, which, however, directly determine the distance between gage marks, grasp the technical extension relative to an initial distance of the measuring marks.

3D measurement with stereo structure

A 3D image correlation system based on the combination of correlation method with photogrammetry. Thus, the corresponding 3D coordinates of the object and the 3D deformation ( displacement vector ) are determined at each camera pixel or surface point of the component. In a stereoscopic structure with two cameras several correlations are necessary to measure the geometry and the deformation / displacement of the component: 1 From the stereo correlation between left and right camera image, the 3D coordinates x, y, z calculated. 2 from the time correlation, for example, between the left and right image reference image in the deformed state, the 3D displacement (u, v, w) is calculated.