Multi-camera DIC offers new dimensions in material testing

Abstract

Optical full field techniques, like digital image correlation (DIC) become more and more standard tools for the determination of material parameters. Especially for anisotropic materials the multidimensional information is important. For example, up to now this is limited to 2D strain information. The use of the innovative cluster approach for DIC and a multi camera setup in a standard tensile test allows the access to the third dimension and measure not just the strain on one surface but on both surfaces and in thickness direction. With the cluster approach the points to be evaluated are not defined by an image of one camera, like in conventional DIC systems, but on the object. In this case every object point seen by two or more cameras can be measured, independently of the arrangement of the cameras. In a front back side arrangement e.g. during a tensile test, both sides of the sample are measured simultaneously. As all cameras are calibrated in a common coordinate system the thickness of sample and any changes are measured directly. In this way the strain in thickness direction is measureable directly. As an example we present the measurement on a simple aluminium sample up to failure. The difference in the strain in direction of thickness and on the surface indicates anisotropic material properties caused by the process of manufacturing.