Digital Image Correlation (DIC) is a non-contact 3D full-field optical technique for measuring contours, deformations, vibrations and strains on almost any material. The technique can be used in many tests, including tensile, torsional, bending and combined loading in both static and dynamic applications.
The full protocol for performing DIC measurements can be seen in the demonstration video bellow we shot for the manufacturer, Dantec Dynamics.
Our multi-camera DIC measurement system (seen in the video) consists of:
The system, with all its accessories and software, allows tremendous flexibility in both the placement of the camera and the objects measured. The system is portable and also enables in situ measurements. So far, we have successfully measured objects ranging in size from 5×20 mm up to 2000×2000 mm. The two extreme measurement cases (in terms of size) are shown in the following pictures.
As mentioned earlier, the DIC measures the contours, displacements, and strains on the observed surfaces of the sample. The number of surface points for which we measure results ranges from 3 000 to 40 000 and depends on the number of cameras used, their placement, and the sample surface. As far as strains are concerned, we have been able to measure strains of more than 500% of rubber seals subjected to tensile loading.
In the following section you will find the results and a brief description of some of the DIC applications performed in our laboratory.
DIC allows not only classical tensile test measurements, but also local measurements of the neck after the occurrence of plastic instability.
With DIC, we can observe changes in the sample material. This image shows the response to tensile loading of a specimen made by two additive methods.
The high spatial resolution of DIC measurements allows the measurement of local effects that occur in the material during tensile loading. One of these effects is the so-called Lüders bands, which are caused by inhomogeneous plastic flow in the material.
DIC is also interesting for bending tests. Stereo DIC (two cameras) can be used to measure displacements and strains of the frontal surface. With a multi-camera DIC setup, the top and bottom surfaces can also be measured, as shown in the right image. This provides additional information about the test, e.g. about the bending Poisson effect.
The presented DIC measurement system is also mobile and allows in situ measurements. The picture shows the deformations of a double-glazed unit subjected to a pressurization test.
With all eight cameras, we can measure the displacements and strains of a complete (360°) outer surface of the sample. For example, we measured the strains of a ball that was being inflated.