Digital Image Correlation Calibration for High Deformation

• Nicholas Duncan, Mechanical Engineering, University of Delaware

• Thomas Cender, Center for Composite Materials, University of Delaware

Digital Image Correlation (DIC) is an analysis technique widely used to describe material deformation during mechanical testing. The method optically tracks changes in images to measure strains and displacements. In standard mechanical tests, where strains are very low, the DIC data can be cross-checked with a parallel measurement, such as an extensometer or strain gage. For samples which experience high deformation alternative validation methods are not available. Since it is not clear how accurate the obtained strain and displacement values are, a calibration methodology was developed and implemented to validate the results from DIC. Extension testing of a sample of A30 silicone was performed using an Instron. The sample was stretched to increasing increments of 0.10 true strain. Sample length was determined at 3 marked locations which were from the video extensometer images using ImageJ. Strain was also manually calculated at each strain increment by measuring the lengths, widths and thickness at the same locations marked on the silicone sample. The results give a way to adjust the parameters within the DIC software to better fit the actual strain values calculated manually in order to most accurately characterize material behavior for future extension tests.