Development of a desktop universal testing machine with a full-field optical extensometer

Abstract

The objective of this research was to develop a 500-N desktop universal testing machine (UTM) with the capability to find the full-field deformation of a sheet specimen during tensile testing. The machine is equipped with a CMOS camera as the sensor to capture the images of the specimen during material tests. Using the open source 2D digital image correlation (DIC) program Ncorr, we can analyze the images and obtain the full-field deformation and strain. In this research, it was found that the speckle patterns generated by a spray paint and an airbrush were equivalently good. The deviation of the displacement measured by the DIC method with the two patterns can be less than 1%. More tests show that the 2/3-inch-diameter lens with a large field of view can have more accurate strains than the other 1-inch-diameter lens with a small field of view used in this research. The static and continuous loading material tests demonstrated that the strains measured on the UTM were consistent with those measured on a commercial system.