Application of Digital Image Correlation Technique for Measurement of Tensile Elastic Constants in Brazilian Tests on a Bi-Modular Crystalline Rock

Parent resource - Faculty Profile

DOI - 10.1520/gtj20170208
Journal Name - Geotechnical Testing Journal
Publisher Name - ASTM International
Document Type - journal-article

Paper Abstract- Abstract Most rocks show different elastic properties in tension and compression (bi-modularity). In this study, we derive new equations to calculate the tensile Young’s modulus and Poisson’s ratio from a Brazilian test by incorporating bi-modularity into stress–strain equations. We tested Brazilian specimens of Lac du Bonnet granite and compared the Young’s modulus and Poisson’s ratio in tension obtained with the values from direct tension tests on dog-bone shaped specimens. Digital image correlation (DIC) and conventional strain gauges were used to extract the strain on the flat surfaces of the Brazilian disks. With the DIC technique, a speckle density of approximately 250 speckles/cm2 was needed to accurately capture the strain pattern. The strain measured using the DIC technique was consistent with the strain measured using the conventional strain gauges. The major advantage of the DIC technique is the ability to map the complete strain pattern over the surface of the Brazilian disk and quantify the uniformity of loading. The Young’s modulus and Poisson’s ratio in tension were obtained using the new equations and were found to be in general agreement with the values obtained from the direct tension tests.