Issue 40

K. Kaklis et alii, Frattura ed Integrità Strutturale, 40 (2017) 18-31; DOI: 10.3221/IGF-ESIS.40.02 26 to the indirect tensile stress for the same specimen. Experimental values represented by these curves remain almost constant at about 50% of the indirect tensile strength. (a) (b) (c) (d) (e) Figure 9: Typical diagrams for Brazilian tests. (a) Stress-strain curves from the two biaxial strain-gages, (b) Stress-difference strain curves from the two biaxial strain-gages, (c) Mean values stress-strain curves, (d) Intact rock modulus and (e) Poisson’s ratio in correlation with the indirect tensile stress. The issue of the different strain values measured on the opposite sides of the disc specimens is intriguing and a number of experimental options are currently being studied / explored by the authors in order to investigation this discrepancy. One way to reduce experimental errors due to utilization of strain gages is to use optical techniques such as the procedure of Digital Image Correlation (DIC) [23, 24] which does not depend on the accurate placement of measuring devices on each specimen. In order to investigate this issue, both sides of a specimen need to be monitored at the same time. An approach