Issue 40

K. Kaklis et alii, Frattura ed Integrità Strutturale, 40 (2017) 18-31; DOI: 10.3221/IGF-ESIS.40.02 21 1 3 3 xx yy xx yy v                        (3) (a) (b) Figure 2: (a) Load configuration of the Brazilian test, (b) Distribution of the horizontal Stress Concentration factor q xx =σ xx /( p a/π) calculated according to the theory of elasticity [21]. E XPERIMENTAL PROCEDURE sufficient number of block samples for the Alfas stone was collected from the quarry near the Alfas village in Rethymnon, Crete, Greece, and subsequently carefully checked to ensure the homogeneity of the materials. The size of these blocks was 25x30x30 cm. Specimens were prepared for uniaxial compression and indirect tension testing as detailed below. In all testing, load was applied by a stiff 1600 kN MTS-815 hydraulic testing frame and a 500 kN load cell using a load control mode. Uniaxial compression test Using the freshly quarried Alfas stone, three sets of cylindrical specimens were prepared according to the ISRM specifications [19] for the uniaxial compression test (Fig. 3a). In order to investigate the size effect, specimens were prepared with diameters D =54, 75 and 100 mm. The height h to diameter D ratio for the uniaxial compression test remained constant and equal to 2. Special care was taken to ensure that the two bases of the cylinders were parallel to each other and perpendicular to the longitudinal axis of the specimens. All experiments were carried out using a very thin film of vaseline jelly as lubrication between the bases of the specimens and the loading platens. The loading rate was 3 kN/s. In order to measure the axial and lateral strain during the UCS test, three biaxial 0/90 strain gages were appropriately attached at 120 o to each other on the curved surface of the cylindrical specimens, midway between the cylinder bases (Fig. 3b). The use of three strain gages per specimen was deemed appropriate (especially for the larger specimens) in order to check the symmetry of the generated surface strains on the specimen during loading. Indirect tensile test Three sets of circular discs were prepared according to the ISRM specifications [22] for the Brazilian test (Fig. 4a). The ratio of the diameter D to thickness t for the Brazilian test remained constant and equal to 2. In order to investigate the size effect, specimens were prepared with diameters D =54, 75 and 100 mm. Subsequently, two strain gages were attached on the center of each flat surface of the circular discs used for the Brazilian tests (Fig. 4b). The specimens were placed between two steel loading jaws designed to contact diametrically opposed surfaces over an arc of approximately 0.1 radians, (as suggested by ISRM [22]), and the test was conducted with a loading rate of 200 N/s. A