Indirect tensile test assessments for rock materials using 3-D disc-type specimens
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ORIGINAL PAPER
Indirect tensile test assessments for rock materials using 3-D disc-type specimens M. R. M. Aliha
Received: 5 October 2012 / Accepted: 19 July 2013 # Saudi Society for Geosciences 2013
Abstract Indirect test methods are usually the preferred approach for determining the tensile strength of brittle and quasibrittle materials such as ceramics, rocks, and concrete. In this paper, the tensile strength of a rock material (Iranian Harsin marble) was obtained indirectly by means of two disc type samples. The test samples were the well-known Brazilian disc and semi-disc specimen under three-point bend loading. Since the existing formula for determining the indirect tensile strength is based on 2-D stress assumption which ignores the effects of specimen thickness, a general 3-D tensile strength formulation was derived for each sample by employing finite element analysis. A series of tensile strength tests were conducted on Harsin white marble using disc and semi-disc specimens with different thicknesses in parallel to finite element analysis. The test results using 3-D formulation showed that the tensile strength of the tested marble depends on the thickness/diameter ratio of the specimen and generally decreases from 11.5 to 7 MPa on increasing the thickness of test samples. The average values of tensile strength were about 8.8 MPa for the Brazilian disc specimen and 9.8 MPa for the semi-disc specimen. The good agreement existing between the results of the two specimens suggests that the semi-disc specimen can also be used for determining the rock tensile strength in addition to using the conventional Brazilian test. Keywords Rock . Tensile strength . Disc type samples . 3-D numerical analyses . Harsin marble . Experiments Nomenclature d r
Disc diameter Coefficient of correlation
M. R. M. Aliha (*) Welding and Joining Research Center, School of Industrial Engineering and Fatigue and Fracture Laboratory, School of Mechanical Engineering, Iran University of Science and Technology Narmak, 16846-13114 Tehran, Iran e-mail: [email protected]
t t/d BD C E FE ISRM KtBD KtSDB P Pf S S/d SDB
Thickness Thickness to diameter ratio Brazilian disc Loading span correction factor for SDB specimen Modulus of elasticity Finite element International Society for Rock Mechanics Thickness correction factor for BD specimen Thickness correction factor for SDB specimen Applied load Critical fracture load Loading span in the SDB test Loading span to diameter ratio in the SDB specimen Semi-disc bend
Greek symbols σt σxx v
Tensile strength Tensile stress component Poisson's ratio
Introduction Strength properties of rocks such as tensile, shear, and compressive strengths are important mechanical characteristics which are used as input design parameters in various rock-related projects such as civil and mining fields (e.g., slope stability analysis and rockfall hazard assessments (Verma and Singh 2010a; Singh et al. 2011; KhaloKakaie and Zare Naghadehi 2012; Ansari et al. 2013), hydraulic fracturing, and in situ stress measur
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