Application of a disk specimen loaded according to the "Brazilian test" for evaluating the brittle strength of materials of non-geological origin

A.V. Osintsev, V. Goltsev, A. Plotnikov


Basing  on  finite  elements  method  simulations  and  experiments  the stress and strain distributions in surface points of a disk specimen loaded according to  the  "Brazilian  test"  (compression  of  the  disk  in  the  diametrical  plane)  have  been  studied.  The color pattern of the strain distribution εх in the surface of iron sample points: (a) — the initial stage of loading, the (b) — stage preceding the destruction, (c) — stage destruction are shown on the figure.Basing on finite elements method simulations by means of ANSYS software of version 14.0 and experiments using the method of digital image correlation the stress and strain distributions in surface points of a disk specimen loaded according to the "Brazilian test" (compression of the disk in the diametrical plane) have been studied. On the general background of compressive stresses, the presence of tensile stresses in the axial plane of the disk has been detected. These stresses arise in the zone of contact between the sample and loading surfaces and displaces then to the disk center with an increase of external load. The dependences of the maximum tensile stress, tensile stress in the center of the disk and in the center of its surface on the stress parameter determined by the formula recommended by ASTM are obtained. Acceptable ratios between the specimen diameter and thickness for a correct determination of ultimate tensile stress are determined. Results of the numerical analysis are compared with test results carried out on cast iron and graphite specimens. Specimens failed in the plane of tensile stresses action. Difference in the character of fracture of cast iron and graphite specimens is identified, which consists in the fact that fracture of cast iron specimens is ductile while it is brittle for graphite. Good agreement between numerical and experimental results when using the formula provided by ASTM standard to determine the ultimate tensile stress of rock materials was obtained. Possibility of application of the method of testing small samples under the "Brazilian test" for indirect estimation of tensile strength of brittle materials of a non-geological origin is confirmed.

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