PSI - Issue 42

Christos F. Markides et al. / Procedia Structural Integrity 42 (2022) 202–209 Stavros K. Kourkoulis and Christos F. Markides et al. / Structural Integrity Procedia 00 (2022) 000 – 000

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in Tables 1(a, b, c)), may ensure good prediction for the tensile strength of the material and, simultaneously, the minimum possibility of premature fracture at the contact region. Table I. The role of the materials’ stiffness (a), of the cavity’s radius, (b) and of the parameter h (c), on the results of the CTBD test. T he “reference” configuration (i.e., that with E 1 =50 GPa, R 1 =R/5, h =5 R /6) is shown in red lettering. (a) (b) (c) E 1 R 2 ( E 1 ) P c ( E 1 ) σ t ( E 1 ) R 1 R 2 ( R 1 ) P c ( R 1 ) σ t ( R 1 ) h R 2 ( h ) P c ( h ) σ t ( h ) GPa cm MPa MPa cm cm MPa MPa cm cm MPa MPa 10 0.980 118.90 9.48 R /6 0.829 136.18 9.58 5.5R/6 0.993 100.06 9.41 20 0.993 117.37 9.47 R /5 0.995 117.07 9.47 5.0R/6 0.995 117.07 9.47 50 0.995 117.07 9.47 2 R /5 1.992 78.07 9.07 4.0R/6 0.993 141.93 10.06 70 0.996 116.95 9.47 3 R /5 2.986 66.20 8.81 3.7R/6 0.997 260.51 10.15 90 0.997 116.88 9.47 110 0.997 116.83 9.46 Keeping constant: Keeping constant: Keeping constant: P frame =15 kN, E 1 =50 GPa, P frame =15 kN, E 1 =50 GPa, P frame =15 kN, R 1 =R/5, h =5 R /6 h =5 R /6, ν =0.3 h =5 R /6, ν =0.3 4. Conclusions and discussion The CTBD test was introduced here, as an alternative “indirect” tensile test, in order to reduce the possibility of premature fracture at the disc-loading frame contact region often appear in the case of the classic BD test. In addi tion, the specific configuration reduces significantly the influence of the material ’s stiffness and that of the geometry o n the test’s outcomes , since it is characterized by predefined contact length without severe stress concentrations at the ends of the loaded rim. It was, also, revealed that even in the case of the CTBD the choice of the proper geome try should be made with utmost care. It is emphasized that further analytic study is required, including a wider range of materials for each one of the specific geometries suggested. Finally, definite conclusions should only be drawn after an extensive experimental protocol, for various brittle materials tested by means of the CTBD configuration, together with a comparative con sideration of the results of already used “indirect” tensile tests, as it is , for example, the FBD test. References Akazawa, S., 1943. Splitting tensile test of cylindrical specimens. Journal of the Japanese Civil Engineering Institute 6(1), 12 – 19. ASTM, 2008. D 3967-08: Standard test method for splitting tensile strength of intact rock core specimens. ASTM International, West Conshohocken, USA. Carneiro, F.L.L.B., 1943. A new method to determine the tensile strength of concrete. In Proceedings of the 5 th meeting of the Brazilian association for technical rules, 3d. section, 16 September 1943, 126 – 129 (in Portuguese). Fairhurst, C., 1964. On the validity of the ‘Bra zil ian’ test for brittle materials. International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts 1, 535 – 546. Hobbs, D.W., 1965. An assessment of a technique for determining the tensile strength of rock. British Journal of Applied Physics 16(2), 259 – 268. Hondros, G., 1959. The evaluation of Poisson’s ratio and the modulus of mat erials of a low tensile resistance by the Brazilian (indirect tensile) test with particular reference to concrete. Aust. J. Appl. Sci. 10, 243 – 268. Hooper, J.A., 1971. The failure of glass cylinders in diametral compression. Journal of Mechanics and Physics of Solids 19, 179 – 200. Hudson, J.A., 1969. Tensile strength and the ring test. International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts 6(1), 91 – 97. ISRM, 1978. Suggested methods for determining tensile strength of rock materials. International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts 15, 99 – 103. Jaeger, J.C., Hoskins, E.R., 1966. Stresses and failure in rings of rock loaded in diametral tension or compression. British Journal of Applied Physics 17(5), 685 – 692. Markides, Ch.F., Kourkoulis, S.K., 2016. The influence of jaw’s curvature on the results of the Brazilian disc test, J. Rock Mech. Geotch. 8, 127– 146. Markides, Ch.F., Kourkoulis, S.K., 2022. Revisiting the flattened Brazilian disc configuration - Part II: Non-constant disc-loading platen contact length. Rock Mechanics and Rock Engineering, Submitted.