PSI - Issue 25

Ch.F. Markides et al. / Procedia Structural Integrity 25 (2020) 214–225

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Ch. F. Markides et al., Structural Integrity Procedia 00 (2019) 000 – 000

3. Conclusions Two configurations for the determination of the tensile strength of brittle materials were discussed, aiming to relief limitations of existing configurations. Closed form solutions were obtained for both the critical stress corresponding to the tensile strength and, also, for the respective components of the displacement field. A series of advantages of the configurations introduced were enlightened, related to the very low level of the force required to fracture the specimens (eliminating the risk of parasitic fracture at the loaded areas of the specimens) and, also, to the fact that the stress field at the critical points consists of a single tensile stress component. Of equal importance is the fact that for the configur ations discussed the ratio of the maximum compressive stress versus the maximum tensile one is not a-priori defined but rather it is controllable by adjusting geometrical features of the specimens. This ratio is always smaller than three (the value for the standardized BD test) and, in some cases, it is smaller than one, rendering these configurations suitable even for brittle materials for which the tensile and compressive strength are relatively close to each other. Another crucial aspect is related to the role of the geometry and the specimen’s dimensions: Ignoring the size effect the tensile strength is a material property and its value is independent of the specimen’s dimensions. The criticism made (Hudson, 1969; Hudson et al., 1972) on Hobbs (1964; 1965) expression providing the tensile strength as a function of the CR dimensions (Eq.(2)) is somehow relieved here since Hobbs ’ correlation factor k , now becomes either k (CSRc) or k (CSRt) given apart from ρ , R 2 and c , also, as a function of the P f (CSRc,t) / P f (BD) ratio (Eqs.(22, 23) of the present analysis). 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