Issue 40

K. Kaklis et alii, Frattura ed Integrità Strutturale, 40 (2017) 18-31; DOI: 10.3221/IGF-ESIS.40.02 28 (a) (b) (c) (d) (e) (f) Figure 11: The dependence of (a) the splitting tensile strength, (b) the intact rock modulus, (c) Poisson’s ratio, (d) the shear modulus, (e) the lateral peak strain and (f) the axial peak strain on the diameter of the specimens. Discussion and Additional Considerations As previously mentioned the so called “size effect” must depend on the bulk material (volume) of the specimen and its limits (external surface) that are exposed to different stress/strain states (plane-stress, plane-strain or triaxial) as well as other factors such as environmental, specimen machining factors, etc. It implies that comparisons must be performed in classes of geometrically self-similar specimens. Consequently, different “shapes” of specimens cannot be compared. This is demonstrated from Fig. 8a and 11a where a qualitatively different behavior of strength is obtained. At the same time, it seems that the size effect may not a material property, but a specimen characteristic and the “law of 3/2”, i.e. the ratio (volume)/(external surface), which in the present case reduces to specimen diameter D , may be an over-simplification.