PSI - Issue 3

S.K. Kourkoulis et al. / Procedia Structural Integrity 3 (2017) 326–333 4 S.K. Kourkoulis, D. Triantis, I. Stavrakas, E.D. Pasiou and I. Dakanali / Structural Integrity Procedia 00 (2017) 000–000

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Fig. 2.(a) The acoustic sensors (1-4, 6-8), the electrodes for the PSC technique (orange ellipses) and the silver line (blue ellipse) needed for the high speed camera; (b) The dots’ pattern for the DIC technique and the two clip-gauges; (c) An overview of the experimental set-up. suitable metallic “knife edges” to measure the Notch Mouth Opening Displacement (NMOD) during the tests. A small preload, equal to about 100 N, was applied to the specimen to keep it in place. This is necessary because the quality of the images of both optical methods strongly depends on the exact distance between the specimen and the cameras. 3. Results 3.1. Mechanical behaviour As it was expected the fracture load (P fr ) varied between broad limits, ranging from about 2.5 to 10 kN. The load displacement relation was almost perfectly linear for all specimens up to the final fracture load, however increased scattering was observed even for specimens of the same group (i.e. the same notch length). This is well attributed to the wavy shape of the material layers of Dionysos marble, which renders almost impossible the preparation of identical specimens with respect to the angle between load and material layers or equivalently between the axis of the notches and the load. The inherent inhomogeneity of rock-like materials makes things worse. This is further supported by the fracture patterns realized, some of which are shown in Fig.3. The absence of any symmetry and similarity is obvious. A

Fig. 3. Characteristic fracture patterns. The variability and randomness of the fracture paths is obvious.