PSI - Issue 46

5

A.S. Voznesenskii et al. / Procedia Structural Integrity 46 (2023) 155–161 A.S. Voznesenskii et al. / Structural Integrity Procedia 00 (2019) 000–000

159

As follows from Fig. 4, a significant part of the section contains a layer of carbonaceous clays. This layer reduces the strength and FT of the GG-1 specimen compared to other specimens of this group. As follows from Fig. 5, the cross-section of the specimen KK-4 does not contain layers of carbonaceous clays. FT of flint for this specimen has a large value and is not reduced by clay layers. 4. Discussion The data presented in Fig. 4–5, allowed calculating the maximum force P max and using formula (1) to determine the coefficient K C . Table 1 shows the calculation results. A small number of specimens did not yield reliable statistical characteristics, but it makes it possible to estimate the range of variation by the minimum and maximum values. For clarity, Fig. 6 shows the data obtained in the form of a diagram.

Table 1. Results of measurements of the K C coefficient of various rocks and interfaces № Specimen a 0 , mm F fr , kN K C, MN•m 1.5 N fr

1 2 3 4 5 6 7 8 9

GG-1 GG-2 GG-3 GG-4 UG-1

6.0 3.0 4.0 4.0 4.0 4.5 3.5 4.0 6.0 3.0 2.0 5.0 6.1 4.0

0.6390 0.9850 0.9881 0.8174 0.8332 0.8250 1.1002 1.1942 1.1475 1.2256

0.8320 0.9950 1.0890 0.9011 0.9186 0.9500 1.1610 1.3170 1.4946 1.3511

2 2 4 2 4 5 3 4 4 5 5 3 3 6

GUK-1 GUK-2 GUK-3 GK-3 GK-5 KK-1 KK-2 KK-3 KK-4

10 11 12 13 14

–

–

2.0390

2.4470

–

–

2.2320

2.4610

Cracks during the destruction of specimens KK-1 and KK-3 passed outside the V-shaped cutout. Therefore, calculations for these specimens were not carried out.

Fig. 6. Range of changes of the K C parameter for different interfaces.

It can immediately be concluded that there is a significant excess of Kc of flint (KK) in its values for gypsum stone (GG). For flint specimens KK-2 and KK-4, fracture cracks passed through the V-shaped part of the stress concentrator. For KK-1 and KK-3, even the presence of a notch did not lead to fracturing along this part of the specimen. In specimen KK-1, the crack passed at a distance of 16 mm from the V-notch, in the lower part of the specimen, where there was a local area of gypsum, 3–10 mm long and 0.01–0.05 mm thick. These inclusions played a role in the destruction. The central part of the specimen with a cut in the flint region remained intact. Similarly, the crack in specimen KK-3 passed away from the notch along the interlayer of carbonaceous clays in the gypsum layer. This fact indicates a significant strength and fracture toughness of flint, which can decrease due to the presence of interlayers of carbonaceous clays or mica, and have an insignificant tensile strength in the direction perpendicular to the bedding plane. The GG group showed lower K C values compared to the KK group. Specimen GG-1, which included interlayers of carbonaceous clays in a significant part of the cross-section and the V-notch tip, is of minimum value. In the other