PSI - Issue 33

Irina A. Bannikova et al. / Procedia Structural Integrity 33 (2021) 357–364 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

358

2

geophysical applications. Test experiments on cylindrical sandstone specimens (height 1 cm and diameter 1 cm) showed that under dynamic loading the specimen fractured with the fragments formation of shapes two types. The first type was commensurate with the size of the sample, and the second type contained many small fragments of various shapes. This formation process can be represented as a combination of fracture two types: first, an impact type crack occurs (one or two main cracks are formed), and then complete fragmentation of the sample. In the cumulative distribution of fragments by mass of sandstone, an "inflection" was observed. We assume that this is due to the presence of two different mechanisms for the formation of fragments during failure. Statistical distributions of fragments in the range of smaller scales (fragment masses), close to power-la w, reflect a “self - sustaining” crack when the limiting energy density in the sample volume is reached and reflect the self-similar nature of crack propagation in a wide range of scales. Large fragments, comparable to the characteristic size of a cylindrical specimen, were formed as a result of the passage of major cracks and were described by an exponential or logarithmic function. Similar behavior (power distribution for 3D fragments and exponential distribution for 2D fragments) was observed for Al 2 O 3 samples (high modulus material) under loading by the EEW (electric explosion wire) method by Bannikova and et al. (2016). In contrast to the results for Al 2 O 3 , the inflection point slightly (or not) shifted towards smaller scales during the failure of the sandstone. In continuation of work with rocks, experiments are being carried out with joint registration of fractoluminescence. Quartz is known to have piezoelectric properties by Kats and Simanovich (1974). It was shown by Davydova (2013) that quasi-static loading of fused silica rods is accompanied by pronounced fractoluminescence. Therefore, quartz-containing rocks should glow when destroyed. In this work, for the study of fragmentation, we selected quartzite as a high-rich quartz rock.

Nomenclature d*

characteristic size of sieve, opening loading force in quasi-static compression

F

m N N t

mass of fragment

number of fragments with the same mass is greater than some given number of identical time intervals in the signal from the photomultiplier tube time of movement of the upper loading plate in the Shimadzu installation time interval between pulses in a signal from a photomultiplier tube pressure of loading machine

p

t

t imp

2. Samples and properties Quartzite was selected for testing because of its high quartz content and pronounced fractoluminescence (Kats and Simanovich (1974)). The samples were cut from a piece of rock with a diamond-coated hollow drill. The cylinder bases were polished in water on p340 and p480 grit sanding sheets to a mirror finish using a Struers polishing machine. Since the samples were from rocks, they had natural cracks and interlayers of media with different contents of quartz and other impurities (granite, etc.). See Fig. 1.

Fig. 1. View of quartzite specimens.