PSI - Issue 50

V.G. Degtiar et al. / Procedia Structural Integrity 50 (2023) 40–49 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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5

Fig. 4. The general view of a tomography system: 1 – object (sample, piece); 2 – compensator; 3 – emitter; 4 – centering seat; 5 – detector.

In the paper the density is converted into parameter  and vice versa by formula

(6)

   1000 1400 

The order of magnitude is  = 0.6…0.7 . The fine roughness is also featured by a scatter in density over volumes with cross sections 0.2 × 0.2 mm that is taken into account in tables of  , scatters of parameter  . Since the equivalent sandy-grained roughness is dependent on both size of roughness elements and their number per unit area, Degtiar et al. (2018), Dirling (1973), a C-C composite passes electron microscopic study to find out typical size of pores, shells, other defects, and the distribution of their numbers over the ranges of size, Degtiar et al. (2018), Degtiar et al. (2020). A scanning high-resolution (3 nm) electronic microscope SEM JEOL 6510LA, Japan, was used for the study. Samples were cut with a diamond tool. Dispersed carbon forming in grinding of the sample surface was removed using a special methodology, Degtiar, Saveliev et al. (2016). Fig. 5 presents electron microscopic shots of surfaces of samp les 16.0 × 11.5 mm 2 of summary area with fragments of 13.0 × 4.0 mm 2 . Since inclination angles to an FV axis of ablated surfaces of a C- C composite element can vary from 0 to 90°, C -C composite samples cut in different meridian planes at different angles were used in the electron microscopic study. The summary shot was composed of 10 fragments. A negative of the considered sample surface with enlarged large defects is shown for illustration purposes. Images of micro structure on the cut surfaces of all samples under study were processed with the ImageJ 1.49v software. An increment for counting the number of defects of a definite size (the defect area governs its size) in X-axis in the histogram was 0.001 mm 2 . The first column of the histogram shows the number of pores which area is less than or equal to 0.001 mm 2 (the size does not exceed  31 microns). The height of the second and succeeding columns equals to the number of particles which size is from  31 to  45 microns, from  45 to  55 microns and so on. The number of small pores is an order of magnitude greater the number of larger defects (pores), and in the first histograms columns of the number of large defects is vanishingly small, so in the second histograms the number of pores is given in logarithmic scale, the fact allows using the data for the computation of parameters of fine-grained roughness. Data on the distribution of defects in other planes (reinforcing directions) are similar.