Issue 43

M. Davydova et alii, Frattura ed Integrità Strutturale, 43 (2018) 106-112; DOI: 10.3221/IGF-ESIS.43.08 109   D S N Cr (1) Figure 3: Sample with porosity 2 %: a) CT image of the sample cross section; b) fragment size distribution function for 3 samples; c) typical time interval distribution function. The value of the power law exponent S D depends on the material porosity and load intensity. The time intervals between the fractoluminiscence impulses was about 2÷10 3 ns in the active fracture stage, while in the final stage it increased up to 10 6 ns. The change in porosity from 10% to 60% led to a growth of the impulse number by a factor of 18. Fig. 2(c) and Fig. 3(c) present the log-log-plots of the time interval distribution function, which depicts the dependence of the number of intervals, t N , with the size larger than or equal to t . The distribution function for the samples with porosity of 10÷45% is well described (R 2 >97%) by two power laws (two straight lines), (Fig. 3(c)). Whereas for the samples with porosity of 60% it is described by power law (one straight line), (Fig. 2(c)):   1 Dt t N C t (2) The value of power law exponent t D in the relation (2) is affected by the porosity and load value. The ceramic material under study has a cellular structure, which is formed by hollow powder particles (particle porosity) separated by interparticle pores [3,4]. Therefore, it was suggested in [5] that the difference in the time interval distribution functions, (Fig. 2(c) and Fig. 3(c)), for samples of different porosity and a weak sensitivity of the power law exponent to load intensity for low porosity samples, (Fig. 3(b)), should be explained by the competition between two pore systems. The a) b)