PSI - Issue 13

Ekaterina Damaskinskaya et al. / Procedia Structural Integrity 13 (2018) 298–303 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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Fig. 4. Energy distribution of AE signals AE in the sample region labeled "Region II" (R 2 is the coefficient of determination).

Figure 4 shows the energy distribution of signals detected from the lower half of sample (Region II). It is evident that the data is approximated by a straight line in double logarithmic coordinates. Therefore, the distribution is a power-law one, which indicates that the defect system of this sample region has reached the state of self-organized criticality. In other words, this region of the sample is at a critical stage of the fracture process. According to the concept of Bak (1996), a further evolution of the process will lead to a loss of the sample integrity (separation into parts). Thus, the analysis of acoustic emission data can reveal the sample region in which the ensemble of defects has reached the state of self-organized criticality, i.e., the material is in a dangerous state. This result was compared with the X-ray tomographic data. For this purpose, the volume fraction of defects in separate slices (2 mm) of the sample was calculated after the last loading (Fig. 5a, curve 1). It can be seen that the volume fraction of defects is much higher in the lower part of the sample (Region II). The highest concentration of AE sources is observed in the same region (Fig. 5a, curve 2). As shown above (Fig. 4), the energy distribution of the AE signals detected from Region II is described by a power-law function. The tomographic slices of this region show cracks (Fig. 5b). (Note that no cracks were found in this region at the previous stages of loading.)

Fig. 5. Last stage of deformation. Distribution of volume fraction of defects (curve 1) and number of AE signals (curve 2) along the sample height (a); an example of a tomographic slice (b) (the black line is the crack).