PSI - Issue 10

D. Mastrogiannis et al. / Procedia Structural Integrity 10 (2018) 319–325 D. Mastrogiannis et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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(a)

(b)

Fig. 2. An overview of the experimental arrangement before (a) and after (b) the fracture of the epistyle.

3. Results

The application of external, mechanical load on the epistyle, as expected, was followed by both AE and PSC. During the loading procedure, AE and PSC are progressively produced while the material is mechanically stressed until fracture (Fig.2b). These signals are indicative of the deformation process and associated with the crack formation and nucleation. The recording of these signals can provide information about the energy released during the de formation process. By calculating the square values of the amplitude of these signals and adding each consecutive value up to the time point of final rupture, one can obtain a rough estimate of the cumulative energy released during the procedure through AE and PSC, respectively. In the present work it is examined whether the log periodic power law model of Eq.(1) is able to efficiently model the AE and PSC cumulative energy released by such complex structural setups such as the aforementioned “ epistyle ” . Specifically, Eq.(1) was used as a fitting function on the two cumulative energy release curves that were calculated using the AE and PSC recordings of Fig.3. The results of the application of the aforementioned log periodic model are shown in Fig.4. The values of the parameters for which Eq.(1) produced the most consistent fittings are listed in next Table 1.

Table 1. The values of the parameters of Eq.(1) corresponding to the fittings presented in Fig.4. Acoustic Emission PSC Parameters Values m 0.8118 ± 0.0236 0.9989 ± 0.0154 C 0.1071 ± 0.0075 0.7009 ± 0.0103 ω 3.5381 ± 0.1240 1.1647 ± 0.0140 Φ 3.0618 ± 0.1015 8.4684 ± 0.0145

In Fig.4, the cumulative energy released through the AE and PSC is denoted with a blue solid curve. It is obvious that in both cases the cumulative energy plot roughly follows a power law form. The black dotted line is the result of fitting the cumulative energy data, using a simple power law of the form:     m f E t t (2) By comparing the blue solid curves with the corresponding black dotted curves, one can easily infer that a simple power law cannot successfully fit the experimental data acquired from such a kind of deformation procedure. On the