18 b[0,18000]= 1.47 b[18000,tf]= 1.16 0 0.5 1 1.5 4.0 4.5 5.0 5.5 6.0 m Log(Nacum) b[0,1200] =1.10 b[1200,tf]= 1.03 0 0.4 0.8 1.2 1.6 2 3 3.4 3.8 4.2 4.6 m Log (Nacum) Figures 9. Determination of b - coefficients for simulated response in (a) uniaxial compression test and (b) three point bending test. The time intervals intervals used in the computation of b values are indicated between brackets. 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 Log A Log( N>=A) 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 Log A Log (N>=A) Figure 10. plots of the logarithm of the number of events with amplitudes larger than A vs. the logarithm of A for the DEM simulations of compression (left) and of three points bending (right). The b values in the high magnitudes regions are b2= 2.40 (compression) and b2= 1.16 (bending). From these analyses, the following conclusions may be drawn. - The comparison between the experimental and numerical results shows reasonable correlations, for both examples, in terms of conventional results, such as load vs. time and final configurations. - In terms of the distribution of AE event amplitudes in time, the results were seen to be consistent, and any differences observed between the experimental and numerical results were accounted for. It is important to point out that the numerical b-values obtained are compatible with the experimental values and in good agreement with damage theories (Carpinteri et. al. (2009) ), showing a tendency to decrease during the damage process. - The low number of AE events analyzed in the numerical simulations (fewer than 200 events in both cases) compared with the number determined by AE monitoring is an issue to be discussed in detail in relation to the results obtained. However, the aim of these numerical simulations, as mentioned above, was to identify the general trends on a preliminary base. To increase the number of AE events analyzed in the numerical simulations you need a finer discretization, something we shall do after this initial exploration of the applicability of DEM simulations to this kind of process. - This study has shown the potential applications of the truss-like Discrete Element Method (DEM) not only to simulate AE monitoring analysis, but also to provide a better understanding of the relationships between the basic AE parameters. (a) (b) (a) (b)
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