PSI - Issue 10

A. Kyriazopoulos et al. / Procedia Structural Integrity 10 (2018) 97–103 A. Kyriazopoulos et al. / Structural Integrity Procedia 00 (2018) 000 – 000

101

5

Fig. 2. A typical temporal recording of the mechanical loading and the corresponding PSC when the load-increase and maintenance is applied.

Fig. 3. A typical loading step (grey line) and the corresponding temporal variation of the PSC emissions for each load application.

where PSC(tm) corresponds to the PSC maximum value that is reached during tm, PSC b corresponds to the back ground PSC level (Fig.2, PSC background ), and PSC(t) correspond t each PSC discrete value. The ξ function may be fitted by the following generalized q-exponential function:

1 1 [1 ( 1) ] q t  

  t

q



  

(   exp

q 

t

)

(8)

q

q

The q -exponent and the βq parameter were calculated after performing fitting for each of the 5 PSC relaxations according to Eq.(8) and the corresponding values are plotted in Fig.4.The left column of Fig.4 shows the temporal variation of the mechanical load and the corresponding PSC recording. The right column shows the calculated ξ function and the corresponding fitting curve. The value of the q -exponent of the fitted curve is also noted on each plot. The calculated values of the q-exponents are plotted and shown in Fig.5 with respect to the sequenced loading cycle. A gradual decrease of the q -exponent for each next loading is observed. This decrease is expected suggesting that as the stress field interactions shield unfavorably positioned cracks, which no longer accumulate grow in length, and also inhibit the nucleation of new cracks, the cracks organized in a way where the largest cracks have a decreased interaction which is observed as a decreasing q value. 4. Conclusions In this work PSC relaxations are studied under the frame of Tsallis’ entropy for cement mortar beams subjected to 3PB repetitive load/unload loops. The results are clearly compatible to already published ones indicating similar PSC relaxations when marble and amphibolite specimens were subjected to repetitive loading/unloading loops.