PSI - Issue 18

Sergey Uvarov et al. / Procedia Structural Integrity 18 (2019) 309–313 Author name / Structural Integrity Procedia 00 (2019) 000–000

312

4

0 10 20 30 40 50

τ, s

ε

0

0,5

1

Fig. 3. Stress-strain diagram (left) and time intervals between the serrations (right) for 2µm/s compression speed of the first batch specimen.

3. Discussion We have calculated time intervals (t) between serrations in the middle part of the diagram far from critical points in the same way as in D’Anna paper and plotted probability distribution function (PDF) (fig. 4). One can note the tail on the right side of the distribution which can be related to the bimodality. It appears that the shape of the distribution remains the same for different compression speeds. We expected that the mean value between serrations will linearly depend on compression speed but mean value remained constant for 1 and 2 µm/s and starts to decrease only at 4 µm/s compression speed (table 3). This can be related to the change of the type of the serrations [Chihab (1987)].

‐8 ‐6 ‐4 ‐2 0

ln P

‐4

‐2

0

2

4

6

(ln t‐)/ ϭ

Fig. 4. Probability (P) density function of the intervals (t) between serrations.

Table 3. Mean value and dispersion (gauss approximation fig. 4) for different compression speeds. Compression speed, µm/s Mean value, s Dispersion (  ) 1 1.7 0.6 2 1.7 0.5 4 1.0 0.5

In order to investigate the role of the stored energy (cold work) mentioned in Froustey( 2016) we have performed differential scanning calorimetry (DSC) measurements for specimens from the second batch loaded up to 15% (no serrations), 30% (developed stage of PLC process) and 50% (close to failure). We found an exotermal peak at 300 °С.