PSI - Issue 28

Stepan Major et al. / Procedia Structural Integrity 28 (2020) 561–576 Stepan Major/ Structural Integrity Procedia 00 (2019) 000–000

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(compare Fig. 7 (b) and (d)), it is clear that the observed mean values of the deviation angle α correlate with the observed value of the inclination of the macroscopic fracture plane, which corresponds to about 35°.

Fig. 7. Histograms showing spatial orientation of surface elements: at the microscopic level, i.e. square side a 05 = 5 μm: (a) simple bending, (b) simple torsion; at macroscopic level, i.e. square side a 99 = 99 μm: (c) simple bending, (d) simple torsion.

Box diagrams were used to more accurately describe the orientation of the fracture surfaces, see. Fig. 8. This type of graph has some advantages, that it allows comparison of several selections. The rectangle (or "box" that gave to this graph a name) delimits the area into which 50% of the data falls, so the lower edge of the "box" represents 25% of the quantile (i.e. the lower quantile) and its upper edge then corresponds to 75% of the quantile. (i.e. upper quantile). The short lines connected to the rectangle represent the area in which 90% of the measured data fell, resp. the lower edge corresponds to 5% of the quantile and the upper edge to 95% of the quantile. Other symbols in the graph represents: median (line inside the rectangle), average (solid square), maximum and minimum value (shown by short thick lines). It is clear from Fig. 8 that with increasing distance of the analyzed area from the sample surface, the average value of the deviation angle α gradually increases in both test specimens. This increase is especially evident in the sample loaded with a simple torsion. If we compare the behavior at the "microscopic" and "macroscopic" level, it is clear that the mentioned trends are much more pronounced at the macroscopic level represented by the network with side length of elementary square a 99 = 99 μm.