to make indentations of different dimensions. Thus, Vickers hard-
ness was considered. The Vickers pyramid has a square base with an
angle between opposite faces of 1361, so a correlation between the
side length of the square (L) and the depth (d) can be computed and
is approximately equal to 5 (L¼d  2  tg(1361/2)) (Fig. 3).
Fig. 4 shows the matrix of defects produced in steel, aluminium
and copper as shown in micrographs presented in Fig. 4b–d,
respectively. Distance between indentations was equal to 300 mm