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366 CONSEQUENCES OF CORROSION

Figure 5.57 Swellex rock bolt. (Figure originally published in Reference 31. Repro-
duced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum.
www.cim.org.)

Figure 5.58 Visual examination of the fracture of a rock bolt (19).

∘
of the fracture of a Swellex bolt. The failure plane at 45 and localized reduction of
the surface were observed.
Brittle fracture is characterized by a rapid rate of crack propagation with very little
deformation and is demonstrated by cleavage. The visual appearance of a fracture is
shown in Figure 5.58.
Figure 5.59 shows a failed bolt, and the dimples are shallow with respect to the
surface. The dimples are parallel to the direction of the fracture and thus denoted as
shear fracture.
Figure 5.60 shows the fracture surface of a bolt from a hard rock mine.
The close-up of dimpled areas is shown in Figure 5.61. The dimples are shallow
and inclined characteristic of ductile fracture. No sign of cleavage or quasi-cleavage
is observed. The absence of river pattern excludes the possibility of brittle fracture.
Figure 5.62 shows an extremely irregular attack of the external surface of a lon-
gitudinal section of the rock bolt. The presence of an oxide layer in Figure 5.62
and the fragmentation of the metallic surface in Figure 5.63 support the analysis