(2) Pressure crushing stage
As shown in Fig. 11.34b, when P continues to increase, cracks a; b extend. The
main pressure body of aob appears, which is called fatigue stage. The surface
cracks no longer disappear and the rock surface breaks up.
(3) Volume crushing stage
As shown in Fig. 11.34c, when P increases to a certain extent, oA and oB cracks
appear on the rock surface from point o to form shear bodies Aoa and Bob. With the
increase of P, the shear body begins to collapse outwards, and the main pressure
body aob is crushed to form a crushing pit.
11.5.3.2 Spherical Teeth Breaking Rock by One Impact
Figure 11.35 shows the principle diagram of spherical teeth impact crushing rock at
one time. After a single impact of spherical teeth on rock, the rock will form three
regions: one-time crushing pit, fatigue failure zone, and nondestructive zone. The
size of fatigue failure zone is related to impact energy, geotechnical characteristics,
and drilling pressure, which is a complex non-linear problem.
One-time crushing pit
Fatigue failure zone
Non-destructive zone
Fig. 11.35 Principle of
spherical teeth impact
crushing rock at one time
Fig. 11.34 Principle of spherical tooth hydrostatic rock crushing. a Elastic deformation stage;
b pressure crushing stage; c volume crushing stage
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11 Pneumatic Down-the-Hole Hammer