Rock Failure Mechanism
Drilling bits cut rock by five basic mechanisms

- Wedging.
- Scraping and Grinding.
- Erosion by fluid jet action.
- Crushing.
- Torsion or Twisting.

While one mechanism may be dominant for a given bit design, more than one mechanism is usually present.

PDC bits shear rock 

PDC Bits

- PDC bits cut rock primarily by wedging, which is more efficient than crushing and grinding. 
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