The Punch Test is best used as a measure of a rock's relative borability.

The test breaks the rock sample in the same way that a disc cutter does.

The test takes into account both the crushing strength of the rock (the failure mechanism beneath the cutter edge) and its resistance to chippinh (the failure mechanism between cutters).

Results from Punch Penetration Test

Penetration Index:

d_i = ((S F/D)/n)(kN/mm)

Compressive Hardness:

S_c = ((S F/Ap)/n) x 0.18 (MPa)

Cutter Penetration:

d = (Fd/d_i)(mm)

Where:
F = Punch Force (kN)
Fd = Design Force for Cutter Edge (kN)
D = Permanent Deformation (mm)
Ap = p(d ctg 30°)² = Projected Area of Indentor Hate (mm²)