The Delft Sand, Clay & Rock Cutting Model, 2019a

Rock Cutting: Atmospheric Conditions.
Substituting the corrected shear angle gives for the mobilized shear strength:
c m
T
/4
sin 2
1
sin
1
/4
cos
cos
2
(8-134)
Now the cutting forces can be determined with:
2c mhi wcos( )sin( )
Fh HT Thi
w
cos( / 4) cos( )
2c mhi wcos( )cos( )
F
VT T hi
w
cos( / 4) cos( )
(8-135)
(8-136)
8.8. Specific Energy.
For the cases as described above, cutting with a straight blade with the direction of the cutting velocity vc
perpendicular to the blade (edge of the blade), the specific cutting energy Esp is:
E
sp
Fh
vc Fh
h w v h w
i c i
(8-137)
The specific energy of the Flow Type or Crushed Type of cutting mechanism can be written as:
E
sp HF
c
(8-138)
The specific energy of the Tear Type or Chip Type of cutting mechanism can be written as:
Esp HT T
(8-139)
Since the specific energy equations are based on the maximum horizontal cutting forces, where the cutting process
is most probably either brittle shear or brittle tensile, the average cutting forces will be smaller. How much smaller
depends on the type of rock, but literature mentions reductions by 30% to 70%. Since the specific energy is based
on the average cutting forces, the values found with the above equations should be multiplied by a factor of 0.3-
0.7.
Copyright © Dr.ir. S.A. Miedema TOC Page 289 of 454