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

The Delft Sand, Clay & Rock Cutting Model.
A mobilized cohesive shear strength cm can be defined, based on the tensile strength σT, by using the equal sign in
equation (8-127). With this mobilized cohesive shear strength Mohr circle 2 can be constructed.
c m
T
sin 2
1
sin
1
cos
cos
2
(8-128)
Substituting equation (8-128) in the equations (8-109) and (8-110) gives for the cutting forces:
2c mhi wcos( )sin( )
Fh HT Thi
w
1
cos( )
2c mhi wcos( )cos( )
F
VT T hi
w
1
cos( )
(8-129)
(8-130)
Figure 8-38 shows the pseudo cohesive shear strength coefficient T /c from equation (8-127). Below the lines
the cutting process is ductile (the Flow Type) or brittle (the Shear Type), while above the lines it is brittle (the
Tear Type). It is clear from this figure that an increasing blade angle α and an increasing internal friction angle φ
suppresses the occurrence of the Tear Type. The coefficients λHT and λVT are shown in Figure 8-42 and Figure
8-43 for a range of blade angles α and internal friction angles φ.
Figure 8-37: The Mohr circles of the Tear Type.
Equation (8-129) gives for the specific energy Esp:
Esp HT T
(8-131)
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