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

12.9. The Dynamic Wedge.
The Delft Sand, Clay & Rock Cutting Model.
As discussed in the above paragraphs, the new research has led to the insight that the wedge in front of the blade
is not static but dynamic. The aim of the new research was to get a good understanding of the mechanisms involved
in the cutting at large cutting angles. To achieve this, vertical bars of about 10 cm deep with colored sand grains
were inserted in the sand as is shown in Figure 12-39. When these bars are cut they will be deformed. If the wedge
in front of the blade is a static wedge, meaning that the grains in the wedge have no velocity relative to the blade,
then the colored grains from the bars will not enter the wedge. If however the colored grains enter the wedge, this
means that the grains in the wedge move with respect to the blade. The research has shown that the colored grains
have entered the wedge according to Figure 12-39. In the layer cut, the colored grains show a straight line, which
is obvious, because of the velocity distribution in the layer cut. In fact the layer cut moves as a rigid body. In the
wedge the colored grains show a curved line. Because of the velocity distribution in the wedge, the grains near the
blade move much slower than the grains in the layer cut. Although Figure 12-39 shows a line between the layer
cut and the wedge, in reality there does not exist a clear boundary between these two surfaces. The grains on both
sides of the drawn boundary line will have (almost) the same velocity, resulting in an internal friction angle ,
which is not fully mobilized. The external friction angle on the blade however is fully mobilized. This contradicts
the findings of Miedema et al. (2002A), from previous research. The value of this internal friction angle is between
0