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

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

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7.6. <strong>The</strong> Curling Type.<br />

7.6.1. Introduction.<br />

<strong>The</strong> <strong>Delft</strong> <strong>Sand</strong>, <strong>Clay</strong> & <strong>Rock</strong> <strong>Cutting</strong> <strong>Model</strong>.<br />

When the layer thickness becomes very small, two things can happen. <strong>The</strong> normal force on the blade may become<br />

negative or there is no equilibrium of moments. In both cases the contact length between the clay and the blade<br />

has to be reduced. <strong>The</strong>re can be different mechanisms for this. In steel cutting the curling of the chip cut is well<br />

known, but there could also be buckling or breaking of the layer cut. <strong>The</strong> result is the same, the clay will have a<br />

reduced contact length with the blade. This type of cutting mechanism is named the Curling Type. Both the normal<br />

force not becoming negative and the equilibrium of moments will be investigated. <strong>The</strong> mechanism with the<br />

smallest cutting forces is assumed to be the correct mechanism.<br />

Figure 7-33: <strong>The</strong> Curling Type cutting mechanism when cutting clay.<br />

7.6.2. <strong>The</strong> Normal Force on the Blade.<br />

From the Flow Type of cutting mechanism the following equation is derived for the normal force on the blade:<br />

N<br />

2<br />

C Acos( )<br />

<br />

sin( )<br />

(7-79)<br />

Substituting the equations (7-43) and (7-44) gives:<br />

N<br />

2<br />

s c hi w s a hb<br />

w<br />

cos( )<br />

sin sin<br />

<br />

sin( )<br />

1 r<br />

cos( )<br />

sin sin<br />

s<br />

c hi<br />

w <br />

sin( )<br />

(7-80)<br />

Dividing the normal force by the surface of the blade gives the average normal stress on the blade:<br />

<br />

N2<br />

b<br />

<br />

N2<br />

sin<br />

<br />

<br />

h w<br />

<br />

(7-81)<br />

Page 222 of 454 TOC Copyright © Dr.ir. S.A. Miedema

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