Agriculture Reference
In-Depth Information
a
b
1000
800
a
600
b
400
200
0 0
2
4 6
Displacement, mm
8
10
12
Fig. 5.3 ( a ) Total ( E t ), cutting ( E c ), and stalk ( E s ) energy required for impact cut of sugar cane
stalks of different diameters. Adapted from [ 20 ]. ( b )CuttingforcerequiredtocutaMiscanthus
stem across its diameter. a, flat cutting blade; b, serrated cutting blade. Adapted from [ 9 ]
uniform stubble height. By equating cutting forces with the expected rigidity of the
plant, Persson and ASAE [ 15 ] provides an equation for this critical speed
æ
ö
z
r
d FF
m
-
cg
v
=
x
b
ç
1
+
÷
(5.1)
k
s
2
è
ø
p
g
where v k = critical knife velocity, m s −1 , d s = stalk diameter, mm, F x = cutting force,
N, F b = bending resistance of stump, N, m p = mass of cut portion of plant, kg, z cg = height
of center of gravity of cut plant, m, r g = radius of gyration of cut portion of plant, m.
A simple approximation to this equation can be obtained by assuming that r g = z cg
[ 16 ].Criticalcuttingspeedsingrassaretypicallyabout25 ms −1 , but commercial
impactcuttingmachineryoperatesat60ms −1 or higher cutting speeds.
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