COSMOS: Complete Online Solutions Manual Organization System
Chapter 9, Solution 97.
From Problem 9.79:
Ix =
Problem 9.67:
I xy =
π
8
a4
Iy =
π
2
a4
1 4
a
2
The Mohr’s circle is defined by the diameter XY, where
1
π
X a4, a4
2
8
I ave =
Now
1
π
Y a4 , − a4
2
2
and
1
1π
π
I x + I y = a 4 + a 4 = 0.98175a 4
2
2 8
2
(
)
and
R=
2
1
2
2 I x − I y + I xy =
(
)
2
1 π 4 π 4
1 4
a − a + a
2
2
2 8
2
= 0.77264a 4
The Mohr’s circle is then drawn as shown.
tan 2θ m = −
=−
2I xy
Ix − I y
π
8
1
2 a4
2
a4 −
π
2
a4
= 0.84883
2θ m = 40.326°
or
θ m = 20.2°
and
∴ The principal axes are obtained by rotating the xy axes through
20.2° counterclockwise
Now
I max, min = I ave ± R = 0.98175a 4 ± 0.77264a 4
or I max = 1.754a 4
and I min = 0.209a 4
From the Mohr’s circle it is seen that the a axis corresponds to I min and
the b axis corresponds to I max .
COSMOS Chapter 9 Solution 97
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