MCE311
Homework # 3
Due on Wed. Oct 26
th
, 2011.
Question 1
: A strip of cast iron is 8in. long and has a cross section of 1.0 by 1/16 in.
It is subject to an axial load of 1000lb. Two strain gauges are attached to the surface,
one in the axial direction and the other in the transverse direction. The axial gauge
indicates a strain of 1143
and the transverse gage indicates an strain of -286
. Estimate the Modulus of elasticity and Poison’s ratio for this material.
Solution:
We first find the axial stress:
F
A
psi
/
/ ( .
/
)
,
1000
1 0
1
16
16 000
Rearranging Eq. 8.1:
E
psi
a
/
/ (
)
.
16000
1143
10
1 40
10
6
7
Rearranging Eq. 8.6:
t
a
/
(
) /
.
286
1143
0 25
Question 2
: A strain gage has a resistance of 120
and a gage factor of 2.09.
If it is
used in a quarter bridge with the other resistors being 120

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