lab 3 report
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School
San Diego State University *
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Course
302
Subject
Mechanical_engineering
Date
May 3, 2024
Type
docx
Pages
4
Uploaded by LieutenantIbex4322
Jesus Rodriguez
CIVE 302 Section 2
Lab #3 Report
Purpose: Part 1 and 2:
The purpose of these labs was to see that strains can also be measured through circuits in a Wheatstone bridge not just in the ways that we have done previously. Procedure:
Part 1:
1.
Turn on all equipment. 2.
Balance the Wheatstone bridge at zero.
3.
Record various new resistance values on the Wheatstone bridge and record the corresponding RG. Part 2:
1.
Set up cantilever beam. 2.
Place a block on end of the beam and record distance from gage and weight of block.
3.
Take block off and change which gage in engaged then place block back and record the distance from gage.
Results/Analysis/Calculations: Part 1:
V =
6.94
Test 1
Test 2
Test 3
Test 4
Test 5
Test 6
R1
120
122
120
126
119
123
R2
120
117
117
120
120
117
R3
120
122
124
120
118
118
R4
123
123
121
123
119
122
RG(total measured)
0
973
32
735
3
860
This comes from equation 3-25 from the lab instruction.
IG(measured 3-25)
#DIV/0!
8.92E-05
4.48E-05 0.000173
4.08E-05 0.000168
The first current was dividing by zero as the was no resistance meaning that would theoretically be infinite. To calculate these answers theoretically you would calculate the value of VG with equation 3-24 from the lab instructions then use Ohm’s Law of V = I*R or in this case IG= VG/RG. VG
0.04284
0.08675 0.001434 0.127474 0.000123 0.144586
IG
#DIV/0!
8.92E-05
4.48E-05 0.000173
4.08E-05 0.000168
Part 2:
width =
1.502 in
Thickness =
0.19 in
w1 =
2.2 lb
D1 =
21.75 in
w2 =
2.2 lb
D2 =
21.75 in
Tensile Results Measured:
ε
=(
30
1000
+
1170
10
6
)−
¿
) =
2
∗
10
−
4
Tensile Results Calculated:
M
T
=
47.85
lb
∗
¿
σ
=
5294.879219
psi
ε
=
1.8258
∗
10
−
4
Compressive Results Measured:
ε
=(
30
1000
+
2480
10
6
)−(
30
1000
+
2680
10
6
)
=
−
2
∗
10
−
4
Compressive Results Calculated:
M
c
=−
47.85
lb
∗
¿
σ
=−
5294.879219
psi
ε
=−
1.8258
∗
10
−
4
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Discussion:
From what I can see when the average resistance of the resistors is high the smaller the
current through the gage seems to be which would make sense and support Ohm’s Law. Also, when performing this part of the lab we ran in an error that caused us to pause and call out a technician, perhaps corrupting some data. The strains that were recorded from the beam portion of the lab seemed to be really similar to the theoretical calculated strains only being .00001742 off from each other. The difference between the half bridge and full bridge would be that a full bridge would have another support on the opposite side making the strains that would be less as they
would not be under the same amount of stress.