Transcript Stress and Strain Lab - Monte Vista School District

Engineering H192 - Computer Programming
Stress and Strain
Lab 4
Winter Quarter
Gateway Engineering Education Coalition
Lab 5
P. 1
Engineering H192 - Computer Programming
Objectives
• To understand how engineers compare different
materials.
• To understand how a strain gage works.
• To collect and analyze experimental data.
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Lab 5
P. 2
Engineering H192 - Computer Programming
Stress vs. Strain
Strain:

Hooke’s law:

Stress:   F
l
A
  E
Where:
E = Modulus of Elasticity


= stress
= strain
For the bike fork material E = 29.0 x 106 psi.
Winter Quarter
Gateway Engineering Education Coalition
Lab 5
P. 3
Engineering H192 - Computer Programming
Measuring Load on a Bicycle Fork
Loads applied by rider
STRAIN GAGE
A sensor that
measures strain
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Gateway Engineering Education Coalition
Lab 5
P. 4
Engineering H192 - Computer Programming
Loads on a Bicycle Fork
Compression
Loads applied by rider
Bending
Loads applied by the road
Winter Quarter
Shearing
The fork is loaded
by a combination
of compression
shear and bending
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Lab 5
P. 5
Engineering H192 - Computer Programming
Data Acquisition System
Strain
Gage
Transducer
Winter Quarter
Wheatstone Bridge
+ Amplifier
Conditioning
Circuits
Recorder
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Data
Processing
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P. 6
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Transducer: Strain Gage
Backing Film
• Translates strain to
electrical resistance.
• Resistance increases with
length.
Grid
(electrical resistor)
Copper-plated
Solder tabs
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P. 7
Engineering H192 - Computer Programming
Strain Gages
• Resistance is Proportional to Length
R

R
or
R
S g 
R
Where: Sg is the “gage factor” and  is the strain.
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Lab 5
P. 8
Engineering H192 - Computer Programming
Strain Gages
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P. 9
Engineering H192 - Computer Programming
Conditioning Module: Wheatstone Bridge
• The strain gages are connected as the four
resistors in the Wheatstone Bridge.
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Engineering H192 - Computer Programming
Conditioning Module: Wheatstone Bridge
Vout  Vin  A  Sg  
Where:
Vin = 5.0 volts
 is the strain
A = 500 (amplification)
Vout is the change in the voltage
Sg = 2.085 (gage factor)
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Lab 5
P. 11
Engineering H192 - Computer Programming
Lab Experience: Part 1 – Static Test
• Part 1 – Static Test: Collect data for bicycle with
no load, with a rider sitting, and with a rider
pedaling.
• Part 2 – Dynamic Test: Collect data while
simulating the bicycle being ridden over
obstacles.
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Lab 5
P. 12
Engineering H192 - Computer Programming
Post-lab Requirements
• STATIC TEST:
– Plot strain vs. time and stress vs. time. Label
events on graphs (ex. “Rider 1 gets on”, “Rider 1
pedals”, etc.)
– Calculate average stress while pedaling for each
rider; plot vs. weight of rider.
– Plot raw voltage data vs. time.
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P. 13
Engineering H192 - Computer Programming
Post-lab Requirements
• DYNAMIC TEST:
– Plot stress vs. time. Label events on graphs.
– Modify assignment A13 to find min and max
stress.
– Compute ratios for each rider:
• Max stress dynamic : max stress static
• Min stress dynamic : min stress static
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Lab 5
P. 14
Engineering H192 - Computer Programming
Lab Memo Guidelines
• Individual memos.
• Follow formatting guidelines in “FEH Guide to
Lab Reports and Memos.”
• “Lab-specific requirements” not listed on the
rubric. You must determine what is appropriate
to include.
Winter Quarter
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Lab 5
P. 15