Stress/Strain Measurement
OPTI421/521L
Materials
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Aluminum beam (1ea)
Milling machine clamp (1set)
Ruler and/or Vernier calipers (1ea)
Strain gage (4ea)
Resistance (4ea)
Bread board (1 ea)
Power supply (1ea)
Digital volt meter (1ea)
Loctite (1ea)
Lead wires (1set)
Scotch tape (1ea)
Pencil (1ea)
Soldering iron and lead (1ea)
• Light Box (1ea)
• Acrylic beam (1set)
• Polarizer (1ea)
• Weight (1ea)
• Dowel pins and fixture (1set)
How to glue the a strain gage
• Locate where the strain gage to be
glued
• Where is the maximum strain observed in a
cantilever beam (or simply supported
beam)?
• Clean the surface using acetone
and alcohol then wait until the
surface is completely dry
• Mark the position where the strain
gage to be glued using a pencil and
ruler.
• Position a strain gage and apply a
piece of Scotch tape on it
temporarily
• Lift one end of the Scotch tape
until the strain gage is exposed
• Apply a drop of Loctite and press
the Scotch tape from a side
• Squeeze Loctite out to build a thin
bond layer
• Wait until the Loctite to be fully cured
• Peel off the Scotch tape from a side
and inspect the Strain gage
Strain Gage Lab
1. Check nominal gage resistance and
gage factor from the specification
• Gage resistance (Ω):
• Gage factor:
2. Measure the dimensions of the
aluminum beam
• Length (in):
• Width (in):
• Thickness (in):
3. Glue 4 strain gages on an aluminum
beam as a cantilever beam
• Two strain gages on each side
• Location of the strain gages from the
fixed(or supported) point of the beam
(in):
• Build a wheatstone bridge on the
bread board using given resistances
• Check voltage output between C and D
Strain Gage Lab
Quarter Bridge
Half Bridge
1.
Configure a Quarter bridge by substituting
R1 to one of strain gages
Measure Vout with no load condition
1.
Apply load by hanging a weight at the end
of the cantilever beam (or the center of
the simply supported beam)
2.
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3.
4.
5.
• R1 and R2 (R3 and R4) to the two strain gages on the
same side
• R1 and R3 (R2 and R4) to the two strain gages on the
opposite side
• Vout (V):
• Weight (lb):
Measure the deflection at the end of the
beam
• Deflection (in):
Measure Vout with no load condition
• Vout (V):
3.
Measure Vout under loading
• Vout (V):
Configure a Half bridge by substituting
Apply load by hanging a weight at the end of
the cantilever beam (or the center of the simply
supported beam)
• Weight (lb):
4.
Measure Vout under loading
• Vout (V):
5.
Measure the deflection at the end of the beam
• Deflection (in):
Strain Gage Lab
Full Bridge
Result
1.
• Apply the strain gage equation and find measured strain
2.
3.
Configure the Full bridge by substituting
R1~R4 to the strain gages
Measure Vout with no load condition
• Vout (V):
Apply load by hanging a weight at the end
of the cantilever beam (or the center of
the simply supported beam)
• Weight (lb):
4.
5.
Measure Vout under loading
• Vout (V):
Measure the deflection at the end of the
beam
• Deflection (in):
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Quarter bridge :
Half bridge :
Full bridge:
• Apply Stress-Strain relation to find measured stress
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Quarter bridge (psi):
Half bridge (psi):
Full bridge (psi):
• Write a beam equation and find the deflection under the
given loading condition
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Deflection (in):
Does it match to your measurement?
• Calculate the stress where the strain gages are using the
beam equation
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Stress (psi):
Does it match to your measurement?
Photo Elasticity
• Install the light box and polarizer
• Configure a cantilever beam using the
transparent Acrylic beam in front of the
light box
• Install the polarizer and observe the
pattern through the beam
• Take a photo
• Apply load by hanging a weight to the end
of the beam
• Install the polarizer and observe the
pattern through the beam
• Take a photo
• Show the two photos and discuss about
your observation
• Install the light box and polarizer
• Configure a simply supported beam using
the transparent Acrylic beam in front of
the light box
• Install the polarizer and observe the
pattern through the beam
• Take a photo
• Apply load by hanging a weight to the
center of the beam
• Install the polarizer and observe the
pattern through the beam
• Take a photo
• Show the two photos and discuss about
your observation