Stress/Strain Measurement

OPTI421/521L

Materials

• 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 Bridge1. Configure a Quarter bridge by substituting R1

to one of strain gages2. Measure Vout with no load condition

• Vout (V):

3. 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):

Half Bridge1. Configure a Half bridge by substituting

• 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

2. Measure Vout with no load condition• Vout (V):

3. 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 Bridge1. Configure the Full bridge by substituting

R1~R4 to the strain gages2. Measure Vout with no load condition

• Vout (V):

3. 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):

Result• Apply the strain gage equation and find measured strain

• Quarter bridge :• Half bridge :• Full bridge:

• Apply Stress-Strain relation to find measured stress• Quarter bridge (psi):• Half bridge (psi):• Full bridge (psi):

• Write a beam equation and find the deflection under the given loading condition• Deflection (in):• Does it match to your measurement?

• Calculate the stress where the strain gages are using the beam equation• 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