Stress/Strain Measurement

1. Stress/Strain Measurement OPTI421/521L

2. 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)

3. 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

4. Strain Gage Lab • Check nominal gage resistance and gage factor from the specification • Gage resistance (Ω): • Gage factor: • Measure the dimensions of the aluminum beam • Length (in): • Width (in): • Thickness (in): • 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

5. Strain Gage Lab Quarter Bridge Half Bridge 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 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): Measure Vout under loading Vout (V): Measure the deflection at the end of the beam Deflection (in): • Configure a Quarter bridge by substituting R1 to one of 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): • Measure Vout under loading • Vout (V): • Measure the deflection at the end of the beam • Deflection (in):

6. Strain Gage Lab Full Bridge 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? • 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): • Measure Vout under loading • Vout (V): • Measure the deflection at the end of the beam • Deflection (in):

7. 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