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Stress and Strain. Lab 4. To understand how engineers compare different materials. To understand how a strain gage works. To collect and analyze experimental data. Objectives. Strain: . Stress:. Hooke’s law:. Where: E = Modulus of Elasticity s = stress e = strain.

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## Stress and Strain

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**Stress and Strain**Lab 4 Winter Quarter**To understand how engineers compare different materials.**To understand how a strain gage works. To collect and analyze experimental data. Objectives Winter Quarter**Strain:**Stress: Hooke’s law: Where: E = Modulus of Elasticity s = stress e = strain For the bike fork material E = 29.0 x 106 psi. Stress vs. Strain Winter Quarter**Measuring Load on a Bicycle Fork**Loads applied by rider STRAIN GAGE A sensor that measures strain Winter Quarter**Loads applied by rider**Compression Shearing Bending The fork is loaded by a combination of compression shear and bending Loads applied by the road Loads on a Bicycle Fork Winter Quarter**Strain**Gage Data Acquisition System Wheatstone Bridge + Amplifier Data Processing Conditioning Circuits Transducer Recorder Winter Quarter**Translates strain to electrical resistance.**Resistance increases with length. Backing Film Grid (electrical resistor) Copper-plated Solder tabs Transducer: Strain Gage Winter Quarter**Strain Gages**• Resistance is Proportional to Length or Where: Sg is the “gage factor” and e is the strain. Winter Quarter**Strain Gages**Winter Quarter**Conditioning Module: Wheatstone Bridge**• The strain gages are connected as the four resistors in the Wheatstone Bridge. Winter Quarter**Conditioning Module: Wheatstone Bridge**Where: Vin = 5.0 volts A = 500 (amplification) Sg = 2.085 (gage factor) Winter Quarter**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. Winter Quarter**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. Winter Quarter**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 Winter Quarter**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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