Lab 5P. 1

1
Stress and Strain

• Lab 4

2
Objectives

• To understand how engineers compare different
  materials.
• To understand how a strain gage works.
• To collect and analyze experimental data.

3
Stress vs. Strain
4
Measuring Load on a Bicycle Fork
Loads applied by rider
STRAIN GAGE A sensor that measures strain
5
Loads on a Bicycle Fork
6
Data Acquisition System
Wheatstone Bridge Amplifier
Data Processing
Conditioning Circuits
Transducer
Recorder
7
Transducer Strain Gage

• Translates strain to electrical resistance.
• Resistance increases with length.

8
Strain Gages

• Resistance is Proportional to Length

or
Where Sg is the gage factor and e is the
strain.
9
Strain Gages
10
Conditioning Module Wheatstone Bridge

• The strain gages are connected as the four
  resistors in the Wheatstone Bridge.

11
Conditioning Module Wheatstone Bridge
Where
Vin 5.0 volts A 500 (amplification) Sg
2.085 (gage factor)
12
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.

13
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.

14
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

15
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.