EGH167 Hands-on Lab

## Lab 3: Stress And Strain

#### Introduction

##### Purpose

The purpose of this lab is to:

1.      Find a correlation between the weight of the bicycle rider and the stress/strain due to loading of the front fork.

2.      Observe the loading conditions in the front fork of a bicycle while being ridden, and to compute the maximum and minimum stress values

##### Lab Experience

The lab experience will encompass:

1)            Static Test using a bicycle rider on stand still, and

2)            Dynamic Test with various loading conditions with a bicycle rider while the bike is being ridden.

#### Lab Experience

##### Static Test: Goal

The goal in this part of the lab is to find a correlation between the weight of the bicycle rider and the stress/strain due to loading of the front fork.

##### Static Test: Procedure

1. Set up the data logger as described in the Quick Reference Guide. Record each rider’s weight.

2. Make sure that the initial output signal without a rider is near zero volts. Record the obtained value.

3. With the bike trainer attached to the bicycle, collect data with the data logger for each member of your group.  Use the following sequence to collect one set of data (all times are approximate). Do not stop the data logger between each step or between each rider.

• 5 seconds for an unloaded bike

• 10 seconds for rider 1 in riding position (no pedaling)

• 15 seconds for rider 1 pedaling

• Repeat for remaining team members

4. Upload your data from the data logger to the PC. Export your data as an ASCII file (consult the Quick Reference Guide) and save it on a diskette.

##### Dynamic Test: Goal

The goal in this part of the lab is to observe the loading conditions in the front fork of a bicycle while being ridden, and to compute  the maximum and minimum stress values.

##### Dynamic Test: Procedure

1. Select the lightest and heaviest person in your team. These two will ride the bike.

2. Set up the data logger as described in the Quick Reference Guide except set the sampling rate of the data acquisition system to 2 seconds (0.5 Hz). Use the “real-time data acquisition” mode to view the data collected by the data logger.

3. Make sure that the initial output signal without a rider is near zero volts. Record the obtained value.

4. With each rider sitting still, record the output signal (in volts). Record the weights of each rider.

5. Reset the data logger to have an acquisition rate of 50 samples/second.

6. Take the bicycle outside following the instructor’s direction and have both riders ride the bike for about 45 seconds each. Leave the bike sit unloaded between riders for a few seconds so you know when you switched riders.

7. Bring the bike back to the lab. Upload your data from the data logger to the PC. Export your data as an ASCII file (consult the Quick Reference Guide) and save it on a diskette.

#### LAB REPORT

##### Format

·  Lab reports must be done individually

·  Follow given lab report format.

·  Maximum 4-5 pages (including figures and tables)

##### General Guidelines

·  Cover page

·  Description of Experimental Apparatus

·  Introduction/Background

·  Description of tests. Obtain graphs and sketch test setups.

·  Static Test:

1. Plot the raw voltage data vs. time and identify each event on the graph, i.e. unloaded bike, rider 1 gets on, rider 1 sits on bike, rider 1 pedals bike, etc.

2. Calculate the strain and the stress at each data point.

3. Create a graph of stress vs. time.  Label your graph.

4. Using average value of stress for each rider in the riding position while pedaling, create a plot of stress vs. weight of each rider.  Create a linear trend line for the data and show the equation of the line on the graph.

5. Include sample calculations (calculating strain from voltage, calculating stress from strain).

·  Dynamic Test:

6. Plot raw voltage data vs. time.

7. Modify assignment D13 to plot stress vs. time. Determine the maximum and minimum peak stresses and the corresponding elapsed times when they occur. Document your program and tabulate the obtained results.

8. For each rider, compare the maximum and minimum stress values to the ones obtained from the static test. What is the ratio of the two quantities?

·  Analysis of results/Summary.