Safety Info

• Safety glasses are required at all times while equipment is turned on.   Not only are safety glasses a good precaution, they prepare students for industry where they are also required.
• Face shields should be used when working close to failing specimens

• Dial calipers
• Instron 4400R testing machine or Instron 4485 testing machine

Procedure

[excel data sheets] right-click, save target as

Each of the 30 specimens will be tested in compression, parallel to the grain, until failure.

1. Before leaving your table, number specimens from 1 to 30, measure and record dimensions with dial calipers.  Enter data in Table 1-1.
2. Use either the Instron 4400R or  Instron 4485 machine.  At the testing machine, verify load application speed of 0.25 inches/minute.
3. Place the specimen in the testing machine and apply load until failure.

Hint: Get the names, email addresses and phone numbers of the students in your lab group, as well as your TA.  Use FirstClass email to send data to everyone and distribute contact information.

Include the following in the results section of your report:

[see the videos on how to do it in MS Excel]

[detailed written instructions on how to do it in MS Excel]

1. Compute the stress at failure (s , in psi) for each specimen.

   The stress at failure equals the load at failure (L, in lbs.) divided by the specimen's cross-sectional area (A, in in²), thus:

   s = L /A

2. Give the range (minimum and maximum) of failure stresses.
3. Compute the mean of the failure stresses.

   Rm = (R1+R2+R3+ ...... + R30)/30

   Rm = mean failure stress
   R1 - R30 (Ri) are the individual failure stresses.

4. Using Table 1-1, compute the standard deviation and coefficient of variation of the failure stresses.

   Standard deviation =

   in which n = sample size = 30 data points

   Coefficient of variation = (Standard deviation)/Rm
    

5. Complete Table 1-2 to create the data to plot the histogram
   
   a.  In the first column list failure stresses (Ri) sorted from lowest (top) to highest (bottom). 
   
   Calculate a suitable number of intervals (whole number larger than the equation below generates) for the data range for plotting a histogram. 
   
   # intervals = 1+3.3 x log(n), say 6
   
   Divide the range of Failure Stress data by the # of intervals and round to a nice even interval size number (like 500 lbs.)
   
   interval size = (max fail stress - min fail stress) / # intervals
   
   Create a table of Interval and Frequency data. 
   The interval is a label (like 2500 - 3000 lbs.).
   Frequency is the number of Failure Stresses that occur within that interval - just count them manually.
    
6. Plot a histogram of your results.

Reference