Experimental Procedures

1. Select an A36 steel bar, place two punch marks 12 inches apart in the center-most portion of the bar, and measure the diameter.
    
2. Put the bar in the torsion testing machine. Correct placement in the jaws is crucial.
    
   • Be sure the specimen makes full contact with the jaws of the testing machine
   • Be sure that the specimen and jaws are centered in the chuck and that the jaws firmly and uniformly grip the specimen.
   • The jaws are easily damaged if the specimen is only partly engaged.
      
3. Place the troptometer on the bar and measure the troptometer radius.  Do not forget to measure from the center of the bar.
    
4. Adjust the ruler on the troptometer to an even number, and zero the digital readout.  Remember that the bar will rotate as it is loaded, so try to insure that the troptometer pointer does not run off the scale during the test.
    
5. Record 10 arc-length readings in 100 in-lb increments of torque.
    
6. Continue, thereafter, recording torque values in 0.10 inch increments of arc length.
    
7. You may quit recording data when fully plastic torque has been clearly established.
    
8. Remove the troptometer.
   
9. Speed up the testing machine, and allow the bar to twist until failure.
    
   • Place a chalk mark along the length of the bar to help visualize the number of twists that will be required to fracture the bar.
   • Note the even distribution of permanent deformation along the full length of the bar.
   • Note the large amount of permanent deformation needed to fracture the bar.
   • At fracture, note the raised temperature of the bar and fracture geometry.
      
10. Try to record the ultimate torque at fracture.