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Experimental
A
selection of cylindrical rods and tubes about 1.5 meters long
and of various diameters are provided.
One end of the sample is fixed to the
torsion testing apparatus and the other end is supported in a
bearing which
permits free rotation about the long axis of the tube. An arm holding a
scale pan can be
attached to this free end and the torque applied to the
sample is controlled by placing various weights in the scale pan.
The
expected rotation of the free end of the tube is small, and to increase the
observed magnitude of the deflection and facilitate its measurement, a diode
laser is mounted on the sample and the laser beam is allowed to fall on a scale
some distance from the laser. This optical lever amplifies the displacement
and permits a more accurate measurement of the deflection. Measure the distance
from the laser to the measuring scale and use this distance and the measured
deflection to compute the angle of rotation of the rod or tube. It may
help to place a paper screen on the wall and on this mark the position of the
beam for various loads both increasing and decreasing in value.
For
a given sample, compute the rotation of the rod at the laser location as a function
of the applied
torque. Enter your data into an Excel spreadsheet as
it is acquired and get the spreadsheet to plot the data points as they are
entered. If any points seem to behave in an unexpected way, repeat your data
taking or check the data entry.
Repeat this procedure for other laser
locations on a given sample, and with other samples. |
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