Operational Manual - DCU

SECTION 3 TORSION TESTING
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General Notes on Experimental Work
The tests possible with Torsion Testing Machine
include the determination of the upper and lower yield
strengths for nonnalised steel specimens, demonstration
of the Bauschinger effect, and other effects relating to
work hardening and heat-treatment. The detailed
procedure outlined below should be followed in each
case in order to maintain consistent readings of
specimen twist using the scales provided. If a
torsiometer is used, or if high accuracy is not required,
there is no need to relevel the displacement arm before
each reading (i.e. there is no need to maintain a zero
reading on the dial gauge). This part of the procedure is
only necessary in order to maintain the position of one
end of the specimen stationary whilst registering the
true angle of twist on the protractor scales. Omitting this
step will not affect the accuracy of the torque readings.
It should be noted here that the protractor scales only
give an approximate measure of the twist of the
specimen since readings include the twist of the drive
shafts and specimen ends, and also any slight movement
of the specimen ends in the drive sockets. These effects
will be most significant in the elastic range where the
load increases rapidly for only a small twist of the
specimen. If the modulus of rigidity is to be determined,
it is recommended that a torsiometer should be used.
Reverse loads are applied by turning the handwheel
anti-clockwise. Note that the Digital Meter reading will
then be negative.
IMPORTANT
Always reduce the load to zero if it is required to
remove a specimen before failure (for exam pIle,
for heat treatment). DO NOT ATTEMPT TO
REMOVE A SPECIMEN WHEN UNDER
LOAD.
Detailed
Procedure
1. For forward loading rotate the input handwheel
clockwise until the input shaft has rotated, for
example, through 0.5° as indicated by the dial.
2. Return the reading on the dial gauge to zero by
rotating the levelling handwheel.
3. Record the torque displayed by the Digital Meter,
noting the units and record the total angle of twist
from zero.
4. Repeathe procedure as required until the specimen
has yielded or until all points of interred have l)een
covered. Note that in the plastic range, angles of
twist can be incremented to 6° or multiples of 6°.
For ductile specimens, increments of up to 60° may
be required, as some specimens require up to
revolutions before failure occurs.
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