@ TQ Education and Training Ltd 2000
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Carefullycheckthe contentsof the package(s)againstthe list. If
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orTQ immediately.
TQ Education and Training Ltt:l
PE/ajp/O200
Products Divislolrl
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Contents
Section
1
INTRODUCTION
1
2
ASSEMBLY
How to Set up the Equipment
3
3
~I
TORSION TESTING
General Notes on Experimental Work
Detailed Procedure
5
USE OF THE TORQUE METER AND PROCEDURE FOR
CALIBRATION
Procedure for Checking the Calibration
Procedure for Full Calibration
7
7
7
5
EXPERIMENTATION
Notes on Laboratory Sheets
Object
Apparatus
Theory
Experimental Procedure
Results
Suggested Increments of Strain
Notes on the Content of the Laboratory Report
Items to be Included
Discussion of Results
9
9
9
9
9
9
9
9
9
10
10
6
TYPICAL EXPERIMENTAL RESULTS
The Bauschinger Effect
Upper and Lower Yield Strength of Mild Steel
Relationship between Torque and Surface Stress
Cast Iron
4
APPENDIX A
APPENDIX B
TORSION TEST SPECIMEN
THE TORSIOMETER
Introduction
Construction
Use and Operation of the Torsiometer
Use
Operation
5
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~t
11
11
11
11
12
A-1
A-2
A-2
A-2
A-2
A-2
A-2
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m
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'1:-
~-
The 8Ml Torsion TestingMachine enablesforward and
reversetests on standard6 mm TQ torsion specimens,
andother hexagonendedspecimensrequiring torquesof
up to 30 Nm. With additional chucks(optional extra) it
can alsobe usedfor testingwire up to a lengthof 0.7 m.
The apparatusis illustratedin Figure2.
The loads are applied manually through a 60:1
reductiongearbox.The torqueis reactedby a torsion bar
(as shownin Figure 3), whosemovement,relative to the
displacementarm, is measuredby a linear potentiometer
connectedto a TQ Digital Torque Meter. This mett:r is
suppliedas standardwith the apparatusand is calibnued
to give a readoutof torque in Nm or lb.in (seeSection4
on page7).
11
TQ Torsion Testing Machine
Torque
shaft
DeftectkJn
81m
gearboxoutput shaft and can be used for measurement
in the plastic range.A resettablecounteris also fitted to
the gearboxinput shaft to give an overall recordof input
revolutions(notethat one revolution represents6°).
Two pairs of hexagonalsocketsare providedfor
holding standard TQ specimens. These sockets fit on the
ends of the input and torque shafts as shown in Figure 2.
The two pairs of hexagonal sockets provided are:
- for all specimens(the smaller
.
3/16" Whitworth
.
sized sockets)
12 mm AF - these can be used for cast iron
specimensin order to accommodateany roughness
on the castends
Lk18ar
potentiometer
Figure3 End view of torque measurement system
The input rotation (the angle of twist of specimen)can
be measuredby three methods as in Figure 2. For
accuratereadingsin the elastic range a protractor scale
reading0.10is fitted to the input shaft of the gearbox.A
second protractor scale reading 10 is fitted to the
In somecasesit may be necessaryto removeexcessive
bumpsor flashing from specimensusing a file.
Accurate measurementof twist angles, and hence
strain, can be obtainedusing the TQ Torsiometerwhich
is an optional extra.
SECTION 2 ASSEMBLY
r
sufficient room to insert a specimenbetween the
sockets.
The apparatus is despatched fully assembled except for
the following:
(a) Adjustable feet (2 oft)
(b) Levelling handwheel and tie rod assembly
(c) Counter assembly
To assemble, first lift each end of the apparatus in turn
and screw an adjustable foot upwards into the
appropriate hole in each of the end castings (see Figure I).
Note that the plastic knob should point downwards and
that there is only one adjustable foot at each end of the
apparatus.
Next fit the levelling handwheel between the torque
arm and the lower bracket at the right of the apparatus.
Secure the tie rod ends in position by inserting the
screwed pins. Lock these in place by fitting the two split
s.
6.
pins provided.
Note: For safety reasons,the screwed pins must be
screwed fully in and the split pins must be fitted to
ensure that the joints do not work loose during
operation.
7:
Fit the counterassemblyas follows:
Set the deflection ann approximately level by
adjustingthe handwheel,then set the dial gau~;eto
read zero by rotating the outer bezel. Tap the
apparatuslightly andrecheckthe dial gauge.
Select the desired range on the Digital Nleter
(metric units or imperial). Setthe readingto zeroby
adjusting the ZERO adjusting knob at the rear of
the meter. Note that the meter is calibrated~:fore
leaving the factory, but if required the calibration
can be checked using the procedure given in
Section4.
If required, fit the Torsiometer to the specunen.
Insert the specimeninto one of the sockets,then
rotate the handwheeluntil the secondsocket will
slide freely onto the other endof the specimen.
1. Removeand retain the two cap headscrewslocated
on the top of the gearbox.
2. Placethe counteron the top of the gearboxwith the
cam follower lever resting on the carn of the
handwheel.
3. Secure the counter to the gearbox with the two
screwsremovedin step(1).
8.
How to Set up the Equipment
I. Levelthe rig on a suitablebenchby adjustingthe
two adjustablefeet.
2. Connectthe electrical lead from the output socket
on the right of the apparatusto the input socketat
the rear of the Digital Meter. Connectthe meterto a
mainssupplyand switch on.
3. Selectthe requireddrive socketsand fit them to the
input andtorqueshafts.
4. Loosen the two locking knobs on the gearbox
carriageand move the carriagealong the bed such
that, with the shaft fully to the left, there is just
r
Take up any free movement by slowly rotatin!~ the
handwheel clockwise until the Digital Meter
reading just changes (i.e. a reading of 0.1 Nm or
1.0 lb. in). Turning the handwheel clockwise ~~ives
forward loading of the specimen, and anticlockwise gives reverse loading.
9. Loosen the grubscrew on the scale, and positi,:>nit
in line with the cursor. Set the reading to zero and
lock the scale in position. Zero the counter by
turning the knob at the far end of the counter.
10. All zeros are now set and testing can commenc<~.
SECTION 3 TORSION TESTING
General Notes on Experimental Work
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The tests possible with Torsion Testing Machine
include the determinationof the upper and lower yield
strengthsfor nonnalisedsteel specimens,demonstration
of the Bauschingereffect, and other effects relating to
work hardening and heat-treatment. The detailed
procedureoutlined below should be followed in each
case in order to maintain consistent readings of
specimen twist using the scales provided. If a
torsiometeris used,or if high accuracyis not required,
there is no needto relevel the displacementarm before
each reading (i.e. there is no need to maintain a zero
readingon the dial gauge).This part of the procedureis
only necessaryin order to maintain the position of one
end of the specimen stationary whilst registering the
true angleof twist on the protractorscales.Omitting this
stepwill not affect the accuracyof the torquereadings.
It shouldbe notedherethat the protractorscalesonly
give an approximate measure of the twist of the
specimensince readingsinclude the twist of the drive
shaftsand specimenends,and also any slight movement
of the specimenendsin the drive sockets.Theseeffects
will be most significant in the elastic range where the
load increasesrapidly for only a small twist of the
specimen.If the modulusof rigidity is to be determined,
it is recommendedthat a torsiometershouldbe used.
Reverseloads are applied by turning the handwheel
anti-clockwise.Note that the Digital Meter readingwill
thenbe negative.
IMPORTANT
Always reduce the load to zero if it is required to
remove a specimen before failure (for exampIle,
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,through0.5° as indicatedby the dial.
2. Return the reading on the dial gauge to zero by
rotatingthe levelling handwheel.
3. Record the torque displayedby the Digital Meter,
noting the units and record the total angle of twist
from zero.
4. Repeatthe procedureasrequireduntil the specimen
hasyielded or until all points of interredhavel)een
covered.Note that in the plastic range, anglesof
twist can be incrementedto 6° or multiples of 6°.
For ductile specimens,incrementsof up to 60° may
be required, as some specimens require up to
revolutionsbeforefailure occurs.
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SECTION 4 USE OF THE TORQUE METER AND PROCEDURE FOR
CALIBRATION
The apparatusis suppliedcompletewith a Digital Meter
for torque measurementand this is calibrated before
leaving the factory. Four trimming controls are fitted to
the rear of the meterasfollows:
4. Removethe load and checkthat the meterretools to
zero.
Note: If the error is greaterthan 0.5 Nm (i.e. 2%)
the calibration should be adjusted using the CAL
screwat the rear of the instrunlentto setthe reading
to 24.5Nm when the load is 5 kg. For refer,ence
purpose,note that the calibration ann is 500 mm
long, hence5 kg gives 5 x 9.81 x 0.5 = 24.53Nm.
a. ZEROadjustmentknob - this is usedfor zeroing
the meter (if necessary) prior to applying load.
b. CAL screw - this can be used to adjust the
calibrationof the meterin the SI units mode.
c. SI/lMP ADJUST screw - this adjusts the ratio
betweenthe SI and IMPERIAL units as selectedby
the SI/IMP switch at the front of the meter.
d. DECIMAL POINTS - this can be usedto determine
the numberof decimalpointsdisplayed.
Controls (b) and (c) should not normally require
adjustment,but if adjustmentbecome necessarythis
shouldbe donewith care,asthe controlsaredelicate.
Procedure
r
for Checking
the Calibration
Deflection
arm "
5.
Procedure
2.
#_.
1"'3
3.
4.
Calibfation
arm
/
Dial
gauge
I.
Levelling
handwheel
Figure4 Meter calibration using the loading arm
1. For the calibration arm onto the squareend of the
torque shaft, then set the deflection arm
approximately level by adjusting the handwheel
(seeFigure4). Setthe dial gaugeto zero by rotating
outer bezel. Tap the equipmentlightly and recheck
the dial gauge.
2. SelectSI units and set the Digital Meter to zero by
adjusting the ZERO knob at the rear of the
instrument.
3. Add a load of 5 kg to the calibrationarm and return
the readingon the dial gaugeto zeroby rotating the
handwheel.Check that the reading on the Digital
Meter is 24.5 :to.5 Nm.
for Full Calibration
For most purposesit can be assumedthat the calibnltion
is linear and setting at one value of load is adeqLlate.
However,if required,the full calibrationover the whole
rangecanbe checkedasfollows:
I.
..,.
If it is requiredto use imperial units (lbf.ft), re'peat
the above procedurewith the units switch sc:t to
IMP and set the SI/IMP ADJ screw to give
17.96Ibf.ft.
S.
Set an initial zero condition as in steps(I) and (2)
in 'Procedurefor Checkingthe Calibration'.
Add weightsto the weight hangerin the increments
available (i.e. 500 g, I kg, 2 kg and a further :Zkg,
plus weight hangerat 500 g) and record the meter
readingat eachvalue up to 6 kg. Returndial gauge
to zero at eachstep,usingthe handwheel.
Reducethe load in the samestepsand againrecord
the meterreadings.
Plot a graphof meterreadingagainstappliedtorque
(which equals0.5 x load x 9.81 Nm). Draw a mean
line through the points and calculate the slOlle of
the line (ideally unity). If there is a significant t:rror,
apply a load of 5 kg, note the reading and divide
this by the averageslope, then reset the meter to
this new value.
The above procedure can then be repeate,:i,if
desired, to check that the resulting calibration is
correct.
It may be noted that the graph plotted in step (4) will
also show the linearity of the torque measuringsystem
and any hysteresiswhich is presentdue to stiction in the
torque shaft bearings.It will be found that both these
sourcesof error are mall, but studentsshould be aware
of their existenceand should commenton them in their
laboratoryreports.
SECTION 5 EXPERIMENTATION
r
The fonn of Laboratory Sheets and Reports quite
obviously will depend very much on the individual
lecturer and the type of experimentbeing carried out;
however for the more elementarywork the following
exampleserveas a guide for the studentoperator.
Notes on Laboratory Sheets
Using a Torsion Test to Destructionas an example,the
following is a suggestedlayout for a laboratorysheet.
Object
To carry out a torsion test to destruction in order to
determinefor a specimen:
(a) The modulusof rigidity
(b) The shearstressat the limit of proportionality
(c) The generalcharacteristicsof the torque, angle of
twist relationship.
Apparatus
Torsion Testing Machine and Torsiometer, steel rule
and micrometer.
Theory
From the generaltorsion theory for a circular specimen:
r
T
J
=
Ge
I
=-
't
r
where:
T= Applied torqueNm or lbfin
J = Polar secondmomentof areamm or in
G = Modulusof rigidity N/mm2of Ibf/in2
e = Angle of twist (over length)radians
I = Gaugelengthmm or in
t = Shearstressat radiusr N/mm2or 1bf/in2
r = Radiusmm or in
Experimental Procedure
I. Measurethe overall length and diameterof the test
sectionof the specimen.
2. Draw a line down the length of the test sectionof
the specimenwith a pencil; this servesas a visual
aid to the degreeof twist being put on the specimen
during loading.
3. Mount the specimenfinnly in the Torsion Testing
Machine. For each increment of strain record the
following:
(a) Angle of twist of the specimenin degrees
(b) Applied torque
(c) Angle of twist over the 50 mm gaugelength in
radians,asrecordedby the dial gaugeindicator
(d) When the elastic limit has been passed
continue to test to destruction with ever
increasingincrementsof strain, recording for
eachstrain increment:
]. Angle of twist in degrees
2. Applied torque
Note: In sometestsit may be found unnecessaryto use
the torsiometerafter the elastic limit has beenreached.
If this is the case,the torsiometercan be removedfrom
the specimenand readingsof twist can be taken din:ctly
from the machine scales.To remove the Torsiom'~ter,
unclampthe two cap screwssecuringit to the specimen
and slip each end clamp off the specimen.The end
clamps have been slotted for this purpose. It is not
possibleto remove the centre cylindrical spacerof the
Torsiometer as this would involve disturbing the end
fixing of the specimen,i.e. releasingit from the chuck.
This should be done under any circumstancesduring
test.
Results
Initial diameter of specinen
Final diameter of soedmen
Gauge length~ specinen
Initial overall length of spec"men
Final overall length of specimen
Tabulate the results under pressureheadings for the
elasticand non-elasticregions.
Suggested Increments of Strain
To ensure that an adequate number of values are
obtained from the test, particularly during the elastic
region of strain,the following is recommended:
Notes
on the Content of the Laboratory
Report
As in the caseof the LaboratorySheetthe contentof the
report will dependlargely on the type of test carrie<1
our
and the detailed investigatedrequired, but for a test
similar to that describedabovethe abovethe follo'wing
suggestionsare offered:
TQ Torsion Testing Machine
Items to be Included
Include in the report a dimensioneddrawing of the
specimen.Using the tabulated results plot a graph of
applied torque, T, againstangle of twist a as a basefor
the elastic region. Use the slope of this graph to
determine the value of the modules of rigidity. Also
from this graphdeterminethe torque,and then calculate
the shear stressat the limit of proportionality. Plot a
graph of applied torque against angle of twist of the
specimenasa base,for the completetest to destruction.
Discussion of Results
1. State,and commentupon, the valuesobtainedfrom
the test.
2. Commentupon the overall result obtainedfrom the
test.
3. Commentuponthe apparatusandprocedures.
4. Discuss the errors involved in determining the
modulus of rigidity using the angle of twist from
the machinedial, and comparethe results obtained
with the value found by usingthe Torsiometer.
SECTION 6 TYPICAL EXPERIMENTAL RESULTS
The Bauschinger Effect
When a metal bar is subjectedto torsional overstrain
and the load then removed,the load-freebar is full of
residualstresses.Thesestressesare of two kinds:
I.
Body stresses which affect a relatively large
volumeof metal (i.e. macrostresses),and
2. Textural stresseswhich are really the residual
stressesin betweenand within the crystals of the
metal causedby deformation of each crystal (i.e.
they are in the actualtextureof the metal).
greaterdIan dIe torque at G. This shift of dIe strength
range in dIe direction of dIe plastic defonnation is
sometimescalledthe 'BauschingerEffect'.
Upper and Lower Yield Strength
Mild StEtel
Normalised mild steel has the peculiar propert)' of
having an upper and lower yield strength.That is, the
initiation of yield occurs at a greater stress than the
propagationof yield alongthe bar.
Fortunately body stresses(which are beneficial) are
more stablethan textural stresses(which are harmful),
the latter being removed by a low temperatureheat
treatmentof 200°C.
This is demonstratedin Figure 6 where,after the ulitial
yielding of the specimen,point A, the load immediately
fallen to a lower value,point B. The strainreducesuntil
the specimenis again in the elastic range,point C, but
whenreloadedit yields at the lower yield strength,lJOint
D, showing that with mild steelthe yield propagatesat
the lower yield strengthstressvalue.
Figure5 Reversetorsiontests
Reversetorsion testsare possibleon the Torsion Testing
Machine, allowing residual stress phenomenato be
readily demonstrated,as shownin Figure 5. In the initial
load cycle the specimen yields at A, is plastically
defoTDledto B, then unloadedand plastically deformed
in the reversedirection to point C. It is then loaded in
the positive direction to point 0, unloadedand given a
low temperatureheat treatment, and then reloaded. It
now yields at F ratherthan O. Thus the harmful effects
of the textural stresses,which were removedby the heat
treatment,were equal to OF. The vertical distanceof
point F representsthe beneficial effect of the body
stresses.
If the material is now strainedto point E and then
strained in the reversedirection to point K (i.e. sight
negativeplastic strain). On reloading it arrives back at
the strainrepresentedby point E at a lower torque value
G. Thus, during the strain cycle the strengthrange has
moved in the negativedirection that is the torque at F is
Relationship
between Torque and Surlace
Stress
During both the elastic and plastic range of torsional
strain, the relationship betweenapplied torque, 7: and
the maximum shearstress,which occursat the surface
'tmax,is proportional to 1/d', the actual relationship
dependingupon the stressstrain characteristicsof the
material being tested. In the elastic range the precise
relationshipis:
't=
16T
-r
Jtd
Normally this relationshipfor stressis usedthrou~~out
the test, but in the plastic region. t is a nominal !;tress
and not the real stress.The real stressis less thw:l the
nominal stress.
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APPENDIX A TORSION TEST SPECIMEN
A standardrange of metric specimenscan be supplied
by TQ. Eachspecimenis stampedwith a codereference
andhasdimensionsas shownin Figure9.
Figure A 1 Standard torsion specimen
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For specimensof gauge 6", see catalogue order no.
TRIO6Oto TRIO85.
APPENDIX B THE TORSIOMETER
Introduction
The TQ Torsiometerhas been specianydesignedto fit
onto the standard test specimens listed above. The
Torsiometercan accommodatethe fun range of strain
by continual adjustmentof its dial indicator and can
thus be used to accuratelymeasurestrains in both the
elasticandplastic regions.
Construction
Note that an angulardisplacementon the dial gauge
representedby 0.001 of an inch is equivalent to an
angular displacementof 0.001 radian. This is because
the dial gauge plunger is exactly 1 inch from the
specimencentreline, acting on a circumferenceof 27t
radians in a circle the angular displacementshown on
the dial gauge in inches is therefore equivalent to
angulardisplacementin radians.
Use and Operation
A sectionalarrangementof the Torsiometeris shown in
Figure 10. It consists of two end clamps, which are
located axially by the centre cylindrical spacer.Each
end clamp containsa 90° conepoint socketheadedcap
screw, used to clamp the Torsiometer onto the
specimen. A gauge length of 50 millimetres is
maintainedbetween the two clamping screws by the
intermediatespacer.
The end clamps are slotted to facilitate easy
insertion and removal of the specimen.Each end cap
contains two hardened steel rollers to locate the
Torsiometercentrally onto the specimenwhen clamped
in position. The two componentparts of the end clamp
are held rigidly together by the knurled nut. The lefthand end clamp carries a dial gauge reading to an
accuracyof 0.00I of an inch. The plunger of the dial
gaugeis positionedexactly one inch from the centre of
the specimenand bears on the flat portion of a rod,
which is integral with right-hand clamp. This
positioning of the dial gaugerelative to the other over
its gaugelength will be representedon the dial gaugein
0.00I of an inch.
Use
The Torsiometershould be used where more accurate
measurementof strain over a precise gauge length is
desired.Strain can be measuredaccuratelyin both the
elasticand plasticregions,thus allowing the Modulus of
Rigidity to the determinedin the elastic region and also
providing very accuratemeansof measuringthe work
hardening properties of the specimen. To continue
readingon the dial indicator over theseregionsit will be
found necessaryto adjust the assemblyas describedat
the end of this section.
Operation
Placethe Torsiometeron the specimen.This is done in
three stages,referringto Figure A2.
I.
Pushone end of the specimenfirmly into the socket
mounted on the tailstock of the Torsion Machine.
Separate the Torsiometer into its three main
components - the two end clamps and the
cylindrical centrespacer.
Rod
I~"
End
cap'"
,I
End
,clamp
-1$1-
r ,
\
-'1~
1t"-T- ,/
End
.-" cap
.~
/
Cap
screw
End
clamp Centre
\
Knurled
of the Torsiometer
'Cap
screw
nut
spacer
Figure A2 Layout of the torsiometer
PageA-2
Ta Torsion Testing Machine
2.
[
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3.
Slide the cylindrical spacerover the specimenand
onto the spigoton the right-handend clamp.
Place the remaining end clamp onto the specimen
taking careto locatethe spigot on this end clamp as
far as possibleinto the openend of the spacer.Turn
the end lamp until the dial gaugeplunger contacts
the flat on the end of the rod. The dial gaugeshould
be in sucha position that the dial is clearly visible.
Hold the three componentstogether and ftTDlly
tighten the cap screw in the left-hand end clamp.
The spacershouldjust be free to rotate without any
end play. The whole assemblyfirmly fixes to the
test specimenand the tailstock can be slid alongthe
bed until the free hexagonend of the specimenis
insidethe headstocksocket.Lock the straininghead
in position.
The Torsiometeris now ready for use. Should the full
scaledeflection of the dial gaugebe insufficient at this
first clamp position of the rod it may be adjustedto
register further straining of the specimen by just
slackeningthe knurled nut and resettingthe position of
the rod. In this way the position of the TorsioI11leter
clampingon the specimenis in no way disturbed, and
continual adjustment throughout the whole loading
rangeis obtained.