@ TQ Education and Training Ltd 2000No part of this publication may be reproduced or transmitted inany form or by any means, electronic or mechanical, includingphotocopy, recording or any information storage and retrievalsystem without the express permission of TQ Education andTraining Limited.All due care has been taken to ensure that the contents of thismanual are accurate and up to date. However, if any errors arediscovered please inform TQ so the problem may be rectified.A Packing Contents List is supplied with the equipment.Carefully check the contents of the package(s) against the list. Ifany items are missing or damaged, contact your local TQ agentorTQ immediately.

TQ Education and Training Ltt:lProducts Divislolrl

PE/ajp/O200

ContentsSection

1 INTRODUCTION 1

2~I

3

ASSEMBLYHow to Set up the Equipment

3 5~'

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5

TORSION TESTINGGeneral Notes on Experimental WorkDetailed Procedure

4777

USE OF THE TORQUE METER AND PROCEDURE FORCALIBRATION

Procedure for Checking the CalibrationProcedure for Full Calibration

5 9999999991010

EXPERIMENTATIONNotes on Laboratory Sheets

ObjectApparatusTheoryExperimental ProcedureResultsSuggested Increments of Strain

Notes on the Content of the Laboratory ReportItems to be IncludedDiscussion of Results

6 1111111112

TYPICAL EXPERIMENTAL RESULTSThe Bauschinger EffectUpper and Lower Yield Strength of Mild SteelRelationship between Torque and Surface StressCast Iron

APPENDIX AAPPENDIX B

A-1A-2A-2A-2A-2A-2A-2

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TORSION TEST SPECIMENTHE TORSIOMETER

IntroductionConstructionUse and Operation of the Torsiometer

UseOperation

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(as shown in Figure 3), whose movement, relative to thedisplacement arm, is measured by a linear potentiometerconnected to a TQ Digital Torque Meter. This mett:r issupplied as standard with the apparatus and is calibnuedto give a readout of torque in Nm or lb.in (see Section 4on page 7).

The 8Ml Torsion Testing Machine enables forward andreverse tests on standard 6 mm TQ torsion specimens,and other hexagon ended specimens requiring torques ofup to 30 Nm. With additional chucks (optional extra) itcan also be used for testing wire up to a length of 0.7 m.The apparatus is illustrated in Figure 2.

The loads are applied manually through a 60: 1reduction gearbox. The torque is reacted by a torsion bar

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TQ Torsion Testing Machine

Torqueshaft

DeftectkJn81m gearbox output shaft and can be used for measurementin the plastic range. A resettable counter is also fitted to

the gearbox input shaft to give an overall record of inputrevolutions (note that one revolution represents 6).

Two pairs of hexagonal sockets are provided forholding standard TQ specimens. These sockets fit on theends of the input and torque shafts as shown in Figure 2.The two pairs of hexagonal sockets provided are:. 3/16" Whitworth - for all specimens (the smaller

sized sockets). 12 mm AF - these can be used for cast iron

specimens in order to accommodate any roughnesson the cast ends

In some cases it may be necessary to remove excessivebumps or flashing from specimens using a file.

Accurate measurement of twist angles, and hencestrain, can be obtained using the TQ Torsiometer whichis an optional extra.

Figure 3 End view of torque measurement system

The input rotation (the angle of twist of specimen) canbe measured by three methods as in Figure 2. Foraccurate readings in the elastic range a protractor scalereading 0.10 is fitted to the input shaft of the gearbox. Asecond protractor scale reading 10 is fitted to the

Lk18arpotentiometer

SECTION 2 ASSEMBLY

r sufficient room to insert a specimen between thesockets.

s.

The apparatus is despatched fully assembled except forthe following:

(a) Adjustable feet (2 oft)(b) Levelling handwheel and tie rod assembly(c) Counter assemblyTo assemble, first lift each end of the apparatus in turnand screw an adjustable foot upwards into theappropriate hole in each of the end castings (see Figure I).Note that the plastic knob should point downwards andthat there is only one adjustable foot at each end of theapparatus.

Next fit the levelling handwheel between the torquearm and the lower bracket at the right of the apparatus.Secure the tie rod ends in position by inserting thescrewed pins. Lock these in place by fitting the two splitpins provided.

6.

Note: For safety reasons, the screwed pins must bescrewed fully in and the split pins must be fitted toensure that the joints do not work loose duringoperation. 7:

Set the deflection ann approximately level byadjusting the handwheel, then set the dial gau~;e toread zero by rotating the outer bezel. Tap theapparatus lightly and recheck the dial gauge.Select the desired range on the Digital Nleter(metric units or imperial). Set the reading to zero byadjusting the ZERO adjusting knob at the rear ofthe meter. Note that the meter is calibrated ~:foreleaving the factory, but if required the calibrationcan be checked using the procedure given inSection 4.If required, fit the Torsiometer to the specunen.Insert the specimen into one of the sockets, thenrotate the handwheel until the second socket willslide freely onto the other end of the specimen.

Fit the counter assembly as follows:1. Remove and retain the two cap head screws located

on the top of the gearbox.2. Place the counter on the top of the gearbox with the

cam follower lever resting on the carn of thehandwheel.

3. Secure the counter to the gearbox with the twoscrews removed in step (1).

8. Take up any free movement by slowly rotatin!~ thehandwheel clockwise until the Digital Meterreading just changes (i.e. a reading of 0.1 Nm or1.0 lb. in). Turning the handwheel clockwise ~~ivesforward loading of the specimen, and anti-clockwise gives reverse loading.

9. Loosen the grubscrew on the scale, and positi,:>n itin line with the cursor. Set the reading to zero andlock the scale in position. Zero the counter byturning the knob at the far end of the counter.

10. All zeros are now set and testing can commenc

SECTION 3 TORSION TESTING

IMPORTANTAlways reduce the load to zero if it is required toremove a specimen before failure (for exam pIle,for heat treatment). DO NOT ATTEMPT TOREMOVE A SPECIMEN WHEN UNDERLOAD.r

Detailed Procedure1. For forward loading rotate the input handwheel

clockwise until the input shaft has rotated, forexample, through 0.5 as indicated by the dial.

2. Return the reading on the dial gauge to zero byrotating the levelling handwheel.

3. Record the torque displayed by the Digital Meter,noting the units and record the total angle of twistfrom zero.

4. Repeat the procedure as required until the specimenhas yielded or until all points of interred have l)eencovered. Note that in the plastic range, angles oftwist can be incremented to 6 or multiples of 6.For ductile specimens, increments of up to 60 maybe required, as some specimens require up torevolutions before failure occurs.

General Notes on Experimental WorkThe tests possible with Torsion Testing Machineinclude the determination of the upper and lower yieldstrengths for nonnalised steel specimens, demonstrationof the Bauschinger effect, and other effects relating towork hardening and heat-treatment. The detailedprocedure outlined below should be followed in eachcase in order to maintain consistent readings ofspecimen twist using the scales provided. If atorsiometer is used, or if high accuracy is not required,there is no need to relevel the displacement arm beforeeach reading (i.e. there is no need to maintain a zeroreading on the dial gauge). This part of the procedure isonly necessary in order to maintain the position of oneend of the specimen stationary whilst registering thetrue angle of twist on the protractor scales. Omitting thisstep will not affect the accuracy of the torque readings.

It should be noted here that the protractor scales onlygive an approximate measure of the twist of thespecimen since readings include the twist of the driveshafts and specimen ends, and also any slight movementof the specimen ends in the drive sockets. These effectswill be most significant in the elastic range where theload increases rapidly for only a small twist of thespecimen. 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 handwheelanti-clockwise. Note that the Digital Meter reading willthen be negative.

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SECTION 4 USE OF THE TORQUE METER AND PROCEDURE FORCALIBRATION

4.

5.

Remove the load and check that the meter retools tozero.

Note: If the error is greater than 0.5 Nm (i.e. 2%)the calibration should be adjusted using the CALscrew at the rear of the instrunlent to set the readingto 24.5 Nm when the load is 5 kg. For refer,encepurpose, note that the calibration ann is 500 mmlong, hence 5 kg gives 5 x 9.81 x 0.5 = 24.53 Nm.

If it is required to use imperial units (lbf.ft), re'peatthe above procedure with the units switch sc:t toIMP and set the SI/IMP ADJ screw to give17.96 Ibf.ft.

The apparatus is supplied complete with a Digital Meterfor torque measurement and this is calibrated beforeleaving the factory. Four trimming controls are fitted tothe rear of the meter as follows:a. ZERO adjustment knob - this is used for zeroing

the meter (if necessary) prior to applying load.b. CAL screw - this can be used to adjust the

calibration of the meter in the SI units mode.c. SI/lMP ADJUST screw - this adjusts the ratio

between the SI and IMPERIAL units as selected bythe SI/IMP switch at the front of the meter.

d. DECIMAL POINTS - this can be used to determinethe number of decimal points displayed.

Controls (b) and (c) should not normally requireadjustment, but if adjustment become necessary thisshould be done with care, as the controls are delicate.

Procedure for Checking the CalibrationDeflection

arm "

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Figure 4 Meter calibration using the loading arm

Levellinghandwheel

Procedure for Full CalibrationFor most purposes it can be assumed that the calibnltionis linear and setting at one value of load is adeqLlate.However, if required, the full calibration over the wholerange can be checked as follows:I. Set an initial zero condition as in steps (I) and (2)

in 'Procedure for Checking the Calibration'.2. Add weights to the weight hanger in the increments

available (i.e. 500 g, I kg, 2 kg and a further :Z kg,plus weight hanger at 500 g) and record the meterreading at each value up to 6 kg. Return dial gaugeto zero at each step, using the handwheel.

3. Reduce the load in the same steps and again recordthe meter readings.

4. Plot a graph of meter reading against applied torque(which equals 0.5 x load x 9.81 Nm). Draw a meanline through the points and calculate the slOlle ofthe line (ideally unity). If there is a significant t:rror,apply a load of 5 kg, note the reading and dividethis by the average slope, then reset the meter tothis new value.

S. The above procedure can then be repeate,:i, ifdesired, to check that the resulting calibration iscorrect.

It may be noted that the graph plotted in step (4) willalso show the linearity of the torque measuring systemand any hysteresis which is present due to stiction in thetorque shaft bearings. It will be found that both thesesources of error are mall, but students should be awareof their existence and should comment on them in theirlaboratory reports.

1. For the calibration arm onto the square end of thetorque shaft, then set the deflection armapproximately level by adjusting the handwheel(see Figure 4). Set the dial gauge to zero by rotatingouter bezel. Tap the equipment lightly and recheckthe dial gauge.

2. Select SI units and set the Digital Meter to zero byadjusting the ZERO knob at the rear of theinstrument.

3. Add a load of 5 kg to the calibration arm and returnthe reading on the dial gauge to zero by rotating thehandwheel. Check that the reading on the DigitalMeter is 24.5 :to.5 Nm.

Calibfation/ I.

arm

Dialgauge

SECTION 5 EXPERIMENTATION

The fonn of Laboratory Sheets and Reports quiteobviously will depend very much on the individuallecturer and the type of experiment being carried out;however for the more elementary work the followingexample serve as a guide for the student operator.

]. Angle of twist in degrees2. Applied torque

r Note: In some tests it may be found unnecessary to usethe torsiometer after the elastic limit has been reached.If this is the case, the torsiometer can be removed fromthe specimen and readings of twist can be taken din:ctlyfrom the machine scales. To remove the Torsiom'~ter,unclamp the two cap screws securing it to the specimenand slip each end clamp off the specimen. The endclamps have been slotted for this purpose. It is notpossible to remove the centre cylindrical spacer of theTorsiometer as this would involve disturbing the endfixing of the specimen, i.e. releasing it from the chuck.This should be done under any circumstances duringtest.

ResultsInitial diameter of specinen

Final diameter of soedmen

Gauge length ~ specinenInitial overall length of spec"men

Notes on Laboratory SheetsUsing a Torsion Test to Destruction as an example, thefollowing is a suggested layout for a laboratory sheet.

ObjectTo carry out a torsion test to destruction in order todetermine for a specimen:(a) The modulus of rigidity(b) The shear stress at the limit of proportionality(c) The general characteristics of the torque, angle of

twist relationship.

ApparatusTorsion Testing Machine and Torsiometer, steel ruleand micrometer.

TheoryFrom the general torsion theory for a circular specimen:

T Ge 't- = =-

J r

Final overall length of specimen

I

r where:Tabulate the results under pressure headings for theelastic and non-elastic regions.Suggested Increments of StrainTo ensure that an adequate number of values areobtained from the test, particularly during the elasticregion of strain, the following is recommended:

Notes on the Content of the LaboratoryReportAs in the case of the Laboratory Sheet the content of thereport will depend largely on the type of test carrie

TQ Torsion Testing Machine

Items to be IncludedInclude in the report a dimensioned drawing of thespecimen. Using the tabulated results plot a graph ofapplied torque, T, against angle of twist a as a base forthe elastic region. Use the slope of this graph todetermine the value of the modules of rigidity. Alsofrom this graph determine the torque, and then calculatethe shear stress at the limit of proportionality. Plot agraph of applied torque against angle of twist of thespecimen as a base, for the complete test to destruction.

Discussion of Results1. State, and comment upon, the values obtained from

the test.2. Comment upon the overall result obtained from the

test.3. Comment upon the apparatus and procedures.4. Discuss the errors involved in determining the

modulus of rigidity using the angle of twist fromthe machine dial, and compare the results obtainedwith the value found by using the Torsiometer.

SECTION 6 TYPICAL EXPERIMENTAL RESULTS

greater dIan dIe torque at G. This shift of dIe strengthrange in dIe direction of dIe plastic defonnation issometimes called the 'Bauschinger Effect'.

Upper and Lower Yield Strength Mild StEtelNormalised mild steel has the peculiar propert)' ofhaving an upper and lower yield strength. That is, theinitiation of yield occurs at a greater stress than thepropagation of yield along the bar.

The Bauschinger EffectWhen a metal bar is subjected to torsional overstrainand the load then removed, the load-free bar is full ofresidual stresses. These stresses are of two kinds:I. Body stresses which affect a relatively large

volume of metal (i.e. macro stresses), and2. Textural stresses which are really the residual

stresses in between and within the crystals of themetal caused by deformation of each crystal (i.e.they are in the actual texture of the metal).

Fortunately body stresses (which are beneficial) aremore stable than textural stresses (which are harmful),the latter being removed by a low temperature heattreatment of 200C.

This is demonstrated in Figure 6 where, after the ulitialyielding of the specimen, point A, the load immediatelyfallen to a lower value, point B. The strain reduces untilthe specimen is again in the elastic range, point C, butwhen reloaded it yields at the lower yield strength, lJOintD, showing that with mild steel the yield propagates atthe lower yield strength stress value.

Figure 5 Reverse torsion tests Relationship between Torque and SurlaceStressDuring both the elastic and plastic range of torsionalstrain, the relationship between applied torque, 7: andthe maximum shear stress, which occurs at the surface'tmax, is proportional to 1/ d', the actual relationshipdepending upon the stress strain characteristics of thematerial being tested. In the elastic range the preciserelationship is:

16T't= -r

Jtd

Normally this relationship for stress is used throu~~outthe test, but in the plastic region. t is a nominal !;tressand not the real stress. The real stress is less thw:l thenominal stress.

Reverse torsion tests are possible on the Torsion TestingMachine, allowing residual stress phenomena to bereadily demonstrated, as shown in Figure 5. In the initialload cycle the specimen yields at A, is plasticallydefoTDled to B, then unloaded and plastically deformedin the reverse direction to point C. It is then loaded inthe positive direction to point 0, unloaded and given alow temperature heat treatment, and then reloaded. Itnow yields at F rather than O. Thus the harmful effectsof the textural stresses, which were removed by the heattreatment, were equal to OF. The vertical distance ofpoint F represents the beneficial effect of the bodystresses.

If the material is now strained to point E and thenstrained in the reverse direction to point K (i.e. sightnegative plastic strain). On reloading it arrives back atthe strain represented by point E at a lower torque valueG. Thus, during the strain cycle the strength range hasmoved in the negative direction that is the torque at F is

r TORSION TEST SPECIMENAPPENDIX A~

For specimens of gauge 6", see catalogue order no.TRIO6O to TRIO85.

A standard range of metric specimens can be suppliedby TQ. Each specimen is stamped with a code referenceand has dimensions as shown in Figure 9.

Figure A 1 Standard torsion specimen.I

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APPENDIX B THE TORSIOMETER

Note that an angular displacement on the dial gaugerepresented by 0.001 of an inch is equivalent to anangular displacement of 0.00 1 radian. This is becausethe dial gauge plunger is exactly 1 inch from thespecimen centreline, acting on a circumference of 27tradians in a circle the angular displacement shown onthe dial gauge in inches is therefore equivalent toangular displacement in radians.

IntroductionThe TQ Torsiometer has been speciany designed to fitonto the standard test specimens listed above. TheTorsiometer can accommodate the fun range of strainby continual adjustment of its dial indicator and canthus be used to accurately measure strains in both theelastic and plastic regions.

ConstructionA sectional arrangement of the Torsiometer is shown inFigure 10. It consists of two end clamps, which arelocated axially by the centre cylindrical spacer. Eachend clamp contains a 90 cone point socket headed capscrew, used to clamp the Torsiometer onto thespecimen. A gauge length of 50 millimetres ismaintained between the two clamping screws by theintermediate spacer.

The end clamps are slotted to facilitate easyinsertion and removal of the specimen. Each end capcontains two hardened steel rollers to locate theTorsiometer centrally onto the specimen when clampedin position. The two component parts of the end clampare held rigidly together by the knurled nut. The left-hand end clamp carries a dial gauge reading to anaccuracy of 0.00 I of an inch. The plunger of the dialgauge is positioned exactly one inch from the centre ofthe specimen and bears on the flat portion of a rod,which is integral with right-hand clamp. Thispositioning of the dial gauge relative to the other overits gauge length will be represented on the dial gauge in0.00 I of an inch.

Use and Operation of the TorsiometerUseThe Torsiometer should be used where more accuratemeasurement of strain over a precise gauge length isdesired. Strain can be measured accurately in both theelastic and plastic regions, thus allowing the Modulus ofRigidity to the determined in the elastic region and alsoproviding very accurate means of measuring the workhardening properties of the specimen. To continuereading on the dial indicator over these regions it will befound necessary to adjust the assembly as described atthe end of this section.

OperationPlace the Torsiometer on the specimen. This is done inthree stages, referring to Figure A2.I. Push one end of the specimen firmly into the socket

mounted on the tailstock of the Torsion Machine.Separate the Torsiometer into its three maincomponents - the two end clamps and thecylindrical centre spacer.

Rod

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End,clamp

-1$1-End

cap'" -'1~ 1t"-T- ,/ End.-" cap

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/'Capscrew

Capscrew \

Knurlednut

Endclamp Centre

spacerFigure A2 Layout of the torsiometer

Page A-2

Ta Torsion Testing Machine

2.

[ 3.Slide the cylindrical spacer over the specimen andonto the spigot on the right-hand end clamp.Place the remaining end clamp onto the specimentaking care to locate the spigot on this end clamp asfar as possible into the open end of the spacer. Turnthe end lamp until the dial gauge plunger contactsthe flat on the end of the rod. The dial gauge shouldbe in such a position that the dial is clearly visible.Hold the three components together and ftTDllytighten the cap screw in the left-hand end clamp.The spacer should just be free to rotate without anyend play. The whole assembly firmly fixes to thetest specimen and the tailstock can be slid along thebed until the free hexagon end of the specimen is

inside the headstock socket. Lock the straining headin position.

The Torsiometer is now ready for use. Should the fullscale deflection of the dial gauge be insufficient at thisfirst clamp position of the rod it may be adjusted toregister further straining of the specimen by justslackening the knurled nut and resetting the position ofthe rod. In this way the position of the TorsioI11leterclamping on the specimen is in no way disturbed, andcontinual adjustment throughout the whole loadingrange is obtained.r:

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