TransverseVibration Loosening
Characteristicsof
High-StrengthFastenedJoints using
Direct TensionIndicators (DTIs)
July 1998
SPSContractResearch
Jenkintown,PA
TransverseVibration Testing
of M16 Class10.9
FastenerSets
Comparisonof fastenersetswith and without
Direct TensionIndicators(DTIs)
Introduction:
In recentyears,Direct TensionIndicators@TIs) designedfor usewith hexheadcapscrewsand
otherfastenersin the automotive,off-highway,andindustrialequipmentmarketshavebeen
introduced.AlthoughDTIs havebeenusedon structuralboltsfor over 35 yearsin dynamically
loadedstructuralapplicationssuchasbridges,buildings,power-plants,andcranes,researchis
waranted for evaluationof service-related
performance
characteristics
of the specificDTI types
usedin thesenew markets.
The"Junker's"transverse
vibration-loosening
testprovidesa simplifiedmethodfor broadscale
testingandinspectionof the transverse
vibration(loosening)propertiesof fasteners.Thetest
machineis ableto generaterelativemotionin the clampedpartsperpendicular
to the a:risof the
fasteners.The Junkersmethodprovidesquantitativeresultsrelatingthe variablesof clamp-load,
numberof cycles,andamplitude.Figure l. depictsa standardconfigurationfor the Junker's
transverse
vibration-loosening
apparatus.
toao cEu,
OJUSIASLE
Etc€rlER
P O I € N I I O X El E R
FOR
FOR
IN TTSY€RS€
loao
FOF
CEIL
Figure1. Junker'sTransverse
Vibration-Loosening
Apparatus
The Junkerstestis considereda 'severe'testof the looseningcharacteristics
of fasteners,
particularlywhencomparedto previouslyintroducedtestmethodswhich rely on axialdynamic
loadingto induceloosening.Junkerlargelyestablished
the viabilityof the currentmethodin a
paperentitled,'Investigationsof the Mechanismof Self-Loosening
andOptimalLocking of
BoltedConnections'.
Background:
This test programwasundertaken,in part,to addressquestionsraisedby OriginalEquipment
Manufacturers(OEMs)of over-the-road
trucks,who haveexpressed
interestin researchdata
joints
aboutthe potentialfor vibrationlooseningof fastened
with andwithoutDTIs.
A comparisontransverse
vibrationtest is designedto exposetwo or morefastenersetsto the
sametest parameters
to determinethe effectsof the differences.The presentresearchcompared
nut-bolt-washerassemblies
with nut-bolt-DTl assemblies.To betterunderstand
vibrationloosening,Junker'sprovidesus with modelsof boltedjoints understaticconditionsandunder
transversevibration. (SeeFigure2a and2b.)
, o , ,=r , [ ? t o n( - e . , f .
].
u]
Figure2a
BoltedJointunderstaticconditions
T o r ir ' r , - |
' t o nG t ) . - r , '
f
. t o ns
Figure2b
vibration
BoltedJointundertransverse
Resultsof transverse
vibrationJoosening
testsareusefulfor deploymentof bolting strategies
which reduceor preventthe risk of vibrationlooseningin service,or mitigateits effectswhereit
cannot be avoidedentirely. Accordingto GerhardH. Junker,originatorof this test,"(I)t is well
established
that a dynamicallyloadedjoint failsin mostcaseseitherby fatiguefailureor by
rotationlooseningof the fastener.Eventhe fatiguefailureis ofteninitiatedby partialloosening."r
TestProcedure:
Specimens
of plainfinishM16-2.0X 85mmClass10.9Hex HeadCapScrewswith matchingzinc
platedClass10Nylon InsertLock Nuts, andanclyellowplatedHardenedWasherswereprovided
by a majormanufacturer
of over-the-road
trucks. All testswere conductedon fastenersetsin the
'as-received'condition,without
the useof supplemental
lubricants.MatchingplainfinishClass
10.9Ml6 DirectTensionIndicatorswereprovidedby J&M Turner,Inc.oflanghorne,PA.
All testswere conductedat SPSContractResearchLaboratoriesin Jenkintown,PA. Each
fastenersetwastestedon the 1" capacitySPSTranverseVibrationMachine,whichis capableof
recording
clamp-loads
of up to 30,000lbs.(133kN).
Steelcouponswere fabricatedandusedto ensurea consistentbearingsurfacefor eachof the
tests.Testswereconducted'nut up', with a hardened
washer(or theDTI, whenonewasused,)
placedunderthe nut. The effectivegrip lengthof the fastenersetswas- 54mm.
Clampingforcewas generatedfor eachtestby turningof the nut until eachfastenersetwas
preloadedto 23,400]bs.,(104 tll), irrespectiveof the torquerequiredto tightenthe standardsets
or the flatnessof the DTI sets. For informationpurposes,sometorquereadingswererecordedin
orderto quantifyvariationin the nut factor 'K' of the fastenersets. The preloadat whichthe
testingstartedrepresents
the OEM's statedtargettension,equalto 80Yoof proof load.
The amplitudeof the transversedisplacement
was setat 10Yo.(i 0.063") of nominalfastener
diameterat a no-loadcondition. Eachfastenersetwastestedat a speedof 750 CPM for 80
secondsin orderto complete1,000transverse-vibration
cycles.
A chartrecorderis usedto plot clamp-loadvs. vibrationcyclesduringeachtest,thereby
permittingmoredetailedanalysisofthe results. Chartsof the clamp-loadvs. vibrationcurves
from the subjecttest programareattachedto this reportas"AppendixA". Cyclesareplotted
alongthe X-axis andthe clamploadof the fastenersetis plottedalongthe Y-axis.
Results:
Vibrationlooseningof the fastenersetswhich did not includeDTIs was clearlyevident.Retained
clamploadafter 1,000cyclesrangedfrom a highof 21,000lbs.to a low of 4,200lbs.Expressed
asa percent,clamploadlosswasbetweenl}oh and82Yo,averaging630/o.Themeanclampload
after 1,000cycleswas 8,660lbs.,or almosta third of the initial preload. Only onesamplefrom
the groupwithout DTIs retainedmorethan 50% of its initial clampload after 1,000cycles.
Exclusiveof this one specimen,
the remainingfastenersets requiredan average(mean)of 473
cyclesto reduceclampforceby 50%.
Vibrationlooseningof the fastenerssetswhichdid includeDTIs was noticeablylessthanthose
without. The differenceis clearlynotablewhenonecomparesthe resultsgraphicallyportrayedby
the chartrecorder. Retainedclampload after 1,000cyclesrangedfrom a hrghof 22,750lbs.to a
low of 20,900lbs. Expressedasa percent,clamploadlosswasbetween3o/o
andllo/o, averaging
8%. Themeanclamploadafter1,000cycleswas21,590lbs.All of the samples
from thisgroup
retainedmorethan(88%)of initialclamploadafter1,000cycles.
Conclusion:
Underthe conditionsof the subjecttest,therewasa significantdifferencein the lossof clampload
betweenfastenersetswith andwithout DTIs. Fastenersetswithout DTIs lost an averageof 63%
of their initial clampforce after 1,000cycles,contrastedwith an averagelossof only 8% in the
fastenersetsin whichDTIs were present.Underthe test parameters
andconditionsof the study,
DTIs appearto provideimprovedresistance
to vibrationJoosening.
The primaryfunctionofDTIs is, of course,to ensurethat properclampforce is attainedin bolted
connections.The scopeof this studydid not includedeterminingthe precisemechanism
whereby
the DTI connectionsaisoappeared
to demonstrate
superiorvibration-loosening
characteristics.
1 Nerv Criteria for Self-Looseningof FastenersUnder Vibration,
GerhardH. Jurker, EuropeanResearch&
Engineering.StandardPressSteelCo., UnbrakoKoblenz 1973
Summaryof Datafrom TransverseVibrationTests
Testson setswith no DTI
sample#
1
2
3
4
5
mean=
numberof
clampload
cyclesto
starting
after
50%original
clamoload 1000cvcles clampload
23,400
4.200
615
23,400
5.000
u5
23.400
5,000
255
23,400
2 1 ,OOO
NotAoplic.
23,400
8 . 10 0
475
23,400
8,660
473
total
clampload
lost(%)
82%
79%
79%
10%
65o/o
63%
Testson setswith DTI
sample#
1
2
3
4
5
mean=
numberof
clampload
cyclesto
starting
after
50%original
clampload 1000cvcles clampload
23.400
21.400
Not Applic.
23,400
22,750
Not Applic.
23.400
21,400
NotAoolic.
23,400
20.900
Not Applic.
23,400
21.500
NotApplic
23,400
21,590
Not Applic.
total
clampload
lost(%)
8o/o
3o/o
8o/o
11o/o
8o/o
8o/o
sP5
ITECHNOLOGIES
TO:
Test Certification
SPSLaboratories
J&MTurnerlnc.
340 E. MapleAvenue
Suite303
Langhorne,
PA 19047
Date:July23, 1998
CERTTFICATION
NO.980301
P . O .N O : 2 1
Attn:DavidSharo
Page1 of3
Transverse vibration
tests of ttli-6-2.0 x g5mm, crass l_0.9, plain
finish
hex head cap screws with zinc-plated
Class 1O nylon--insert
locknuts
and zinc-plated
washers suppried
by pACCAR. Ftain
finish,
Class L0.9, size M16 Direct Tension fnd.icators
and plain
finish
nonlocking
hex nuts were provided
by customer.
Test
Parameters:
Test Machine: one inch diameter,
30,ooo lbs. capacity,
test machine
rfNut-up", washer (or DTr) located
Joint
orientation:
Grip Length:
45 mm
Bearing Surface under Bolt head: rnild steel
Machine frequency:
750 cycles per minute
Seating Torque: various
as specifed
Test Duration:
1000 cycles
Test Anplitude:
various
as specified
rras-receivedrt
Lubricant:
Parts tested
Test
Junkers
under
nut
Program:
The folLowing
tests were performed based on authorization
of
David sharp.
clampload vs. test
cycle plots
furnistred
under
separate
cover.
S u b s c r i b e da n d s w o r n
Mr.
HighlandAvenue
Jenkintown
P e n n s y l v a n i a1 9 0 4 6
( 2 1 55) 7 2 - 3 0 0 0
Fax 1215\572-3193
Telex:83-4254
No
-T'€g\'S
Vf3:
No DTI
NO DTI
\:s
No DTl.
I
i-Esr *1
-a1-., -?
;d
"^ir
.rt
vE..&.
With DTI
D\=-.}rdt
-rs'\o
\ 6 ' g
V \ I
J J F
I W '
Dtr
.J".M
si