32
SC-184 Exhaustion of Ductility in Compressed Bars with Holes by S. KABAYASHI and C. MYLONAS SHIPSTRUCTURECOMMITTEE
SC-184
Exhaustion of Ductility in Compressed
Bars with Holes
by
S. KABAYASHI and C. MYLONAS
SHIPSTRUCTURECOMMITTEE
SHiP STRUCTURE COMMITTEE
MEMBER AGENCIES:u.,, ,. STA T., .0$., , .(,...
..v. i...., 5YSI-. MS cot.w...MILITARY SEA TRANSPOI?TAT!ON ,,!7”,.,MA. IT!ME A.MINISTRATION
.)4,. 1... ,“, ?.,. OF S,,,,.(.C,
ADDRESS CORRESPONDENCE To:s, ...,..,,>{,, ,,. UC, ”RE CO MM, T7. ,U.S. COAST GUARD HE AD O”A17TERS
WL?5H,. G,- O., 0... 2059t
June 1!168
Dear Sir:
Th is prcject is being conducted under the adi,iSOI-!/ gui d-ance of trie Ship Hull ReseEIrc!ICommittee of the National Academy ofSciences-!\!ational Research CoLinci“1.
7}Ii!,report. is being distributed to individual~ and groupsassociated with or intere:,ted in the ~ork of’ the Ship Structure Com-mittee. fCcjnmentsconcerning this re~jort are sol icited.
Sincerely your-s,
d.b. /&D. PI. HendersonRear Admiral , U. S. Coast GuardChdirman, Ship Structure
C.ommittee
SSC - 184
Sixth Progress Report
on
Project SR - 158
“Macrofracture Fundamentals”
to the
Ship Structure Committee
EXHAUSTION OF DUCTILITY IN COMPRESSEDBARS WITH HOLES
by
S. Kobayashi and C. Mylonas
Brown UniversityProvidence, R. I.
under
Department of the NavyNaval Ship Engineering Center
Contract Nobs 88294
U. S. Coast Guard HeadquartersWashington, D. C.
June 1968
Abstract
Thebritt’
compressiveprestra
enessofmildsteelsubjectedtotensionafterpriorninghasbeeninpartattributedtothecollapseof
microscopicflawsorvoidsandtotheresultingseverestraining,work
hardening,andsharpeningofthe flawedges.A similarmechanismof
embrittlementshouldoperatealsowithartificialmacroscopicflawssuch
asholes.ThiswascheckedwithtestsofaxiallycompressedbarsofABS-B
andofE-steelwithtransversepre-or post-drilledsingleor double
holes.Theoverallnominalcompressiveprestrain(exhaustionlimit)caus-
ingbrittlenessinsubsequenttensioninbarswithpre-drilledholeswas
about1/4thecorrespondingprestrainforsolidbarsofE-steelandabout1/2forABS-Bsteel.Thepossiblecausesofthisdifferenceandthemodes
offractureinitiationandpropagationarediscussed.Thestrongdiffer-
entiationofsteelqualityachievedwiththesetestsisverypromisingfor
thedevelopmentofa relatedacceptancetest.
CONTENTS
EMBRITTLEMENTBYPRESTRAINING
TESTSWITHFLATTENEDHOLES
a. Barswithtwotransverseholesdrilledbeforecompression
b. Barswith0.031in.holesdrilledafteruniformcompression
c. Barswithpre-drilledparallelorblindholes
CONCLUSION
ACKNOWLEDGMENT
REFERENCES
Page1
3
3
15
16
20
21
21
SHIPSTRUCTURECONMITTEE
TheSHIPSTRUCTURECO15MITTEEisconstitutedtoprosecutearesearchprogramto improvethehullstructuresofshipsbyanextensionofknowledgepertainingtodesign,materialsandmethodsofFabrication.
RADMD.B.He~derson,USCG- ChairmanChief,OfficeofEngineeringU.S.CoastGuardHeadquarters
CaptainR.T.Miller,USN Mr.E.ScottDillonHead,.ShipEngineeringDepartment Chief,DivisionofShipDesignNavalShipEngineeringCenter OfficeofShipConstruction
MaritimeAdministrationCaptainT.J.Banvard,USNMaintenanceandRepairOfficerMili’cary”SeaTransportationService
Mr.D.B.Bannerman,Jr.VicePresident- TechnicalAmericanBureauofShipping
SHIPSTRUCTURESUBCOMMITTEETheSHIPSTRUCTURXSUBCOMMITTEEactsfortheShipStructureCommitteeontechnical
mattersbyprovidingtechnicalcoordinationforthedeterminationofgoalsandobjectivesof theprogram,andbyevaluatingandinterpretingtheresultsintermsofshipstructuraldesign,const~uctionandoperation.
NAVALSHIPENGINEERINGCENTER OFFICEOFNAiALRESEARCHMr.J.,J.Nachtsheim- Chairman Mr.J.M.Crowley- MemberMr.JohnVasta- ContractAdministrator Dr.Wm.G.Rauch- AlternateMr.GeorgeSorkin-MemberMr.IvoFioriti- Alternate MILITARYSEATRAPISPORTATIONSERVICLMARITIMEADMINISTR4TION LCDRDonaldB.Bosley,USN-MemberMr.R;W.Black- Member Mr.R.R.Askren- MemberMr.”Ana’EoleMaillar- Member U.S.COASTGUARDMr.R.Fall~-.AlternateMr.W.G.Frederick- Alternate CDRC.R,Thompson,USCG-Member
Mr.J.B.Robertson,Jr.-MemberAMERICANBUREAUOFSHIPPING LCDRJamesL.Howard,USCG- AlternateMr.G.F.Casey- Member LCDRR.Nielsen,Jr.,USCG- AlternateMr.F.J.Crum-Member
NAVALSHIPRESEARCH& DEVELOPMENTCENTERMr.
NATIONALACADEMYOFSCIENCES-NATIONALRESEARCHCOUNCIL
A.B.Stavovy- Alternate
LIAISONREPRESENTATIVES
BRITISHl~AVYSTAFFMr.A.C.Law
lip.A.R.Lytle-Director,ShipResearchCommittee ConstructionCD~T.R.Rumens,RCNC
Mr.R.W,Rumke-ExecutiveSecretary,SRC wELDINGRESE~.RCHCOUNCILMr.K.K.~\~ERICANIR(JNANDSTEELINSTITUTE Koopman,DirectorMr.CharlesLarson,Asst,Director
Mr.J.R.LeCron
A reductionoftheinitial
or hotstraininghasbeenshown
ductilityofsteelbysuitablepriorcold
inearlierpapersto be an importantcause
ofbrittlefractureinitiationundersubsequenttension.Inparticular
precompressionofnotchedmildsteelplateshasresultedinfracturein
subsequentstatictensionatloadsaslowas10%oftheloadlimitforgen-
eralyielding[1-5].Uniformaxialprestrainingofsmoothbarsbyabout
0.65ormorewhencold(700F)orabout0.52whenhot(600°F)causeda sud-
dendropofthereductionofareaatfracturefrom0.80ormoretoabout
0.02[3,6,7].Prestrainingincompressionbybendingfollowedbytension
inreversedbending[3,4,7-10]showedembrittlementaftercoldprestraining
ofabout0.50,orafterhotprestrainingofabout0.25.Inallinstances
theductilitywasreducedonlywhentheprestrainreacheda narrowlydefined
value,theexhaustionlimit,butremainedalmostunimpairedatsmallerpre-
st~ains.Lighterprestraining,however,canalsocausebrittlebehavior
whenaggravatedbynotches.Barswithdeepcircumferentialgroovesmachined
afteruniformprestrainingshoweda rapidreductionoffractureelongation
atprestrainsaslowas0.05[6].
Theimportanceofthephenomenonofexhaustionofductilitybysuitable
p~estrainingismadeevidentbynumerousbrittlefracturesofstructuresin
service,whichhavebeenfoundtostartatstressconcentrationswithincold
workedregionsorclosetoweldswhereseverehotstraininghadoccurred.In
generaltheductilityofthesteelwasfoundtodependonthewholehistory
ofstrain(includingtemperature)aswellasontheconditionsatfracture
(stress,strainrate,temperature,etc.).Fewtypesofcontrolledprestrain
2
htstoryhavebeentyiedbecauseofconsiderableexperimentaldifficulties.
Ofthosetested,precompressionseemstobethemostembrittlingina sub-
sequentreversaltotensioninthesamedirection,butnotina transverse
tension[11].Oneexplanationhasbeensuggestedatpastmeetingsofthe
ShipHullResearchCommittee[12].Precompressionflattenspre-existing
flawsorvoids,sharpeningthenotcheswithaxisperpendiculartothedi-
rectionofprecompressionandbluntingthosewithaxisparallel.The
sharpernotchesarealsowork-hardenedincompression,andtheyareat
rightanglestotheappliedtensionparalleltotheprecompression,hence
giverisetoveryhighlocalstresses.Onthecontra~y,thesharpened
notchaxesareparallelandthebluntededgesperpendiculartoanapplied
transversetension,hencebotharerelativelyinoffensive.Ina studyof
thepossibleexplanationsofmacroscopicpropertiesbasedona continuum
approach,D.C.I)rucker[4]discussesthemechanismofflawsharpeningby
precompression.Heshowsthattheresultingstrainingandhardeningdoes
explaintheobservedbehavior.Healsoexplainswhyprestrainingintor-
sioncauseslessembrittlementthanircompression.Itisinterestingto
notethatini?iallyoblateflawswiththeirlargedimensionnormaltothe
precompressionmaycloseupandavoidfurtherlocalwork-hardening.Con-
verselyoblongflawscompressedalongtheirlengthmaynevergettobetoo
sharp,andstartingwitha smallfactorofstressconcentration,maynever
causemuchworkhardening,exceptatextremelylargeprestrains.Theshape
oftheworseflawwillliebetweenthetwoextremesandwillcausethewomse
combinationofhighstrainingandnotchsharpening.
Alltheabovemaybeextendedtothecaseofa flawwithinthestrained
reg?onofa largerflawwithonlya substitutionofthestrainatthelarge
flawfortheoverallmacroscopicstrain.Itmaybenecessarytoconsider
3
alsothesizeofthestrainedregionandof-thehighlystressedregion,
andtheirdistributiondensitywhenseveralexist.Thesizeeffectin
brittlefracturehasbeendisputed[13],buttheproblemissomewhatbe-
cloudedbythedifferencebetweeninitiationandpropagationoffracture
[2,5,14].
TestswithFlattenedHoles
Theexplanationofembrittlementbyprecompressionasduetotheflat-
teningofholeswascheckedbytestsofspecimenscontainingcontrolled
knownflawsorcavities.A generalstudywithvariouscavityshapesand
sizesdidnotappearpossible,butmeaningfullimitedtestscouldbedone
withdrilledcylindricalholes.Theroundhole,thoughprobablynotthe
JJworstltshape, is in~ermediate to theoblongandoblate,andthecY~indri-
calformensurestheconstraintseverityofplatesfrainfor,thelocal
straining.Eveniftheholesapenotthemostdamagingcavities,theydo
causemuchlargerlocalcompressivestrainingandworkhardeningthanthe
averageinthespecimenandgive~isetohighstressconcentrationinten-
sion,hencetheyshouldintensifythedamageandcausebrittlenessatlower
overallstrains.
Threetypesoftestsweremadewithbarsof0.75in.squarecross-
sectionand9 in.lengthcutinthedirectionofrollingof0.75in.thick
platesofABS-BandofE-steel(compositionandpropertiesinTableI).
a. Barswithtwotransverseholesdrilledbeforecompression.Onehole
wasperpendicular,theotherparalleltotheas-rolledsurfacesandfar
enoughnottoaffectthefirst(Fig.3,inset).bothof0.031in.dia.The
4
TABLE1. TYPICALCOMPOSITIONANDPROPERTIESOFSTEELS.
II I IUltimateIElon~ationI CharpvI< Element,percent Yield Tensile per’ten? Impa;t
m StrengthStrengthIn Tenp.z In Ft-de+
c Mn P s Si Cn Ni Cr Mo psi psi 8in.2in.lb Fah@.
E 0.200.330.0130.0200.010.180.15 0.09 0.02 32 000 65 000 36 30 15 55to to3.3 -11
0.141.040.0110.0180.0560.0830.0230.031 33800$ 58400 33 20 18to to
ABS-B 10 -5
0.150.940.0090.0270.0460.094O.OQO0.023 35700 59800 32 20 11to to10 -11
—-...—-——.— .-—.--—-—-,----------------———---
bar-swereprestrainedaxiallyin
scribedinanearlierpaper[31,
300°Fandmachinedintostandard
thentestedintensionat-160F.
compressionatabout700Fina machined@-
wereartificiallyaged
0.505in.dia.tension
Theresultsaregiven
ure1 forARS-BsteelandinTable111andFigure2 for
for90minutesat
specimens,andwere
inTable11andFlg-
E-steel,
Nominalprestrainsupto0.60(lengthcompressedby60%:naturalstrain
-0.92)wereappliedtoABS-Bandupto0.30(naturalstrain-0.36)toE–steel
bars,Thest~ainnon-uniformityaroundi-heholeswascheckedwithmeasure-
mentsofthedeformationofscribed1/4in.squarescenteredontheholes
(Fig.3,inset)andwithm;crophotographsoftheflatteningoftheholes.The
changeofholediameteralongthebarwasmuchgreate~butproportionalwith
theappliednominalprest~ainuptoabout0.18-0.20,whentheholesclosedup
(uppertwocurvesofFig.3). Thecurvesoftransversediameterexpansion
showeda gradualchangeofslopeatthesameprest~ainofabout0.20andin-
creasedrapidlyatprest~ainsofabout0.k5to0.60.Thecu~vesoflateral
expansionoverthe1/4in.grids,parallelandacrosstheinitialplatethick-
ness(twolowercurvesinFig.3)matchedreasonablywelltheoverallexpan-
s;oncurvesofABS–Bbarswithoutholesgiveninanearlier~eport[6],except
—
51
0 PRESTRAINEDWITHOUTHOLESI50- ● PRESTRAINEDWITHHOLES 0.5
x FLATTENEDMOLESF!EDRILLED
I 1 I Io
x 8 0.4125– 0
xm 0w O*cca Id
● zG ● ~o,3u:* 8“”
uuu~100
[
ua 9 +<LO: z0.2cc G~ E
●k
Id
t
J~ 75 -#u ~ 0.1/ ~“z ~?a Uo.1, A z
/x/
/
I I I I 1 Io
00
Xo0●
● ● ✌
0
●
,0U+-+-JJ 01 1 IX*. h0.6NOMINAL o 0.2~1 1 I 1 I I I
o 0.2 0.4 0.6 0.8 NATURAL o 0.2 0.4 0.60.8COMPRESSIVEPRESTRAIN COMPRESSIVEPRESTRAIN
z~.mmNE2
OMINAL
IATuRAL
Fig.1. ABS-BSteelBam JFLthHolesComp~eszwiandAgedTe6tedInTensionAt-16°F.
I10 I0 PRE5TRA1NE0WITHOUTHOLES.PRESTRAINEDWITHHOLES
1 I I I
~ 105— o 0
Jcc>F-UurL●loo—c1m;:u: 95— ●a.z
● ●●
o
0
o
0 00
● 1●
● ●
,old+-+-L&J*L o, I o!,, 0,1,, I /I I ! I I I
o 0.1 ~’NAL0.2 0,3 NATURAL o 0.3 NATURALCOMPRESSIVEPRESTRAIN COMPRESSIVEPRESTRAIN
Fig.2. ProjectE-SteelBarsWithHolesCompressedAndAgedT@stedInTensionAt-16”F.
..-
6
TABLEII. ABS-BSTEELBARSWITHHOLES,AXIALLYPRECOMPRESSEDAT72°FAGED2 HRS.AT330”F,TESTEDINTENSIONAT-16°F.
TABLE11
BAR
B-272
B-273
B-227
B-228
B-229
B-230
B-270
B-237:
B-249
B-246
B-231
B-239
B-238
B-271
B-245
B-232
-NOM.
:OMPR.
0
0
0.10
0.15
0.20
0.25
0.30
0.30
0.40
0.40
0.41
0.41
0.43
0.50
0.50
0.56
BARSWITHHOLES,AXIALLYPKSCOMPRESSEDAT72°FAGED2hrs.AT330”F,TESTEDINTENSIONAT-16°F
BARDIA.,in.
Orig.
0.501
0.501
0.505
0.504
0.500
0.504
0.504
0.507
0.504
0.498
0.510
0.501
0.504
0.504
0.496
0,499
Fract.a
P 0.432N0.374
P0.435N0.394
P0.465N0.387
P 0.473N 0.391
P 0.479N0.410
P 0.h84N0.392
P 0.470N 0.425
P 0.440N 0.393
P 0.491N 0.Q41
P 0.450N 0.436
P 0.465N 0.410
P 0.460N 0.403
P 0.502N 0.502
P 0.502N 0.501
P 0.488N 0.477
P 0.499N 0.498
HOLEDIA., 10-3in.
Orig.
30
31
32
32
33
32
31
31
32
32
31
31
32
Compr.]
30
31
T 35L 18
T 36L8
T 40LO
T 43LO
‘r+LO
T 41LO
T+LO
T 50LO
T 50LO
T 50LO
T 52LO
T+LO
T+LO
T+Lo
cract.
20
20
28
34
40
43
41
41
45
48
45
49
52
49
55
55
FRACTURE
ksid
103
79
104
120
113
118
106
131
111
131
132
122
61
95
106
73
train<
0.43
0.36
0.37
0.34
0.27
0.32
0.26
0.43
0.17
0.25
0.33
0.34
0.01
0.005
0.06
0.005
ABS-BSTEEL
.—+.,Directionf
and‘Tact.Type
shear
shear
PF,shear
NF,shear
PF,shear
NF,shear
55%sh.
shear
shear
25%sh.
NF,shear
PF,shear
NF,cleav.
cleav.
3%sh.
cleav.
—
7
TABLEII.(continued)ABS-BSTEELBARSWITHHOLES,AXIALLY~D AT72°FAGED2 HRS.AT330”F,TESTEDINTENSIONAT-16°F,
BAR
B-248
B-247
B-235
B-236
B-234
B-235
B-243
B-244
NOM.
:OMPR.
0.60
0.60
0.10
0.15
0.20
0.25
0.40
0.60
BARDIA., in.
=70.502
0.503
0.496
0.512
0.502
0.510
0.502
0.498
P 0.502N 0.502
P 0.503N 0.502
P 0.430N 0.380
P 0.420N 0.375
P 0.420N 0.375
P 0.430N 0.360
P 0.416N 0.383
P 0.445N 0.424
HOLEDIA.,10-3in,
)rig.
3U
33
32
32
32
32
32
32
T+LO
T+Lo
Holes
made
after
cOm-
pres-
sion
cract.
59
58
22
23
24
24
17
16
ksid
52
69
103
120
118
125
136
121
train{
0.002
0.003
0.40
0.49
0.1+6
0.52
0.43
0,23
Direction’and
‘ract.Type
cleav.
cleav.
NF,shea~
PF,shear
PF,shear
NF,shear
PF,shear
NF,shear
a.b.c.d.e.f.
9.h,
ii
i-
Bardiameterparallel(P)ornormal(N)toaxisofholeHolediametertransverse(T)orlongitudinal(L)tolengthofbarTransversediameterofholeafterfractureAveragefracturestressbasedonnetareaatfractureNaturalstrainbasedonchangeofnetareaatfractureEachbarhadtwoholes,oneparallel(PF)andonenormal(NF)totheoriginalfaceoftheparentplate.Thefractureinitiatingholeisindicated.Holesredrilledat18%nominalstrain.Holediameterwas0,038in.Holesredrilledat18%and31%nominalstrain.Holediameterswere0,038in,and0.046in.,respectively.Holesredrilledat18%and33%nominalstrain.Holediameterswere0,038in.and0.046in.,respectively.Closed-upholecouldnotbeseen.
8
-l● HOLEA
O HOLEB+ SQUAREA
XSQUAHEB
II PARALLELTOBARAXIS1 TRANSVERSETOBARAXIS
I I I I I I I I 1 I I I I I Io 0.I 0.2 0.3 0.4 0.5 0.60.70.8 1.0 1.2 1.4 NATURAL
COMPRESSIVEPRESTRAIN
Fig.3 DimensionChangesOfABS-BSteeLBayWithHolesDuringCompassion.
atcompressionratiosof 0.60ormore,whenthelateralexpansiona~oundhole
B (lowestcurve+,II)increasedfaster,andaroundholeA (curvex)slower
thantheexpansionintheabsenceofholes.Thegridcontractionparallelto
thebaraxis(curves+ andx, 11)wasalmostexzctlylinearbutslightly
fasterthantheappliedprestrai~upto0.20,whentheholesclosed.Atpre-
strainsabove0.20thelongitudinalgridcontractionmatchedexactlythe
nominalbarcompression.Itappears,therefo~e,thatallthest~ainconcen-
?~ationcausedbytheholeoccurredwithfntheregionofthe1/4in.squares
,— -
andmaybewit%:nanevensmallerregion,asindicatedbymicrophotograph
oftheetchedsurfaces.
Thestrainconcentrationarounda flattenedholeisalsoindicatedby
‘thesurfacedeformationasinFigure4 fora 0.03in.holeaftera nomihal
5 afterre-drillingtoa O.O&lin.dia.atprestrainof0.18,andinFig. .
a p~estrainof0.10andthencontinuingtheaxialprestrainingupto0.31
(nominaltotal).Attheupperleftofeachfigureisa photographofthe
freesurfaceshowingshadowscausedbytheridgesoflateralexpansionat
thesharpcornersandalongtheshearzonesemanatingfromthem.Thelower
leftcornershowsa polishedsectionalongthelongitudinalmid-plane,and
theuppe~right+hesameareaafterheatingto400°Fandetchingbyrepeated
immersionina solutionof6 g~.eachofcupricandferricchlorideand10
ml.hydrochloricacidin100ml.ofethylalcohol.Thedeformationofthe
bandedstructureindicatesthemorehighlystrainedregionsandtheshear
zonesemanatingfromthesharpcorners.Completelyflattenedholesafter
prestrainsof0.32and0.60areshowninFigure6 (notre-drilled).
TheresultsofmaininterestinTables11and111arethefracture
strainandstressateachp~estrainshowninthe2ndand3rdcolumnsbefore
thelastandinFigures1 and2. AtprestrainsbetweenO and0.41t~efrac-
turestraimofABS-Bbars(Fig.1,right)showa lotofscatterbutgener-
allydecreasefromabout0.40* 0.03toabout0.25* 0.08.Thisisakou?a
halftoa thirdofthefracturestrainofsolidbars[6]butstilllarge
enoughtoqualifythebehaviorasductile.A reductionofthefracture
straintoabout0.01[withanexceptionof0.05)wasfoundtooccuratnom-
inalprestrainsbetween0.41and0.50or about2/3oftheexhaustionlimiT
Forsolidbars(0.75).Thediffe~enceisactuallymuchbigger.asshownby
.-
10
TABLEIII E-STEELBARSWITHHflLES,AXIALLYPRECOMPRESSEDANDAGED,TESTEDINTENSIONAT-16*F
lVJiCTUREDirectionfand
?Pact. Type
PF,50%sh.
NF,cLeav.
NF,cleav.
PF,cleav.
PF,cleav.
lTF, shear
NF, 15%sh.
PF,15%sh.
PF,101sh.
HOLEDIA.,10-3in.NOM.
:OMPR.
0.10
0.15
0.20
0.25
0.30
0.10
0.15
0.20
0.25
BARDIA.,in,BAR d(si
94
92
92
95
90
105
95
98
105
FracT.a Compr.b c“&act.Orig.
E-318
E-319
E-320
E-321
E-322
0.504
0.504
0.495
0.505
0.500
0.491
0.502
0.510
0.512
P 0.U74N 0.428
P 0.480N 0.467
P 0.482N 0.478
P 0.495N 0.493
P 0.491N 0.483
33
32
33
32
32
T 36Lla
T 36L10
T 37Lo
T40LO
T44LO
30
35
37
~o
44
0.21
0.13
0.06
0.06
0.05
E-326
E-327
E–324
E-325
P 0.420N 0.392
P 0.450N O.440
P0.460N 0.450
P0.460N 0.455
32
32
32
32
Holes
made
after
com-
pres-
sion
26
30
31
31
0.37
0.24
0.23
0.25
jardiameternarallel(P)ornormal(N)to axisofholeiolediametertransverse(T)orlongitudinal“~gth ofbartransversediameterofholeafterfracture
a.Il.c.d. Averagefracturestressbasedonnetareaatfracturee. Naturalstrainbasedonchangeofnetareaatfracturef. Eachbarhadtwoholes.one~arallel(PF)andonenormal(NF)
totheoriginalfaceoftheparentPlate’.Thefractureinitiatingholeisindicated,
,—— .__..._ .— ——. -..— —..— ..— -.
11
Uppmleft:SuPfaee
LowexJleft:Mid-plane
Upperleft:Surface
Lowerleft:Mid-plane
Fig.4 Deformationof0.031in.By0.18.
Right:Etchedmid-plane
Dia.HoleDuringComp~ession
Right:Etchedmid-p2ane
Pig.5Deformationof0.031in.Dia.HoleAfterCompress{onBy0.18Red~{12ingTO0.041in.D{a.AndCompz%ss%ngTo0.31.
12
0-004 INIT.DIA.0.032 in. ~..o.32
B-005 INITDIA. 0.032 Cn=0.60
Fig.6 Comp~etelyFZattenedHoles
thecomespondingnaturalstrains:-0.51to-0.64VS. -1.30for solidbar-s.
Thenetfracturestressexceeded100ksi(withoneexception)atprestrains
upto0.50.Thisiswellabovethe0.1%offsetyieldstrengthofsolidbars
whichrisesgraduallyfromabout36ksiatOprestraintoabout70ksiat
0.50prestrain[6],butlessthantheircorrespondingfracturestress(about
150ksi).Atprestrainsof0.56and0.60thefracturestresswasbetween73
and52ksi,whichisaboutequalwi-ththecorresponding0.1%offsetvalue
13
(about71ksi)andmuchsmallerthantheFracturestress(aboutA60ksi)of
solidbars.
WithE-steelthefracturestrainwas0.21ata prestrainof0.10(FiR.2,
right).whichisa qua~terorfifthofthefractures-trainofsolidbars[3,5].
andwasreducedtoabout0.05atprestrainsof0.20ormore.Thedropinduc-
tilityoccurredatthelowprest~ainsofabout0.15to0.20(naturalprestrains
-0.15to-0.21),muchlessthanwithsolidbars(nominal-0.60,natural-0.85).
Thereducedductilityof0.05,thoughhigherthanwithsolidbars(about0.02).
islowenoughtoqualifythebarsasbrittle.
ThereductionoftheexhaustionlimitinE-steelto1/3or1/4itsvalue
forsolidbarsappearsasa reasonableconsequenceofthelocalstraining,
wo~khardening,andstressconcentrationofcollapsingholes.Thecorrespond-
ingreductionto2/3ofthenominalor1/2ofthenatu~alprestraininABS-B
steelcouldbeattributedtoanearlyclosingoftheholeswhichstopsfur-
therstrainconcentrationandhardening.Enlargementorre-drillingof-the
holesbeforecontinuingtheprestrainingwouldthenpermitadditionalstrain-
ingandhardening.Accordinglyata compressiveprestrainof0.18,theholes
ofbarB-237werere-drilledtoa 0.038in.diameter,slightlysmallerthan
thewidthofthecollapsedholeandprestrainin~wascontinued.BarsB-239andB-238(TableITandFig.1)werere-drilledtwice,ata nominalpre-
strainof0.18(newdiameter0.038in.)andatabout0.32(newdiameter
0.046in.),whentheyappearedtohaveclosedagain.There-drillingdid
notreducetheductilityofbarsB-237(prestrain0.30)orB-239(pre-
strain0.41).Theirfracturestrainswereaboutthesameorslightly
largerthanbarsofequalprestrainbutnore-drilling.BarB-238(pre-
strain0.43)didfracturewiththesmallstrainof0.01,butitsprestrain
14
wasintheregionbetween0.41-0.50whereductilitywasfoundtodropeven
withoutre-drilling,hencethebrittlefracturecannotbeattributedmainly
tore-drilling.Apparentlyre-drillingandre-compressingdidnotcause
fractu~eatsmallerprestrainsthanwithoutre-drilling.TheresultsOF
thesefewtests,ifconfirmed,arenotincompatiblewiththediscussedcon-
ceptofembrittlementbythecollapseofvoids.Thelocalworkhardening
maybesohighastop~oducearrestedc~acksatverylowloadsasinearlier
testsofnotchedprecompressedplates[2,5]andintestsofplatescontain-
ingweldsFunningovernotches[15-20],occasionallyeven“spontaneouscracb”
withoutanyexternalloading.Suchanam-estedcleavagecrackfollowedbya
rougherjaggedfracturesurfacecouldbeseeninbarB-239.Inallthese
casesthearrestistheyesultofa lowcrackvelocityattheendofthe
smalldamagedregion,insufficientforpropagationinthesoundregionat
lowstress.Re-initiationoffractureinthesoundregionisnoteasywhen
thetriggeringeffectofthedamagedregionisusedup. Infact,fracture
wasthenfoundtooccuronlywhentheloadwasincreasedtothelevelof
generalyielding.Earlyarrestedcrackscanhavethepeculiarresultof
strengtheninga strwcture.Thiswouldexplaintheexistenceofmanyarres-
tedcracksinwelded-regionsofstressconcentrationobservedinshipsT211.Ifsucharrestedcracksdooccurinthecompressedbarswithre-drilled
holes,thefinalfractureshoulddependonthebrittlenessorductility
oftheregionbeyondthehighlywork-hardenededgesoftheflattenedre-
drille~holeswherefracturemustre-initiate.Indeedthisseemstobe
thecasesinceallba~sofonesteel,whetherFe-drilledornot,became
embrittledat the sameoverallprestrain.
It wouldthenseemthattheprocessofembrittlementreauiresnot
15
justsufficientlocalwork hardeningand stressconcentrationtosTarta
c~ack,butalsoconditionswhichwillensurepropagationintheregion
beyondthelocaldamage.Thenecessaryconditionmustcombinesuitable
degreesofworkhardeningandstressconcentrationanda sufficientsize
oftheembrittledregion.Suchanexplanationofthesizeeffectwasad-
vancedinearlierpapers[14].Exactsimilarityispossiblebetweenspeci-
mensofdifferentsizesunde~staticloading.Thestressandstraindis-
tributionscanbeexactlysimilarandtheirpeaksequal,sothatthesize
effectcannotbeexplainedona basisofstressmagnitude.Similarity
breaksdowninThedynamiccaseofanadvancingcrack.asvelocitiesand
s?rainra?eorinertiaeffectscannotbesimilar,hencewillcausea size
effect. This is clearlya dynamicsizeeffectindirectlyrelatedwith the
staticstresstiistributionor with the singularityat the cracktip.
b. F?arswith0.031in.holesdrilledafteruniformcompression.Another--
checkontheeffectoflocalworkhardeningandstressconcentrationwas
madewithuniformlyprestrainedbarsdrilledtransverselyaftercompres-
sion.SixbarsofARS-Bweretested,fiveprestrainedby0.10toO.L+fl
(endofTable11andFig.1)givingfracturest~ainsbetween0.40and0.52
andoneprestrainedby0.60Rivinga f~acturestrainof0.23.Fourbars
ofE-steelwerealsotested(endofTable111andFig.v)>onePrestrained
by0.10whichfracturedwitha strainof0.37,and
to0.25whichfracturedatstrainsofabout0.25.
brittle,evenatthehighestprestrains.Theyall
higherductilitythanbarswithpre-drilledholes,
bars.
threeprestrainedby0.15
Nobaywasconsidered
exhibitedappreciably
butmuchlowerthansolid
16
TABLEIV ABS-BSTEEL BARSWITHPARALLELANDWITHBLINDHOLESAXIALLYCOMPRESSEDAGEDANDTESTEDAT-16”F.
3AR
—
1P
2P
3P
UP
lB
2B
3B
UB
NOM.:OMPR.
0.20
0.20
0.20
0.20
0.20
0.20
0.20
0.20
ORIG.DIA.in.
0,5065
0.5050
0.5055
0.5055
0.5045
0.5045
0.5055
0.50U5
AFEA,in?OHG.aFRACT.
0.16,5OmR
0.16530.1316
0.17220X3
0.1s200.1418
0.1s530.1332
0.18890=6
0.1933Omio
0,1961Oml
LOADkpMAX.F=T.
15.6l?%
15.7lCO
16.21K5
16.0lCO
15.91T2
15.9lKO
16.2l~B
16.21C2
FR4CTUK3<sibStrain<
LOO.90.10
L06.20.23
106.70.17
91.70,25
99.1 0.39
96.3 0.U2
116,B 0.65
lQ1.6 0.91
‘Qc-
c
d = 0.089,(
d = 0.181,,
d = 0,285,(
d = 0.3861~
c . O,lho,,
c = 0.2147,
c . o.31g,,
c = 0.905,,
a. Netoriginalareaandatfractureaftersubtractionofholes.
b. Averagefracturestressbasedonnetarea.c. Naturalstrainatfracturebasedonchangeofnet
area,ornaturallogarithmofratioofinitialtofracturearea.
c. Barswithpre-drilledparallelorblindholes.Attemptswerealsomade
tofindmoredamagingconfigu~ationswithdoubleholesinbarsofABS-Bsteel.
Twotransve~sesymmetrical0.032in.dia.holeswithaxeslyingina cross-
sectionweredrilledbeforecompression(insetinTableIV,topright).Four
testsweremadewitha distanced betweenparallelholeschangingfrom
0.089in.to0.386in.,allwiththesamecompressiveprestrainof 0.20.The
closestholespacinggavethelowestfracturestrainof0.10.Theotherth~
gavefracturestrainsbetween0.17and0.25,thehighestfopthewidestspac-
ing.Fourmoretestsweremadewithaligneddoubleblindholes,drilledfrvm
diametrically
solidcentral
to 0.405 in.,
oppositepointsof a cross-sectionsoastoleaveanundrilled
lengthc . Testsweremadewithvaluesof c fromO.lQOin.
allwithprestrainsof0.20.Allfourgaveappreciablefracture
17
strains,increasingwiththelengthc from0.33to0.91,equalorlarger
thanbarsofthesameprestrainanda singlethroughhole.
Theworseeffectwasachievedwithparallelholesoftheclosestspacing
whichgavethelowestfracturestrainof0.10,muchlessthanwitha single
holeatthesameprestrain,andsmallenoughtoborderonthebrittle.Prob-
ablytheregionbetweenholesgetsdamagedmoreandfracturesmoreeasily.
SeveralfracturedbarsareshowninFigures7-9.SynmeTricinclined
yieldzonesemanatingfromtheflattenededgeswerevisibleinall butthe
Fig.7 BeginningOfy{e2dingAndFraetu~eOfBarsWithHolesDrilledBefo~e.Prest~ain-ing.
18
Fig.8 FractureOfBarsWithHolesD?illedBeforeComp~ession.
tiostbrittlebars.Figure7 left,showsthebeginningofyieldingalong
symmetricplanesintersectingalongtheholeandinclinedbyaboutQ5Qto
thebaraxis.Figu~e7,B-231,showshowsuchintensecross-yieldingforms
a neckbylateralcontractionmostlyacrosstheholeaxis,andleadstoa
shearfractu~ealongtheinclinedplanes.Th~smechanismofyieldingand
19
B-244 GO=0.60 Ef =0.23!“
F{g.9 FractureOfBarsVithHoles
“fracturewasevidentinallductilebars.The
wasseldomasun’iformasin“barB-?31(Fig.7,
tureappearedtooccuralongchanginginclined
familiarshapeknownas“dog’sears”(BarsB-228
Athigherprestrainsfractureagainstarted
clinedplanesofcrossyieldingandchangedinto
fracturesurface,however,
center).Instead,thefrac-
planes,soastoformthe
andB-229,Fig.7).
inshea~alongthein-
a fracturepe~pendicular
to thebaraxis(BarB-270,Fig.8,topright)’butnotwitha typically
cleavageappearance.Astheprestrainincreasedtheinclinedshearfrac-
turewasconfinedtoanevernarrowerzoneparalleltotheholeaxis,un-
tilwif+brittlebarsitvanishedcompletely(BarB-2b8,Fig.8),though
tracesofinclinedyieldzoneswereoccasionallyvisibleonthecylindrical
barsurfaceveryclosetothehole.ThebehaviorofbarsofE-steelwasin
generalsimilar,butthechangesfromobliquetonormalfractureoccurred
atlowerprestrains(E-318,E-322,Fig.8). Theobliquefractureiscalled
a “shear”fractureandthenormal“cleavage,“andthepercentageofshear
failureisindicatedinthelastcolumnsofTables11and111.
20
Theobliqueyieldingandinitiationoffracturebyshearatthehole
edgeswasevidentalsowhentheholesweredrilledafteruniformprestrain-
ing.AllABS-Bbarshad100%“shear”(oblique)failures(B-244,Fig.9).
InbarsofE-steelprestrainedby0.15ormore,thefractu’rechangedffim
obliquetonormala shortdistanceawayfromtheholeeventhoughthetotal
ductilitywasrelativelyhigh(0.25).
Conclusion
Theex~stenceofholesreducedtheamountofcompressivep~estrain
causing“brittlenessto1/3or1/4theamountneededinsolidbarsofE-
steeland to2/3or1/2ofABS-Bsteel.
ag~eementwiththenotionofcompressive
voidsOPflaws,lesssotheresultswith
enceobservedbetweenE andABS-Bsteels
TheresultswithE-steelarein
embrittlementbythecollapseof
ABS-Bsteel.Thelargediffer-
indicatesthat
be quitesuitablefordistinguishingsteelsastotheir
brittlementandfracture.
thesetestscould
resistanceto em-
Thegeometryofthespecimensappearstofacili-tatecrossyieldingby
shearalonginclinedplanescontainingtheaxisofthehole,duringboth
prestraining(Figs.4-6)andfinaltesting.Such~eversedshearingdefor-
mationislessseverethancompressionreversedtotension[u]andmaybe
thecauseoftheobservedrelativelyhighductility.Containmentofglas-
ticdeformationwouldthenleadtoamorebrittlebehavior.Sucha con-
straintofextremeseveritydevelopsinbarswithdeepcircumferential
groovesmachinedafteruniformstrainingandcausesextremebrittlenessat
prestrainsaslowas0.05[5].A furthercheckcouldbeobtainedwithtests
ofbarsprestrainedafternotching.Suchtestswereincludedintheinit!al
planshutwerenotcompleted.
21
Acknowledgment
Theresults
searchsponsoced
presentedinthispaperwereohtalnedinthecourseofre-
initsmajorpartbytheShipStructureCommitteeunder
ContractNObs-88294oftheNavalShipEnginee~ingCen-ter.Departmentofthe
Navy,andInpartbytheAdvancedResearchProjectsAgencyunderContract
SD-86.
References
1. Mylonas,C.,Drucker,D.C.,tureInitiationatNetmitteeReportSSC-116,
andBrunton,J.D.,“StaticBrittleFrac-Stress40%ofYield,”ShipStructureCom-1958.AlsotheWeldingJourmalV, No.
10,ResearchSupplement,pp.473-sto479-s,1958.
2.
3.
4.
5.
6.
7.
8.
9.
Mylonas,C.,“Prestrain,Size,andResidualStressesinStaticB~ittleFracturwInitiation,!!RepofiNObs_65917/4Of theDivision‘fEngineering,BrownUniversity,totheShipStructureCommittee,1959.TheWeldingJournal,Vol.38,No.10,ResearchSupplement,pp.414-sto424-s,195g.
Mylonas,C.,“ExhaustionofDuctilityandBrittleFractureofE-SteelCausedbyPrestrainandAging,”ShipStructureCommitteeReportSSC-162,1964.
Drucker,D.C.,“AContinuumApproachtotheFPactureofSolids,”Chap-terI in“BrittleFracture”(D.C.DruckerandJ-J.Gilman,Editors),Interscience,1963.
MY~onas,c.,l!~eMechanicsofBrittleFracture,”PFOC.llth~nte~at.Cong.App.Mech.,Munich,1964,Springer,1966,pp.652-660.
Mylonas,C.,Kobayashi,S.,andArmenakas,A.,“ExhaustionofDuctilityUnderNotchConstraintFollowingUniformPrestraining,”ShipStructureCommitteeReportSSC-173,1966.
Dvorak,J.,andMylonas,C.,“EffectofSurfaceConditionontheExhaus-tionofDuctilitybyHotorColdStraining,”ReportNObs-88294/6oftheDivisionofEngineering,BrownUniversity,totheShipStructureCommittee,Sept.1967.
Ludley,J.H. I?AReversed.BendTesttoStudy‘uc-,andDrucker,D.C.,tiletoB~ittleTransition,”NObs-78440/3,theWeldingJournal,Vol.39,No.12,ResearchSupplement,1959.
Rockey,K.C.,Ludley,J.H.,andMylonas,C.,“ExhaustionofExtensionalDuctilityDeterminedbyReversedBendingof5 Steels,’’NObs-78Q4O/5,March1961,Proc.ASTM,Vol.62,pp.1120-1133,1962.
22
10.Mylonas,C.,andBeaulieu,R.StrainedABS-BSteelby
J.,“RestorationofDuctilitvofHotorColdHeatTreatmentat
tureCommitteeReportSSC-167,1964.
11. Allen,N.P.,“TheMechanicalPropertiesoftheHatfieldMemorialLecture,JournalIron&Part1,pp.1-18,Jan.1959.
12. Robertson,J.B.,Jr.,OralCommunication.
13. Ludley,J.H.,andDrucker,D.C.,“SizeEffect
700to115;°F,”Sh;pStruc-
FerriteCrystal?”EleventhSteelInst.,Voli191,
inBrittleFractureofNotchedSteelPlatesinTension,”App.Mech.~, p.137,“196~,
14. Mylonas,C.,“Conditionsfavorablea l’initiationdelarupturefragile,”BulletinduCERES,Vol.XI,pp.141-166,1961.
15. Greene,T.W.,“EvaluationofEffectofResidualStresses,”TheWeldingJournal,~, 5,Res.Supplement,pp.193-sto204-s,1949.
16. DeGarmo,E.P.,“Preheatvs.Low-andHigh-TemperatureStressRelief
17. Week,
18. Wells,
Treatments,u TheweldingJournal,31, 5,”ResearchSupplement>PP.233-stO 237-s,1952.
—
R.YlfExperiments on BrittleFractureofSteelResultingfromResid-ualWeldingStresses,V!WeldingResearch,~,pp. To-rto es-p,1952.
A.A.,“TheMechanicsofNotchB~ittleFracture,WeldingResearch~,pp.34-rto56-r;“1953.
19. Kennedy,R.,“TheInfluenceofStress-RelievingontheInitiationofBrittleFractureinWeldedPlateSpecimens,”Brit.WeldingJnl.~,11,pp.529-534,1957.
20. Wells,A.A.,lfBrittle ~FactuFe strength ofWeldedSteelplates-”BritishWeldingJournal(5),pp.259-277,1961.
21. Vedeler,G.,“OnVariousProblemsofImmediateInteresttoa ShipClassi-fication~an,!lshipStructureCommitteeReportSSC-136,August1961.
NONFSecurityClassification *
DOCUMENTCONTROLDATA-R&D(5e.urit~cleasjiicatiOn01t,tle, bodyofabst,ac~and,~da~i~gsmIotatioqrnuslbe~nt~~~dWfICfltheover.qllfcpo,!I. cla.s,f,ed)
t ORIGINATING ACTIVITY (cO~Or~tm~pthor) 2B REPORT SECURITY C LAS51F!CATION
BROWNUNIVERSITY NONEZb GROUP
3. REPORT TITLEI ExhaustionofDuctilityinCompressedBarswithHolesI
4. DESCRIPTIVE NOTES(Typoof reportandinclu$zvedates)SixthProgressReportonProjectSR-158
5 AUTHOR(S)(Lirstname,fir.t name,jriitial)
S. KobayashiandC.Mylonas6. REPORTDATE 78. TOTALMO.OF PAGE5 7b. NO OFREF5
June1968 22 21Ea.CONTRACTORGRANTt.Io, 9a. ORIGINATOR,.5REPORTNUM@Ee(S)
Nobs88294 Nobs-88294/5b. PROJECT NO,
SR-158c, 9b. OTHERREPORTNO(S)(Anyoth.,nurnbarshatmaybe azs,~odthisreport)
d SSC-18410.AVAILABILITY/LIMITATIONNOTICES
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Thiswasa ShipStructureCommitteeProject. NavalShipSystemsCommand
3. ABSTRACTThebrittlenessofmildsteelsubjectedtotensionafterpriorcompressive
prestraininghasbeeni.npartattributedtothecollapseofmicroscopicflawsorvoidsandtotheresultingseverestraining,workhardening,andsharpeningoftheflawedges.A similarmechanismofembrittlementshouldoperatealsowithartifi-cialmacroscopicflawssuchasholes.Thiswascheckedwithtestsofaxiallycom-pressedbarsofABS-BandofE-steelwithtransversepre-orpost-drilledsingleoldoubleholes.Theoverallnominalcompressiveprestrain(exhaustionlimit)causingbrittlenessinsubsequenttesnioninbarswithpre-drilledholeswasabout1/4thecorrespondingprestrainforsolidbarsofE-steelandabout1/2forABS-Bsteel. Thepossiblecausesofthisdifferenceandthemodesoffractureinitiationandpropagationarediscussed.Thestrongdifferentiationofsteelqualityachievedwiththesetestsisverypromisingforthedevelopmentofa relatedacceptancetest.
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Ship Straim Measurement 4 Ana2ysisShip structural DesignMetallurgical Studies
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SHIP STRUCTURE COMMITTEE PUBLICATIONS
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Index of Ship Structure CorinnitteePublications (1946 - Apri
SSC- 171, Micro- and Maerocrack Formation by B. !_. Averbach.AD 473496.
SSC - 172, Crack Extension and Propagation Under PZane StressRosenfield, P. K. Dai and G. T. Hahn. March 1966.
1965 )
October 1965.
by A. R.AD 480619.
SSC - 173, Exhaustion of Ductility Under Notch Constraint FoZZowing UniformPrestraining by C. Mylonas, S. Kobayashi and A. Armenakas.August 1966. AD 637143.
SSC-174, Investigation of Residual St?esses in SteeZ WeZiknentsby K.Masubuchi and D. C. Martin. September 1966. AD 639619.
SSC-175 , Mechanical Properties of a High-Manganese, Low-Carbon SteeZ fo?WeZded Seavy-Section Ship PZate by R. D. Stout and C. R. Roper, Jr.August 1966. AD 637211.
SSC- 176, BienniaZ Report of the Ship Structure Committee. June 1966.AD 641333.
SSC - 177, Guide foy Interpretation of Non-Destructive Tests of WeZds in ShipHuZZ Structures by the Weld Flaw Evaluation Committee.September 1966. AD 639053.
SSC -178, A Survey of Some Recent British Work on the Behavior of WarshipStructures by J. Clarkson. November 1966. AD 644738.
SSC- 179, Residwzl Strains and Displacements within the PZastic Zone Aheadof,4Crack by J. Cammett, A. R. Rosenfield, and G. T. Hahn.November 1966. AD 644815.
SSC- 180, EzpetimentaZ Determination of Plastic ConstraintA{leadof a SharpCrack under PZane-Strain Conditions by G. T. Hahn and A. R.Rosenfield. December 1966. AD 646034.
SSC- 181, ResuZts from FuZLSeaZe Measurements of Midship Bending Stresses onTwo Dry-Cargo Ships- Report #2 by D. J. Fritch, F. C. Bailey, J. W.Wheaton. March 1967. AD 650239.
SSC- 182, !l%entyYears of Research under the Ship Structure CormnitteebyA. R. Lytle, S. R. Heller, R. Nielsen, Jr. , and John Vasta.December 1967. AD 663677.
SSC- 183, MetaZZurgieaZ Structure ati the Brittle Behavior of SteeZ byMorris Cohen. May 1968.
