Investigation of methods of supporting single-thickness specimens in a fixture for determination of compressive stress-s...

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Title:
Investigation of methods of supporting single-thickness specimens in a fixture for determination of compressive stress-strain curves
Series Title:
NACA WR
Alternate Title:
NACA wartime reports
Physical Description:
10 p., 9 leaves : ill. ; 28 cm.
Language:
English
Creator:
Kotanchik, Joseph N
Woods, Walter
Weinberger, Robert A
Langley Aeronautical Laboratory
United States -- National Advisory Committee for Aeronautics
Publisher:
Langley Memorial Aeronautical Laboratory
Place of Publication:
Langley Field, VA
Publication Date:

Subjects

Subjects / Keywords:
Airplanes -- Design and construction   ( lcsh )
Aerodynamics -- Research   ( lcsh )
Genre:
federal government publication   ( marcgt )
bibliography   ( marcgt )
technical report   ( marcgt )
non-fiction   ( marcgt )

Notes

Summary:
Summary: An investigation was made of the methods of supporting single-thickness specimens of aluminum-alloy sheet material in a fixture for determination of compressive stress-strain curves. The specimens were supported in the fixture by rollers, offset-grooved plates, opposite-grooved plates, flat brass plates, or flat wooden plates. It was found that the measured values of compressive yield stress and modulus of elasticity obtained with the roller supports were independent of the supporting force applied to the specimen provided that a sufficient minimum force is used to overcome initial deviations from flatness. The stress-strain curves obtained by the use of the plate types of support were affected by an increase in the supporting force. Satisfactory stress-strain curves were obtained with all types of support, however, when the supporting force was approximately 45 pounds. The investigation also showed that the compression fixture, the specimen support, and the single-thickness specimens must be accurately made in order to obtain accurate stress-strain curves consistently.
Bibliography:
Includes bibliographic references (p. 8).
Statement of Responsibility:
by Joseph N. Lotanchik, Walter Woods, and Robert A. Weinberger.
General Note:
"Originally issued May 1945 as Restricted Bulletin L5E15."
General Note:
"NACA WARTIME REPORTS are reprints of papers originally issued to provide rapid distribution of advance research results to an authorized group requiring them for the war effort. They were previously held under a security status but are now unclassified. Some of these reports were not technically edited. All have been reproduced without change in order to expedite general distribution."

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 003806564
oclc - 124083251
System ID:
AA00009374:00001


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Full Text

RB No. L5E15


NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS





WA RTI llE RE .PORT


ORIGINALLY ISSUED
May 1945 as
Restricted Bulletin L5E15

INVESTIGATION OF METHODS OF SUPPORTING SINGLE-THICKNESS
SPECIMENS IN A FIXTURE FOR DETERMINATION
OF COMPRESSIVE STRESS-STRAIN CURVES
By Joseph N. Kotanchik, Walter Woods,
and Robert A. Weinberger

Langley Memorial Aeronautical Laboratory
Langley Field, Va.
MiV' ,,'ERSlT L1' F L'- .


', ,. Il,-LE. FL 2.2611 'A


N`


NACA.,


WASHINGTON
NACA WARTIME REPOPTS are reprints of papers originally issued tu provide rapid distribution of
advance research results to an authorized group requiring them for the war effort. They were pre-
viously held under a security status but are now unclassified. Some of these reports were not tech-
nically edited. All have been reproduced without change in order to expedite general distribution.

L 1P9


/V :- L -i .I "ZI



































Digitized by the Internet Archive
in 2011 with funding from
University of Florida, George A. Smathers Libraries with support from LYRASIS and the Sloan Foundation


http://www.archive.org/details/investigationofm001ang








NACA RB No. LEl15


NATIONAL ADVISORY COIC:ITTE7 FOR A RONAUTI CS


RESTRICTED BULL 'T_!



I",'TSTIGATION CF C,.:'TODS CF STUP TING SI::.L-THIC:'t

SPECI ..[3 II A FIXTURE FOR DETI IATIOJ

OF CC PRESSIV7 ST- S-S TAIN r'-v

3y Joseph N. cota.clkix, :aslter ;oods
and Robert A. :einberger


S *' ARY


An investigpt ion nas mae of the methods of supporting
single-thickness secim3ns of elu2-iinurl-alloy sheet rcteriel
in a fixture for dcter-Inaetior of cocmrre.esive stres-strain
curves. The ,o-ecimens were sup -rted in the fixture
rollers, offset-grooved plate;, o. -osite-groovea pirtes,
flat brass olrtes, or fait %voo
It -es found thet the mrasured values of comoressive
yield stress and modulus of' ,lsticity obtained vith the
roller supports wire inieroendent of th. suoporting force
aoplied to the so-.cimen 'ro.-'idd chnt a sufficient minimum
force is used to overcor. inib.ipl deviations from flstness.
The stress-scbrin curve obtned bbt~r the use of the plate
types of support were affected b-, an increase in the sup-
porting force. Satisfactcry stress-strain curves were
ootained with all types of support, boNvever, when the sup-
porting fcrce was P.oroximately 1j5 pounds.

Fc investigation also showed that the comrpression
fixture, the specimen support, and the single-thickness
specimens must be, accurately made in order to obtain accu-
rate stress-strain curves consistently.


INTRODUCTION


Compressive stress-strain curves for almninum-alloy
sheet material are beinr obtained in many laboratories
throughout the aircraft industry to provide information
on the orooerties of the mantarials used in aircraft It









L"ACAM RB .io. L;j.15


is i!rportrnt tlht the :ethcd for determin-tion of the curves
be reliable, Pccuree, .n..' iel tivl] simple. Armong the
various et..ho's nro csea:, the !in uie-thicknesr s irethod
introduced by .. P. 'on 1poier of -cugh it-Sikorsky Aircraft
sapefreOd to be tahe mrost romirniq'c. In the ine hc pcposed
by lony-o-rys '-nd further developed et the Alur.inura
Recesrich Lebo-rtories of' ths Aluminur. Company of America,
a fixture 'ys used for csupiorfcng a single thickness of
sheet material so rs to prevent ouckrlin. (See reference 1.)
In thio fixture, clos1ey sp-e-: rollers on ach side of
the snaclren Grovided tc. Ierl suLort and 'ca itted
sh-rtenirne of the s:ecn-rn uxe r io'<. In order to
si".1'lify the cut ..-'oery T-y co .: pressicn rfiYtule, the
Natijon1q E aeu of Staderds uostitubeLd solid brass
olates for the roller. (Se3 referee 2-.)

In exoeriPnt A*l1 vo'k et the L'1nily. structure
rese-rch lbOorrtor;- in vlic1i thb si: -le-thickness method
and. : c -o rre::ion fixtIue s. .lsr to tncse of references 1
and 2 werie usec, ; -re't Cifflculty .;s e countered :i
consistentl-y btainin, 'ccur'Oe s toss-stPrin curves. It
was therefore aecid e to e:f e ti reouih inve r-ision o of
the sin-tle- chicknes- nt,} cd of deC ie; .ni co;:;pre: ive
stress-strain curvc. feor th n she.t ir-atri l. Verious
types of 2un-ort .ere usia in the co ..r ,Cio fixture and
ste-se trsi-,-'n curves w.~L; obtc-.ind for s ciiLens thi't
weore I:0oPote, wth dif'er.:~ t vsluiis of supportr i. force.


SPEC,:,7 SJ.PFORTS AN:D TC :?.tiSSION FIAXTUEf


In the sinrle-thic'l iceC .et hd the function of the
corpre ic n i tu i o :.'. rt %- c. -cre.. oi.' thin sneet
materiaL So thrt t'ie st,'-s s-i i"iLi curve obtained ls tne
sparie as vwcull be ota.i.n'd fo.e -n un:rno'e ted ,-ecuirn of
the s 9T^ n.Ftori l h'vi..:- s"c. i ir-': ico')o t o s tn.. bua Cling
could not occrn., ahe Jdrea to ."v.i. thle cornrossion
fixture Jul ills its function 1s1onDs lrely; orn n. per-
foriLaznce of the su ancr'., such as ir : rolle s or .'lt
brcea ostes, tfht co rie RnoO crtanct with the !speci.cr.
For 1ie:i e 'icr.:: nce, he suatporc: hoii Cold the1
snecim.en.: str' gh t not suld not .r ist clhen e in lansbh,
thicknses, or v.idch of tlie socimen.

Rollers, p'ro- d b. ci ss t-lctes, fle t bras:r plates,
and' fl 'l: 'oier .-ICs ve,:e jed in the )resent investi-
gatn .car sl- 2 .rtir trie s irer :ans. f'trse supports apre
shuo'n in fi o' 1 n:d carr dscrribeol cs follows:









NACA RB No. L5E15


(1) Steel rollers In the roller type of support,
25 hardened steel rollers 0.0525 inch in diameter and
spaced 0.10 inch supported the specimen on each side.
The rollers were supported at their conical ends by spring-
brass plates that Permitted the rollers to roll downward
as the specimen shortened during lodin-.

(2) Grooved brass plates 1 : types of grooved brass
plate were included in the investigation. In the first
type, the grooves of one plate were opposite the grooves
of the other plate mna, in the second type, the grooves
of one plate were offset so ss to be opposite the crests
of the other nlete (fig. 2). ..ith the offset-grooved
plates, there is less resistance to increase of specimen
thickness during loading than there is with the opposite-
grooved plates. Both types of grooved plate were lubri-
cated with a hsevy grease ( arfax Fo. 2).

(3) Flet brass plates The birss plates were machined
to a smooth flat finish. The plates were lubricated with
grease in one series of tests Fnd with a mixture of
graphite end oil in another series.

(4) Flat wooden nlates The plates were made of
hardwood (mnple) finished to a smooth flat surface end
were lubricated with a heavy grease (Ivarfax No. 2).

The various types of support were used in the com-
pression fixture that is sho3V.w in figure 7. L:" fixture
is composed of a steae holder that is mounted on a hardened
steel base and inco which ari fitted two steel blocks.
One of the steel blocks is cylindrically seated to make
it self-slining, and the otinr is a sliding block that
permits adju:-tment of the compression fixture for specimens
of various thickn sses. The test specimen and the sports
that come into coiitect with the soecimen ere inserted
betve: the self-3.inini: and the sliding steel blocks.
A leading screw acting upon a loading plite provides a
means of ePpI!ying the supporting load to the supports for
the specimen.


TESTS


Specimens 0.5r inch wide, 2.53 inches long, and
0.064 inch thick were cut fro:.- one sheet of 24S-T aluminum
alloy with the grain of the sheet parallel to the direction









V.;CA R3 ;-.. LT5E15


of 3oedinir. These speciiens were tested in the compression
fix:ure "-'ith the 'four T'Les o' sue ort nd th1 four values
of surortin: I'rcre shove n in trble T.

Du'-Ir. routine tesuing for investigations other than
th'e .::nt invres Ligtionr it ;;s sometimes observed that
for s' :.-u-menj of hC b-strength maturil, C.53 incr '.,id,
ther .e C evi encer of o2ncin in the lInne of the sPecimin.
It -s '_e '. e rdcidei to cir-cres t he with f the
s-:oci is to ..>OI inch. The rubs p .ti -1 increase in width
fro-, '. c -to u.FC :ir.n s select. in order hart the
sn cT'i- e.. :'f.'ht bc. of tr ol. : io s for t stir not
onI the t l. i' eu?: lo: oi o ith co-m ,)e: sive yialh stressss
of :--'o:ir S- 'O to o,, ks-l in rPe ic use but also for
tsiJ. al tP, ri he. da,3Io v;:ich eve-n hihCer
yield stress.

3 ie1;7 of &S-T *'.nd 81- 1 ;.rinur iloy 0.50 inch
e, e2.-l 2 i~. es ior .nr 0,(.04 _c ;hick were tested
wiet rollers -r ro c.- n:roCve7d :': .Lort3 ard
with thi s-.r.e vilUs o supo't:)in or3' th -c were used
for t,-he 0.i.; c.- ce Cs n.s. ,Se t-lle II.)

3'r-irf c '.- rr e' ccl'i.;;n co-v s or 2,-S-T ?1nd R501-T
elu.cinul;;; e lo-^ i -.1CFcs t.. tu11i r.a3en rXollers

sccrdiwn ly wre Q o 0. C.'3-inch-"'ids scenes of
O.029-inct-t 1ti'k t -d- aa- C. 02Q-inch- IC:k RUl-T -alumi-
C). 1.. -t ile '{U1-T alunmi-
nu:1 .5lov sur u rti in r: co::-: ras -cn fi:' lur with roller
sup- ort. SI .-15e- s~?ect i.enrs ,- o.-co:T. *.:d by offset-grooved
Cl t, s v:S 1-e Loste :. r cTr Crs-Con.

In a 1 tle t9 e,: 3 crl.i.s were measured on the two
fr.oe eda cf eC h r. I.t..r or ....'..... a e. of 1-in :c ", r lan th. ..,- sno s a the co'---
paresio&I fixu'e -;iL s en .nd sctrin F, e'. in position
s3 'ore -he te::*.

'L rI.. 3 Al'D i? Caa ""CF



rasts rhic. vahCC tht the atrss -st "-:n curves obtained
fre.. ::,: -t'ic'inss ecra in.ns r v' deoendent cn the type
of ., usa d in tie r-' e.s c- i tu'w o, n tha n.:- i-
to U o' c .'- s n)cr' .i f o rc 90 I to ho se c i n.n, and
on .: i itv of the test pof r- tus nnd the t.st specimen.
The aro:u Ly Lvhico the m, surerd v ais of c-.;-ressive








NACA RB No. L5E15


yield stress and modulus of elscicjty varied with the
type of support and the magnitude of the supncrting force
is illustrated in table I and in figure 5 for the 0.53-
inch-wide specimens and in table II and in figure b for
the 0, .:-inch-vide specimens. The.e tables and figures
show that:

(1) Ti; values of compressive yield stress obtained
from tests with bhe roller t: ,e of su-port were iir.-dendent
of the magnitude of the supporting force, For supports
other then rollers, the measured eld stress increased
as the supporting force initially apollied to the specimen
was increased. The greatest increase was obtained with
the flat wooden plates.

(2) The values of compressive modulus of elasticity
obtained from tests with tne rollers and with the offset-
grooved plates were independent of thi supporting force.
For supports other than rollers rnd offsfet-rooved plates,
the values of tne modulus of elasticl-:y increased as the
supporting force was increased. The greatest increase
was obtained with the flat brass lates lubricated with
Merfax 1o. 2.

(?) The stres.-strein curves for rpecimens supported
by other than rollers were distorted by, increasi.s:c amounts
as the, suonorting force 'a's increased. 7'. distortion was
;. atest for soecimens su ported by flat brass pltes or
:-- flat wooden plates. As an example of the distortion
which occurred, figure 7 shows that the compressive yield
stress, the orocortional limit, the compressive modulus
of elasticity, and the initial part of the stress-strain
curve were changed when the --cieien was supported between
flat brass plates and the su-ortl. force was increased
from 2L to 380 pounds.

The stress-strain curves that vwee obtained for the
roller type of support v:ere more accurate than the curves
obtained for the other tyoes of support. I,-r: roller type
of support, however, is more difficult to construct then
the other types and must be constructed with precision to
ensure accurate results. This fact was enahsasized in the
present investigation when one inaccurately constructed
roller sc.:oort had to be discarded because of the
unreliable test results that were obtained. The flat-
plate and -_-. oved-plate tyoes of suoport are easier to
construct than the roller ty.e but more care must be
exercised in their use to obtain an accurate stress-strain









NACA RB No. L5E15


curve fo' the :m-teral. 'i en the sulorting force was in
the r ane of 22 to i45 poiuos, tie rslits obtained with
the flat-plets or grcov-.d-pls3to supports agreed very
closely with the results obtained with the rollers. These
re-ults are illustLrtLcd for the offset-gPooved plates L.
tn3 typical stress-strain. curves given in figures 8 and 9.

The results of the tests of O.80-inch-wide s specimens
wich roller support indicated thLt n suboortin; force of
22 pounds vas v .in sdnuet.I AlhKou,,h the'o v., s no evidence
that tn' C.O0.-inch-tLhick specicen buckeloua between rollers
as the co]umrn curve: htkd indi;P. ted they might, examinfltion
of these e.pec:1.ends ,.'ter test rv-alcdw buckles of wave
length .restc,"- than the sp''cin o: th_ e rillY-r It js
b lievsd th et this hb'c rlt:.. occur:" -' bec u:ie the sunporting
force of c <.un. v's i u I;ri isit Ito >' ve the -liht
devietioins fr'x flftness tnec uu'fi e .:1st in the sreci-
mens. !Wi.h ? cuopo_,tin: force-; of rotucos, s ti.sfl.ctory
strees-t trKin coure.:- v,..-u obtir.ed cor:si;s:tentl'y v.th all
t -.s i_ su :-.rt. I "t bcklin" of' the '1 zo lla --sep ptorted
s ecim.ens (.scr '.s i I ccat s tlu .: i : out:. sufficient
sa'.orbi,' force, ,1 rl ler-p.uported specimens may give
unS ti.,: rector s t r;. -. Z s 2 rt, l c,_urv s .

'Th press, hc inves bi0.:tion end subsoque t routine
laboratc -* terts s.v3,d thj t sccu"ate stress-strain curves
could not b3 r bbt: :.c c.rncist~ently unless the fixture and
sp'ec0in7ns we", Ec';:.. ely rnaJe. 7Vai'ia~.tions in the test
results were c'usoe by sc ci.:no'i defects or inaccuracies
,ch as: er:.s not i. 'll-L.', not flpt, or net irpendicular
to th3 long dinal o xi'r of the spe.ci.Lmen free ed, os of
the s-ocineai not sitr'. ~ '.1t and sallelo and f-ces of the
s,'eci:.; r sc atei ed o ir iar-;d so t ha't intorferance occurred
with snrtn< 'n of tof l pci.:! -n. The accuracy cf the
sincle--thicone: s o:cii:on .: co imorta rb that production
of th3 neoi;i~ens by ;'u nch s:ddie or by a nheoring
process is not recoI::meidecl even if it can be shown that
the material roepertiis sr'oe rot a pprec:iably affected by
the cold work in th ess :.roce:sos.








TT~."I RB No. L5E15 7


CONC LUS '


An investigation was made of the methods of supporting
single-thickness specimens of aluminum-alloy sheet material
in P fixture for determination of cr .ressive stress-strain
curves. As e general conclusion, the results showed that
for the roller type of support th3 accuracy of the stress-
strain curves obtained as independent of the supporting
force used. Plate types of support, however, also gave
satisfactory results provided that the supporting f oce
somlied to the specimen was approximately 45 pounds.

For the types of support and values of supporting
force used, the follcv.'inr detailed conclusions wer3 dr;an:

1. The values of compressive yield stress obtained
from tests with roller supports were independent of the
sup1)orting force. For sunports other then rollers, the
yield stress increased with the supo ortinog force and was
largest in tests with flat wooden oltes.

2. The values of compressive modulac of eirsticity
obtained from tests with rollers and offset-grooved plates
were independent of the supportinS force. For supports
other than rollers and offset-grooved plates, the cocn-
pressive rodulus of elasticity increased with the sup-
porting force.

7. As the supporting force was increased, stress-
strain curves obtained with plate L es of supports were
distorted and the coi;pressive yield stress and modulus
of elasticity were raised '.. increasing amounts.

L-. A supporting force sufficient to overcome the
slight devi etions from: flttness that usually exist in
the specimens must be used.

5. The compression fixture, the specimen supports,
san the single-thickness specimens must be accurately
made.


Langley Aemorlal Aeronautical Laboratory
National Advisory Comnittee for Aeronautics
Langley Field, Va.








8 ::.:A RB U'. L5E15





1. Paul, D. A., Hov:ell, F. Y., end Grieshaber, H. E.:
Coirparlson of Stress- train Curves Obtained by
Sirgle-Thickness Rnrd Pack s etbods. EACA TN
No. CIq, 19 1l.

2. Anon.: -o-pre-sive Tests of Sleet Ictesl vrith Solid
Guides for Lateral S-uport. Struck. :e:mo. No. 10,
Bur. Aero., I'vy Dept., Fov. 10, 1"L_.





















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NACA RB No. L5E15


ii!III,

SI ii


(a) Steel rollers.


(c) Flat brass plates.


(b) Grooved brass plates.


(d) Flat wooden plates.


NATIONAL ADVISORY
CONNITTEE FOR AERONAUTICS
Figure l.-Types of support used in the fixture for determination of compressive
stress- strain curves.


Fig. la-d






NACA RB No. L5E15


S3 0.53-inch-wide
specimen




(a) Opposite-grooved brass plates.







0.60-inch-wide
Specimen





(b)Offset-grooved brass plates.

NATIONAL ADVISORY
COMMITTEE FOI AERONAUTICS


Figure 2.- Opposite-and offset-grooved supporting plate.
sections are perpendicular to direction of load
application.


Fig. 2a,b









NACA RB No. L5E15


0
o



r0
4-I


O 0 0 0-



w -1 4-'.)





= w C 1 3- [ w .-
CO C 0 C

U) c ** ~ -I d -
0) rL i -u (



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( cd -i -i* rigia


Fig. 3























































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--4,
--I











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a C

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f.;. e
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% yr:.d ~E-H
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NACA RB No. L5E15


Fig. 4






NACA RB No. L5E15


wooden plates

site-grooved brass plates


S46 Flat brass plates (Marfax No.

SFlat brass plates (graphite and
L
S44 1J 8 -Rollers
o


42,-

0o I I I I I I
0 100 200 300 400
Supporting force, lb



3c 11,400- Flat brass plates (Marfax No.;
LL
Flat brass plates (graphite and
.5
S11,000 Flat wooden plates

'6 / Opposite-grooved brass plates

10.600- Rollers

0
0 100 200 300 400
Supporting force, Ib NATIONAL ADVISORY
COMMITTEE FOR AERONAUTICS
Figure 5.- influence of type of support and supporting force on compressive
yield stress and modulus of elasticity. Z4S-T aluminum alloy 0.064
inch thick and 0.53 inch wide.


ol)
oil)


Z)

oil)


Fig. 5







NACA RB No. L5E15






61 R 301-T

60
I Q


59-


I I


451-


0


I I I I


24 S-T-


- 8


3


I I


- R3


01-T


24S-T o

0 0
0 O
- I


o Rollers

n Offset-grooved
brass plates


I I I
100
supporting


I I
200
force, I b


I
300


400
NATIONAL ADVISORY
COMMITTEE FOR AERONAUTICS


Figure 6. Influence of type of support and supporting force on
compressive yield stress and modulus of elasticity.
Specimens 0.064 inch thick and 0.80 inch wide.


Fig. 6


j 10,800

S10,60C

0
0S)


- 10,800
-o
S 10.600


0


I


I


I I


I I


)









NACA RB No. L5E15 Fig. 7


























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NACA RB No. L5E15 Fig. 8









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NACA RB No. L5E15 Fig. 9














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UNIVERSITY OF FLORIDA

3 1262 08106 508 7


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