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Distribution authorized to DoD only;Administrative/Operational Use; APR 1944. Otherrequests shall be referred to Office ofScientific Research and Development,Washington, DC. Pre-dates formal DoDdistribution statements. Treat as DoD only.

OTS index dtd Jun 1947

T Nt\TION�.L DE:FENSE RESE.J;RCH co: JITTTEE

of

OFFICE OF SCIENTIFIC RESEJJWH . ."1-JD DEVELOPfiE, T

\7.tR :..LET •• LLURGY DIVISION

Progress Report

on

PLnSTIC FLO\! OF ;,r,ur::nm .. ... D1CFl.i'.FT

SHE�T UNDER COi: BIN3:D LO;..Ds-II (Ni.-150)

by

JOHN R. LO\:, JR. JUJD T . ... PR.i.'I'J� PEl'nTSl'LV"Nii. S'f,.,TE COLLEGE

OSRD No. 3 53 Serit.l No. M:-249

DISTRI.Bl!flf?N STATEMENT E: DlstrrbutJon authorized to DoD Components only.

Other requests shall be referred t9:

Best Available Copy Thill document contains information affectin&"

the national defense of the Unit t t within

ct. u. s. c.

of its contents in ny manner to n

person is prohibited by w.

ffNIOAL INFOR OR :VA C, E. , ATION BRANCH

I r:. D '

. CH C EN 'T' r:nR n ' N p_.. )VIN'• � OJ •

'1 G OUND AR ';A D

To: Dr. James B. Conant, Chairman

RESTR CTED

1�pril 19, 1944

National Defense Research Committee of the Office of Scientific Rcsc�rch and Development

From: War Metallurgy Division (Div. 18), NDHC

Subject: Progress Report on 11Plastic Flow of Aluminum i�ircrr.ft Sheet Under Combined Loads-II11 (N,i-150)

I The attached progress report submitted by John R. Low, Jr. ,

Technical Representative on NDRC Research Project NRC-52, has boon approved by represent<:.tives of the War Metallurgy Committee in charee of tho work.

This report describes the results of a stuGy of the effect of specimen size (length and width) on the limiting elongation v�lues in tension and the distribution of these vr�lues as a function of gage length for 0.04011 Alclad 24-SO sheet.

I recommend acceptance as a satisfactory progress report under Contract OEMsr-864 with Pennsylvania State College.

��ncl osure

RESTRICTED

·Respectfully submitted,

<" ( ' -'L(\.'(\n . ' ·- � lZP v J...XYJ.-. CU..J....C...-f'

Clyde Vflllinms, Chief ·

\''iar M:etallurgy Division, NDRC

DISTRIBUTION STATEMENT E: Distribution authorized to

DoD Components only. Other requests shall be referred to:

•

RESTR CTED

This report is pertinent to the problems designated by the Office of the Coordinatbr of Research and Development, Navy Departntent, as NA-150, and to the project designated by �he Vla.r >1etallurg;y• Committee as Nr:RC Research Project NRC·-52 •

The distribution of this report ·is as follows:

Copies No. 1 thru 30 - Dr. Irvin Stewart, ·Executive Secretary, OSRD Copy No. 31- Clyde lilliams, Chief, 1far Metallurgy Division (Div. 18), NDRC

and Chairman, VIar �/etallurgy Committee Copy No. 32 - Office of the Executive Secretary, War Metallurgy Comrn.::..ttee Copy No. 33 - V. H. Schnee, Chairman, Products Research Division,

War , Metallurgy Commit tee ·

Copy No. 34 - R. C. ToDnan, Chairman, Sub-Comnittee for· Division 18, ND�C Copy No. 35 ... Roger A:dams, Member Sub-Committee for Division 18, NDUC Copy No. 36 - J. E. Jackson;· ·Staff ·Aide for Division 18, NDRC Copies No. 37 thru 39 - Har Department Liaison Officer with NDRC

.He<\_dque..rters,. Aimy- Service Forces Copies No. 40 thru 53 - Army Air Forces, Commanding General, Wright Field

·Attn: Inspection Division, Materials & Processes Branch Copy No. 54 - Army Air Forces Board, Orlando, Florida. Attn: Secretary of Board Copy No. 55 - Army Service Forces, Commanding General, Watertown Arsenal

Attn: Colonel H. H. Zornig, Director of Laboratories Copy No. 56 -G. W, Lewis, Director of Aeronautical Research

National Advisory Oommittee for Aeronautics Copy No. 57 - Navy Department', .Bureau of Aeronautics

Attn: Lt� Comdr. Wm. P. Goepfert, Project Liaison Officer. Copy No. 53- J. E. Darn, Technical Representative, NDRC nesearch Project,NRC-h4 Copy No. 59 - John R. Low, Jr.,Technical Representative, NDRC Research Project NRC-52 Copy No. 60 - T. A. Prater, Investigator, NDRC Research Project NJC-5�

Members of the Project Committee

Copy No. 61 - L. L. Wyman, Chairman· Copy No. 62 - E. H. Dix, Jr. Copy No. 63 - E. S. Jenkins

CopJ No. 64 -George Sachs Copy No. 65 F. R. Shanley

Members of the Project Committee NDRC Research Project NaC-43

Copy No. 61 - L. L. Wyman, Chairman Copy No. 66 � Capt. J� P. Awlerter Copy No. 67 - R. Bateman· Copy No. 68 - J. L. B�nnett Copy No. 6'9 - M. Gensa.mer Copy No. 57 -Lt. Comdr. Wm. P. Goepfert Copy No. 70 - R. B. Gray Copy No. 63 - E. S� Jenkins

RESTRICTED

Copy No. 71- J. B. Johnson Copy No. 72 - V. N. Krivobok Copy No. 73 - Major B. C. l�ddcn Copy No. 74 - C. F. Nagel Copy No. 75 - Ensign G. 1\f� Onken Copy No. 76 - T, E. Piper Copy· No .• ·77 - A. B. Richards

· Copy No. 7 8 - Lt. B. Rubinstein Copy·No. 79 -Major E. H. Schwartz Copy No, 80 - 0. A. Wheelan

Members of the F.ngincering Conunittee J.ircraft War Production Council, Inc.

Copy No. 81- Boeing ld.rcru.ft Company, Vi. E. Beall 'Copy N-o� 82 - Consolidu.ted- Vultoe hircruft Corp. , Vultee Field Div. , J •• P. Fontaine Copy No. 83 - Db.uglas. J.j.rcraft Company, Inc., : •• E. Raymonq. Copy No. 84- Lo.ckhee d Aircraft Corp., Factory rr;.rr, Mac '.Shor.t·. Copy No. 85 -North American Aviation; Inc. , Gordon Throne Copy No. 86 - Northrop 1\ircraft, Inc. , R. A. D1:1t ton Copy No. 8? - Ryan Aeronautical Company, B. T. Salmon, Chairman

. . . ·· Members. of the Plant Production Section

.Aircraft War Production Ccnincil·� Inc.

Copy No. 8 8 - B.oeing. Aircraft Company, H. o .• vV,es� , ,

Copy No. 89 - Consolidated- Vultee Aircraft GQ!P•, San qi�.�o Div. , H. Bowling Copy No. 90 r Lockh€le d !dpcraft Corp. ,. Fact.ory ":•", ·George H. Prudden Copy No. 91 - ·NQ!'th American l.viation, Inc •. , R • .

E. Dawe Copy No. 92 - Northrop Aircraft, Inc. , Paul .. Buckner ·

Copy No. 93 - Ry�n i:>eronautical Company,. G. E • . �arto·n ,,

. .

. . ··

Members of the Test.ing and. ��

·se

.;irch Panel

1\ircraft War Production Council, Inc •

Copy No •. ·8!1... .- Boeing Aircraft. Company:, V¢. E .• ' Beall Copy No. 94 � �onsQlidated-Vultee Aircraft Corp. ; Vultee F{eld Div. , Harold Boyvey Copy No. 95 - Douglas· Aircraft. Compa�y; Inc.,'. J,,.· B.. Go.ldstein Copy No. 80 - Lockheed Aircraft. -CorP;, , Factory . "B.'', F .• R. Shanley Copy No. 96 - North American .h,.viaticm,. Inc. , L,.. P •

. ppa�ding

Cop-.f No• 73 - .Northrop; J�ircraft, Inc.; �. :E!. Pipe� Copy No. 97 - Ryan Aeronautical· .Comp�ny 1 .. J. C • . Scurlock

� .

Copy No. 9 8 - Aircraft :War Produc·tion Council, .. Jam�s L� Straight Copy No. 99 - Consolidated- Vultee Aircraft Corporation, James Kelley Copy No. 100 - Gurtiss- Wr,ight Corporation, G. H. Cartledge Copy No • . lOl - Curtiss-Wright Corporation, C. C. ·FUr-ncis Copy No. 102- Douglas Aircraft Company, Incorporated, j. C. Buckwalter Copy No. 103 - Douglas J.ircraft Company; Incorporated, ·E . F. Burton Copy No. 104 - Douglas Aircraft Company,. Incorporated, L. l •• Carter Copy No. 105 - Douglas .h.ircraft G.ompa.ny; Incorporated, F. Vi. Conant Copy No. 106 - Douglas Aircraft Company, Incorporated; D. E. Dunlap Copy No. 107 - Douglas .k.ircr�ft Company; Incorporated,. E. H -. � Heinemann Copy No. 108 - Douglq.s h.irc·rt:J.ft Company, Incorp()rated:, .F . . Vi • • Herman Copy No. 109 - Douglas l�.ircrq.�.t Company; Incorporated; J. M, Sc�uma,nn Copy No. 110- Douglas Aircraft Company, Incorporated, . M. G. Simpson Copy No. 111 - General Electric Company, D. Basch Copy No. 112 - Harvard Unive�s:i.ty, P. W. Bridgman . .

Copy No. 113 -..Lockheed 1\irc�aft Corp. , Factory riB", L. H. P<;>tter i.J,F Materiel & Process Unit Representative

•

RESTRI CTED

Copy No. 114 -Northrop Aircraft, Inc., R. R. Nolan . Copy No. 115 - War Production Board, Industrial Processes Branch, Office of

Production Research and Development, Maurice Nelles Copy No. 116 -Copy No. 117 -Copy Nq. 11 8 -

Copy No. 119 -Copy No. 120 -Copy No. 121 -Copy No. 122 -

copy No . 123 -

Copy No. 124 -

Copy No. 125 -

Copy No. 126 -Copy No. 127 -Copy No. 12 8 -Copy No. 129 -Copy No. 130 -Copy No. 131 -

Copy No. 132 -Copy No. 133 -

Copy No. 134 -Copy No. 135 -Copy No. 136 -Copy No. 137 -

Copy No. 13 8 -

Copy No. 139 -Copy No. 140 -

Copy No� 141 -Copy No. 142 -

Copy No. 143 -Copy No. 144 -

Copy No. 145 -Copy No. 146 -Copy No. 147 -Copy No. 14 8 -

Copy No. 149 -Copy No. 150 -

RESTRICTED

Total number of copies - 150

FOURTH QUARTERLY

PROGRESS REPORT

N.D.R.C. Research r.roject NRC-52

RESTR CTED

Contract No. OEMsr B64

PLASTIC FLm�' OF ALUMINUM AIRCRAFT

SHEET UNDER COM3INSD LOADS-II

November 1, 1943 to February 1, 1944

From: Department of Metallurgy, The Pennsylvania State Col1e�c

Report prepared by: John �. Low, Jr. T. A. Prater

RESTR'ICTED

•

FOURTH QUARTERLY

PROGRESS REPORT

N. D. R. C. Research Project NRC-52 Contract No. OE sr R64

PLASTIC FLOW OF ALUMINUM AIRCRAFT

SHEET UNDER COMBINED LOADS-II

November 1, 1943 to February 1, 1944

From: Department of Metallurgy, The Pennsylvania State College

Report prepared by: John R. Low, Jr. T. A. Prater

ABSTRACT

This report describes the results of A study of the effect

of specimen size (length and width) on the limiting elongation

values in tension and their distribution as a �unction of gage

length for 0.04011 Alclad 24-SO sheet. On the basis of these

results it is proposed to confine future tests on othPr grades

and tempers to two modified tension specimens and the standard

A. S. T. M. sheet specimen. One of the modified tension specimens

will be of sufficient length ( 1211 ) so that the uniform as rell

as the local elongation may be determined. The othor will be

a wide specimen with curved edges so designed as to limit

lateral contraction to a minimum during stretchi ng in the

tension direction.

RESTRICTED

•

RESTRI CTED

FOURTH C'UARTERLY

PROGRESS REPORT

N.D.R.C. Research Project NRC-52 Contract No. OEMsr 864

PLASTIC FLO\�r OF ALU.,UNU�.[ AIRCRAFT

�HEET UNDER COMBINED LOADS-II

November 1, 19�3 to February 1, 1944

Fro�: Department of Metallurgy, T�e Pennsylvania State Colle�e

Report prepared by: John R. Low, Jr. T. A. Prater

CONTENTS

P ge

I. Introduction................................... 1

II. Experimental Procedure......................... 2

Specimen Preparation......................... 2

Gripping and Alignment .. · . . . . . . . . . . . . • . . . . . . . . 2

Material ............... . .. . .. . ....... o • • • � . . . 3

III. Effect of Specimen Size........................ 3

Table I. Effect of Specimen Dimensions on Elongation and Lateral Contrection.. 6

Fig. I. Method of Determining Length in Simple Tension from Lateral Contraction Measurements ........... .

Fi�. II. Effect of Specimen Dimensions on Fraction of Reduced Area in Simple

5

Tension ..... . . . ..... . . . .... G • • • • • • • • 7

Fig. III. Effect of 3iaxial Stress Condition in Plane of the Specimen on Elongation to Fracture............. 9

Fig. IV. Effect of Specimen !idth on Local Elongation near Fracture............ 10

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IV.

v.

VI.

Summary . ... ..... . ' • o o • a • • • ., • • .. • � • • • • • • • • • • • • •

Plans for Future Work . . . . . . . . . . . . • . . . • • . . . . . • .

References . . . . . . . . . . . . . . . . a • • • • • • • • • • • • • • • • • • •

Page

11

12

13

•

RESTRI CTED

FOURTH 0UARTERLY

PROGl\ESS REPORT

N.D.R.C • . Rese�rch Project NRC-52 Contract No. OEMsr _64

PLASTIC FLOW OF ALUMINIDA AIRCRAFT

SHEET UNDER COMBINED LOADS-II

November 1, 1943 to February l, 1944

From: Department of Metallurgy, The Pennsylvania Sta.te College

Report prepared by: John R. Low, Jr. T. A. Prater

I. Introduction

T�e purpose of the present investigation is to determine the

plastic behavior of aluminum aircraft sheets for various combinations

of the principal strains in the plane of the sheet. As a part of

this testing program it is necessary to know the effect of

specimen size and shape on the amount of flow which precedes

fracture·in the simple tension test. The results of such a study

will, for example, indicate to what extent ductility values

obtained from a standard sheet tensill. s�ecimen are represent�tive

of those to be expected in stretching sheets of larger dimensions.

Further, the present investigation provides information on the

manner in which the elongation vs. gage length curves are changed

when the deformation is confined to short gage lengths under

conditions of severe lateral restraint.

RES�RICTED

"tti

II. Experimental Procedure

Specimen Preparation:

2

The specimens us2d in the investigation varied in width from

�" to 10" and in gage length ·from 111 to 1 2 11, giving length/width

ratios ranging from 0.10 to 17. The edges of the specimen were

milled oarallel and any burrs resulting from this step -vvere

removed with a sharp.$C�aper .. No filing or polishing of the

specimen edges was done. A 100 line per inch grid was then

printed on each specimen employing the 11photo-grid11 technique.

The grid obtained by this process was accurate within �4-.0� over a gage length of 0.01"; �l.O%over a 0.05" gage; and �0.2% over

a 1.011 gage.

Gripping and Alignment:

In some of the tests simple rectan�ular specimens '"i th no

reduced section were employed. Although four different m�thods

of gripping the specimen were tried, it was found that in most

instances specimens of this design fractured in or very close to

the front edge of the grip. Later specimens were milled with a

fillet of 1�-11 radius and e.. shoulder t" ��rider than the gage section

(Fig. 1) • This design proved satisfactory for specimens not

exceeding 511 in width, but for the wider specimens it ·was necessary

to increase the fillet radius to 3" and the shoulder width to l"

greater than the gage section to ensure a fracture within the

section of reduced *idth. All data reoorted are taken from

. .

•

RESTR CTED

3

specimens with a reduced section except where otherwise designated.

The specimens �11 wide were gripped in Te'Tlplin sheet grips

which were held in modified.Robertson shackles. Each was care-

fully'aligned by placing·l'' �age length Tuckerman optical exten­

someters on either side of the specimen and .shifting the grips until

the elongation on each side was the same for any given change in

load. The wider specimens were gripped between files and ali_ned

by keeping the specimen_edges perpendicular to the front edges of

the two sets of gripping files. Before testing the distance

between the two sets of. j�ws was .measured at the two ed�es of the

specimen to further check the alignment.

Material:

All of the results herein described apnly to 0.040" Alclad

248-0 sheet �ested in the rolling direction.

III. Effect of Specimen Size

� Photo-elastic studies (l) show that the portion of a tensile

test specimen which is not in simple tension varies ,ri th spE:>cirnen

width and radius of fillet. Dorn and Finch ( 2) , in th8ir 'ork on

magnesium alloys, have found that, if the radius of the fillet is

k�pt equal to the width of the gage section, the portion of the

test specimen not in simple tension extends from the fillet into

the reduced section to a . distance approximately equal to the

specimen idth. In the present tests, the portion of the test

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4

specimen in simple tension ��s taken as that section �hich had a

uniform percentage of lateral contrc?ction. The extent of this

section was determinsd after the completion of the test by

measuring the lateral contraction over a 0. 211 ga.ge length along

the center line of the specimen at convenient intervals. The pr::r-

cent contraction at each point was then calculated from the

-w

o - wf relationship: % contr. - W x 100 where W0 = 0.2n, and

0

Wf

= distance across 20 grid sauares after test. These values

were then plotted against their positions along the gage section

(Fig. 1) and the length with uniform lateral contraction determined

graphically. The percent uniform lateral contraction appears to

be independent of specimen width and varies between 5.0% -and 6.5%. (Table I) It appears that the only effect of snecimen width on

lateral contraction is that the narrower specimens sho ' some

lateral necking in the immediate vicinity of frocture thus prou1cing

greater elongations (and contractions ) over short ga�e lengths near

the fracture. Curve 11blf in Fig. l has been drawn for a specimen

that shows a uniform lateral contr.s.ction lower than that found to

be representative of a condition of simple tension. This "behavj_or

was also exhibited by a specimen 1011 wide with a 111 gage length.

It appears the.t these specirnens are of such shape and dimensions

that equal lateral stresses are set up over an appreciable gage

length resulting in a section of uniform lateral contrPction

although none of the specimen is in simple tension.

� t),. � � <:S

'I

p

·� � '-6

I �

§ .:.;:;:

....

-� _1_

t . t - ---r--L r

00 a, -

/ �� I <r

( . .,. �t/ �_h "o

'fjc!J"

., ---'.---t:-

-0 t•

0 c v

•

..L if. A/clad 24S-O a 2.511 4 75.

0040" Sheel h 2.0 5.0 (no fillels) c 4.5 2.0 d 4.5 �.15

. e IO.S IQO ( R=3'l

0 'n 0-.

/n - '-.n

y/ / ( u

""·

d cV � g

� �i/ If �I\. c:: <3 � � .� '-J

'

s

t

� 2

� � 0 � � �

y·

=H-

�r 0 cb

/ ( � �) I '-englh. in sim p/e len >ion J � r I

e 1+-/ , ---+-. ----

Dis lance along cenfer line Fig. 1 Me/hod of delermining /englh in simple lension from

/a/era/ conlraclion measurernenls

�

\It

m

a

� b

RESTRI CTED

6

TABLE I.

Effect of Specimen DimPnsions on Elong·- tion and

Specimen Dimensions

(inches) L W

2�· 1 2

4� _)" 2

12 � 4

4Q 2

2"� 4�

4� 4i

10-:1. :2 10

Laternl Contraction· ; Uniform Lnteral Elongation Lateral Contre.ction for Zero Contraction at Fracture Ga(e Lenyth

(in/in) (in/in) in/in

.059 . 101 1. 1 1

.059 .076 1.18

.050 .106 1.35

.062 .064 1.52

.056 .057 1.21

.065 .066 1.1 1

.053 .053 1 . .33

All values refer to region in simple tension.

The percentage of the gage section with uniform

Limiting Uniform

Elon�ation (in in)

.165

.159

.160

.198

. 195

.180

.165

lcteral

contraction, i.e., in simple tension, has been pl�tted against

the ratio: L/W, where L = the l�ngth between fillets and W == the

gage width, (cf. Fig. 2). It is seen from this plot thC;t for

the design specimens used in this investigation the length of

the reduced sectiJn must be �t least one-half as gr�at es its

width or there will be no SPcti�n in simple tensi,n. The

fraction in simple tensi�n increased rapidly �s 1/W is incrc�sed

until that ratio reaches a value of Appr�ximRtely 2 after vhich

the increase is c�mparatively sl�w.

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•

•

RESTRICTED

0

�-------

� I --Q: � 1-.--

I . , �

�M-. � 0 ......J cu

a ....... I . � y, cu cu cu I � � I �C\J "b

� I <:::) ,,f-1 � � � � 1-L-(..) .......... j \ � C) �--- -----

-""

� � .... e <=>· li

8 � dU,17 't3Jd/Ud[) �UOfD � 8

7

UO.JFJDJ/UOD fDJaiD7 WJOj,IUn 1.{/.IM 7 JO UO.JI�DJ..:f RESTRICTED

RESTRICTED

8

In Figure 3 elongation hQs been plotted as 8 function of

gage len�th for six specimens. In three of these the entire

length covered by the curves is in simple tension, 8nd in the other

three there is no region in which that condition exists. The

curves fall into two distinct groups with the specimens in simple .

tension exhibiting the greater elongRtion. This effect is most

marked for gage lengths under one to one and one-half inches.

From these curves it is observed th�t elongation to fracture is

not affected by specimen width provided the specimen length is

great enough to permit a state of simple tension. The only

exception to this is a slight lowering of the elongation-gage

length curve in the rBgion of short gage lengths in the cese nf

wide specimens. This minor variati,n is due to the lateral

necking which occurs in the narrower specimens, but is not observed

in those exceeding 211 in width. While the el�ngati�n �v9r

zer: gage length does not seem to be a functinn :)f ·width, the

el0ngation over c�mparatively short gage lengths (i.e., . 05 11 t0

.5011) is increased in the narrower s ecimens because 'If' the

greater gage l8ngth affected by the neck. As sh��n in Fi . 4

this regi0n extends f0r approxirna.tely 1�11 in the �" snecimen

and f-::>r Jnly abc)ut !" in the 1011 specimen.

RESTRI-CTED

� rn (I} � � r;1 �

� .s

14

I 12

I 10

�08 . c::: �

c::: �06 C) � Q llJ 04

I 02

�. �

p

�

'l � � h-

4

I I A/clad 245-0 0040'' Sheel BlilS

000

. !laA

• • •

• • •

• • •

simp) lens ion ':\ -

• - • - • ...

- -� QO" o, ,-gage Venglh ' n simple lens;or,

0 02 04 Q6 08 10 12 14 Gage Lenglh (.;nc hes)

•

I I lf L

I# II

� 4� .J. 1/

*' 12�" 10" !012

,,

10'' I " I� •

10'' 2Jf''

10" I. II 4J2

r.. "" � - a -

.

16 ·/8 20

Effecl of biaxial slress c ondilion tn lhe plane of ff1e spec imen on e l ongalion lo fraclure

Fig. 3

i i i

i I I I I I

I

-

� l'rJ

2." VJ .L � � � ..0

� v

:., � � � � ni �

A/clad 245-0 0040" Sheel

021 �. I I � I\.. ·I . I I L'.. I I I I ' I I Q

roc lure ,,

� wide specimen 12'' long

10" wide specimen tO" long

�Dis lanc e along Cenler Line of Specimen--.

Fig. 4 Ef fecl of specimen wid lh on local elongalion near fi-aclure

•

b

�

� � til \j·

RESTRI CTED

11 IV. SummEry

It has been Lmnd thc-t lateral c··ntre.ctirm measured at

intervals along the spEcimen center line parallel to the

direction of loading is a sensitive measure ·or stress conditions

in the plane of the sheet end can be used to determine the

actual length in · p�re tension, that is; the length of the

specimen �thich is not affected by the fillets or grips.

Within the region of simple tension neither the lateral

contraction nb� the elongation to fr�cture appear to be atfected

by increasing the specimen width or length except that fo-r very

narrow specimens ( less than 2" wide) some lateral necking occurs.

As a result the elongation values �easured in the immediate

vicinity of fracture ( i. e. , over short �age len�ths) are

slightly higher th2n those obtained with wide specimens.

The frection of the specimen length in simple tension may

be plotted as a function of the ratio:· length/width. · When

this is done it is found thet for the 0.04" thick sheets beintS

tested and the particular shape used, this fraction begins to

decrease rapidly as L/W decreases below 2.0 a.nd becomes zero·

in the vicinity of L/W : 0. 5. As the ·fraction of the length

in simple tension decreases the curve for elongation vs . gage

length is·shifted to lower elongatiqn values�

RESTRICTED

I·

12

The above observ2 tions e.re bnsed on tests on Alcl:>.d 248-0

specimens 0.0411. thick o.nd vc.rying ·in length from one to twelve

inches and in width from one-half to ten inches.

V. Plans for Future Work

On the basis of these results it is proposed to standardi�e

on two tests in the future: one, a tension test on a specimen

of sufficient length to obtain simple tension conditions over

I

sufficiently long gage lengths to be Qble to evaluate the uniform

elongation (i.e., infinite gage length) as well as the elongation

values for shorter gage lengths; the other, a tension test using

a wide sp�cimen with curved edges ( cf. Third Quarterly Progress

Report) . so d�signed as to l1mit the lateral contraction to a

very small value approaching zero. .

These two tests togethar with the elliptical and spherical

bulge tests of NRC-51 at The Carnegie Institute of Technology

will make it possible to obtain elongation values for a large

variety of combinations of the principal strains. 'I'ests are.

to be in·ade in both the rolling and transverse directions and

in sufficient number to indicate the ra.nge of scatter which

may.be expected.

At the present time 0.04" sheets are on hand in the following

grades: Alclad 248-0, 248-T, and 24SR-T. OthPr alloys and

te�pers are to be included in the testing program as soon as

sheets can be obtained for testing.

•

.

'

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VI. References

l) E. G. Coker and L. N. G. Filon: Photo-elasticity,

Cambridge University Press 1931, pp. 560-578.

2) J. E. Dorn and D. M. Finch: Finel Report on

"Properties and Hea.t Treatment of .MR.�?;nesium Alloys:

Part I The Effect of Size upon Tensile Properties

of Specimens of Magnesium Alloy Sheet" (NA-144).

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