V^cAl-IIO AEE No. L5F01 1 NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS If WARTIME REPORT ORIGINALLY ISSUED June I9U5 as Advance Has trie ted Beport L5FOI COLUMN AND PLATE COMPEESSIVE STRENGTHS OF AIRCRAFT STRUCTURAL MATERIAI£ 2l^S-T ALUMINUM- ALLOY SHEET By Eugene E. Lundquist, Evan H, Schuette, George J. Heimerl, and J. Albert Ro/ Langley Memorial Aeronautical Laboratory Langley Field, Ya. UNtVERSlTY OF FLOPiDA DOCUMENTS DEPARTMENT 1 20 MARSTON SCIENCE LIBRARY k P.O. BOX 117011 GAINESVILLE, FL 32611-7011 USA WASHINGTON NAC A WARTIME REPORTS are reprints of papers originaUy issued to 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 - 190 Digitized by tine Internet Archive in 2011 witln funding from University of Florida, George A. Smathers Libraries with support from LYRASIS and the Sloan Foundation http://www.archive.org/details/columnplatecomprOOIang \v» \-x3 y^'? ^'^'^ •?sO*^7^ 1 NAG A A.^R No. L^FOl NATIONAL ADVISORY COMMITTEE FOR /iERONAUTICS ADVA^IGE RESTRICTED -JEPORT COLUMI AND PLATE COMPRESSIVE STRENGTHS OF AIRGR/iFT STRUG TUR..L MATERIALS 2I4.S-T ALUMINUM- ALLOY SHEET By Eugene E. Lundquist, Evan H. Schuette George J. Heimerl, and J. Albert Roy SIJIViMARY Column and plate compressive strengths of 2lj.S-T alu- minum-alloy sheet were determined both within and beyond the elastic r^nge from tests of thin-strip columns and from local-instability tests of formtad 2- and channel- section columns. These tests are the first of a series in an extensive research investigation to provide data on the structural strength of various aircraft m.aterials. The results, which are pre>-ente5. in the form of curves and charts that may be used in the design and analysis of aircraft structures, supersede preliminary results published previousl^f. INTRODUCTION Column and plate members in an aircraft structure are the basic elements that fail by instability. If efficient structures are to be designed, the strength of these ele- ments must be known for the various aircraft materials. Aji extensive research program has therefore been under- taken at the Langley Memorial Aeronautical Laboratory to ..establish the column and plate compressive strengths for a number of the alloys available for use in aircraft structures. Reliable and rapid pi-'ocedures for testing such matei'isls have already been developed and are described in referencjes 1 and 2. The first m.aterlal tested during the present investi- gation was 2[t.3-T aluminum- alloy sheot. The results for this material, given herein, supersede those contained In a preliminary report (reference 2). 2 NAG A ARR No. L^FOl SYMBOLS L length of column p rr^dius of gyrstion c fixity coefficient used in Suler column formula — p effective slenderne^s I'-atio of thin-stx-'io column p^fc b width of piste brp width of flfinge of Z- or channel section (see fig. 1) b™ width of web of Z- or channel section (see fig. 1) r inside radius of bend of Z- or channel section (see fig. 1) t thickness of pl-^te k nondimensional coeffj.cient used in plate-buckling formula k^ coefficient k used with bjy- pjid t in plate - buckling formula (see fig. 2 and reference 3) Sq modulus of elasticity in comoression, taken as 10,700 ksi for ^i+S-T aluminum alloy T nondimensional coefficient for columns (The value of T is so determined that when the effective modulus TE(, is substituted for En in the equation for elastic buckling of columns, the computed critical stress agrees with the experimentally observed value. The coefficient t is equal to unity within the elastic range and decreases with Increasing stress beyond the elastic range. ) r\ nondimensional coefficient for plates corresponding to T for colu:nns |j, Pois son's ratio, taken as O.3 for 2[|.S-T alumlniun alloy NAG A AR'R No. L5F01 ^ Q-p criticsl coiTiprsssive stress <7^„„ sver^ee comoressiva stress at inaximurn load o compressive yisld stress ]\STHODS OP TESTING M3D ANALYSIS All tests were irisde in hydraulic testing machines accurate to within three-fourths of 1 percent. The ends of the stress-strain specimens and the colunins were ground flat end square. Stress-stra in curves .- The compressive stress-strain data, which identify the material for correlation v/ith its column and plate compressive strengths, were obtained from tests of single -thickness sceclinens in a compression fixture of the Montgomery-Temp lin type shovm in figure 5' This fixture v/as used only for flat compression specimens, which represented the material before forming. Infor- mation on the teclinique used in maklnn these tests is presented in reference Ij.. For the bent material in the corners of the formed Z- and channel sections, compression specimens were cut from^ the corner portion and tested in the special fixture shoivn in figure k. Column strength. - The column strength and the asso- ciated effective column modulus were obtained by testing thin-strip columns of the m^aterial with the ends clamped in fixtures of the type shown in figure 5. The use of end fixtures of this type is discussed in detail in reference 1. The fixtures used have been improved, and the method of analysis has been modified since the publication of reference 1. The method now used results in a columji curve representative of nearly perfect column specimens. In addition, the miethod now takes into account the fact that columns of the dimensions tested are actually plates with two free edges. Plate compressi ve stre ngcii.- The plate compressive strength of 'the material was obtained from compression tests on Z- and channel-section columns so proportioned as to develop local instability, that is, instability of the plate elements of which they are comiprised. (See fig. 6.) Inasmuch as the flanges and webs of such columns are in reality plates with various ■ kinds of edge suoport. i| KAGA ARR No. L5?01 the problem cf Iccel instability of these colur.ms Is a plete-buckllng pi'obleiii, aiicl tiie plate compressive strength of the ..ripterlal wss evsluated frcm these tests. The lengtlis of the colurniis were so chosen as to avoid colunxi faiiui'e and still provide satlsf actoi^y local- Inatfbllity data. These conslderptious ere discussed in reference 5» The Z- and chaiinel-section cclanms were tested v/ith the ends bearing directly agginst the testing-machine heads, which were carefully alined to insure uniform bearing on the colamia ends. A Z-section colioirji urider test is shov.n in figure 7« Th'- relative displacemencs of pointers, which 'vvera supported by extension arms attached to the fl-snges of the specimens, were measiared by the cpticfl -Tiicroirietyrs thet can bo seen in figure 7* Ttie displacement was taken as a measure of the cross-sectional distoi'tion, and the critical compressive stress was obtained from stress-distortion curves of the type illustrated in figure 3, The critical stress y»as determined as the stress at the point near the top of the iaiee of the stress- distortion curve at vjhich a marked increase in distortion first occurred w3 th sm.all increase in stress. (See fig. 3.) RESULTS AJTD DISCXjSSIOK Because the compressive properties of aluminxxm-alloy sheet may vary appreciabl;/ , the data and charts of the present report should not be applied to the desifxi of structures of 2IlS-T aluminum- allov sheet having compressive properties appreciably different from those reported herein unless a suitable method is devised for adjusting test x'-esalts to account for variations in material properties. Compressive Stress-Strain Curves Com.pressive stress-strain curves obtained for tne flat sheet material used in marine; the colui:Xi3 are given in figure Q for both directions of grain. The Z-, channel, or thin-strip colutmis to which a particular stress-strain curve applies are indicated in table 1, to^^ether with the value of the coiiipressive yield stress CJ^^. for that stresS' strain curve. These values average approximately i|Ij. ksi for the flat sheet material in the v/ith-grrdn direction NAG A ARR No. L5F01 5 and Ij.9 Ksl in the cross -grain direction. The modulus of elasticity in compression v/as taken as 10,700 ksi, the accepted value for 2lj.S-T aluminum alloy. When the flat sheet mrterial is bent to an inside radius r of Jt to form a Z or channel, the cold vifork done on the material evidently raises the compressive yield stress for the curved corner portion above that for the flat web or flange, about lei percent for the with- grain and 10 percent for the cross-grain direction. (See fig. 10. ) Because the curved corner specimens included along their edges some flat material (about 1^.0 percent of the total area) for which the yield stress is lower than that for the curved portion, the actual increase in the compressive yield stress for the corner portion may be scir-ewhat greater than the Increase indicated in fig- ure 10. The important result to note is that the com- pressive properties of a formed section may not be uniform over the cross section. Col^ormi Stz-'ength The results of the tests of the thin-strip columns are given by the coluinn curves of figure 11 for the two directions of grain. At stresses beyond the elastic range, the experi- mental values of a^^^ are lov/er than those computed by the Euler column formula (see elastic-buckling curve, fig. 11), because of the I'eduction in the effective modulus of elasticity. The effective modulus to be substituted for E^ in the Euler coluirm formula to bring calculatsd and experimental values of o^^ into agreement is givexi as tEc where t Is a coefficient that is equal tc unity in the elastic range and decreases with Increasing stress beyond the elastic range. In structural calculations in vifhlch it is impossible to use directly values obtained from the column curve (fig. 11), the value of t for a given stress must be known. The variation of t with stress for columns is therefore showi in figure 12 for both directions of grain. D NACA ARR Uo. LSFOl Fl?fcF> ComnressT ve 3tren.2;th The i-esults o'f ths local-instability tests of the forined Z- rnd chaixne 3 -section col''aiiii"s , used to determine the plate compressive strength, ar'e Piver. in tables 2 and 5. The important ralationcbips for corr.pressed platos obtained from these testr are sho«vn on the curves ajid design charts presented in the follov.'in^ paragraohs. Plate-buck] ing c urve . - The plate-buckling curve, which is analo.:ous to the colur::n .curve , is shovm in fig- ure 15 for olstes loaded in the wlth-grain direction. The abscissa Ir figure I3 is suggested by transposing the plate-buckling equation cr krr^^t- 12(l-i..^)b' (1) to the form a. cr TT^Hl, ----|2 (2) whore the subscript W is added to r.aice the terms b and k of the equation correspond to the entries in tables 2 smd 5« The siir.ilarity between the form of equation (2) .and the follovv'lng form of the 3uler colur.xi for.iuls 1? to be noted: cr ■J C Vp,v (5) At stresses bejor.d the elastic range, as in the case cf colii/iins, the experimental values of Q for plates are lovvex* than those given by equation (2) for clastic buck]. ing (see elastic-bucicling curve, fig. 15), because of the reduction in the effective modulus of elasticity. The effective plate modulus corresoonding to tS_ for columns is rlv-n as rS c» rnd the varlftion ol c r th NACA ARR No. L5FOI ( stress is given, togethex" with the variation of t, in figure 12. The crossing of tne t_ and r:-curves shown in figure 12 occurs because the formed columns apparently had an appreciable degree of imperfection, which resulted in the deviation of the r,- curve from unity at a lower stress than that at which th3 T-curve, reoresentative of nearly perfect columns, deviates from unity. Relationshio of a to o_„/n for plates.- In cr cr problems concerned with the strength of plates, it is sometimes desirable to insert the value of nS^ for E^ in the plate-buckling formula, equation (1), and to write the eqiistion in the transposed form ('-^) In this form the v?lue of "^cr/^^ ^-'^ given by the modulus of elasticity, Poisson's ratio, the ji.eometric dimensions of the elate, and the coefficient Ic, The value of a^^ can then be obtplned by use of the curve of o^^ against o^-p/v given in figure l!|. This curve m.ay be obtained by plottinT the data directly or by plotting from the faired curves of figure 15. As in the case of equation (1), the subscripts W may be added to k end b of equation (I).), and ^cr^''^' m.ay be determined for a Z- or channel-section by the use of the formula and curve of figure 2. Maximum compressive strength of plate elements . - In the case of a plate loaded in long i tud in a 1 c ompre s s i on , the supported, or restrained and supported, side edges remain essentially straight after buckling and ore capable of carrying additional load. As a consequence, there is a 'maximum strength for the plate that is greater than the buckling strength. Theoreticrl studies that appear in the literature concerning the ultimate strength of plates and the asso- ciated effective width of the plates after buckling indicate that the average stress at miaxiraum load is related to the critical stress. It is therefore reason- able to assum.e that the average stress at maximmn loed 8 FACA .Al^R No. L5FOI a„, „^ for tli-^ co'.nbinatiori of "olgte elsL-'ents that ms-ke up the 2- or chc' o OT O «fj E HO H > M QQ §H CO W §^ M m OT g SiJ M O Q O I IK ID K -H Q 0} o n olfT a ^ O \ M — (\J I rH it < ^ ^ ^ > ^ G M-a ••J c o o CD 43 vO LPivOsO -d' f\) '^ r— f^ lTiCO o on OsONONCTNC^GNONCT^ONCrNCX) ONCO rH ,o -c--r>- K^trV^tCO-jd-J-t— CO ONiH irNrH_:t JvO fVJr-4 rvJvO lOi-H rH KAQNO ON ONKV^Ot^^OOJ i-i O ifMrMrM/M hKN -fN^ NO c~-r~-r-coa3 ^-^NO to _j- j- j- KMOv KN rf\rr\ ^f^ WN _;tC^L'^CrMJ><-t l/VX)CO O ONfM KN NO r— NO (V t— ON '*N •-< '<^ LTl fvj »C\0 ONONKNOJ OCO rH_:ivO l/N r-iM ir>r-uxt> <\i c~-^o 'Mno t^r-t r~.NO trM/vd''-< Kvd-f-F- i/MTN^-it^ '<^ ><> ><> OOnOCOnOnOnO o oco_d- iTvUMfMCv K> KN fCv tr\ f\J f\J o c^ononc^u>vO itmh Kvzto r— ^(M LncoaN«-i co ctnonod c^-no f-- KSTVJvOnO t~-KNKSO o ooococo (DrH (M^iTMfVIXJNCOCO rVJrvJ«-trHiHi-I.Hr-trHrH fVI rVJ (\l (-4 r^ . 03 rvj KNhfNso o tr\0-;tONir\r-KN r~ONO O ONO ONO O O r^ r^ r-l t^-oD »CMrN(7NCr>KO r>i_d-i/N OD 0>r4 OvOnO O O O miOsOCD (vt>-(7\ONONO nj rvjcoco ONtM H ococo t~-coco pH rHHTH H i-l rH r-(«-4iHHH r-l i-ti-»lHr-trHiHr-(r-t(Mr-t »f\ji-t"-a5 CTso irvo OTO CTnOnOOOOCO OnCOOO ONCO rHKN<\lC\J(MrHf\l(MON _:t_d-J-0S0N0N>-? 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Eh O CO tJ ta cd Eh > oq Q Q < CO X g^ M c/3 CO 2 ta rD Si-) M O Q O I en ■a: Ic (D n Sh -I U CO D -^ CM rvj S ^ s ^ .-I c: i3 .H •P c o CJ CO u w si lPilOO O OrH CJSMDvO o r^-co ON ON On CJN ON ONCE) CO CO 03 ^-f^ irv^ONr-i f^NiTv^cocoxo irv^ .hco w^l<^o^- c\j o cm ^<^l-l^^ vo ltnn^ltno cmvo irNfOO f-t as C — CO CO rH CM »H Lr\^^ O KV^ f o oncu co irsLTNu^i-iKvcto n>c r-{ r-i (M CM Lrsa^fCMM r-t [ — CO ITV LO ltn lp> lPvJ- J'-d'-J" -^ KN K> ^<^ J^vOM3 C— coco iH i-H rHvO MDvO _d-_j-^tCNrOvKNKAKNro,rM -\J CM O t — K^i-f^-D CMTvO KNhfNrvJ fO» o r— ltnvoco cm j-Lr>LrNKNvo J- r-iojcocovo r^LpM-rMrvd-_:j--3" _:j-crNr-t a^^vl^r^ J-fM irxj-rvj c^ OnO r-iKO C^r^-LTNsOvD D—COCO ONvO cm O CM tH OCOxO ''>C0 iTN CM C~-vO LfN'^'NONLOC^NOD CM NAO O _d- ltmj^ C7NCO -:± N> roi cTN ^-<3^ N>rc\rOiN>r rH rM [>-r-l i—i C^r— C — rCALPvrH «— i I— I O^C^»C7^ r--vOsococovo ^ o o^a\so c^t~-r— ononctncm cm cm t-->-r-- CM ■ rf\hr\rO\rvjfMCMC\JrM (\l r-t r-i r-{ rH J-iH NACTnOCO rH LfVj-CWX) o CO o-sco CO _^ crxOT cJ\cr) ltnco [^ [■— CO O O 'K-V4--4-'<^ 7^ rH H rH TH 7?'3 "(M CM rg" ON KVxJ-CTN ON rH O O O O lOvO LOvD lTNLOlO^O r— O fM ONLOtM C^CM J-ONJ-CM rHfM(MrHrHfMrHrHrHO C — C^C^f— r— C — C — r— ^c^^c^K^^r^^r^KAK^K^K^^r^^r^K^ vO O O a\ir\r-< rH O O k^cm f'N CO o o cr\f-f r-i H\t NAJ- LPi_d-_C)- J- CM _^_zt oooooooooooo _:d" LO lCVJ- LO lTvJ- lOvO -d^D LO OOOOOOOOOOOO (O^oajjDeoxiocOXio rH CM fM CM KNKV:t_^_:t lOlOlO aSX'oaiX'oaiXioaiX'O vO^XlMD f-t^t~-COOOCO CTvONON CO O l-H >* 2 K < O if: CO O M a: > M - < 9 iJ o < &, is O M l-H M El Eh < Eh S 1-1 O o O II 171 o o m L, o 3 M U) -H Ch 0) t, (1) (D ® x: a » ^ ^ ^ CM ^ ?5 (M J3 -P Ch O fM O CM i m t rH (D i« . * n ^ CM rH rH a > II L ^, O O fT u. D (0 ^ NACA ARR No. L5F01 18 o E-> oa • w 3 M-P « C |5 &< M >-] m M E-« CD ►J < c/J CO M Z S M HH CO < 6a o Eh O Q •-) o m MQ CO ze- w < sx M E-i Q rO • Z CD 6h t,| s o e D llD «• tQ Id ^^ o a D -X c\j CVJ ^ ^ X) »-> c ^5 ■P c o o 0) •p O r-t r— O rHCO O t^LPihr\f— J" (Mco r— lpkovo c\i ltvOnco K^o _ct CTn NV:}^© fM CO "H tM i-H r\j CVJ lTS rH u>,vO i-t ONf^NOO C^N^CO CO r^r-^f\JOOocoa^a^'^f^'*^ ^r^^f^^f^^f^K^^r^c^J rvj (M.^i^-d'-d" 00 CTvoo (\j K^^f^o i-h r-n onono K^^r^^f^K^K^^r^N^K^^<^rvJ ru k^ vO r-c\JC0f-^O f\J rvj O ro>r~-(M ^-iTNM I-l_:J■r^^^ t~-c^o '<^lr^ CM CMi-i lOCOsO ITS-;}- '<^C0C0 rH C\jrVJr\J'-<'HiH rfN onCO C^ rH irvo CD '*^cot\Jvo f-i-tcJNoD \o '<^^-'-^vo f\j (^J_:J•l/^o r~-Lr> (M c\j c\j r- CO r-j-_J-.^cKa crs <-ic\j ^h ajrvj f\or-tco ^^^r-t t-t o o^cr^a^^<^-d■'<^ _d•Lr^c^>co r^o^^^-0'-^^-K^ C^C^C-OO C7NCTNhr\fo>t\jr\jc\it\jojfvji r— /H LrMrMrN.-( ooo rHcnco ^r\ r— CDCO f-CO OODCO O OOnO OC0_:tfVJ ONO Jro OCO-J-CM o C7NONO a^o oco o cTvco crs ^ fo\ K> irvj- a^vo iTNvo -vO ^o vo J- oco K^^f^^r^r^ fVJ cjnaJ »<^"CO CD cr^j:tNOoo_d-Lr J- CVJ V43 _:t '<^ O J- NXJ-_d"-:d- '<^ nj CVJ o] cvjcvj rQ rvj Iv] rQ tvjcvi f\J C^^ONC^-C^^C^-CNC^^C^^O^C^^C7^C^^ cvjcvicvjcvjcvjfvjcvjcvjrvjcvjcvjcvj i-HiHi-tOrHiHOi-lCVJCVJrHt-i iHrHrHi— lrHiHrHO>-lr-IO<— I <\JJ-CTvJC0_d-iO,C7NO iH-O C^ iH r-H rH i-H i-H r-i >-l i— t r I rvj %0 OvO ^^ O J-CJNN>t^vO l/NvO f-J-M3 \^\J3 vO ^sO^X) vO ^-O nD MD vO ^O vO fTv rrv K^ K> K^ rfv hr\ ro» hr\ LTNLfN lP» rHrHr-ti-li-lrHMrHrHrHrHrH l^^lr^Lr^lr^Lr^"^'r^L^^l^Lr^^J^lr^ r-i rH cvjcocD Ox£) irvo '<>fVJ f*^ K>fvj CVJ ^^ rr\j_d- O o o (M tvj KMrvirMTNCTNCTNCrN cvj fvj cvj irscrvLrNCDCDot) <-i r-i7-! O O O (M tVJ KMrVLTMrNCTNCTN (Mcvjcvjcvjrucvjtvjajcvj CM CVJ fVI ONp— t~-rHCOvO iHCOsO fOvf— P- L/^l^vlr^O ltmtnvo itmtnoO o t~-CO CTsvO ONv^ f-"-! O CO iH CTs OOOOOOOiHi-lOrHO rorVICVJCVJCVjrVJCVjrVJCVJ rrv^fNH^ K^K^K^^r^K^^f^K^^CVK^^f^K^K^ oooooooooooo oooooooooooo OOOi-lrH.-lCVJ(VjOj rCvN> MA J- J- J" ITN ITN ITNVJD ^^ ^4D C-- C~- 1~- rH<-trHrHr-(i-lrHrHi-l.-('-lrH iHiHrH.HrHi-t.Hi-Hr-lr-lrH.H rvj en o E-i tC < O Z tn o > w § z o DC o tu ca ta < H z t-t s o o r II L, t, O " f u. D CD X) NACA ARR No. L5F01 19 o l-H Eh O "d W O 00 3 •J %^ » C E O < o O I g^ &. M t-1 CO M H cn !Z) (/) gg CO < w o ^s Q < o CO M ?:> o w CO W < S £E H-. Eh Q CO '.i rCN!3 1-1 O o CO < Eh a; X o S X -H as m |c — o m D ^ OJ zL I r-i ■P s ►J c ^^ ^a -P c 0! x: 4J _d- LTN-d" LTVJ--^ '<>-J CTN ON ON ON tfVri-CO O f-M5 CO ir»rH t^i-t o o j-o a^'-i aN[~-j-ONrH coco r-^O ITNnO J- LTN LTA K\J- COnO O C^ONrH^O f\J LPirH [^ ^JM> CO ITN N"VJ- O ONM3 (\J KN rvjojojrvjrvjojrxjcxjKNNNKNNN CD CD ON C~-CO CO NO iTNvO LfN LfN c\jc\jojr\jf\j(\jf\ic\jnjc\joj coco o c^-^ono rH ojvo c--^Lr\ 00 o ^f^L^^aMrNO onJ-o J- ^fV4■'<^^nO O O iH iH rH rH I-t rH rHKNKNKNKN ■•VJ-_4<^ CTNCO^J-N-MH i-l ij rO rv] r^ rH i-hT-I 7-4 i-l rH rH CM c~-o_dNocr)co iH ctsnocd (M o vo r— cvj n-\co ojcoco '<^J-l r-i ONON'<-I KNf-• LTMTN ir>MD O 03 J-KNLfN-l O r-t L/NLPvLTNLrNLPvLTM/M/NlTMrNLrNl/N LfN LfN ITN L/NlXM/N LPvl/N LTN LfN LP> t^— OnO r^NONO LfNr-l C3NfufNLr>cooococo co co co co coco coco go cdco -d-LfNLTNvo LfNJDNO^ococo j-ir\ ONcrsiH LfNNNLfNrH o L^^^-c~- _i_d■J■^-^-^-o o o o j-_:d- C^C^-CO rS rH rH UNLrNLfNODOO CM CM CM (M CM CM r-• KNCOOO CTNKN OlHi-»Or-(«Hi-li-( ITNLfNirNNO CM CnO 1-1 cm cm •-! 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NACA ARR No. L5F01 Fig. 2 ^W 1 1 1 1 /Buckling of web \ ^ \ restrained bv flanq e y • > s 1 / \ / \, / A ' \ V, buckling of flange ' — — A| rest rainec i by web NATION L ADVISORY \ lUMMlUtt UR AtRONA IIICS bp/b .fi 1.0 w "igure 2. -Values of k^^ for Z- and channel- section columns of uniform thickness (from reference 3). -n I2(i-ju^)bw' I i NACA ARR No. L5F01 Fig. 3a, b V, J -^ ^- ^ ^►^^3^,345^ »HCH 2 (a) Unassembled. (b) Assembled with Tuckerman optical strain gage in place on specimen. Figure 3.- Fixture for obtaining compressive stress-strain curves of flat sheet. NACA ARR No. L5F01 Fig. 4a, b r I nj tc o — i --^ S-i +J 0) Q. +J O 03 • E c T3 a 0) +J E ^ C S-, O (U 0) Oj ^ ^ +J o +-3 <^ D td o E-H ,. +j cd tj c; •^ bD 3 E s O D E ,— T3 -.H c c (U tt3 •H c M L4 o3 J3 ♦3 U c E to fj o 03 ■-i x: CO o CO o -Q CJ O • E TD Ij o ai^^.... Cr ticai 1 stressj — *»-:-^U — G ^ / y / i o • ) NATI ;oMMin )NAL A! E FOR fl VISORY [RONAUl iCS Cross - sectional distortion (Pointer displocement) Figure 8- Illustrative stress - distortion curve for determination of critical stress for Jr or channel section colunr^ns loaded in compression . NACA ARR No. L5F01 Fig. 9 0) to •v ■V \ \ \, " \ 1 V N^ =^ \ \ ^^^ \, / - \^ \, ^^^ \ \ \ ^^ s ^ \ \ ^v. ■^ J \ \ v^^ I j^ \ A, X \, ^ \ \ \, iJ- V \ \ \ ^= ^ ^ ^0 ^ \ \ \ , --V ^ ^. \( _J \ V ^ s. ^ \ \ ^ J) - \ ^. ^v^k \ \ ^ s ^ \ A (- r- ^ s/^ / \ \ si s^^^L T <\ ^ U) ^ ( T) \ , ,.^^^ « < ^ ^ s 3 c CN O o lO o o O (M L ISVJ •■ SS3J|5 "o I E D C CO .0 .i> ^ 5 3 — o 2 ° OJ CO > .. \n ^ l> o ^ ^ !^ I O) 0) 1. NACA ARR No. L5F01 Fig. 10 60 50 40 I/) J/) 30 20 10 Formed material from curved corner , inside radius, 3t h- .002 -H S+ra'in Figure 10.- Effect of forming on compressive stress - strain curves for 245-T aluminum - alloy Z- section; t =0.125 inches . NACA ARR No. L5F01 Fig. 11 i th grain Dss grain / o o / / 3 JO o n y / //\ ^ / } // \;5 t!o^ " o ^u ^ o o (0 o 2 o o o o <0 J o (0 o o GO o |- 0) — 1 ° lA O LU ^i o I E 3 C £ _3 O h I Q_ O O o IQ o «A > w 3 U c E o u 0> I. 3 iZ NACA ARR No. L5F01 Fig. 12 60 5trcs5 , ksi Figure \Z. - Variation of T and T] with stress for 2.45-T aluminunn - alloy sheet, (r) obtained from tests of formed columns.) NACA ARR No. L5F01 Fig. 13 £> .1 J " Z- section ° Channel sec |< > "^r n < ^ a -> ^Ir 1 ) rklir c Q^ 3 XI ^ a J^ 4r^ UJ \ ■^ * __J ^ jiVo -^ .^ ^ ^ 1 < 5 c D C D c 5 , c 3 r ^- o — >» "I o ee Diuminu s of for o irt CO 1 % -^ 245-T rom te . M— o ^^ > ^- > o » o c o o 1 "u F X QJ 3 g to C P m E Vr D b c D D o _c V- U 1 CO • ^ -^ -D^ (U « to o «*^ U c ^.Q -t— xO OO) E.i= .ip-O i^c (J — Dt! C7» -C 1 ■^-C 5-t ._5 o Oa) S Q \ S -t- a; D-o i- 1 V. o b" N ^o - — » 1 ^ !0 u 1- D CD b" NACA ARR No. L5F01 Fig. 16a, b (O c E 3 o c o O u ._ ^ 1/5 o -iC (U a o ^ in 0) P" E \ fll g with a rain dir o o 10 C o of G he w f=r (U -t— \ iD 1 §-^ § g" N 5, >-2 a; ■D cn X o E O NACA ARR No. L5F01 Fig. 17a, b o o o « o lO o '^ o P 8 o lO o >o o '^ o fNJ p o _o E i O E liO >^ (L) cn l/l - ^ to "t/i P^ ° ^ u si C - c a 1 (T> . i 5| r^ o ^ C 1- <. C O o O s "ormed ch in curves X O E iG \ \ \^ - '- ^ W c \, -C D cn \ \ in O xS "< \ u ^^ -^ ^^ c z> C D c D C D C 3 C \ o u O O c o "*- D:i= ° I .b F^ o \f) ■ {T> r! ' > — ul •" H ^ J) ^ o £ \^ '*- ^'- O CPO C ,^ 0) .— 1_ — o *" Qroc ^ cn4f NACA ARR No. L5F01 Fig. 19 60 50 40 ksi 30 20 \o bw ^i^' 20 18 16 14 ^VvX \xr\ 24 k \\\N \\V\ 26 Ln s\\\ \ 2eL N 30 L\ \\\ v$w ^\ \\\ \ \ N. k\\\ -kN \ XNX ^NN\ 36. X \\\\ \\\ $$^ 38 ^N \\\N \ \ \ XV 40 V \ SSNa \\\ \ \N ^*K ^ Xv\ N ^ Si i -^ 'w .8 I.O NATIONAL ADVISORY COMMinEE FOR AESONAUTICS Rgure 19. - Design chart for a^p ^o^ formed Z45-T alurninum - alloij Z- and channel -sec+ion colunnns that develop local instabilittj loaded in the with -grain direction CTq^ = 44 ksi. NACA ARR No. L5F01 Fig. 20 60 50 40 30 ksi 20 10 . 1 t 20 18 16 15 ^."^ ^^^. 22 \ \ N <:^^ V 24 \\N \Vv ^ 26 s\ \ \J\\ nN^. 30 >$$ ■•n^^V^^>^ 34 ^^^^ >^\ ^^^;;^^ 38 =^ ^ fc - NATIONAL / COMMinEE FOR DVISORY \ERONAUTICS .6 .S 1.0 'W Figure 20.- Design chart for CT>„ax for formed 24S-T aluminum - alloy Z- section columns that develop local instability loaded in the with- groin direction *, 0'j.ys44ksi NACA ARR No. L5F01 Fig. 21 60 50 40 30 'max ksi 20 lO o 20 Id 6 15 \^ n\\ zek \ \\ ^\^ ^^^^^ . \" ^^Jx K\ \ \\ ""v \;^ ^^^:>^ "^ V \ \\ ^^ 36 ^ ^ C:\ ^^^$^ \::^ 42 ^ V NATIONAL A[ VISORY ;OMMinEE FOR A ;ronautics a i.o Figure Zl. - Design chart for o-j^qx for formed Z45-T aluminum - alloy channel - section columns that develop locol instability loaded in the with -grain direction j