REG NACA-ARR-L4H29-1944 CHARTS FOR CALCULATING THE CRITICAL COMPRESSIVE STRESS FOR LOCAL INSTABILITY OF IDEALIZED WEB - AND T-STIFFENED PANELS.pdf

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1、, NATIONAL,. ADVISORY COMMITTEE FOR AERONAUTICSWAITIME IUIPOITORIGINALLY ISSUEDAuet 1944 aaAdvanceRestrictedReportCHARTSJK)RCALCTJIATIONOF CRITICAIL4H29COMPRESSIVE STRESSFORM)CALINSTABILITYOFIDEALIZEDWEB-ANDT-STIFEENEDPANELSByRollsB.BoughanandGeorgeW.BaabLangley14emorialAeronauticalLaboratoryLangley

2、Field,Va.k”,- “.!- :,+ .“*$ :-” .,“-NACA”.,.,.,. : :, ,b- “.,., -,-WASHINGTON . . .NACA WARTIME REPORTS are reprints of papers originally issued to provide rapid distribution ofadvance research results to an authorized group requiring them for the war effort. They were pre-viously held under a secur

3、ity status but =e now unclassified. Some of these reports were not tech-nically edited. All have been reproduced without change in order to expedite general distribution.L- 204Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-“u,:.,.,31176013649662,.NA

4、CA ARR No. 14.H29NATIONAL ADVISORY COMMITTEE FOR AERON4.UTICS-,. , , ,.- . . .ADVAl?-,FtESTRICTEIIREPORT,.:-.,.CHARTS F(lRCALCUZATIOI?(3?!JIKEOXUTIC4LCOMPRESSIVE STRESSFOR LOCAL 1NSTABILIT% IIl13ALIZEDWEB- AND T-STIFF3NED PANELSBY Rolls B. Boan andSUMMARYGeorge W. Baa?3Charts ar presented for the ca

5、lculatIon of thscritical cmlprassve stress - the stress at which localnstabilit es- fcr ldealiedweb- ant!T-stiffenedpanels, and examples of the us of She charts are given.The present trend toward the use of low-drag wingSOCtOIIS on airplanes necessitates a wi. d9Sigll thatmaintains the wing contour

6、up to high valuer of appliedload if full advantac is to be taken Gf the aerodynamicproperties of the section. In urder that a wing may beso .desiped, the critical stress - the stress at whichbuckling of the plate elements occurs - must be knownfop the stiffened compression panels that make up thewin

7、g surface. Tests on I-, Z-, and channel sections,moreover, have established the fact that a definite rela-tionship exists for these sections between the criticaltress and the averaSe stress at maxhum load. (Seefig. 10 of reference 1.and fig. 7 of reference 2.) Itis l?.kelytkat similar relationships

8、exist for stiffenedcompression panels.The foregoing considerationsmake It desirable tohavti,for ready use in design, wcrklng charts for use incalculating the critical compressive stress of stiffenedpanels. Charts have previously been presented for thecritical stress of I-, Z-, and channel sections (

9、refer-ence ) and their validity has been experimentally verl- .fied (references 1 and 2). In the present report, chartsProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-2 NACA ARR No. I)+H29are presented for the critical compressive stress ofpanel with

10、 web stiffeners or T-section stiffeners inte-gral with the skin. Such panels would be obtained ifthey were extruded as complete skin-and-stiffenerassem-blies; they may, however,be regarded as Idealizationsofpanels stiffened with angles or with T-sections.SYMBOISb width of plate element of panelt thi

11、ckness of plate element of panelkS nondimensional coefficientfor skin dependentupon relative dhensions of cross sectionE modulus of elasticityP Poissons ratioocr critical compressive stressn nondimensional coefficientthat takes into accountreduction of modulus of elasticity for stressesbeyond elasti

12、c range; within elasticrange, q = 1Subscripts:F flanges skin?/ webDISCUSSION OF XARTSCalculation of critical compressive stress.- Thaidealized cross sections considered in this report areshown in figure 1. The critical compressive stress foreither the web- or the T-stiffened panel may be ccmputedfro

13、m the formula.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-iNACA liRRNoa I29 - 32+2%?= ksm EUS “-.-+ ,., (1).-n”“-“K:(l-, in the other region the stiffener1s primarfiy responsible for instability. This line ofdivision on figures , 4, and 5 was det

14、ermined from con-siderations similar to those used in reference 3 fordetermining responslblllty for instability.Studies of the efficiency of columns of I-, Z-,channe1, and rectanlar-tube section indicate that themaximum efficiency Sor local instability Is In the rangeof dimensims near the point at w

15、hich buckling is equallydL19to both elements. (Compare figs. 1 and 11, 3 and 12, ,and 5 and 13 in reference 3.) It is considered likelythat the maxhum efficiency for local Instability ofIdealizedpanels may also be in the range of dimensionsnear the point at which uckling Is due equally to skinor sti

16、ffener.1LIJJSTRATIV2EXAMPLESIt Is desired to calculate the critical compressive -stress for an idealized wob-sttffenedpanel and anIdealized T-stiffened panel constructed of 21+9-Taluminum.,Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-1!,“.:.,. .,A

17、_,-?:,“”!.-.r4.,“,.,NACA AR?Now L29 5alloy and for the same types.ofpanel oonstruotedof XB75S-T aluminum alloy. “Thedimensions of the two“pEflblsand the dimensin,ratios are as follows: Dlmenslon orratio. ., ,-Web-stiffenedpanel;:-0.10.1-0.333-1.0-.- ,. ,_, . . .T-stiffenedpane1.“1.”03.0O*40.10.10.1”

18、0.3330941.01.0The values of kS taken from figu?as3 and L are: forthe web-stiffened panel, !.Og, and for the T-stiffenedpanel, 5.21.The value of OcJq can now be computed fromequation (l). The material-property values used in thecalculatlor.sare E =“10.7 x 106 psi for 24s-T,E= 10.5 X.106 psl for XB75S

19、-T, and = 0.3 for bothmaterials. The values of urfl and the correspondingvalues of Ucr obtained from figure 2 are listed in thefollowlng table:?lsb-.stiffenedpanel T-stiffened panelMaterial d,.rn cr ucr/m i Ucr .(psi) (psi) (psi) (psi)=- . -. -2ra71 $9%.ti1:;.-4. 18zJ.154.26g3.5302.7022.L261.74.8j.

20、9232. 92.32k29065 I 1.470.2 - 5.5345.320-.- -4.714.23?3.J+70.91.0$.578L)u3725.5552.922t.N/ts = 1.5. 6.3206.1516.0205. 2585. 505.8055*7525. 07z5. 60-. .-.-.-;:y; !35.725. 4135. 45.633.75 -u -5: i . 055.629 z, 5. 56.2a71 7Ia71 -.- -5.,/ .i NACA ARR No.L4H29.”%76,52IoFig. 5I I I I I I I I I I I I I I I

21、 I I I I I I I 1 I I I I I I I I I I I I I I I I I_”I .&/7hL . . . . . . . . . . .Solid curves valid in”allcascs“HAT mu NmcwiUIMMlr /E Fc41mlmA11 nI I I I I I I I I I I 1 I I I I I I I I I I I I I I I I I I I I I I I I I I Io,2 4 .5 .8 Lob:Figure 5.Values of k for a uniformly loaded idealizedcompres

22、sion panel with T-stiffeners, tw tr = 0.7./ocr kn2Et29 - 12(1-2) bzProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Fig. 6.-T(a) Distortion onlu4.T(b) Distortion and lateral movement of flanqcs .Figure 6. Casesfor adNATIONALADVISORYCOMMITTEEFORAEROMUTICSof local instability considered- Stiffehed pane!.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-.?lllllllllllwltMinnlllBllllll!3 1176013649562.IProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-