1、$“-, _.1t NATIONAL ADVISORY COMMITTEE FOR AERONAUTICSI WAlrnm Iuwolrl”EFFECT OFORIGINALLYISSUEDMarch 1945asAdvance Restricted Report LZ1ONORM%:”,.-;: “ F A c A m3RAR-Y“., .: , MEhiIAL ONAtiIWWASHINGTON JJU30.RATORYLaneYFI&; vaNACA WARTIME REPORTS are reprints of papers orginally issued to provide ra
2、pid distribution ofadvance research results to aii authorized group requiring them for the war effort. They were pre-viwsly held under a security status but are now unclasstiied. Some of these reports were not tech-nically edited. All have been reproduced without change in order to expedite general
3、distribution.L- 57Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACA ARR NO a71 L5B1O “NATIONAL ADVISORY COMMITTEE FOR J4ESONAUTICSADVANCE RESTRICTED EMPORT. EFFECT OF NORM PRESSURE ON THE CRITIC-M COitiRMSIVEAND SHEA?.?w Norman RafelSTRESS OF CURV
4、ED SHEETand Charles W. Sandlln, Jr.SUMMARYResults are presented of tests of two sets of 20curved-sheet specimens to determine the effect of normalpressure on the critical compressive snd shear stress ofcurved sheet. It was found that normel pressure raisedthe critical compressive and shear stress of
5、 curved sheetextent when outward bulging occurred In compression, inwhich case the critical stress was lowered by normalpressure.INTRODUCTIONIn a pure shell-type wing structure, failure isgenerally associated with buckling of the upper surfacedue to combinations of compressive snd shear loads. Thene
6、t outward-acting pressure on the upper surface tends todelq buckling and to increase the critical buckling stress.Preliminary tests have been made of curved-sheetspecimens (references 1 and 2) to determine the effect ofnormal prassura on the critical compressive md shearstress of curved sheet. In th
7、ese tests, increases incritical stress with increases in normal pressure wereso decided that a more complete investigation seemednecessary. As a result, tests have been made of 40 curved-sheet specimens in which combinations of five differentradii of curvature end four different rib spacings wereuse
8、d. One set of 20 specimens was tested to determinethe effect of normal pressure on the critical compressivestress, and a stmilar set of 20 specimens was tested todetermine the effect of normal pressure on the criticalshear stress. It Is the purpose of this report to presentthe results of these tests
9、.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-2 NACA ARR No. L5B1QTEST SPECIMEl! and holes drilled through the twocenter ribs ensured equal prassura in the three bays.ThtiPrassure was measured by maans of a mercury mnomtar.Resistance-type wire str
10、ain-ga:a rosettes were ettachadin ths centar bay of tha specimen to gach side of onesheet as shown in figure 1. These gaas wsrs used tochack for uniform loading and to datect the formtion oflmckles,which did not appsar with a snap diaphragm action= .?ETHODCF TESTI?:GCompression TestsA speciman place
11、d in the tastingin figure 2. The testing machine had-1r,achinais shownan accuracy of+ percant of load.-2 The ends of the spacimen waraground flat and psrellel to ansura uniform distributionof load during the tests.A small initial axial load was eplied and readingsof all the gages wara takan. The axi
12、al load wes thanincreased in staos until buckling occurred. Aftar aachlod incramant had bean applied, readings of all thega.eswere takan. So long as no buckling occurred,thelongitudinal agas indicated increasing compressivestrain with load. Whan buckling bagm, tha strain on thaconvex side of the buc
13、kla was reduced by tha tansile stressincident to buckling; the raading of the gage on this side,Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,- . .NAOA”ARR No. L5B1O 3consequently, did not continue to Increase uniformly withload but reached a maximu
14、m and then started to decrease.* -.The.load cornespad-ing-to -the maximum gage -zwradlngwasconsidered the buckltig load for all panels in which nosnap buckling occurred.A similar procedure was then used to test eachspecimen with internal air pressure. The air pressurewas admitted after readings were
15、 “taken at the initialload. The pressure was then held constant and the axialload was increased in steps until buckling occurred. Thetests were continued at several different higher pressureswith the highest permissible pressure being determinedboth by visual inspection of the smount of quilting and
16、by approximate computations based on reference 3. Thehighest permissible pressure is defined as that pressurewhich can be admitted without exceedir,gthe yield stressof the matarial. When the highest permissible prassureaxceeded 6 psi,only pressures up to 6 psi wera used.Torsion TestsThe testing proc
17、edura for the torsion tests wassimilar to that used in the compression tests with thaexcaption that there was no initial load on the specimen.Figure 3 illustrates the msnnar of loading a specimen Intorsion and shows the locations of the dial gagas usedto maasure the amount of rotation. The steel pla
18、te towhich the snecimen was fastened was conr.ectedto aweighing system that measured torque and vertical loadwith an accuracy of *1 percent. In testing, the onlyload applied to the speciman was a pur torque.RESULTSThe results of the tests are given in figures L to 8.Figures L and 5 show the effacts
19、of R/t and rib spacing onthe critical stresses without normal pressure, where R isthe radius of curvature of the sheet and t is thethiclmess of the sheet. The critical compressive stresswas obtained by dividing the buckling load by the totalcross-sectional area of the specimen=TIM critical com ressi
20、ve stresses indicated by pointswith tails in figurec are stresses that correspond to the. . -Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-4 NAOA ARR No. L5B1Oloads at which the staln-gege readings reversed dtrection.For the specimens with 6-inch r
21、ib spacing, the points withtails represent tests in which the sheets bulged outwardin all bays. All other tailed points represent tests inwhich combinations of inward end outward buckling occurredgradually. Points without tails represent tests in whichsnap diaphragm buckling occurred.The critical sh
22、ear stress was obtained from thefOrmulawhereT shear stress, PSIT buckling torque, inch-poundsA erea enclosed by median line of shaet edspars,square inchest thickness of sheet, inchesThe criticel sheer stresses indicated by the tailedpoints in figure 5 are stresses that correspond to thestrain-gage r
23、eversals associated with gradual buckling.The effect of normai pressure on the critical Com-pressive stress is shown in figura 6. The spacimans witha rib spacing of 6 inchas end en R/t of 700 end 1000show a decreasa in critical comprassiva stress withincreasing normal pressure. With these specimens
24、noinward buckling occurred but, since the introduction ofpressure causad the sheat to bulge out under the initialcompression load, the load at which the strain-gagaraadings raversed wes lowared. In specimens in whichsnap diaphragm buckling occurred, there was a pronouncedincreas in critical compress
25、ive stress with increasingnormal Prassure. The results of the tests of tha specimanswith an infinite radius do ot show eny dacisive trend andin most cesas no buckling load could ba obtained.The effact of normal prassura on the critical shearstrass is shown in figure 7. In ell ceses an increase innor
26、mal pressure caused en increase in crltlcal shear strass.This rasult was independent of ti.etherbuckling occurradslowly or with a snep.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NAOA ARR NtI.L5B1OThe data of fi urea 6,and 7fthe .gr.eat.e.rthe. R
27、 t -ratio, theincrease In critical compressiveincreasing normal pressure.5show tht, In general,great,erthe percentageand sheax”stress wtthExperimental rotation is compared with theoreticalrotation for the torsion specimens at various R/t ratios,rib spacings, and nomnal pressures in figure 8. Theo-re
28、tical rotation was obtained from the formulawheree rotation, radians per inch of lengthT measured torque, inch-poundsG 6shesr modulus (here taken as )+.0x 10 psi)J torsional-stiffness constant, inches4The data of figure 8 show that the torsional stiffness ofthe specimens before buckling is slitly in
29、creased byincreasing normsl pressure. These slight increcses Intorsional stiffness might be explained, at least h part,by the fact that bulging of the sheet resulting frominternal pressure produced an increase in the enclosedarea of the specimen. This effect is more pronounced inthe spcimens with a
30、2L-inch rib spacing than in thespecimens with a 6-inch rib spacing, as evidenced by thetest rasults in figure 8.CONCLUSIONSThe results of tests of LO specimens to determinethe effect of normal prassure on the critical compressiveand shear stress of curved sheet Indicated the followingconclusions:1.
31、Normal pressure apD9eciably raised the criticalcompressive stress f,orcurved shest when inward snapdiaphrat buckling occurred.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-I62, Normal pressure lowered thestress for curved sheet when outwardNACA ARR
32、 NO. L5B1Ocritfcsl compressivebulging occurred.3* Normal pressure raised the critical shear stressfor curved and flat sheet regardless of whether bucklesformed slowly or with a snap.4. The greater the ratio of realus of curvature tothlcluaessof the sheet, the greater the percentage increasein critic
33、al compressive and shear stress with Increasingnormal pressure.Langley Memorial Aeronautical LaboratoryNational Advisory Committee for AeronauticsLsngley Field, Va.REFERENCES1. R&fel, Nogn: Effect of Noal Pressure on theCriticei Compressive Stress of Curved Sheet.HACA H3, lflov.lq a712. Rsfel, Norma
34、n: Effect of Normcl Pressure on theCritical Shear Strass of Curved SheSt. NACA RB,Jsn. 1943.3- Timoshenko, S.: Theory of Plates and Shells.McGraw-Hill Book Co., Inc., 1940, pP. 347-350.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-yNACA ARR NO. L5?
35、31OTABIE I* . - -. . . ,- “- NOMINAL DIKENSXONS -OFTEST SPECIMENSymbds are defined In fig. 1.All dlmenaions are given in inches.3Speoimen d a L R R/t1, 2 3 6 25.5 25.6 4003, 4 5 12 47.5 25.6 4005, 6 5 18 65.5 25.6 4007, 8 5 24 83.5 25.6 4009, 10 3 6 25.5 44.8 70011, 12 5 12 47.5 44.8 70013, 14 5 18
36、65.5 44.8 70015, 16 5 24 83.5 44.8 70017, 18 3 6 25.5 64.0 100019, 20 5 12 4795 64.0 100C21, 22 5 18 65.5 64.o 100023, 24 5 24 83.5 64.0 100025, 26 3 6 25.5 76.9 120027, 28 5 12 47.5 76.9 120029J 3 5 18 65.5 76.9 120031, 32 5 24 83.5 76.9 120033s 34 3 6 25.5 CO m35, 36 5 12 4795 “ m37, 58 5 18 65.5
37、w m39, 40 5 24 83.5 t= m7NATIONAL ADVISORYCOMMITTEE FOR AERONAUTICS. -Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-,7NACA ARR No”. L5B10i= - . . .Fig. 1+%-dI icun,round-hecxlrivets. Sring dapprox. inchused throughout Stro.h-gagrosettesIJ/$a71.kNAT
38、IONAL ADVISORYHITEE FOR AERONAUTICSFigure 1.- Test specimen. (Fw “dimensions not shown, seetable 1). .Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-.-. .NACA A.RRNo. L5BI0 Fig. 2. .,.IProvided by IHSNot for ResaleNo reproduction or networking permi
39、tted without license from IHS-,-,-A .,Fgure 3.-Test specimenin torsti dwving locations of dial gages.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Fig. 4.-2fn-U)alLt)NACA ARR No. L5B1O1614 -10 a75 ,8L6 a75+4 $fI , ,Rib Snap Stram-gaspacing buckle5$
40、rwersa Tz - 6 0 $12 0 #10 0 #24 A # outward bulglng1“ 1 1 1 1 I 1 1ZOO 600600 UMOHO0 aR/t NATIONM ADVISORYCOMMITTEE FOR AERONAUTICSMe 4.- Effect of R/t and rib spacing on critical compressistress without normal pressure.veProvided by IHSNot for ResaleNo reproduction or networking permitted without l
41、icense from IHS-,-,-.NACA ARR No. L5B1O Fig. 5.6 1 1 I 1 I 1 I I I I IW)mlwwFigure 5.- Effect ofstress - withoutR/l NATIONAL ADVISORYCOMMIHU FOR AERONAUTICSR/t and rib spacing on critical 6hearnormal pressure.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from I
42、HS-,-,-Fig. 6 NACA ARR No. L5B1Oc.$3!%16 iyt=400840 4ml12041200t0246nAnoNAL AowxlwmMlllEE FORAERONAUllCSRibq)acing,a Snap buckle .3rain-gage reversal0 2 4 6Normal pressure, psiFigure 6.- Effect of normal ssure oncritical compressive stress.Provided by IHSNot for ResaleNo reproduction or networking p
43、ermitted without license from IHS-,-,-NACA ARR No. L5B1O Fig. 7100012Io0 246Normal700- - 4I-_ -. - .(!-L512000 2 46N4nwl#IlviSOFIYCJJMMII?EE FOR AHONWRibqxxing,a06a75 12 18A 24Snap buckle- 5tmin-gagereversalpressure, psiFigure 7. Effect of normal pressure on critical sheur stress.Provided by IHSNot
44、for ResaleNo reproduction or networking permitted without license from IHS-,-,-.t 400 mRibqacincj6 24Normalpressure,O 6 041000606 03 06 0 212.00051+1 1 Rotation,radiins per id of length &oa71Figure 8.- Shear stress -rotation curves for torsion specimens with mrious R/t ratios, r0rib spacings, and normal pressures, ml1-0Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
