REG NACA-TN-427-1932 Strength tests on thin-walled duralumin cylinders in torsion.pdf
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1、gREPROOUCEDBY -; 74;_ -NATIONAL TECHNICALINFORMATION SERVICE “ -_: .u.s. DEPARTMENTOf COMMRCSPRIICGIqELD,YA. 221_1Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Provided by IHSNot for ResaleNo reproduction or networking permitted without license fro
2、m IHS-,-,-NOTICETHIS DOCUMENT HAS BEEN REPRODUCEDFROM THE BEST COPY FURNISHED US BYTHE SPONSORING AGENCY. ALTHOUGH ITIS RECOGNIZED THAT CERTAIN PORTIONSARE ILLEGIBLE, IT IS BEING RELEASEDIN THE INTEREST OF MAKING AVAILABLEAS MUCH INFORMATION AS POSSIBLE.Provided by IHSNot for ResaleNo reproduction o
3、r networking permitted without license from IHS-,-,-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NATIONAL ADVISORY COMMITTEE FOR AERONAUTICSTECHNICAL NOTE NO. 427STRENGTH TESTS ON THIN-WALLED DURALUMIN CYLINDERSIN TORSIONBy Eugene E. LundquistSUMM
4、ARYThis report is the first of a series presenting theresults of strength tests on thin-walled cylinders andtruncated cones of circular and elliptical section; itcomprises the results obtained to date from torsion (pureshear) tests on 65 thin-walled duralumin cylinders of cir-cular section with ends
5、 clamped to rigid bulkheads. Theeffect of variations in the length/radius and radius/thick-ness ratios on the type of failure is indicated, and asemi-empirical equation for the shearing stress at maximumload is given.INTRODUCTIONA survey made about a year ago of the available in-formation and the me
6、thods employed in the design ofstressed-skin structures for aircraft revealed that the de-sign of structures of this type is based largely upon theresults of experience and data obtained either from testson structures similar to the one under consideration orfrom tests on the particular structure un
7、der consideration.A study of the existing reports of static tests upon mon-ocoque fuselages and stressed-skin wings resulted in theconclusion that very little reliable informatiom of a funda-mental character concerning allowable stresses could be ob-tained from full-scale tests already made because
8、no men-tion was made of the properties of the material and be-cause failure of the structure as a whole was caused by avariety of different types of failure in the skin, rein-forcement, and connections. Consequently, the _TationalAdvisory Committee for Aeronautics, in cooperation withthe Army Air Co
9、rps, Navy Bureau of Aeronautics, and the Bu-reau of Standards, Department of Commerce, has outlined aresearch program to investigate stressed-skin structuresfor aircraft.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-2 N.A.C.A. Technical Note 5re. 4
10、27As a part of this research program an extensive seriesof tests on thin-walled duralumin cylinders and truncatedcones of circular and elliptical section is being made atLangley Field, Va. In these tests, the absolute and rela-tive dimensions of the specimens are being varied to studythe types of fa
11、ilure and to establish useful quantitatived_.ta in the following loading conditions: torsion, com-pression, bending, and combined loading.This report is the first of a series presenting theresults of these tests; it comprises the data obtained inthe torsion (pure shear) tests on thin-walled duralumi
12、ncylinders. Although the tests have not as yet been com-pleted, it was thought advisable to publishthe resultsthus far obtained.MATERI ALThe duralumin (AI. Co. of Am, 17ST) used in thesetests was obtained from the manufacturer in sheet form inthicknesses ranging from 0.0105 to 0.0228 inch. The prop-
13、erties of the material as determined by the Bureau of Stand-ards from specimens selected at random are given in TableI, Typical stress-straln curves taken longitudinally andtransversely to the direction of rolling are given in Fig-ures I and 2.Upon reference to the above-mentioned table and fig-uros
14、 it will be observed that the modulus of elasticity issubstantially the same in the two directions of the sheetbut that the ultimate strength and yield point are consid-erably lower transversely to the direction of rolling thanlongitudinally. However, as all the cylinders testedfailed at stresses co
15、nsiderably below the yield-pointstress, the difference in the strength properties in thetwo directions has no bearing on the results.SPECIMENSThe test specimens consisted of right cixcular cylin-ders of 7.5 and 15.0 inch radius with length_ ranging from2.25 to 45.0 inches, which were constructed in
16、the follow-ins manner. FSr_-t, a duralumin sheet _as cut to the di-mensions of the developed surface, The sheet was thenwrapped about and clamped to the end bulkheads, (See figs.iProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-q , ,N.A.C.A. Technical
17、 Note No. 4273, 4, and 6.) With the cylinder thus assembled, a buttstrap 1 inch wide and of the Same thickness as the sheetwas fitted, drilled, and bolted in place to close theseam. In the assembly of the specimen, care was taken toavoid having either “soft Spots“ or wrinkles in the wallswhen finall
18、y constructed_iThe end bulkheads, to which the loads were applied,were each constructed of two steel plates one-fourth inchthick separated by 1 inches of plywood core. The_e p_rtswere bolted together and turned to the specifled outsid_diameter. Steel bands approximately one-f0urth inch thickwere use
19、d to clamp the duralumin sheet to the bulkheads.The_e bands were bored to the same diameter as th_ bulk-heads.APPARATUS AND _ETHODThe thickness of each sheet was measured to an esti-mated precision of_.0003 inch at a large number of sta-tions by means of a dial gauge mounte_ in a special Jig.The ave
20、rage thicknesses of the sheets were used in allcalculations of radius/thlckness ratio and stress.A photograph of the loading appare.tus used in thetorsion tests is shown in Figure 3. The lead from thejack was applied through a thrust bearlng to a yoke. Bymeans of a flexible cable that passed over _.
21、 series of _,ul-leys, half of the load was tranBmltted to one end of thelower horlzonta_ beam as an up load and the other half wa_transmitted tu_,ugh the rectangular frame to the Otlo_r endof the same be(_m as a down load In this nanner tor_-_eunaccompanied by transverse shear, was applied to th_ _D
22、ec-imen. A shec_r load on the cylinder caused by the weightof the apparatus, including the forward bulkhead and b_nd,was balanced by a counterweight as shown in Figure S.In order to determine the possible errors caused byfriction in the joints of the frame, _ spe_isl test w_smade in which thu moment
23、 applied to the loJer beam wasmeasured directS y and compared with the monent calculatedfrom the force applied by the jack. Theso two momentswere found to _iree within i per cent throughout the r_ngcof moments applied.Loads were applied by the jack in increments of _bout1 per cent of the estimated l
24、oad at failure, except afterProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-4 N.A,G.A. Technical Note No. 427the first few tests had been made when the first incrementof lead was about half the estimated load at first wrln_;le.At first wrinkling Ohm
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