, N U No TORSIOI_AL S _TP_ENG_'w OF N!oKEL,4 STEEL AND DURALU}_iN TUBING. AS AFFECTED BY THE RATIO OF DIA}:_ETER TO CCaGE THICKNESS.

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1 ,,-, j - X, N U i i u, TECHNICAL NOTES NATIONAL _- o - ADv IoORY CO_,_{ITTEE FOR AERONAUTICS. cas COp.y LE: No. 189 TORSIOI_AL S _TP_ENG_'w OF N!oKEL,4 STEEL AND DURALU}_iN TUBING AS AFFECTED BY THE RATIO OF DIA}:_ETER TO CCaGE THICKNESS. By N. S. Otey_ U,S, Naval Aircraft Factory " flc,o:,-:, _ To b_ re,turr_cl to the fl}ss of'the ]','._tion_.} Advisory Ce':nmitt_. or A_ronautics 1, April) Washin_to% D, O.

2 J NATIONAL ADVISORY C01_ITTEE FOR AERONAUTICS. TECHNICAL NOTE NO TORSIONAL STRENGTH OF NICKEL STEEL AND DURALUMIN TUBING AS AFFECTED BY THE RATIO OF DIA_TER TO GAGE THICKNESS.*_ By N. S. 0tey.! Introduction. This investigation was made at the request of the Bureau of Aeronautics. Since the ordinary torsion formula is based on elastic resistance to deformation, it is inaccurate for determination of ultimate stresses in thin wall tubing subjected to torsional loads. It has been found that the torsional modulus of rupture varies with the ratio of diameter to gage thickness and the object of these tests was to determine the extent of these variations fo_: subject materials. This Ss somewhat of a prorogation of wot.k** done by the Army Air Service at NcCook Field. Conclusions. I. The torsional modulus of rupture of nickel steel (2ZS0) and duralumin tubing varies with the ratio of diameter to gage thickness (D/t) as follows: (a) Nickel steel heat-treated for 125,000 Psi ultimate tensile strength. * Originally prepared as Report No. 6T2.Z-5, U. S Naval Aircraft Factory. * Air Service Information Circular No. 26Z, Volume III, dated. July 20, 19_I.

3 - 2 - Zodulus of rupture (M) = 135,500 S/D/t d (b) Duralumin treated for 55,000 Psi. ultimate tensile strength. Modulus of rupture (M) _-=- -v Mater ials. 2. The steel tubing used in this investigation was taken from stock having the following specified analysis" The heat treatment given this tubing was that of quenching in oil at 15B5 F. and drawing at 800 to ilo0 F. depending on the brinell hardness after quenching. 3. The duralumin tubing was standard stock material and since it had been heat-treated by the manufacturer, no further treatment was given. The specified chemical analysis is" _,ofe. Si.. Ca.,, ] l ' 9_ o !.o.e.4 '}.4 Max. tltax. I IvIax. iin. I!

4 - 3 - procedure. 4. Twelve steel and ten duralumin tubes of diameters and gages shown in Table I were supplied in 60-inch lengths. From each ot these a 13-inch specimen was cut for tensile tests and the 48-inch lengths used for torsion tests. In the case of i steel, the tensile specimens had to be cut before heat _reatment due to size of furnace available, which, through heat treatment, resulted in variations in physical properties of the tensile and torsion specimen_:as will be shown later. The torsion specimens were tested in an 01sen torsion machine at Drexel Institute. The set-up used is shown in photographs (Figures I and 2_). Data. 5. Complete results of these tests are shown in Table I and Figures 8 to 15 inclusive. 8., The curves in Fioomres 5 and 8 show graphically the changes in moduli of rupture as affected by the D/t ratio. These curves were plotted under the following procedure: (a) Average curves were dravrn through the empirical points for convenience in obtaining the final curves. (b)] Values taken from these average curves were plotted to 10g scale as sho_rn in Figure 7, from which the slope of the average curves was determined.

5 - 4- (c) Using the slopes thus determined, equations were found from which the final curves shown on Figures 5 and 6 were plotted. These final curves were found to agree very favorably with the original average curves. 7. In Figures 8 to 15 inclusive, the torsional load/ deformation data is plotted. Curve Gi, (Fig. 13), shows irregularities in the region of the yield point which is characteristic of duralumin. 8. Photographs (Figures 3 and 4) show torsion specimens after test. It will be noted that in all cases but three, failure occurred by buckling or collapsing rather than shear, Discussion. 9. In the Case of the steel tubing, it will be noted that the empirical values are erratic as shown in Figure 5, This may be due to two causes" (a) Variations in physical properties of the material. (b)' Failure by crinkling or collapsing rather than shear. The first cause is not considered entirely responsible as examination of brinell hardness and moduli of rupture of the torsion specimens indicate more uniform physical properties than the tensile values shown in Table I, would suggest. AT-.. though the tensile and torsion specimens were heat-treated in

6 the same furnace and at the same time_ their differences in size likely caused considerable variations in physical properties. _Yith due consideration for. these erratic Tesults and their causes, the curve is considered sufficiently accurate for reliable desi_m data. _.,_uchcredit is due Drexel Institute for courtesies extended in permitting the use of their torsion testing equipment and for generous aid in conducting these tests,

7 - 6- Table I. STEEl: _TT_ T ]\'[_-, T e n s i 1 e P r o p e r t i e s.,_ No. Size Stress Stress E!ong. Psi 2" AI 1.000" W.038"Oa A2!,000 x BI ].,250 x ] B2!.250 x Cl x ,5 C x, D1!. 500 x D2!. 500 x.] I0.0 E ,065 ' I0.0 EPo i ,8700 I I0.3 i FI x,084 : ,, 10.8 F l DURALU_,_IN TUBING Gl B7.5 G2 0,749 x.057 _ ,5 H1 0,998 x ,0 H x tl!,375 x, I_ ,5 Jl t.495 x ,4.0 J2 1,490 x.0_ ,6.0 K1 1,500 x, , 25,0 K2!,500 x, I Notes: I, J = polar moment of inertia. 2. c = distance from polar axis to extreme fiber or D/2. 3. Load P. limit is torque in inch pounds, 4. Ult. load is torque in inch _ounds to rupture. 5, Torsion formula is S x J/C : Pp where Pp = torque in inch pounds. o

8 Table I (Contd.) STEEL TUBING Torsional Properties. # No, Brinali D/t J C J/C Hardness A AS _2, B , B ,05,0703 0,625.1].24 Cl v?0,1245 0, C , D ,750 4:593 D ,3445 O E! I E2 ' I, 125,4737 FI F ! Shore DURALUMIN TUBING Hardness GI 30,0 ' , G O HI O, 499,074.9 H I[! 24, , I , J! J " , K _ K O

9 Table I (Cont.) STEEL TUBING To r sional Prop ert ics. Load at Load at _odulus Modulus No. P. Limit Rupture of Rupture of Rupture 1_. Lira. _at Ult. A1 _ s_125- _.Z A :3400 BI B u0_ 75_00R CI I1800 II C2 III D D E l E_ F ,$ I ] F S DUFuiLUMiN TUBING GI G HI O H _ } 2375 _ I ,900 Jl 2500 SO , J , 2950 t ' K ! KS ]

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17 Fig. i0

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22 Fig. 15