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Aviation History
1931
1931 - 0513.PDF
MAY 29, 1931 THE AIRCRAFT ENGINEER SUPPLEMENT TO FLIGHT permissible shear stress of the material, i.e., x /,. Its bearing strength in a plate is given by the thick- ness of plate (t) multiplied by the diameter of the shank id) and the maximum permissible bearing stress of the material, i.e., t X d X /(,. RADIUS. -A-H NECESSARY FLAT Diagram for Table 2. Assuming that both rivet and plate are of the same or similar materials, we get a relation between these two strengths such that, if made equal, i.e., Xf tdf the collapse will be simultaneous. This gives us the most economical size of rivet for any given thickness of plate. In duralumin, taking /, = 16 tons per sq. in. and /& = 32 tons per sq. in., •K X d* X 16 = t yd x 32 4 12-56^ = 32-t.d 12-56 d = 32 t d = 2-55 t fitting. The appropriate sizes may follows: — TABLE 3. be tabulated as Thickness of Plate. 22 s.w.g. 20 „ 18 „ 16 .. 14 .. 12 „ 10 „ Diameter of Rivet. Alum. Alloy and Mild Steel. V^-in. dia. 8 " " i <> „ Stainless and H.T. Steel. i 8 »• i It will be noticed that thicknesses below 22 s.w.g. have not been considered. Tests June shown* that the relationship breaks down. This is an important point, as a very considerable amount of aircraft riveting is done in structures, such as strip steel spars, which are frequently in thicknesses down to 28 s.w.g. Mr. Rad- cliffe is led to the conclusion that the bearing strength of the rivet need not be considered in these cases, the criteria of strength being the shear value of the rivet and the bearing and buckling values of the plate. This being so, he concludes that rivets in single shear are F16.I FIG.2 FIG 3 FIG. FIG.5 F1G.6 FIG.8 Similarly in mild steel where/, = 18 tons per eq. in. and fb = 38 „ d ^ stainless steel rivets (D.T.D. 24A) kigh-tensile steel d= 3-18 *. Cl this it appears that the most economical size of i act Dlatl fv, aPProxima*«ly three times the thickness of the »<* b.» ?Ugh wh^ch i* Passes. This ideal condition can- " observed in practice, particularly where several thicknesses are used in making up a part or 478c FIG. 9 more efficient than those in double shear. He tabulates a number of tests on both single and double shear joints, which may be of assistance to designers. Until more data are in existence, the strengths of riveted joints in thin materials should be made the subject of tests in all critical cases. Buckling of the material round the rivet is a factor which defies calculation, as it varies accord- ing to the local conditions. The following Strength Tables give the values of the most usual rivet sizes in plate thicknesses from 22 s.w.g. to 8 s.w.g. Extreme cases, such as 1/16 in. diameter rivet in 10 s.w.g. and i in. diameter rivet in 22 s.w.g., have been missed as unlikely to occur in practice. • See R.Ae.S. Journal, WOT. 19*0, Radcliffc, p 951.
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