"Laboratory tests were made to obtain information on the load-resisting properties of X76S-T aluminum alloy when subjected to static, impact, and repeated loads. Results are presented from static-load test of unnotched specimens in tension and in torsion and of notched specimens in tension. Charpy impact values obtained from bend tests on notched specimens and tension impact values for both notched and unnotched specimens tested at several different temperatures are included" (p. 1).

"The Von Karman equations for a thin flat plate with large deflections are solved for the special case of a plate with clamped edges having a ratio of length to width of 1.5 and loaded by uniform normal pressure. Center deflections, membrane stresses, and extreme-fiber bending stresses are given as a function of pressure for center deflections up to twice the thickness of the plate. For small deflections the results coincide with those obtained by Hencky from the linear theory" (p. 1).

A fixture is described for making normal-pressure tests of flat plates 5 inches in diameter in which particular care was taken to obtain rigid clamping at the edges. Results are given for 19 plates, ranging in thickness from 0.015 to 0.072 inch. The center deflections and the extreme-fiber stresses at low pressures were found to agree with theoretical values; the center deflections at high pressures were 4 to 12 percent greater than the theoretical values. Empirical curves are derived of the pressure for the beginning of permanent set as a function of the dimensions of the plate and the tensile properties of the material.

A criterion is developed for the stiffness required of elastic lateral supports at the ends of a compression member to provide stability. A method based on this criterion is then developed for checking the stability of a continuous beam-column. A related method is also developed for checking the stability of a member of a pin-jointed truss against rotation in the plane of the truss.

A monocoque box beam consisting of a 24S-T aluminum-alloy sheet reinforced by four bulkheads and by longitudinal stringers and corner posts was subjected to bending loads as follows: pure bending about the lift axis, cantilever bending about the lift axis, and pure bending about both lift and drag axis. Longitudinal strains were measured for loads up to a load at which permanent set became measurable. The loads were sufficient to produce buckling of the sheet between stringers on the compression side of the box. The only noticeable effect of this buckling was a small increase in extreme-fiber strain on the compression side. The measured strains and measured deflections differed less than 10 percent from those computed from the simple beam theory after taking account of the effective width of the buckled sheet. The effect of the bulkheads on the distribution of stringer strain was negligible.

"A theoretical analysis is given for the stresses and deflections of a square plate with clamped edges under normal pressure producing large deflections. Values of the bending stress and membrane stress at the center of the plate and at the midpoint of the edge are given for center deflections up to 1.9 times the plate thickness. The shape of the deflected surface is given for low pressures and for the highest pressure considered" (p. 1).

From Summary: "Normal-pressure tests were made of 56 rectangular plates with clamped edges and of 5 plats with freely supported edges. Pressure was applied and the center deflection and the permanent set at the center were measured. For some of the plates, strains and contours were measured in addition."

Note presenting a study of the electrical charge structure of thunderstorms by the use of continuously synchronized records of the electrical-potential gradient at the surface of the earth under the influence of active storms.

An analysis is presented of the results of tests made by the Massachusetts Institute of Technology and by the National Advisory Committee for Aeronautics on an investigation of the strength of thin-walled circular and elliptic cylinders in pure bending and in combined torsion and bending. In each of the loading conditions, the bending moments were applied in the plane of the major axis of the ellipse.

"A set of dimpling tools was designed for 0.040-inch 24S-T sheet and flush-type rivets 1/8 inch in diameter with 100 degree countersunk heads. The dimples produced under different conditions of pressure, sheet thickness, and drill diameter are presented as cross-sectional photographs magnified 20 times. The most satisfactory values for the dimpling tools were found to be: maximum punch diameter, 0.231 inch; maximum die diameter, 0.223 inch; maximum mandrel diameter, 0.128 inch; dimple angle, 100 degree; punch springback angle, 1 1/2 degree; and die springback angle, 2 degree" (p. 1).

"A graphical method is described for finding the shape (camber and twist) of an airfoil having an arbitrary distribution of lift. The method consists in replacing the lifting surface and its wake with an equivalent arrangement of vortices and in finding the associated vertical velocities. By a division of the vortex pattern into circular strips concentric about the downwash point instead of into the usual rectangular strips, the lifting surface is reduced for each downwash point to an equivalent loaded line for which the induced velocity is readily computed" (p. 1).

Report presenting testing of eighteen 24S-T aluminum alloy sheet-stringer panels in end compression under carefully controlled edge conditions. Results regarding the strains, deflections, failure, and buckling of the sheet are provided.

"Fatigue tests were made on some 1.375-inch-diameter and 0.300-inch diameter specimens of a 17S-T aluminum alloy rod. One test of a large specimen was run continuously to failure at a maximum stress of 22,000 pounds per square inch. In two other tests of large specimens, thin surface layers were removed periodically until failure occurred. The same nominal maximum stress of 22,000 pounds per square inch was used throughout the two tests and the load on the fatigue machine was lowered accordingly after the removal of each surface layer" (p. 1).

From Summary: "A 1/6-full-size model of the hull of the British Singapore IIC flying boat was tested in the NACA tank. The results are given in the form of charts and are compared with the results of previous tests made in the NACA tank of a 1/12-full-size model, published in NACA T.N. No. 580, and with the results of tests made in the British R.A.E. tank of another 1/6-full-size model of the same hull. When the data from the tests of the 1/6- and 1/12-full-size models were compared on the basis of Froude's law of comparison, differences were found."

Note presenting the results of an investigation on the distribution of stress in a plate elastically supported along two edges and subjected to compressive loads in a direction parallel to the elastically supported edges. A theoretical calculation was carried out in which the influence of the elastic support was taken into account.

"Tensile and compressive stress-strain curves, stress-deviation curves, and secant modulus-stress curves are given for longitudinal and transverse specimens of 17S-T, 24S-T, and 24S-RT aluminum-alloy sheet in thicknesses from 0.032 to 0.081 inch, 1025 carbon steel sheet in thicknesses of 0.054 and 0.120 inch, and chromium-nickel steel sheet in thicknesses form 0.020 to 0.0275 inch. Significant differences were found between the tensile and the compressive stress-strain curves, and also the corresponding corollary curves; similarly, differences were found between the curves for the longitudinal and transverse directions" (p. 1).

"This report is an addendum to NACA Technical Note No. 736, which dealt with tidewater and weather-exposure tests being conducted by the National Bureau of Standards on various aluminum alloys, magnesium alloys, and stainless steels used in aircraft. The exposures were begun in June 1938 and were terminated, for this particular series, in June 1941. The methods of exposure and the materials being investigated are described, and the more important results obtained up to the conclusion of the second year's exposure are reported" (p. 1).

From Summary: "The results of 60 different tests on 2 aluminum alloy 17S-T plate girders are presented to show the influence of size and spacing of stiffeners upon the buckling characteristics of shear-resistant webs within the elastic range. It is demonstrated that stiffeners increase the stability of a web by retarding the formation subdivided panels. An empirical method of proportioning stiffeners is proposed which recognizes both of these stiffener functions, and comparisons are made with design procedures based upon theoretical considerations of the buckling problem. Also, some experimental data are provided to show the effect of stiffener size and spacing upon ultimate web strengths."

Note presenting an investigation to determine the possibility of using the photoelastic method for the stress analysis of bulkheads in monocoque structures. The method was applied to several typical bulkheads including a circular ring with floor beam, a circular ring attached to the main wing spar, and a flying-boat bulkhead.

Report presenting testing of a monocoque box of aluminum alloy, which had torques applied to the ends. The twist, strain in the stringers, plate, and corner posts, and the buckling load were measured. A new analysis was developed for the twisting of a monocoque box reinforced by stringers, corner posts, and bulkheads, and the measured twist agreed within 10 percent of the analytical value.

Note presenting a summary of the results of an investigation of the curing of resin-wood combinations by high-frequency heating. The physical facts pertinent to high-frequency heating are introduced and the procedure is described for measuring dielectric constant and loss from 1 to 100 megacycles. The results indicated that the high-frequency heating process is feasible, flexible, and timesaving.

Note presenting a description of an electrical apparatus that serves as a computer for the evaluation of linear strain measurements taken in rosette fashion on the surface of a structural element carrying tension or compression and shear. The solution of the strain circle is accomplished by coupled rotary transformers, one representing each of the rosette gages.

Note presenting measurements made on a large number of corrugated diaphragms of similar shapes but of various sizes and various metals. Some of the materials studied include phosphor bronze, beryllium copper, A-Nickel, B-Monel, K-Monel, and Inconel. Results regarding pressure deflection, hysteresis, drift, aftereffect, recovery, and zero shift, and design and selection of diaphragms are provided.

Note presenting an investigation of tensile and compressive properties of specimens cut from an extruded shape of 24S-T aluminum alloy. The tensile strengths, tensile yield strengths, elongations, and compressive yield strengths of both the uncrystallized and recrystallized portions were determined. The strength of a cross section of an extruded shape is the weighted average of the strengths of the unrecrystallized and the recrystallized areas.