NACA ARR 3K04

Abstract

INTRODUCTION <br>One of the important requirements in the design of thin-metal columns for aircraft is the determination of the critical compressive stress at which local instability occurs. Local instability of a column is defined as any type of instability in which the cross sections are distorted in their own planes but are not translated or rotated. <br>The critical stress for local instability can usually be given in terms of the geometry of the section, the properties of the material, and a coefficient. Reference 1 presented charts for the determination of such coefficients for columns of I-, Z-, channel, and rectangular-tube sections. These charts, however, and rectangular-tube sections. These charts, however, contained relatively few curves and in some cases required interpolation over a wide range. <br>In order to make the charts of reference 1 more nearly complete and to reduce the necessary range of interpolation, each chart has been extended to include eight intermediate curves. The values used in extending the charts are computed by moment-distribution methods that give somewhat more accurate values than the energy method previously used and also make it possible to determine theoretically which element of the cross section is primarily responsible for instability. <br>The present report includes the extended charts, along with tables of the values used in preparing the charts, and is intended to supersede references 1. An experimental curve is included for use in taking into account the effect of stresses above the elastic range account the effect of stresses above the elastic range on the modulus of elasticity of 24S-T aluminum alloy. A determination of the dimensions of a thin-metal column for maximum critical stress with certain given conditions is presented.