柱の強度に及ぼす残留応力の影響について

抄録

The subject of inelastic buckling of columns and flat plates has been studied by several investigators.¹⁾ Residual stresses have considerable effects on the inelastic buckling strength of columns, and several researches have hitherto been reported on this problem.³⁾⁴⁾ Especially, Osgood made a clear analysis on the column with a simple rectangular cross section, assuming an ideally plastic material and an unfavorable distribution of residual stress, which showed a remarkable reduction of column strength.²⁾
The authors extended the analysis to the case of favorable distribution of residual stress, and also to the case of material with a linear strain-hardening characteristic. Although the analysis failed to give an explicit expression of the column strength, the column curves could be drawn by taking successively arbitrary values for the amount of spread of the plastic region. The theoretical column curves showed a noteworthy difference between the two cases of favorable and unfavorable distributions of residual stress.
Experiments were carried out to verify the analysis. Two sorts of materials, low and medium carbon steels, were used as specimens. The dimension of the cross section was 6×9mm, the length being variously changed to give the slenderness ratios from about 40 to 100. The specimens were tested in a special device prepared for this purpose. The transverse deflection as well as the axial diaplacement were measured by two dial gages, respectively. As the treatment introducing residual stresses, low temperature quenching (quenched from 700°C into ice-water) and machining by a shaper (depth of cut was 1mm) were adopted, of course, the former giving unfavorable and the latter favorable distributions of residual stress. The residual stress distribution was measured by the X-ray film method, using CrKα beams. Thin layers were etched off successively from both sides of the specimen, and the surface residual stress was measured each time by the sin²ψ method. The original distribution of residual stress was obtained by using the correction formula.⁵⁾ The experimental results showed considerably lower values as compared with the theoretical ones, due probably to the eccentricity of axial loading and the initial curvature of the column etc., however, a marked effect of residual stress distribution on the column strength was verified.