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This paper describes the torsion test results and plastic characteristics of mild steel bars (C=0.053,Si=0.015,P=0.067,S=0.052%) with five different sections including a circle, three kinds of curved-sided regular triangle and a regular triangle. These triangles inscribe to a base circle of 10 mm radius, the boundary shapes of which are obtained by computating from the following equation : -[numerical formula] where K is a profile constant. Two sets of these test pieces were finished with accuracy only by the hands of skilful workman, using the special profile gauges, and were ground and lapped like a mirror surface. One set was broken by twisting. The other was only twisted until the elastic limit and further again twisted after thirty one months to ascertain the time effect upon the strength. According to the test results, there were found two modes of a characteristic curve of torque-angle diagram during the yielding of material from an elastic range to a plastic. Along with the gradual change in section from a circle to a regular triangle, the curvature of the characteristic curve becomes larger, which means the gradual increase of the maximum shearing stress induced on the middle point of a curved-side. To a strange matter, there happened some irregular plottings on the torque-angle diagrams, the reason of which will be necessary to seek ior. The results brought us the following linear relation : -Q_p=0.78 Q', Q'=0.342(Q_<max>-500), where Q_p=the moment in elastic limit in kg.cm, Q'=the constant moment in plastic range in kg.cm, Q_<max>=the maximum breaking moment in kg.cm. Number of twisting until breaking varied also with the sectional area and the fracttures were almost plane. The average values of modulus of rigidity for the same test pieces were as follows : -[table] The circular bar in the second test indicated the very high value of 11.98×10^5kg/cm^2,which was not included in the above figure. These facts will be taken as the time effect upon the strength of bars. The stress ratio of zθ^^^⌒_max at elastic limit to zθ^^^⌒'_max (constant) in plastic range varies from 1・33 to 2・3 according to the gradual change of section from a circle to a regular triangle. As the true torque at elastic limit, however, was really lower than the constant torque in plastic range, the true stress ratio varies from 1・068 to 1・733. The torque formula used in this calculation was verified as reliable by these tests
社団法人日本船舶海洋工学会の論文
1939-09-15

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