Recent Investigations in Plastic Torsion

Tension, double-shear, and torsion tests on cast iron, S.A.E. 1045 annealed steel, and S.A.E. 1112 annealed steel are described in which the quantitative relations between the so-called modulus of rupture, double shear strength, and actual maximum shear stress in the bar at fracture are given for each material. The shear stress distribution over the cross section of each bar at fracture is also determined. Further, the data obtained from tension and torsion tests on the two steels are plotted on a single set of coordinates, namely the octahedral shearing stress τn and the octahedral shearing strain γn. A reasonable check is obtained between the two curves when the shear strain is less than that corresponding to the tensile strength. Finally, there is described a series of plastic-torsion tests on bars of mild steel with various new cross sections of practical interest, namely, the splined shaft, the circular shaft with two shallow rectangular keyways, double- and four-lipped drills, and I-beams. In these tests, the regions of initial yielding are determined by means of the Fry etching method.