抄録
It is generally considered that stress-strain curve is smooth in plastic range, but the author found that it is not smooth when strained very slowly. From the auther's experiments with solid round bars and thin hollow cylinders under torsion, and with round bar under tension, the following are concluded. 1. Stress-strain curve in plastic range is discontinuous ; it consists of several branches convex downward. 2. Yield point of mild steel is the first discontinuous point. 3. The difference between the stress-strain curve of solid cylinder and that of hollow one, as shown in Fig.5, is due to the influence of stress distribution. 4. The stress-strain relation at the ultimate strength under tension is just similar to the yield point of mild steel.
