Effect of Strain Rate on Yield Behavior of Cold-rolled Sheet Steel

The yield behavior of low-carbon sheet steel (0.07%C) has been examined under the strain rate of 10-4 to 10-1/sec at room temperature using an Instron type tensile machine. The stress-strain curves have been recorded by using a transient converter (8 bits×1024 words), since the response of an X-Y recorder is not sufficient for the measurements under high strain rates. The experimental results by the transient converter show that the upper yield points appear clearly before the crosshead speed reaches a given value of high strain rate. The transient converter is most desirable in order to observe the yield behavior under high strain rates. The results also show another break point of the dependence of the yield stress on the strain rate at the strain rate of -3×10-3/sec, which is different from M. J. Manjoin (1944)'s strain rate, i.e., -10-1/sec. The dependence of the yield stress, yield point elongation, and tensile strength on the strain rate in the range of high strain rate above -3×10-3/sec is larger than that at lower strain rates. The yield stress is much more sensitive to the strain rate as compared with the tensile strength.