THE INFLUENCE OF STRAIN-RATE HISTORY AND TEMPERATURE ON THE SHEAR STRENGTH OF COPPER, TITANIUM AND MILD STEEL

摘要

Incremental strain rate change tests were performed using a modified torsional split Hopkinson bar in which a high shear strain rate is suddenly imposed on a short specimen while it is being plastically deformed at a much lower rate. The length of the loading bar system provides a useful torsional pulse of 1 ms duration which enables specimen shear strain up to 1.0 to be achieved at a strain rate of 1,000/s. Provision is also made for testing at temperatures up to 500 C. On this apparatus OFHC copper was tested at temperatures of 24, 200, and 400 C. Specimens were twisted at an average shear strain rate of 0.003/s, and the rate was suddenly increased to 900/s at predetermined values of the static shear strain, nominally 0.10, 0.25, and 0.50. The subsequent dynamic behavior was recorded and compared with that of similar specimens deformed at an average strain rate of 900/s without pre-straining. Similar tests have also been performed at room temperature on commercially pure titanium. (Author)