New technique for rapid measurement of high-temperature flow stress

Abstract

Previously used methods of measuring the high-temperature, high strain rate flow stresses of metals have involved highly specialized apparatus which is time consuming to use. In the present paper a technique which uses a relatively simple machine and allows determinations to be made very rapidly is described. The method relies on the simultaneous indentation of a hot metal surface by two projectiles with hemispherical ends. These projectiles impact with velocities which are approximately in the ratio of 2:1 and the individual impact velocities together with the diameter of the indentations are accurately measured. Analysis shows that a knowledge of these quantities allows a calculation of the effective flow stress and its strain-rate sensitivity to be made. An initial series of tests have been conducted on aluminium alloys at strain rates up to 530s⁻¹. A comparison with results obtained by conventional camplastometer compression testing indicates that the new technique produces reasonable assessments of strength.