1994 Volume 43 Issue 495 Pages 1559-1563
This paper presents some experimental results carried out to investigate dynamic constitutive relationship of material from a view point of dynamic plasticity. Three kinds of experiments were executed on annealed pure copper; the jump test in which the strain rate is suddenly changed from quasi-static to dynamic, the dynamic test in which dynamic load is applied to the specimen and the dynamic reloading test in which a dynamic load is applied to the specimen previously strain-hardened to some extent. The experimental procedure is based on the torsional stress bar method, where the dynamic stress and the corresponding strain are measured at one point of the specimen in purely dynamic manner. It has been revealed that in the jump test the over-stress is uniquely related to the instantaneous plastic strain rate all through the dynamic deformation process. On the other hand, in the dynamic and dynamic reloading tests the behavior was different from the jump test such that in the initial stage of increasing strain rate the over-stress lies above the curve determined from the jump test but tend to coincide in the decreasing stage.
These results are interpreted from microscopic viewpoint of dislocation motion and it is concluded that the mechanism of the rate sensitivity is same in all the cases, but the mobile dislocation density is different at the start of the dynamic plastic deformation in each test.