抄録
The stress-strain curve of the dynamic test is higher than that of the static test. This difference would be due to the two factors. First, the mechamism of work hardening at impact differs from that of the static test, resulting in the difference of mecanical properties of specimens. The secondary cause may be the intrinsic strain rate dependence of flow stress in both tests, even if the mechanical properties of both specimens are assumed to be equal.
To check the difference of mechanical properties, the following tests were carried out.
The pure Al polycrystalline specimens were prestrained about 5 to 30% dynamically at room temperature and −196°C, and then tested statically at the same temperatures. The initial flow stress of the former specimens was always greater than that of the latter when compared at a same strain.
The dynamically prestrained specimen showed the so-called work softening in the static test. This phenomenon may be due to a sudden collapse of the work hardened structure established by dynamic prestrain, when the stress is applied statically.
Another extraordinary phenomenon, a remarkable decrease of elongation (tearing off of specimens) accompanying the work softening, was observed and discussed.
The dislocation structures of the work hardened state in both static and dynamic tests were investigated by means of transmission electron microscopy.
