Abstract
The influence of high hydrostatic pressure on the stress-strain behaviour of high-purity aluminium polycrystals at room temperature has been investigated. A magnetostrictive load cell has been employed for measuring loads under hydrostatic pressures. Results obtained are as follows : (1) Pressurizing under a pressure of 15000 kg/cm2 has no effect on the flow stress of annealed polycrystals pulled at atmospheric pressure. (2) Tensile tests under constant hydrostatic pressures up to 12000 kg/cm2 show that the flow stress at a constant strain increases with increasing pressure. The rate of increase of the flow stress under a constant pressure as compared with that at atmospheric pressure increases with increasing strain and becomes constant above 15% strain. (3) The rate of increase of the flow stress under a hydrostatic pressure as compared with that at atmospheric pressure for the same specimen measured by the differential pressure method is constant over the strains tested. It is a little larger than the rate of increase of the shear modulus of the material due to hydrostatic pressure. (4) The amount of work-hardening for a constant strain increases with increasing hydrostatic pressure. This phenomenon is explained by the decrease due to hydrostatic pressure of both the dislocation mobility and the density of mobile dislocations. (5) A phenomenon that is similar to work-softening is observed for a spceimen which is pulled under hydrostatic pressure, then unloaded and reloaded at atmospheric pressure.
