An Experimental Study on the Deformation of Materials under High Hydrostatic Pressures : 2nd Report, On Torsional Deformation

Abstract

Many papers on the behaviour of materials under hydrostatic pressure have been published; but it is still not sufficiently clear whether hydrostatic pressure has any effect on the elasto-plastic properties of metals. This may possibly be due to the difficulties in the measurement of the stress and strain under hydrostatic pressure, where various measuring errors are likely to be involved. In the present investigation on torsion, in order to eliminate the largest conceivable of these measuring errors, namely those due to friction and distortion of torsion grips, a new apparatus is introduced. In this apparatus, the specimen, with a torque bar connected in series, is twisted in a high pressure vessel and both the strains of the specimen and torque bar are measured by electric-resistance strain gages. The effects of hydrostatic pressures up to 4000 kg/cm² on the deformation of aluminum and a zinc alloy and on the lower yield point of low carbon steel were investigated, and the results are as follows: (1) With aluminum, in both annealed and extruded states, there is no effect on the shape of stress-strain curve. (2) With low carbon steel, there is no effect on the lower yield point. (3) With a zinc alloy, there is evidence of a little rise in the stress-strain curve.