1971 年 20 巻 215 号 p. 937-944
Hereunder is presented a report of an experimental study in which tests were made, under hydrostatic pressure up to 3000kg/cm2, of three polycrystalline metals, mild steel, 70-30 brass and pure industrial aluminium, with respect both to their tension and torsion, with a view to finding the characteristics in their increase in ductility due to the pressure superimposed on them. Besides these tests a tension test of aluminium crystals of high purity was also carried out under various pressures. The main results of the study are summarized as follows.
(1) The increase in ductility due to the superimposed pressure is meant, concerning the tensile deformation, by the increase not in uniform elongation but local elongation or in fracture strain, and, concerning the torsional deformation, by the increase in uniform shear strain, leading to the failure along the axis of the specimen.
(2) When two specimens of one metal were subjected to incipient strain under certain pressure, to be more precise, when one of the specimens was subjected to as large strain as the other, but while the one was processed under atmospheric pressure, the other was processed under high hydrostatic pressure, and when the strain has since been kept on both the specimens under as high pressure as at the beginning until the failure has begun to occur, the larger residual strain has been being presented up to the failure in that specimen which was subjected to the incipient strain under high hydrostatic pressure, than in the other that was processed under atmospheric pressure. These different effects from each other given on the specimens can be considered as suggestive of their origin intrinsically impressed in the structure of these specimens which were differently affected incipiently from each other, i. e. one under atmospheric pressure and the other under hydrostatic pressure. It is noteworthy, on the other hand, however, that there is no such intrinsic difference effected on the specimens in evidence as has been suggested above in the microscopic examination which was conducted for comparative studies of dislocation cell structure of mild steel and of slip line patterns in single crystalline high purity aluminium. These metals were stretched or twisted, each under the respective kind of pressure either atmospheric or hydrostatic. Neither of the specimens presented any difference in the result of its treatment.
(3) In mild steel its fracture strain increases to the failure due to tension under high hydrostatic pressure. In pure industrial aluminium its shear strain increases to the failure due to torsion under high hydrostatic pressure. It is noteworthy in this connection that the lower the speed of deformation in these metals drops, the higher the rate of increase in the strain in them rises, though it is not known yet how the phenomena are to be accounted for.