The Effect of Hydrostatic Pressure on the Plastic Flow and Fracture of Metals

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Abstract
A description is given of an apparatus for carrying out tension tests under hydrostatic pressures of 60 ton/in2 or more. The results of an investigation of the effect of hydrostatic pressure on the tensile properties of a number of metals are given. It was found necessary to protect cast materials with a rubber sleeve. The fracture strain increased with hydrostatic pressure, but this increase was not linear but varied with the crystal structure of the metal. In zinc and Mazak a sudden transition from brittle to completely ductile behaviour occurred at a critical pressure; this was probably due to a flat stress/strain curve. It was found in tension tests under pressure that specimens could deform and neck in a characteristic tensile manner, even though all the stresses were compressive. Fracture also could occur when the axial stress was compressive. It was found that the present results on tension, and previous results in torsion on cast iron, conformed either to a criterion that fracture occurred when the largest tensile stress reached a critical value which decreased as the volumetric compressive stress increased, or to a maximum deviatoric stress criterion, the critical value increasing with volumetric stress.