The effect of hydrostatic pressure, up to 112,000 lb/in.2, on the tensile properties of four polymers is reported. The pressure soaking of polystyrene in castor oil had no significant effect on the material's residual properties when tested under ambient conditions. When tested under pressure polystyrene necked, like a metal, and exhibited a brittle ductile transition at 40,000 lb/in2. Between 40,000 to 112,000 lb/in.2 the tensile strength increased by about 30%. Young's modulus and yield strength were only slightly affected by pressure. Similar results were obtained for specimens sheathed to prevent possible plasticization of the polystyrene. Polymethylmethacrylate tested at 112,000 lb/in.2 failed just short of its instability point and with only a slight increase in Young's modulus. These amorphous polymers thus behaved under pressure in a generally similar manner to metals. Pressure had a marked effect on the stress‐strain curves of two crystalline polymers polyethylene and nylon. Young's modulus and tensile strength were considerably increased and elongation decreased. Pressure inhibited ‘drawing’ of the materials. Deformation was restricted to a small necked region.

An investigation has been made of the effect of specimen surface finish and sheathing on the tensile properties of both cast and extruded ingot and hot-pressed powder beryllium, under the influence of an applied hydrostatic pressure of 78.7 kg mm -2 (7.72 kbar). Three surface finishes -as-machined, chemically etched and electropolishedwere investigated. For each surface finish, specimens of both materials were tested with their gauge length sections bare and sheathed with a rubberized coating. The chemical etching and the electropolishing treatments were designed to remove the damage induced by the specimen machining operations and the rubberized coating was applied to prevent the pressurizing fluid wetting the specimens. Other workers have claimed that electropolishing alone is sufficient to enable the maximum ductility of beryllium to be realized in a hydrostatic environment. However, the present investigation shows that both a post-machining surface treatment and the application of a rubberized coating are necessary before this condition is attained. The data also suggest that beryllium exhibits a Rebinder effect.