Work-Hardened Metals

Abstract

ONE of the most interesting of the papers presented at the autumn meeting of the Institute of Metals was that by Prof. Jeffries, of the Case School of Applied Science, Cleveland, U.S.A. Hanriot came to the conclusion in 1912 that metals subjected to very high hydrostatic pressures, of the order of 10,000 kilograms per square centimetre, even though they underwent no change of shape, showed an increase of hardness (Brinell test). Although cubes of silver, copper, and aluminium showed a considerable increase of ball-hardness in these experiments, he decided that in no case were they appreciably deformed, and that the pressure was sufficient for hard-hammering the metals without deformation. Prof. Jeffries reviews this'work, and has repeated the experiments. Tests were carried out by Dr. Bridgman with pure aluminium and an alloy containing 88 per cent, of aluminium and 12 per cent, of copper, in the form of cylinders 7/16 in. diameter by 5 in. long, the dimensions of which were accurately measured. The tensile strengths and scleroscope hardness values of the materials were determined with the following results:—