The Criterion of ‘Yield’ of Gun Steels

Abstract

This paper describes tests carried out on standard nickel-chromium-molybdenum gun steel in the form of bar material and in the form of gun-barrel forgings, and on seven alternative gun steels in the form of forgings produced experimentally during the 1939–45 war, with the object of determining the criterion of “yield” of these materials. The standard gun steel in the form of bar material gives a drop in stress at yield: the same steel in the form of forgings does not, nor do any of the alternative steels. In the first case, the criterion for the occurrence of the initial yielding is found to be the existence of a critical maximum shear stress; plastic flow continues in accordance with the Mises-Hencky criterion. In all the other steels the plastic flow occurs and continues in accordance with predictions based on the Mises-Hencky criterion. A brief additional note compares these results with those of earlier work, and draws attention to an earlier theoretical analysis which offers an explanation of them. The following paper is an abridgement of a monograph written for the Permanent Records of Research and Development of the Ministry of Supply.