Bakerian Lecture - Physics above 20,000 kg./cm. 2

Abstract

Pressures up to the general order of 20,000 kg. /cm. 2 may be obtained and their effects measured in vessels made of single blocks of the best grades of steel. There is no sharp limit to the pressures which may be so obtained, for the life of the apparatus decreases rapidly in the 20,000 region, so that the upper limit is dictated by considerations of economy in conjunction with the significance of the phenomenon under investigation. The absolute limit for such mono-bloc apparatus for even a single application of pressure is, in my own experience, something less than 30,000 kg. /cm. 2 . To reach higher pressures some different principle of construction must be employed. In this lecture I propose to review some of the technical problems which arise in constructing such apparatus and to indicate some of the experimental results in the pressure range above 20,000 kg. /cm. 2 . In the construction of apparatus for this range it is almost necessary to afford external support for the vessel in such a way that the support becomes more effective the higher the internal pressure. This rules out for our consideration apparatus of the conventional built-up construction, in which the support is supplied by shrunk-on hoops, or in similar ways, as by wire winding as in a gun. Furthermore, there is no essential advantage in such built-up construction, for a true mono-bloc apparatus can be thrown into a state of stress similar to the built-up apparatus by a preliminary stretching beyond the elastic limit. All my mono-bloc apparatus does receive such a preliminary treatment. In fact, the distribution of stress so produced in a mono-bloc apparatus is somewhat more effective than that in the equivalent composite apparatus, because the distribution of stress is uniform. The built-up or the ‘auto-frettaged ’ mono-bloc apparatus reaches an obvious upper limit when the initial compressive stress at the inner surface exceeds the critical plastic flow stress.