Theory of the physical characteristics of tensile fracture under pressure.

(1) Bridgman's Observational Results.-It was observed by Bridgman' that there is a linear relationship between the hydrostatic pressure p and the natural strain at fracture, i.e., the ductility, in tensile tests on steel cylinders, and that this relationship persists regardless of the type of fracture which occurs. A theoretical explanation of the foregoing result has been given in an earlier paper in these PROCEEDINGS.2 When fracture takes place at atmospheric pressure, it is almost always of the cup-cone type and the flat bottom or tensile part of the break is accurately situated along the minimum section of the neck. The line of separation of the flat bottom and the sides of the crater is circular and is usually quite definitely defined; hence, one can determine the area of the flat bottom as well as the area of the minimum section of the neck of the fractured cylinder. The ratio of the area of the flat bottom to the area of the minimum section after fracture appears to be one of the characteristics of the steel. Bridgman found that the effect of pressure is to diminish the ratio of these areas. His results for the steel designated as C14 are represented graphically in Figure 1. Analogous results were obtained for steels in the 19-1, .. ., 19-4 series; the data for these steels is given in the table and is used for the construction of the graphs in Figure 2. It appears from