Critical Stresses in a Circular Ring

Many times, in investigations of the physical properties of foundation rock samples, tensile strength tests are required. Usually, the sample consists of one or more short cylindrical prisms of the type taken by core drilling, and then the conventional tension test (in which axial forces are applied to pull the specimen apart) is absolutely inadequate. As a suitable test for use under such circumstances and 'with such material the Soils Laboratory, U.S. Engineer Office, Pittsburgh, Pa. (later, the Soils Engineering Section, Cincinnati, Ohio, Testing Laboratory), devised and in:vestigated the “ring test” described in this paper. As the name implies, specimens for this test are rings formed by' cutting disks about 1 in. thick from cylindrical cores and by drilling a small hole in the centers of the disks. These rings are then placed in a standard testing machine and loaded in compression until failure occurs. The results of the tests have been interpreted in the light of certain unpublished data which Max Frocht obtained using photoelastic methods.