Behavior of Steel Under Biaxial Stress as Determined by Tests on Tubes

The experimental work is described and results presented for tests on twelve 5¼-in-diam thin-walled tubes of low-carbon steel subjected to various conditions of biaxial stress. These experiments composed the “pilot” series of tests in a larger investigation on the behavior of ship-plate steel under multiaxial stress conditions. The ductility of the metal under various biaxial stress conditions and at two temperatures, 70 F and −138F, is reported. The evidence indicates that the metal is reasonably ductile, even at the low temperature, provided it is subjected only to a state of plane stress. If a state of triaxial stress is induced by restraint or by discontinuities in the material, the ductility may be greatly reduced at the low temperature. Evidence is presented to indicate that fracture may occur either by shear or by cleavage, depending upon the stress and temperature conditions. In a majority of cases, reasonable prediction of the stress-strain behavior of the metal in the plastic range can be made for various biaxial stress conditions from the data of the simple tension test, by use of the modified octahedral-shear concept.