A Comparison of the Axial and Reversed-Torsional Strain Cycling Low-Cycle Fatigue Strength of Several Structural Materials

Abstract

As a part of series investigation on the low-cycle fatigue properties under the multiaxial stress condition, low-cycle fatigue tests were conducted under axial and reversed-torsion strain cycling conditions. Two kinds of carbon steel, a Ni-Cr-Mo steel, a commercially pure aluminum, a 7075-T6 aluminum alloy, and cold-worked and annealed coppers were tested in this investigation. The equivalent plastic strain range based on the octahedral shear strain theory was used in comparing these axial and reversed-torsional results. In general fairly good agreement was observed between the two cycling results, although some discrepancies existed in the case of the carbon steels and the annealed copper investigated. Some amount of anisotropy was found in fracture ductility between the axial direction and the diametral direction of specimens. This might affect more the reversed-torsion results. For more precise correlation of the two cycling test results, therefore, the influence of the anisotropy as well as that of the crack propagation characteristics should be taken into consideration.