Abstract
An analytical determination of the forming limits of metals requires knowledge of plastic flow, buckling characteristics, local plastic behavior, and fracture laws of metals under combined stresses. Although the plastic flow of work-hardenable metals is now a fairly well-developed subject, our information on the remaining topics is incomplete; there is a great need for additional data on the fracture of metals under combined stresses. This need was recognized by the Office of Production Research and Development, which sponsored the following investigation as part of its “Study of the Forming Properties of Aluminum Alloy Sheet.” The data reported herein were selected exclusively from Part 19, OPRD. Report No. W-225, July 27, 1945, which has been released by the OPRD. In order to study the fracture of metals under combined stresses thin-walled tubular specimens of aluminum alloys 24S-T, 24S-T80, and 24S-T81 were subjected to axial loads and internal pressures. The ratios of load to pressure were adjusted to give stress ratios covering the tension-tension and tension-compression fields of biaxial stress. Predictions based upon the “critical normal stress law” and the “critical hydrostatic tension stress law” were in serious disagreement with the experimental facts, while predictions based upon the “critical shear stress law” were in approximate agreement.
