Experimental Investigation of Corners in the Yield Surface

Abstract

The results of fourteen combined stress tests with variable stress ratios on annealed commercially pure aluminum are reported. These tests were made on a combined tension-torsion testing machine of a dead-load type. It is shown that the loading path carries a pointed vertex with it. However, the direction of the plastic-strain increment vector differs only slightly from the direction predicted by the Mises theory. Finally, the experiments indicate that the form of the yield surface at a considerable distance from the stress increment vector agrees much better with the prediction of the slip theory than it does with the prediction of the Mises theory.