| The definition of yield plays an important role in determining the mechanical response of a metal. In this dissertation we propose a criterion to select the best definition of yield for the problem under consideration. Two problems that require different definitions of yield are studied in detail: the first one is the phenomenon of stagnation in the stress-strain curve of metals at points of loading reversals (Rauch and Schmitt, 1989). We will model this phenomenon by linking the hardening behavior of the material to thermodynamic quantities, such as the rate of dissipation and the stored energy of cold work. The other problem we will study is the formulation of yield criteria for anisotropic materials. In particular, we will introduce a new yield surface that can describe the behavior of anisotropic sheets loaded in plane stress. The new yield surface includes several yield surfaces available in the literature as particular cases and is able to reproduce accurately experimental yield surfaces and yield surfaces obtained with polycrystal theories. |
