Crystallographic texture, anisotropic yield surfaces and forming limits of sheet metals

Abstract

A concise review of different proposed phenomenological equations that describe the behavior of sheet metals and their influence on theoretical forming limits is presented. Also, geometrical features of yield surface shapes necessary to achieve high formability are discussed. An existing predictive model (the model of Marciniak and coworkers) of localized plastic flow in sheet material was redeveloped to take into account any anisotropic yield function together with isotropic work hardening. The main parameter of this new model is the yield surface shape. Forming limit diagrams (FLDs) were computed using yield surfaces described either by a phenomenological equation or by the procedure of Taylor/Bishop and Hill for polycrystalline aggregates. In the last case, three-dimensional yield surfaces ( σ xx , σ yy , σ xy ) were generated in order to calculate the entire FLD. Some examples are given, including the case of an aluminum alloy, where the crystallite orientation distribution function is the basic input to the model.