ON THE ASYMMETRIC YIELD SURFACE OF PLASTICALLY ORTHOTROPIC MATERIALS - A PHENOMENOLOGICAL STUDY

Hill's (1948) yield criterion for plastically orthotropic solids is ex tended to include materials whose tensile and compressive yield stress es, obtained from uniaxial loading tests, are different. First, we rev iew and discuss the classic yield criteria in plasticity theory includ ing plastically isotropic and anisotropic materials. Then, we present a yield criterion for plastic anisotropic solids whose initial yield s urface may not be symmetric about the origin in stress space. The new criterion is based on the criterion given by Hill (Proc. Roy. Soc. Lon don A, 1948, 193, 281) for anisotropic solids and the criterion propos ed by Drucker and Prager (Q. Appl. Math., 1952, 10, 157) for soil whos e tensile and compressive strengths are far apart. The coefficients th at appear in the new criterion can be determined from uniaxial tension and compression, and simple shearing tests. The formulae for the dete rmination of those coefficients are given. Specifically, the new crite rion is applied to the yielding of thin sheets where a plane stress co ndition prevails. Finally, the prediction of the criterion is compared with the experimental data obtained by Lee and Backofen (Trans. Metal l. Soc. AIME, 1966, 236, 1966) on titanium alloy sheets. (C) 1997 Acta Metallurgica Inc.