NUMERICAL-SIMULATION OF YIELD LOCI FOR PST CRYSTALS OF TIAL

The yield strength of polysynthetically twinned (PST) crystals of TiAl depends on the orientation angle between the lamellar boundaries and the load axis. It is the aim of this work to model this anisotropic be haviour. A micromechanical model is employed which considers the lamel lar microstructure and the deformation mechanisms such as ordinary sli p and deformation twinning in gamma-TiAl. Since the calculated and mea sured yield strength data show good agreement in the case of uniaxial loading, there is a real motivation to study numerically the behaviour of a PST crystal under biaxial loading. Yield points are calculated f or various proportional stress paths defined by the ratio of the princ ipal stresses sigma(1)/sigma(2) in relation to the orientations of the load axes towards the lamellae. These predicted yield loci are compar ed with the von Mises and the Hill yield criteria. (C) 1997 Elsevier S cience S.A.