Non-Schmid Effects on the Behavior of Polycrystals -- with
Applications to Ni3Al
M. Dao, B. J. Lee and R. J. Asaro
Metall. Trans. A, 27 (1996) 81-99
ABSTRACT
The elastoviscoplastic single crystal constitutive model incorporating
non-Schmid effects developed by Dao and Asaro (Mater. Sci. Eng. A, 1993,
vol. 170, pp. 143-60) is introduced into Asaro and Needleman's
(Acta Metall., 1985, vol. 33, pp. 923-53) Taylor-like polycrystal model
as well as Harren and Asaro's (J. Mech. Phys. Solids, 1989, vol. 37, pp. 191-232)
finite element polycrystal model. The single crystal non-Schmid effects,
strain hardening, latent hardening, and rate sensitivity, are all described
on the individual slip system level, while polycrystal mechanical
properties on macroscale are predicted. In general, it is found that
non-Schmid effects can have important influences on the "constant offset
plastic strain yield surfaces," stress-strain behavior, texture development,
and shear band formation. Finite element calculations show that with moderate
non-Schmid effects, localized deformation within a polycrystal aggregate tends
to initiate earlier and form sharper and more intense shear bands. Heavy
shear banding is found to produce less pronounced textures, which is
consistent with existing experimental evidence on Ni3Al. Examples with
Ni3Al demonstrate that the kind of non-Schmid effects existing in Ni3Al
can increase the generalized Taylor factor to values much higher than 3.06,
raise the polycrystal strain hardening rate much higher than that which would
be obtained using Schmid's rule, and influence the deformation texture.