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Stefan C. Soare's blog

On the overall yield function of a hollow sphere

  Motivated mostly by analytical (or formal) considerations, a vast majority of the works dedicated to the study of the overall plastic response of a porous metal assumes that the sound material (or matrix) obeys a quadratic yielding criterion (von Mises or Hill'48). However, most metals of technological interest today feature significant deviations from the quadratic form of yielding. Therefore a realistic modeling of their behavior, while sustaining damage,  requires appropriate consideration of their yielding properties.

On the modeling of asymmetric yield functions

In the context of metal plasticity, the yield function of a metal polycrystal is its most complex macro-characteristic. Letting aside the questions of kinematic or distortional hardening, the basic problem is geometric in nature: to design a family of convex surfaces capable of reproducing a wide range of experimental, or theoretically predicted data. While many satisfactory solutions have been proposed for the modeling of symmetric (with respect to the origin of the stress space) yield functions, the more general case of asymmetric functions has not witnessed comparable progress.

Plasticity and non-Schmid effects

If slip is the only mechanism of
plastic deformation of a crystal and Schmid law governs the slip
activity, the overall response of an aggregate of such crystals
features the normality rule of classical plasticity, see
for a rigorous recent proof. Any deviation from Schmid law is
referred to as a non-Schmid effect. In general, these effects may be
of two kinds: in addition to the resolved shear stress (on a slip
system), other stress components may influence slip activity or/and
the hardening of a slip system (representative examples for each kind
are described, for example, in Qin and Bassani(1992) and Spitzig

Plastic Spin

In the classical (rate-independent)
theory of metal plasticity, the plastic spin has been an issue of
research and debate for about thirty years. Judging by the content
of current publications on the topic (regarding modeling
possibilities, consequences and applications), it seems that the
concept has acquired a certain degree of acceptance, although no
rigorous justification, at theoretical level, has ever been provided.
In the attached preprint this matter is investigated starting from

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