Convergence of rotational hardening with bounds in clay plasticity

Convergence of the rotational hardening variable alpha used in the anisotropic models of clay plasticity, with a constitutively defined attractor/bound alpha(b)(eta), function of the stress ratio eta , under fixed eta loading, is analytically investigated. It is analytically shown that depending on various parameters of the rate equation of the evolution of alpha, such convergence may or may not occur despite the apparent necessity of convergence stemming from the form of the evolution equation of alpha.