Hardening rules for finite deformation micropolar plasticity: Restrictionsimposed by the second law of thermodynamics and the postulate of Il'iushin

A finite deformation micropolar plasticity theory exhibiting kinematic and isotropic hardening is developed. Characteristic features of the theory are the multiplicative decomposition of the deformation gradient and the micro polar rotation tensor into elastic and plastic parts, respectively. The ela sticity law is derived from the second law of thermodynamics in the form of the Clausius-Duhem-inequality. Also, in defining the yield function use is made of a stress tensor, which corresponds to the Mandel stress tensor wit hin the framework of classical (non-polar) plasticity. The flow rule is obt ained from the postulate of Il'iushin, which is formulated appropriately fo r micropolar continua. The hardening properties are incorporated in the fre e energy and the yield function, the associated evolution equations being d erived as sufficient conditions for the validity of the so-called internal dissipation inequality. This way, the established micropolar plasticity law s are thermodynamically consistent.