Abstract
Directors and slip vectors are introduced to the theory of plasticity in order to take account of microstructures in crystalline materials in the range of the finite deformation. The notion of additive decomposition of the strain and curvature rate into elastic and plastic components is introduced in terms of directors and slip vectors, which represent the elastic and plastic microstructural change. The relation between the proposed theory and the couple stress theory of elasticity is discussed. The constitutive relation considering couple stress for plastic materials is also developed and an example of the rate-type constitutive equation is derived, where the yield condition depends on not only the usual Cauchy stress but also on the couple stress.
