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A micromechanical model for finite single crystal plasticity was introduced by Kochmann & Hackl (2011 Contin. Mech. Thermodyn. 23, 63-85 (doi:10.1007). This model is based on thermodynamic variational principles and leads to a non-convex variational problem. Based on the Lagrange functional, an incremental strategy was outlined to model the time-continuous evolution of a first-order laminate microstructure. Although this model provides interesting results on the material point level, owing to the global minimization in the evolution equations, the calculation time and numerical instabilities may cause problems when applying this model to macroscopic specimens. In this paper, a smooth transition zone between the laminates is introduced to avoid global minimization, which makes the numerical calculations cumbersome compared with the model in Kochmann & Hackl. By introducing a smooth viscous transition zone, the dissipation potential and its numerical treatment have to be adapted. We outline rate-dependent timeevolution equations for the internal variables based on variational techniques and show as first examples single-slip shear and tension/compression tests. IntroductionThe concept of crystal plasticity was first introduced by Ewing & Rosenhain in 1899 [1]. They observed that slip steps on the surface of metals under plastic deformation arise owing to slip bands inside the metal. They thus concluded that plastic deformations appear owing to shearing of certain crystal planes. This evolving microstructure (e.g. figure 1) strongly influences the macroscopic behaviour and hence it has to be transferred to appropriate simulation schemes by micromechanical 2015 The Author(s) Published by the Royal Society. All rights reserved.

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