A Geometrically Nonlinear Cosserat (Micropolar) Curvy Shell Model Via Gamma Convergence

Using Γ-convergence arguments, we construct a nonlinear membrane-like Cosserat shell model on a curvy reference configuration starting from a geometrically nonlinear, physically linear three-dimensional isotropic Cosserat model. Even if the theory is of order O(h) in the shell thickness h, by comparison to the membrane shell models proposed in classical nonlinear elasticity, beside the change of metric, the membrane-like Cosserat shell model is still capable of capturing the transverse shear deformation and the Cosserat-curvature due to remaining Cosserat effects. We formulate the limit problem by scaling both unknowns, the deformation and the microrotation tensor, and by expressing the parental three-dimensional Cosserat energy with respect to a fictitious flat configuration. The model obtained via Γ-convergence is similar to the membrane (no O(h3) flexural terms, but still depending on the Cosserat-curvature) Cosserat shell model derived via a derivation approach, but these two models do not coincide. Comparisons to other shell models are also included.