The importance of the exact satisfaction of the incompressibility constraint in nonlinear elasticity: mixed FEMs versus NURBS-based approximations

In the present paper we investigate the capability of finite element methods to correctly reproduce the stability range of finite strain problems in the incompressible regime. To this end, we develop a numerical scheme, obtained combining a stream function formulation with an isogeometric NURBS approach, which is able to sharply estimate the stability limits of the continuous problem. Using such a method, we show a pair of benchmark problems on which various well-known finite element methods largely fail in approximating the correct stability range.