Strain smoothed for compressible and nearly-incompressible finite elasticity

We present a robust and efficient form of the smoothed finite element method (S-FEM) to simulate hyperelastic bodies with compressible and nearly-incompressible neo-Hookean behaviour.
The resulting method is stable, free from volumetric locking and robust on highly distorted meshes.
To ensure inf-sup stability of our method we add a cubic bubble function to each element.
The weak form for the smoothed hyperelastic problem is derived analogously to that of smoothed linear elastic problem.
Smoothed strains and smoothed deformation gradients are evaluated on sub-domains selected by either edge information (edge-based S-FEM, ES-FEM) or nodal information (node-based S-FEM, NS-FEM).
Numerical examples are shown that demonstrate the efficiency and reliability of the proposed approach in the nearly-incompressible limit and on highly distorted meshes.
We conclude that, strain smoothing is at least as accurate and stable, as the MINI element, for an equivalent problem size.