Open issues on the eas method and mesh distortion insensitive locking-free low-order unsymmetric eas elements

One of the most popular mixed finite elements is the enhanced assumed strain (EAS) approach. However, despite numerous advantages there are still some open issues. Three of the most important, namely robustness in nonlinear simulations, hourglassing instabilities and sensitivity to mesh distortion, are discussed in the present contribution. Furthermore, we propose a novel Petrov-Galerkin based EAS method. It is shown that three conditions have to be fulfilled to construct elements that are exact for a specific displacement mode regardless of mesh distortion. The so constructed novel element is lockingfree, exact for bending problems, insensitive to mesh distortion and has improved coarse mesh accuracy.