Enhanced assumed strain elements and locking in membrane problems Original Research Article

The assumptions which guarantee convergence of EAS elements first introduced by Simo and Rifai, can be reduced to two postulates. Specifically, the stability condition refers to a relaxed stability of an associated Hu-Washizu principle. We investigate the problem of volume locking of membrane problems. Estimates of a certain type which for instance imply volume locking of the Q1-element, are fortunately not present with EAS elements. Finally we verify an equivalence of the EAS concept with a Hellinger-Reissner method which was observed in numerical computations by Andelfinger and Ramm.