Well-posedness and numerical performances of the strain gap method

A mixed method of approximation is discussed starting from a suitably modif ied expression of the Hu-Washizu variational principle in which the indepen dent fields are displacements, stresses and strain gaps defined as the diff erence between compatible strains and strain fields. The well-posedness of the discrete problem is discussed and necessary and sufficient conditions a re provided. The analysis of the mixed method reveals that the discrete pro blem can be split into a reduced problem and in a stress recovery. Accordin gly, the discrete stress solution is univocally determined once an interpol ating stress subspace is chosen. The enhanced assumed strain method by Simo and Rifai is based on an orthogonality condition between stresses and enha nced strains and coincides with the reduced problem. It is shown that the m ixed method is stable and converges. Computational issues in the context of the finite element method are discussed in detail and numerical performanc es and comparisons are carried out. Copyright (C) 2001 John Wiley & Sons, L td.