Triangular finite elements with rotational degrees of freedom and enhanced strain modes

Three sets of enhanced strain functions are considered for the improvement of the three-node triangular finite element with rotational degrees of freedom. In each case, four enhanced strain terms are used. The four unknowns associated with the enhanced strain terms can be eliminated by static condensation so that nine degrees of freedom remain for the enhanced elements. Faster convergence in the energy norm is achieved. The enhanced elements are also able to deal with nearly incompressible plane strain problems considered, provided all rotational degrees of freedom do not vanish at all element nodes.