Triangular composite finite elements

Composite triangles consisting of four three-node triangles originally proposed by Camacho and Ortiz are studied. It is shown that the original element does not satisfy the Babu ska{Brezzi condition nor pass the patch test. Remedies for these shortcomings are described. It is shown that the resulting elements are very robust for large deformation problems. In addition, composite triangular elements generated from four-node quadrilaterals are brie y examined; their accuracy is found to be not as good as the composite triangles