The correct choice of element for a particular simulation is vital if accurate results are to be obtained at a reasonable cost. You will undoubtedly develop your own guidelines for selecting elements for your own particular applications as you become more experienced in using ABAQUS. However, as you begin to use ABAQUS, you should consider the following guidelines:
Use quadratic, reduced-integration elements (CAX8R, CPE8R, CPS8R, C3D20R, etc.) for general analysis work, unless you need to model very large strains or have a simulation with complex, changing contact conditions.
Use quadratic, fully integrated elements (CAX8, CPE8, CPS8, C3D20, etc.) locally where stress concentrations may exist. They provide the best resolution of the stress gradients at the lowest cost.
Use a fine mesh of linear, reduced-integration elements (CAX4R, CPE4R, CPS4R, C3D8R, etc.) for simulations involving very large mesh distortions (large-strain analysis).
For contact problems use a fine mesh of linear, reduced-integration elements or incompatible mode elements (CAX4I, CPE4I, CPS4I, C3D8I, etc.). See Chapter 11, “Contact.”
Minimize the mesh distortion as much as possible. Coarse meshes with distorted linear elements can give very poor results.
In three dimensions use hexahedral (brick-shaped) elements wherever possible. They give the best results for the minimum cost. Complex geometries can be difficult to mesh completely with hexahedrons; therefore, wedge and tetrahedral elements may be necessary. The linear versions of these elements, C3D6 and C3D4, are poor elements (fine meshes are needed to obtain accurate results); as a result, these elements should generally be used only when necessary to complete a mesh, and, even then, they should be far from any areas where accurate results are needed.
Some preprocessors contain free-meshing algorithms that mesh arbitrary geometries with tetrahedral elements. As long as you use quadratic tetrahedral elements (C3D10), you should get reasonable results for small-displacement problems without contact. An alternative to this element is the modified quadratic tetrahedral element (C3D10M), which is robust for large-deformation and contact problems and exhibits minimal shear and volumetric locking. With either element, however, the analysis will take longer to run than an equivalent mesh of hexahedral elements. You should not use a mesh containing only linear tetrahedral elements (C3D4): the results will be inaccurate unless you use an extremely large number of elements.