Consider the case of a simple rectangular cross-section, cantilever beam. This beam has a 1 inch by 1 inch cross section and is 12 inches long. It is made from steel and has a 200 lb load applied at the "tip". Simple beam theory approximates the tip deflection to be 0.0133 inches. If the beam is modeled using 4-node tetrahedrons (constant strain elements) the resulting stress field is,

Comparison of this stress distribution with that assumed in beam theory may help explain why the tip displacement predicted using this model is only about 0.0045 inches. If the model used 10 node tetrahedrons which allow for a linear variation in strain within the element the resulting stress and displacement are given as:

These compare more favorably with the stress distribution and displacement field predicted using beam theory.