Modified items

The most common mechanical test for characterizing metals is the tension test. A specimen is put in a machine which pulls it at a prescribed rate and simultaneously records the load on the specimen.

A material is said to have deformed plastically if it doesn't return to its original shape after the load is removed. The most common application for plasticity in nite element analysis is modeling the deformation of metals. While a great deal of research is available on the plasticity of metals at a very fundamental level, the majority of plasticity models are phenomenological and have no motivation beyond duplicating experimental data. The models discussed here are among the simpler plasticity models, and they are, indeed, completely phenomenological. While there are post hoc rationalizations of why these simple models perform as well as they do, they are still rationalizations.

A deìnitive way to determine whether locking will occur is the Babuska- Brezzi condition, but it is di cult to apply. Constraint counting, however, is an easy-to-apply, rough guide to determining whether an element formulation is likely to lock for incompressible problems.

Locking in linear quadrilateral elements occurs when they are subjected to bending. For simplicity, letês examine the simplest case of a quad in bending.

Under some circumstances the displacements calculated by the finite element method are orders of magnitude smaller than they should be, and when this happens, the elements are said to be locking. The two most common types of locking are shear and pressure locking. Locking occurs in lower order elements because an elementes kinematics arenet rich enough to represent the correct solution. Shear locking occurs when elements are subjected to bending, and pressure locking occurs when the material is incompressible. Most of the research on reducing locking is devoted to elements with linear shape functions, with the remainder devoted to quadratic elements.

The energy data which is printed in the d3hsp and glstat files forms a useful check on an analysis.