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