Plastic instability: Criteria and computational approaches

General criteria of instability in time-independent elastic-plastic solids and the related computational approaches are reviewed. The distinction between instability of equilibrium and instability of a deformation process is discussed with reference to instabilities of dynamic, geometric or material type. Comparison is made between the bifurcation, energy and initial imperfection approaches. The effect of incremental nonlinearity of the constitutive law associated with formation of a yield-surface vertex; on instability predictions is examined. A survey of the methods of post-critical analysis is presented.