Remaining at Yield During Unloading and Other Unconventional Elastic-Plastic Response

A rather special time-independent or elastic-plastic response is proposed in which, although there is elastic response to unloading, the material remains at yield for all or a significant portion of the unloading path following plastic deformation. In the most elementary form, the material exhibits no memory of prior plastic deformation; the current state of the material is given solely by the current state of stress. A simple but unconventional field of plastic moduli then can be chosen to produce a limit surface that cuts through a nested set of yield surfaces and to model critical aspects of the behavior of sand.