Introduction
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Model CJS is an elasto-plastic behavior law adapted to the modeling of granular materials. It was developed at École Centrale de Lyon ([:ref:`bib1 <bib1>`], [:ref:`bib2 <bib2>`], [:ref:`bib3 <bib3>`]).

Version CJS implemented in *Code_Aster* is a hierarchical model with several levels of complexity. In its most complete expression, the model has two load surfaces: one is activated by isotropic stresses, the other by deviatory stresses. The first undergoes isotropic work hardening and the second a mixed work hardening (isotropic and kinematic). The elastic law is of the nonlinear hypoelastic type.