Introduction
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The NLH_CSRM model will eventually replace the LKR and LETK laws of behavior. This "modernization" work is part of the development actions of the EDF -R&D project "Radioactive Waste Management" (GDR2).

The scope of use of model NLH_CSRM is currently limited to **isotropic mechanical behavior**. Taking into account **structural anisotropy** and the dependence of work hardenings on **temperature** — effective in the latest version of model LKR — will be the subject of future renderings; as will the dependence of the criteria on the third invariant of the stress deflector (Lode angle).

The NLH_CSRM model is part of the **thermodynamic framework of generalized standard materials** with two irreversible mechanisms,


* **Plastic mechanism** —irreversible **instantaneous behavior:** hardening and/or softening workings, contracting or expanding volume behavior, influence of the average stress on the fragile nature of the compression response,...;


* **Viscoplastic mechanism** — irreversible **delayed** behavior (Perzyna type): primary, secondary, and tertiary creep (ruin).

A **coupling between these two mechanisms** makes it possible — among other things — to represent the dependence of the maximum resistance of certain geomaterials on the stress rate.

This "modernization" work is motivated by the desire to increase the robustness and efficiency of the model used to describe the behavior of Callovo-Oxfordian argillite — host rock constituting the first geological barrier of Cigéo — in order to be able to consider its use on 3D problems requiring memory and calculation time.