NEML: the Nuclear Engineering material Model Library

NEML (the Nuclear Engineering Material model Library) is a tool for creating and running structural material models. While it was originally developed to model high temperature nuclear reactors, the tool is general enough to apply to most types of structural materials.

The focus of NEML is on modularity and extensibility. The library is structured so that adding a new feature to an existing material model should be as simple as possible and require as little code as possible.

NEML material models are modular -- they are built up from smaller pieces into a complete model. For example, a model might piece together a temperature-dependent elasticity model, a yield surface, a flow rule, and several hardening rules. Each of these submodels is independent of the other objects so that, for example, switching from conventional J2 plasticity to a J2 theory requires only a one line change in an input file, if the model is already implemented, or a relatively small amount of coding to add the new yield surface if it has not been implemented. All of these objects are interchangeable. For example, the damage, viscoplastic, and rate-independent plasticity models all use the same yield (flow) surfaces, hardening rules, elasticity models, and so on.

As part of this philosophy, the library only requires new components provide a few partial derivatives and NEML uses this information to assemble the Jacobian needed to do a fully implement, backward Euler integration of the ordinary differential equations comprising the model form and to provide the algorithmic tangent needed to integrate the model into an implicit finite element framework.

Documentation and tutorials are available here.