neml

neml is an open-source software library used for developing and evaluating nonlinear constitutive models in computational mechanics. It provides a framework to describe material behavior through constitutive equations, manage internal state variables, and perform time integration of rate-dependent models such as elastoplastic and viscoplastic formulations. The library is designed to support model development, testing, and validation, and to facilitate integration with finite element analysis workflows.

In neml, users define material models by specifying the governing equations that relate stress, strain, and internal variables, along with the rules that govern hardening, softening, and rate effects. The software typically supports incremental loading with numerical solvers for updating the material state at each step. The modular design aims to make it straightforward to implement new constitutive laws, combine models, and compare predictions under different loading paths. This makes neml a tool for researchers and engineers working on material behavior under complex loading, including metal plasticity, damage, and time-dependent responses.

Usage and impact: neml is employed for academic research and industrial investigations into material performance, enabling parameter identification from experiments, rapid prototyping of new models, and systematic study of model behavior across loading regimes. Its emphasis on a clear interface and reusability helps facilitate collaboration and reproducibility in materials modeling projects.

History and availability: neml originated as an open-source project within the computational mechanics community and is distributed with public documentation and examples. It is commonly referred to by the project’s name in literature and software repositories, where users can access source code, contribute improvements, and report issues.