New Repo: ExaCMech

ExaCMech is a GPU-friendly library of constitutive models. The models are based on standard continuum mechanics concepts. Crystal-mechanics-based and porosity-mechanics-based models are a principal focus. Models are meant for standard crystalline metallic materials deforming under quasi-static conditions. Constitutive model response is a main ingredient in the simulation of deformation of material, and the constitutive model has two main jobs: It provides the stress tensor that goes into the balance of linear momentum, and it updates the evolving state of the material. This state can be tracked by variables for the stress, dislocation density, orientation of crystal lattices, grain size, and so on. For context, the GitHub repository includes links to relevant journal articles that reference similar models and algorithms.