Material models (also called constitutive models), are the mathematical representation of a material's response to an applied load.

Typical model classes include the relationships between stress-strain, heat flux-temperature gradient, voltage-strain, and current-voltage, but also include more general behaviors such as friction and bonding, and response due to changes in the physical environment such as thermal expansion and swelling.

This reference provides information about material model behavior and application, including details about the load-response relationship and the necessary information required to use the material models in an analysis. The models are grouped based on the degrees of freedom that, directly or indirectly, give the loading function that serves as the input for the material model.