User subroutine to define a material's mechanical behavior.

Warning: The use of this subroutine generally requires considerable expertise. You are cautioned that the implementation of any realistic constitutive model requires extensive development and testing. Initial testing on a single-element model with prescribed traction loading is strongly recommended.

User subroutine UMAT:

  • can be used to define the mechanical constitutive behavior of a material;

  • will be called at all material calculation points of elements for which the material definition includes a user-defined material behavior;

  • can be used with any procedure that includes mechanical behavior;

  • can use solution-dependent state variables;

  • must update the stresses and solution-dependent state variables to their values at the end of the increment for which it is called;

  • must provide the material Jacobian matrix, σ/ε, for the mechanical constitutive model;

  • can be used in conjunction with user subroutine USDFLD to redefine any field variables before they are passed in; and

  • is described further in User-defined mechanical material behavior.

The following topics are discussed:

Related Topics
In Other Guides
User-defined mechanical material behavior
User-defined thermal material behavior