20.8.2 User-defined thermal material behavior

Products: ABAQUS/Standard  ABAQUS/CAE  



User-defined thermal material behavior in ABAQUS/Standard:

  • is provided by means of an interface whereby any thermal constitutive model can be added to the library;

  • requires that a constitutive model (or a library of models) is programmed in user subroutine UMATHT; and

  • requires considerable effort and expertise: the feature is very general and powerful, but its use is not a routine exercise.

Material constants

Any material constants that are needed in user subroutine UMATHT must be specified as part of a user-defined thermal material behavior definition. Any other thermal material behaviors included in the same material definition will be ignored: the user-defined thermal material behavior requires that all thermal behavior calculations are programmed in user subroutine UMATHT.

Input File Usage:           

You must specify the number of constants being entered.


Property module: material editor: GeneralUser Material: User material type: Thermal

Unsymmetric equation solver

When the conductivity is defined in user subroutine UMATHT as a strong function of temperature, the heat transfer equilibrium equations become nonsymmetric and you may choose to invoke the unsymmetric equation solution capability; otherwise, convergence may be poor.

Input File Usage:           


Property module: material editor: GeneralUser Material: User material type: Thermal, toggle on Use unsymmetric material stiffness matrix

Material state

Many thermal constitutive models require the storage of solution-dependent state variables. These state variables might include microstructure or phase content information when the material undergoes phase changes. You should allocate storage for these variables in the associated material definition (see Allocating space” in “User subroutines: overview, Section 13.2.1). There is no restriction on the number of state variables associated with a user-defined material.

User subroutine UMATHT is called for each material point at each iteration of every increment. It is provided with the thermal state of the material at the start of the increment (solution-dependent state variables, temperature, and any predefined field variables) and with the increments in temperature, predefined state variables, and time.

Required calculations

Subroutine UMATHT must perform the following functions: it must define the internal energy per unit mass and its variation with temperature and spatial gradients of temperature; it must define the heat flux vector and its variation with respect to temperature and spatial gradients of temperature; and it must update the solution-dependent state variables to their values at the end of the increment. The components of the heat flux and spatial gradients in user subroutine UMATHT are in directions that depend on the use of local orientations (see Orientations, Section 2.2.5).

Use with other user subroutines

User subroutine UMAT can be used in conjunction with UMATHT to define the constitutive mechanical behavior of the material. The solution-dependent variables allocated in the material definition are accessible in both UMATHT and UMAT. In addition, user subroutines FRIC, GAPCON, and GAPELECTR are available for defining mechanical, thermal, and electrical interactions between surfaces.

Material options

Density, mechanical properties, and electrical properties can be included in the definition of a material whose constitutive thermal behavior is defined by user subroutine UMATHT.


User subroutine UMATHT can be used with all elements in ABAQUS/Standard that include thermal behavior (elements with temperature degrees of freedom such as pure heat transfer, coupled thermal-stress, and coupled thermal-electrical elements).