16.1.3 Combining material behaviors

Products: ABAQUS/Standard  ABAQUS/Explicit  ABAQUS/CAE  



ABAQUS provides a broad range of possible material behaviors. A material is defined by choosing the appropriate behaviors for the purpose of an analysis. This section describes the general rules for combining material behaviors. Specific information for each material behavior is also summarized at the end of each material behavior description section in this chapter.

Some of the material behaviors in ABAQUS are completely unrestricted: they can be used alone or together with other behaviors. For example, thermal properties such as conductivity can be used in any material definition. They will be used in an analysis if the material is associated with elements that can solve heat transfer problems and if the analysis procedure allows for the thermal equilibrium equation to be solved.

Some material behaviors in ABAQUS require the presence of other material behaviors, and some exclude the use of other material behaviors. For example, metal plasticity requires the definition of elastic material behavior or an equation of state and excludes all other rate-independent plasticity behaviors.

Complete material definitions

ABAQUS requires that the material be sufficiently defined to provide suitable properties for those elements with which the material is associated and for all of the analysis procedures through which the model will be run. Thus, a material associated with displacement or structural elements must include either a “Complete mechanical” category behavior or an “Elasticity” category behavior, as discussed below. In ABAQUS/Explicit density (Density, Section 16.2.1) is required for all materials except hydrostatic fluids.

It is not possible to modify or add to material definitions once an analysis is started. However, material definitions can be modified in an import analysis. For example, a static analysis can be run in ABAQUS/Standard using a material definition that does not include a density specification. Density can be added to the material definition when the analysis is imported into ABAQUS/Explicit.

All aspects of a material's behavior need not be fully defined; any behavior that is omitted is assumed not to exist in that part of the model. For example, if elastic material behavior is defined for a metal but metal plasticity is not defined, the material is assumed not to have a yield stress. You must ensure that the material is adequately defined for the purpose of the analysis. The material can include behaviors that are not relevant for the analysis, as described in Material library: overview, Section 16.1.1. Thus, you can include general material behavior libraries, without having to delete those behaviors that are not needed for a particular application. This generality offers great flexibility in material modeling.

Material behavior combination tables

The material behavior combination tables that follow explain which behaviors must be used together. The tables also show the material behaviors that cannot be combined. Behaviors designated with an (S) are available only in ABAQUS/Standard; behaviors designated with an (E) are available only in ABAQUS/Explicit.

The behaviors are assigned to categories because exclusions are best described in terms of those categories. Some of the categories require explanation:

  • “Complete mechanical behaviors” are those behaviors in ABAQUS that, individually, completely define a material's mechanical (stress-strain) behavior. A behavior in this category, therefore, excludes any other such behavior and also excludes any behavior that defines part of a material's mechanical behavior: those behaviors that belong to the elasticity and plasticity categories.

  • “Elasticity and equation of state behaviors” contains all of the basic elasticity behaviors in ABAQUS. If a behavior from the “Complete mechanical behaviors” category is not used and mechanical behavior is required, a behavior must be selected from this category. This selection then excludes any other elasticity behavior.

  • “Enhancements for elasticity behaviors” contains behaviors that extend the modeling provided by the elasticity behaviors in ABAQUS.

  • “Rate-independent plasticity behaviors” contains all of the basic plasticity behaviors in ABAQUS except deformation plasticity, which is in the “Complete mechanical behaviors” category because it completely defines the material's mechanical behavior.

  • “Rate-dependent plasticity behaviors” contains behaviors that extend the modeling provided by the rate-independent plasticity behaviors and by the linear elastic material behavior.

If elastic-plastic behavior must be modeled, you should select an appropriate plasticity behavior from one of the plasticity behaviors categories and an elasticity behavior from one of the elasticity behaviors categories.

General behaviors:

These behaviors are unrestricted.

Material damping*DAMPINGElasticity, hyperelasticity, or hyperfoam (except when used with beam or shell general sections or substructures)
Density *DENSITYRequired in ABAQUS/Explicit, except for hydrostatic fluid elements
Solution-dependent state variables*DEPVAR 
Thermal expansion*EXPANSION 

Complete mechanical behaviors:

These behaviors are mutually exclusive and exclude all behaviors listed for elasticity, plasticity, and hydrostatic fluid behaviors, including all related enhancements.

Acoustic medium*ACOUSTIC MEDIUMDensity
Deformation plasticity(S)*DEFORMATION PLASTICITY 
Mechanical user material*USER MATERIAL (, TYPE=MECHANICAL in ABAQUS/Standard) 

Elasticity and equation of state behaviors:

These behaviors are mutually exclusive.

Equation of state(E)*EOS 
Porous elasticity(S)*POROUS ELASTIC 

Enhancements for elasticity behaviors:

Shear behavior for an equation of state(E)*EOS SHEAREquation of state
Strain-based failure measures*FAIL STRAINElasticity
Stress-based failure measures*FAIL STRESSElasticity
Hysteresis(S)*HYSTERESISHyperelasticity (excludes all plasticity behaviors and Mullins effect)
Mullins effect*MULLINS EFFECTHyperelasticity (excludes all plasticity behaviors, viscoelasticity, and hysteresis)
Compressive failure theory(S)*NO COMPRESSIONElasticity
Tension failure theory(S)*NO TENSIONElasticity
Viscoelasticity*VISCOELASTICElasticity, hyperelasticity, or hyperfoam (excludes all plasticity behaviors, all associated plasticity enhancements, and Mullins effect)

Rate-independent plasticity behaviors:

These behaviors are mutually exclusive.

Brittle cracking(E)*BRITTLE CRACKINGIsotropic elasticity and brittle shear
Modified Drucker-Prager/Cap plasticity*CAP PLASTICITYDrucker-Prager/Cap plasticity hardening and isotropic elasticity or porous elasticity
Cast iron plasticity(S)*CAST IRON PLASTICITYCast iron compression hardening, cast iron tension hardening, and isotropic elasticity
Cam-clay plasticity(S)*CLAY PLASTICITYElasticity or porous elasticity
Concrete(S)*CONCRETE Isotropic elasticity
Concrete damaged plasticity*CONCRETE DAMAGED PLASTICITYConcrete compression hardening, concrete tension stiffening, and isotropic elasticity
Crushable foam plasticity*CRUSHABLE FOAMCrushable foam hardening and isotropic elasticity
Drucker-Prager plasticity*DRUCKER PRAGERDrucker-Prager hardening and isotropic elasticity or porous elasticity
Plastic compaction behavior for an equation of state(E)*EOS COMPACTIONLinear equation of state
Jointed material(S)*JOINTED MATERIALIsotropic elasticity and a local orientation
Mohr-Coulomb plasticity(S)*MOHR COULOMBMohr-Coulomb hardening and isotropic elasticity
Metal plasticity*PLASTICElasticity (in ABAQUS/Standard)
Isotropic elasticity, orthotropic elasticity (requires anisotropic yield), or the combination of an equation of state and isotropic linear elastic shear behavior for an equation of state (in ABAQUS/Explicit)

Rate-dependent plasticity behaviors:

These behaviors are mutually exclusive, except metal creep and time-dependent volumetric swelling.

Cap creep(S)*CAP CREEPElasticity, modified Drucker-Prager/Cap plasticity, and Drucker-Prager/Cap plasticity hardening
Metal creep(S)*CREEPElasticity (except when used to define rate-dependent gasket behavior; excludes all rate-independent plasticity behaviors except metal plasticity)
Drucker-Prager creep(S)*DRUCKER PRAGER CREEPElasticity, Drucker-Prager plasticity, and Drucker-Prager hardening
Metal plasticity*PLASTIC, RATEElasticity (in ABAQUS/Standard)
Isotropic elasticity, orthotropic elasticity (requires anisotropic yield), or the combination of an equation of state and isotropic linear elastic shear behavior for an equation of state (in ABAQUS/Explicit)
Rate-dependent viscoplasticity*RATE DEPENDENTDrucker-Prager plasticity, crushable foam plasticity, or metal plasticity
Time-dependent volumetric swelling(S)*SWELLINGElasticity (excludes all rate-independent plasticity behaviors except metal plasticity)
Two-layer viscoplasticity(S)*VISCOUSElasticity and metal plasticity

Enhancements for plasticity behaviors:

Annealing temperature*ANNEAL TEMPERATUREMetal plasticity
Brittle failure(E)*BRITTLE FAILUREBrittle cracking and brittle shear
Cyclic hardening*CYCLIC HARDENINGMetal plasticity with nonlinear isotropic/kinematic hardening
Inelastic heat fraction*INELASTIC HEAT FRACTIONMetal plasticity and specific heat
Oak Ridge National Laboratory constitutive model(S)*ORNLMetal plasticity, cycled yield stress data, and, usually, metal creep
Porous material failure criteria(E)*POROUS FAILURE CRITERIAPorous metal plasticity
Porous metal plasticity*POROUS METAL PLASTICITYMetal plasticity
Anisotropic yield/creep*POTENTIALMetal plasticity, metal creep, or two-layer viscoplasticity
Shear failure(E)*SHEAR FAILUREMetal plasticity

Enhancement for elasticity or plasticity behaviors:

Tensile failure(E)*TENSILE FAILUREMetal plasticity or equation of state
Damage initiation*DAMAGE INITIATIONFor elasticity behaviors: elasticity based on a traction-separation description for cohesive elements (in ABAQUS/Standard or ABAQUS/Explicit) or elasticity model for fiber-reinforced composites (in ABAQUS/Standard)
For plasticity behaviors (ABAQUS/Explicit only): metal plasticity or Drucker-Prager plasticity
Damage evolution*DAMAGE EVOLUTIONDamage initiation
Damage stabilization(S)*DAMAGE STABILIZATIONDamage evolution

Thermal behaviors:

These behaviors are unrestricted but exclude thermal user materials.

Thermal conductivity*CONDUCTIVITY 
Volumetric heat generation(S)*HEAT GENERATION 
Latent heat*LATENT HEATDensity
Specific heat*SPECIFIC HEATDensity

Complete thermal behavior:

This behavior is unrestricted but excludes the thermal behaviors in the previous table.

Thermal user material(S)*USER MATERIAL, TYPE=THERMALDensity

Pore fluid flow behaviors:

These behaviors are unrestricted.

Swelling gel(S)*GELPermeability, porous bulk moduli, and absorption/exsorption behavior
Moisture-driven swelling(S)*MOISTURE SWELLINGPermeability and absorption/exsorption behavior
Porous bulk moduli(S)*POROUS BULK MODULIPermeability and either elasticity or porous elasticity
Absorption/exsorption behavior(S)*SORPTIONPermeability

Electrical behaviors:

These behaviors are unrestricted.

Electrical conductivity(S)*ELECTRICAL CONDUCTIVITY 
Fraction of electric energy released as heat(S)*JOULE HEAT FRACTION 

Mass diffusion behaviors:

These behaviors exclude all other behaviors.

Mass diffusivity(S)*DIFFUSIVITYSolubility
Solubility(S)*SOLUBILITYMass diffusivity

Hydrostatic fluid behaviors:

Fluid bulk modulus(S)*FLUID BULK MODULUSHydraulic fluid
Hydrostatic fluid density*FLUID DENSITY 
Fluid thermal expansion coefficient(S)*FLUID EXPANSIONHydraulic fluid