21.1.3 Combining material behaviors
Products: Abaqus/Standard Abaqus/Explicit Abaqus/CAE
References
Overview
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 21.2.1) 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 21.1.1. 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.
In Abaqus/Standard any material behaviors defined using a distribution (“Distribution definition,” Section 2.8.1) can be combined with almost all material behaviors in a manner identical to how they are combined when no distributions are used. For example, if the linear elastic material behavior is defined using a distribution, it can be combined with metal plasticity or any other material behavior that can normally be combined with linear elastic behavior. In addition, more than one material behavior defined with a distribution (linear elastic behavior and thermal expansion, for example) can be included in the same material definition. The only exception is that a material defined with concrete damaged plasticity (“Concrete damaged plasticity,” Section 23.6.3) cannot have any material behaviors defined with a distribution.
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, fabric, 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.
General behaviors:
These behaviors are unrestricted.
| Behavior | Keyword | Requires |
|---|---|---|
| Material damping | *DAMPING | Elasticity, fabric, hyperelasticity, hyperfoam, low-density foam, or anisotropic hyperelasticity (except when used with beam or shell general sections or substructures) |
| Density | *DENSITY | Required 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. However, when an element is enriched (“Modeling discontinuities as an enriched feature using the extended finite element method,” Section 10.7.1), the mechanical user material behavior can be used in conjunction with the progressive damage and failure behavior, which is in the enhancement for elasticity or plasticity behaviors category.
| Behavior | Keyword | Requires |
|---|---|---|
| Acoustic medium | *ACOUSTIC MEDIUM | Density |
| Deformation plasticity(S) | *DEFORMATION PLASTICITY | |
| Mechanical user material | *USER MATERIAL (, TYPE=MECHANICAL in Abaqus/Standard) |
Elasticity, fabric, and equation of state behaviors:
These behaviors are mutually exclusive.
| Behavior | Keyword | Requires |
|---|---|---|
| Elasticity | *ELASTIC | |
| Equation of state(E) | *EOS | |
| Fabric(E) | *FABRIC | |
| Hyperelasticity | *HYPERELASTIC | |
| Hyperfoam | *HYPERFOAM | |
| Anisotropic hyperelasticity | *ANISOTROPIC HYPERELASTIC | |
| Hypoelasticity(S) | *HYPOELASTIC | |
| Porous elasticity (S) | *POROUS ELASTIC | |
| Low-density foam (E) | *LOW DENSITY FOAM |
Enhancements for elasticity behaviors:
| Behavior | Keyword | Requires |
|---|---|---|
| Elastic shear behavior for an equation of state(E) | *ELASTIC, TYPE=SHEAR | Equation of state |
| Strain-based failure measures | *FAIL STRAIN | Elasticity |
| Stress-based failure measures | *FAIL STRESS | Elasticity |
| Hysteresis(S) | *HYSTERESIS | Hyperelasticity (excludes all plasticity behaviors and Mullins effect) |
| Mullins effect | *MULLINS EFFECT | Hyperelasticity (excludes hysteresis), hyperfoam or anisotropic hyperelasticity |
| Compressive failure theory(S) | *NO COMPRESSION | Elasticity |
| Tension failure theory(S) | *NO TENSION | Elasticity |
| Viscoelasticity | *VISCOELASTIC | Elasticity, hyperelasticity, or hyperfoam (excludes all plasticity behaviors and all associated plasticity enhancements); or anisotropic hyperelasticity |
| Shear viscosity for an equation of state(E) | *VISCOSITY | Equation of state |
Rate-independent plasticity behaviors:
These behaviors are mutually exclusive.
| Behavior | Keyword | Requires |
|---|---|---|
| Brittle cracking(E) | *BRITTLE CRACKING | Isotropic elasticity and brittle shear |
| Modified Drucker-Prager/Cap plasticity | *CAP PLASTICITY | Drucker-Prager/Cap plasticity hardening and isotropic elasticity or porous elasticity |
| Cast iron plasticity | *CAST IRON PLASTICITY | Cast iron compression hardening, cast iron tension hardening, and isotropic elasticity |
| Cam-clay plasticity | *CLAY PLASTICITY | Isotropic elasticity, orthotropic elasticity, or porous elasticity (in Abaqus/Standard) |
| Isotropic elasticity or orthotropic elasticity (in Abaqus/Explicit) | ||
| Concrete(S) | *CONCRETE | Isotropic elasticity |
| Concrete damaged plasticity | *CONCRETE DAMAGED PLASTICITY | Concrete compression hardening, concrete tension stiffening, and isotropic elasticity |
| Crushable foam plasticity | *CRUSHABLE FOAM | Crushable foam hardening and isotropic elasticity |
| Drucker-Prager plasticity | *DRUCKER PRAGER | Drucker-Prager hardening and isotropic elasticity or porous elasticity (in Abaqus/Standard) |
| Drucker-Prager hardening and isotropic elasticity or the combination of an equation of state and isotropic linear elastic shear behavior for an equation of state (in Abaqus/Explicit) | ||
| Plastic compaction behavior for an equation of state(E) | *EOS COMPACTION | Linear  equation of state |
| Jointed material(S) | *JOINTED MATERIAL | Isotropic elasticity and a local orientation |
| Mohr-Coulomb plasticity | *MOHR COULOMB | Mohr-Coulomb hardening and isotropic elasticity |
| Metal plasticity | *PLASTIC | Elasticity or hyperelasticity (in Abaqus/Standard) |
| Isotropic elasticity, orthotropic elasticity (requires anisotropic yield), hyperelasticity, 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.
| Behavior | Keyword | Requires |
|---|---|---|
| Cap creep(S) | *CAP CREEP | Elasticity, modified Drucker-Prager/Cap plasticity, and Drucker-Prager/Cap plasticity hardening |
| Metal creep(S) | *CREEP | Elasticity (except when used to define rate-dependent gasket behavior; excludes all rate-independent plasticity behaviors except metal plasticity) |
| Drucker-Prager creep(S) | *DRUCKER PRAGER CREEP | Elasticity, Drucker-Prager plasticity, and Drucker-Prager hardening |
| Metal plasticity | *PLASTIC, RATE | Elasticity or hyperelasticity (in Abaqus/Standard) |
| Isotropic elasticity, orthotropic elasticity (requires anisotropic yield), hyperelasticity, or the combination of an equation of state and isotropic linear elastic shear behavior for an equation of state (in Abaqus/Explicit) | ||
| Nonlinear viscoelasticity | *VISCOELASTIC, NONLINEAR | Hyperelasticity |
| Rate-dependent viscoplasticity | *RATE DEPENDENT | Drucker-Prager plasticity, crushable foam plasticity, or metal plasticity |
| Time-dependent volumetric swelling(S) | *SWELLING | Elasticity (excludes all rate-independent plasticity behaviors except metal plasticity) |
| Two-layer viscoplasticity(S) | *VISCOUS | Elasticity and metal plasticity |
Enhancements for plasticity behaviors:
| Behavior | Keyword | Requires |
|---|---|---|
| Annealing temperature | *ANNEAL TEMPERATURE | Metal plasticity |
| Brittle failure(E) | *BRITTLE FAILURE | Brittle cracking and brittle shear |
| Cyclic hardening | *CYCLIC HARDENING | Metal plasticity with nonlinear isotropic/kinematic hardening |
| Inelastic heat fraction | *INELASTIC HEAT FRACTION | Metal plasticity and specific heat |
| Oak Ridge National Laboratory constitutive model(S) | *ORNL | Metal plasticity, cycled yield stress data, and, usually, metal creep |
| Porous material failure criteria(E) | *POROUS FAILURE CRITERIA | Porous metal plasticity |
| Porous metal plasticity | *POROUS METAL PLASTICITY | Metal plasticity |
| Anisotropic yield/creep | *POTENTIAL | Metal plasticity, metal creep, Cam-clay plasticity, or two-layer viscoplasticity |
| Shear failure(E) | *SHEAR FAILURE | Metal plasticity |
| Tension cutoff | *TENSION CUTOFF | Mohr-Coulomb plasticity |
Enhancement for elasticity or plasticity behaviors:
| Behavior | Keyword | Requires |
|---|---|---|
| Tensile failure(E) | *TENSILE FAILURE | Metal plasticity or equation of state |
| Damage initiation | *DAMAGE INITIATION | For elasticity behaviors: elasticity based on a traction-separation description for cohesive elements or elasticity model for fiber-reinforced composites For plasticity behaviors: elasticity and metal plasticity or Drucker-Prager plasticity |
| Damage evolution | *DAMAGE EVOLUTION | Damage initiation |
| Damage stabilization | *DAMAGE STABILIZATION | Damage evolution |
Thermal behaviors:
These behaviors are unrestricted but exclude thermal user materials.
| Behavior | Keyword | Requires |
|---|---|---|
| Thermal conductivity | *CONDUCTIVITY | |
| Volumetric heat generation(S) | *HEAT GENERATION | |
| Latent heat | *LATENT HEAT | Density |
| Specific heat | *SPECIFIC HEAT | Density |
Complete thermal behavior:
This behavior is unrestricted but excludes the thermal behaviors in the previous table.
Pore fluid flow behaviors:
These behaviors are unrestricted.
| Behavior | Keyword | Requires |
|---|---|---|
| Swelling gel(S) | *GEL | Permeability, porous bulk moduli, and absorption/exsorption behavior |
| Moisture-driven swelling(S) | *MOISTURE SWELLING | Permeability and absorption/exsorption behavior |
| Permeability(S) | *PERMEABILITY | |
| Porous bulk moduli(S) | *POROUS BULK MODULI | Permeability and either elasticity or porous elasticity |
| Absorption/exsorption behavior(S) | *SORPTION | Permeability |
Electrical behaviors:
These behaviors are unrestricted.
| Behavior | Keyword | Requires |
|---|---|---|
| Dielectricity(S) | *DIELECTRIC | |
| Electrical conductivity(S) | *ELECTRICAL CONDUCTIVITY | |
| Fraction of electric energy released as heat(S) | *JOULE HEAT FRACTION | |
| Piezoelectricity(S) | *PIEZOELECTRIC |
Mass diffusion behaviors:
These behaviors exclude all other behaviors.
| Behavior | Keyword | Requires |
|---|---|---|
| Mass diffusivity(S) | *DIFFUSIVITY | Solubility |
| Solubility(S) | *SOLUBILITY | Mass diffusivity |
Hydrostatic fluid behaviors:
| Behavior | Keyword | Requires |
|---|---|---|
| Fluid bulk modulus(S) | *FLUID BULK MODULUS | Hydraulic fluid |
| Hydrostatic fluid density | *FLUID DENSITY | |
| Fluid thermal expansion coefficient(S) | *FLUID EXPANSION | Hydraulic fluid |