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Radioss Reference Guide
This manual provides a detailed list of all the input keywords and options available in Radioss.
LS-DYNA Input
This manual provides a list of LS-DYNA input files available in Radioss.
*MAT
*MAT_001_FLUID (ELASTIC_FLUID)
LS-DYNA Input Interface KeywordDefines an isotropic, linear elastic material using Hooke’s law.

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Radioss User Guide
This manual provides details on the features, functionality, and simulation methods available in Altair Radioss.
Radioss Reference Guide
This manual provides a detailed list of all the input keywords and options available in Radioss.
- File Extensions and Formats
  Current Radioss format uses the 12x extension format.
- Single File Input
  This format allows running either Starter or Engine with the same file.
- New Keywords in 2026
  New and modified features in Radioss.
- Starter Input
  This manual provides a list of all the model definition keywords and options available in Radioss.
- Engine Input
  This manual provides a list of all the solution definition keywords and options available in Radioss.
- LS-DYNA Input
  This manual provides a list of LS-DYNA input files available in Radioss.
  - *AIRBAG
  - *BOUNDARY
  - *CONSTRAINED
  - *CONTACT
  - *CONTROL
  - *DAMPING
  - *DATABASE
  - *DEFINE
  - *ELEMENT
  - *EOS
  - *HOURGLASS
    LS-DYNA Input Interface KeywordDefine solid and hourglass formulation for 8-node solid elements.
  - *INCLUDE
  - *INITIAL
  - *INTEGRATION_SHELL
    LS-DYNA Input Interface KeywordDefine user-defined through the thickness integration rules for the composite shell element.
  - *INTERFACE_SPRINGBACK
    LS-DYNA Input Interface KeywordDescribes the variables to output in an initial state file or DYNAIN file at the end of the analysis.
  - *KEYWORD
    LS-DYNA Input Interface KeywordThis keyword should always be the first card of the input file. Optionally used with *CONTROL_UNITS card to specify model units.
  - *LOAD
  - *MAT
    - *MAT_001 (ELASTIC)
      LS-DYNA Input Interface KeywordDefines an isotropic, linear elastic material using Hooke’s law.
    - *MAT_001_FLUID (ELASTIC_FLUID)
      LS-DYNA Input Interface KeywordDefines an isotropic, linear elastic material using Hooke’s law.
    - *MAT_002 (ORTHOTROPIC_ELASTIC)
      LS-DYNA Input Interface KeywordThis model expresses a simple orthotropic elastic material.
    - *MAT_003 (PLASTIC_KINEMATIC)
      LS-DYNA Input Interface KeywordDefines an isotropic, elasto-plastic material with s Cowper-Symonds strain rate model.
    - *MAT_005 (SOIL_AND_FOAM)
      LS-DYNA Input Interface KeywordDefines an isotropic, elastic-plastic simple material model for representing soil, concrete, or crushable foam.
    - *MAT_006 (VISCOELASTIC)
      LS-DYNA Input Interface KeywordThis keyword defines an isotropic, visco-elastic material. It is generally used to model incompressible rubbers, polymers, foams, and elastomers.
    - *MAT_007 (BLATZ_KO_RUBBER)
      LS-DYNA Input Interface KeywordThis keyword defines an isotropic, incompressible, Neo-Hookean hyperelastic material.
    - *MAT_009 (NULL)
      LS-DYNA Input Interface KeywordDefines a void material without stiffness.
    - *MAT_012 (ISOTROPIC_ELASTIC_PLASTIC)
      LS-DYNA Input Interface KeywordDefines an isotropic, elasto-plastic material.
    - *MAT_015 (JOHNSON_COOK)
      LS-DYNA Input Interface KeywordThis model expresses material stress as a function of strain, strain rate, temperature dependency and plastic strain failure criterion.
    - *MAT_018 (POWER_LAW_PLASTICITY)
      LS-DYNA Input Interface KeywordThis model expresses isotropic plasticity model with rate effects which uses a power law hardening.
    - *MAT_020 (RIGID)
      LS-DYNA Input Interface KeywordDefines a rigid material assigned to a part.
    - *MAT_024 (PIECEWISE_LINEAR_PLASTICITY)
      LS-DYNA Input Interface KeywordDefines an isotropic elasto-plastic material using tabulated stress versus plastic strain input for different strain rates.
    - *MAT_026 (HONEYCOMB)
      LS-DYNA Input Interface KeywordThis keyword defines an orthotropic compressible honeycomb material.
    - *MAT_027 (MOONEY-RIVLIN_RUBBER)
      LS-DYNA Input Interface KeywordDefines a Mooney-Rivlin isotropic hyperelastic incompressible material.
    - *MAT_030 (SHAPE_MEMORY)
      LS-DYNA Input Interface KeywordDefines a super-elastic memory shape alloy material (SMA) compatible with integrated beam, solid and shell elements.
    - *MAT_032 (LAMINATED_GLASS)
      LS-DYNA Input Interface KeywordThis keyword defines a layered glass with polymeric layers material models.
    - *MAT_034 (FABRIC)
      LS-DYNA Input Interface KeywordDefines an orthotropic elastic material with softening in compression.
    - *MAT_054 (ENHANCED_COMPOSITE_DAMAGE)
      LS-DYNA Input Interface KeywordDefines an orthotropic shell composite material for unidirectional layers with Chang-Chang failure model.
    - *MAT_057 (LOW_DENSITY_FOAM)
      LS-DYNA Input Interface KeywordDefines an isotropic, visco-elastic, low density foam.
    - *MAT_058 (LAMINATED_COMPOSITE_FABRIC)
      LS-DYNA Input Interface KeywordDefines an orthotropic shell composite material for unidirectional layers, complete laminates, and woven fabrics material.
    - *MAT_061 (KELVIN_MAXWELL_VISCOELASTIC)
      LS-DYNA Input Interface KeywordDefines an isotropic, visco-elastic material for solid elements.
    - *MAT_062 (VISCOUS_FOAM)
      LS-DYNA Input Interface KeywordDefines an open-celled urethane foam material used for the ribs of a Euro-SID side impact dummy. Only available for solid.
    - *MAT_063 (CRUSHABLE_FOAM)
      LS-DYNA Input Interface KeywordThis keyword defines a crushable foam material with optional tension cutoff and elastic unloading.
    - *MAT_066 (LINEAR_ELASTIC_DISCRETE_BEAM)
      LS-DYNA Input Interface KeywordThis keyword defines a linear elastic discrete beam material with 6 decoupled degrees of freedom and an optional preload option.
    - *MAT_067 (NONLINEAR_ELASTIC_DISCRETE_BEAM)
      LS-DYNA Input Interface KeywordThis keyword defines a nonlinear elastic discrete beam material with 6 decoupled DOFs with an optional preload.
    - *MAT_068 (NONLINEAR_PLASTIC_DISCRETE_BEAM)
      LS-DYNA Input Interface KeywordDefines a nonlinear elasto-plastic discrete beam material with 6 decoupled DOFs with an optional preload.
    - *MAT_071 (CABLE_DISCRETE_BEAM)
      LS-DYNA Input Interface KeywordThis keyword defines an elastic cable material with no stiffness in compression.
    - *MAT_073 (LOW_DENSITY_VISCOUS_FOAM)
      LS-DYNA Input Interface KeywordDefines a visco-elastic low density foam tabulated material for solid elements.
    - *MAT_074 (ELASTIC_SPRING_DISCRETE_BEAM)
      LS-DYNA Input Interface KeywordThis keyword defines a nonlinear elasto-plastic discrete beam material with one DOFs and optional preload option.
    - *MAT_076 (GENERAL_VISCOELASTIC)
      LS-DYNA Input Interface KeywordDefines an isotropic, visco-elastic material. It is generally used to model incompressible elastomers.
    - *MAT_077_H (HYPERELASTIC_RUBBER)
      LS-DYNA Input Interface KeywordDefines an isotropic, hyperelastic, viscous, and incompressible material specified from uniaxial experimental data.
    - *MAT_077_O (OGDEN_RUBBER)
      LS-DYNA Input Interface KeywordDefines an isotropic, hyperelastic, viscous, and incompressible material specified using the Ogden material models.
    - *MAT_081 (PLASTICITY_WITH_DAMAGE)
      LS-DYNA Input Interface KeywordDefines an isotropic elasto-plastic material using tabulated stress versus plastic strain input for different strain rates and simple damage model.
    - *MAT_083 (FU_CHANG_FOAM)
      LS-DYNA Input Interface KeywordDefines an isotropic, highly compressible Fu Chang foam.
    - *MAT_091 (SOFT_TISSUE)
      LS-DYNA Input Interface KeywordThis material is used to represent biological soft tissues such as ligaments based on Mooney-Rivlin formulation.
    - *MAT_092 (SOFT_TISSUE_VISCO)
      LS-DYNA Input Interface KeywordThis material is used to represent biological soft tissues such as ligaments based on Mooney-Rivlin formulation.
    - *MAT_098 (SIMPLIFIED_JOHNSON_COOK)
      LS-DYNA Input Interface KeywordDefines an isotropic elasto-plastic material using the Johnson-Cook material model.
    - *MAT_099 (SIMPLIFIED_JOHNSON_COOK_ORTHOTROPIC_DAMAGE)
      LS-DYNA Input Interface KeywordDefines an isotropic elasto-plastic material using the Johnson-Cook material model.
    - *MAT_100 (SPOTWELD)
      LS-DYNA Input Interface KeywordDefines an elasto-plastic spotweld material for beam element (elform=9) or solid element.
    - *MAT_105 (DAMAGE_2)
      LS-DYNA Input Interface KeywordDefines an elastic viscoplastic material model.
    - *MAT_111 (JOHNSON_HOLMQUIST_CONCRETE)
      LS-DYNA Input Interface KeywordDefines a material law that is based on the theory of Johnson-Holmquist-Cook model theory (also called Johnson-Holmquist-Concrete).
    - *MAT_119 (GENERAL_NONLINEAR_6DOF_DISCRETE_BEAM)
      LS-DYNA Input Interface KeywordDefines a nonlinear elasto-plastic discrete beam material with 6 degrees of freedom (DOFs). Different loading and unloading behavior can be specified.
    - *MAT_120 (GURSON)
      LS-DYNA Input Interface KeywordDefines a nonlinear elasto-plastic based on the Gurson constitutive law, which is used to model visco-elastic-plastic strain rate dependent porous metals.
    - *MAT_121 (GENERAL_NONLINEAR_1DOF_DISCRETE_BEAM)
      LS-DYNA Input Interface KeywordDefines a nonlinear elasto-plastic discrete beam material with one degree of freedom (DOF). Different loading and unloading behavior can be specified.
    - *MAT_122 (HILL_3R)
      LS-DYNA Input Interface KeywordDefines an orthotropic elastoplastic material using linear or tabulated stress versus plastic strain input.
    - *MAT_123 (MODIFIED_PIECEWISE_LINEAR_PLASTICITY)
      LS-DYNA Input Interface KeywordDefines an isotropic elasto-plastic material using tabulated stress versus plastic strain input for different strain rates. Material thinning and FLD failure are also included.
    - *MAT_124 (PLASTICITY_COMPRESSION_TENSION)
      LS-DYNA Input Interface KeywordDefines an isotropic elasto-plastic material with tension and compression yield stress curves as a function of plastic strain.
    - *MAT_126 (MODIFIED_HONEYCOMB)
      LS-DYNA Input Interface KeywordThis model expresses a three-dimension orthotropic nonlinear elasto-plastic material, usually used to model honeycomb or foam material.
    - *MAT_138 (COHESIVE_MIXED_MODE)
      LS-DYNA Input Interface KeywordThis model expresses a constitutive relation of ductile adhesive materials in 2 modes for normal and tangential directions.
    - *MAT_154 (DESHPANDE_FLECK_FOAM)
      LS-DYNA Input Interface KeywordDefines a material for modeling aluminum foam.
    - *MAT_156 (MUSCLE)
      LS-DYNA Input Interface KeywordDefines a muscle model for safety applications. Used only with truss elements.
    - *MAT_163 (MODIFIED_CRUSHABLE_FOAM)
      LS-DYNA Input Interface KeywordThis model expresses a strain rate dependent crushable foam material. This law is applicable only for solid elements and is typically used to model low density, closed cell polyurethane foams.
    - *MAT_169 (ARUP_ADHESIVE)
      LS-DYNA Input Interface KeywordDefines adhesive bonding material.
    - *MAT_177 (HILL_FOAM)
      LS-DYNA Input Interface KeywordDefines a highly compressible foam based on the strain energy function proposed by Hill.
    - *MAT_181 (SIMPLIFIED_RUBBER/FOAM)
      LS-DYNA Input Interface KeywordDefines a rubber material with uniaxial tensile/compression test results as input curve. This material can be used with solid elements only.
    - *MAT_183 (MAT_SIMPLIFIED_RUBBER_WITH_DAMAGE)
      LS-DYNA Input Interface KeywordDefines an incompressible rubber material with uniaxial tensile/compression test results as input curve. Unloading damage curve can be specified.
    - *MAT_187 (SAMP-1)
      LS-DYNA Input Interface KeywordDefines a semi-analytical model for polymers material. This is an isotropic tabulated elasto-plastic material.
    - *MAT_196 (GENERAL_SPRING_DISCRETE_BEAM)
      LS-DYNA Input Interface KeywordDefines a nonlinear elasto-plastic discrete beam material with 6 degrees of freedom.
    - *MAT_224 (TABULATED_JOHNSON_COOK)
      LS-DYNA Input Interface KeywordThis model expresses material stress as a function of strain, strain rate, temperature dependency and plastic strain failure criterion.
    - *MAT_240 (COHESIVE_MIXED_MODE_ELASTOPLASTIC_RATE)
      LS-DYNA Input Interface KeywordDefines a perfectly plastic cohesive material with state dependency, normal and shear damage, and normal and shear failure.
    - *MAT_252 (TOUGHENED_ADHESIVE_POLYMER)
      LS-DYNA Input Interface KeywordThis is a non-associated elasto-plastic model for polymer adhesives.
    - *MAT_ADD_DAMAGE_DIEM
      LS-DYNA Input Interface KeywordDefines failure criteria in which damage initiation and damage evolution can be separately defined.
    - *MAT_ADD_DAMAGE_GISSMO
      LS-DYNA Input Interface KeywordAdditional failure model defining the plastic strain at failure, function of stress triaxiality, strain rate, Lode angle, element size, and temperature.
    - *MAT_ADD_EROSION
      LS-DYNA Input Interface KeywordDefines a cumulative failure model.
    - *MAT_ADD_THERMAL_EXPANSION
      LS-DYNA Input Interface KeywordUsed to add thermal expansion property for material.
    - *MAT_B01 (SEATBELT)
      LS-DYNA Input Interface KeywordDefines a 1D seatbelt material.
    - *MAT_S01 (SPRING_ELASTIC)
      LS-DYNA Input Interface KeywordDefines a linear spring material.
    - *MAT_S02 (DAMPER_VISCOUS)
      LS-DYNA Input Interface KeywordDefines a linear damper spring material.
    - *MAT_S03 (SPRING_ELASTOPLASTIC)
      LS-DYNA Input Interface KeywordDefines an elasto-plastic spring material.
    - *MAT_S04 (SPRING_NONLINEAR_ELASTIC)
      LS-DYNA Input Interface KeywordDefines a nonlinear elastic spring material.
    - *MAT_S05 (DAMPER_NONLINEAR_VISCOUS)
      LS-DYNA Input Interface KeywordDefines a nonlinear damper spring material.
    - *MAT_S06 (SPRING_GENERAL_NONLINEAR)
      LS-DYNA Input Interface KeywordDefines a nonlinear spring material with loading and unloading options.
    - *MAT_S08 (SPRING_INELASTIC)
      LS-DYNA Input Interface KeywordDefines a nonlinear spring material with stiffness available only in tension or in compression.
    - *MAT_S15 (SPRING_MUSCLE)
      LS-DYNA Input Interface KeywordDefines a muscle model for discrete elements.
  - *NODE
    LS-DYNA Input Interface KeywordDefines a node number and nodal coordinates in the global coordinate system.
  - *PART
    LS-DYNA Input Interface KeywordDefines a part, which combines material and property information.
  - *RIGIDWALL
  - *SECTION
  - *SET
- Multi-Domain
  This manual contains the description of the keywords for the Radioss Multi-Domain.
- Obsolete Keywords
  Keywords that are still supported, but no longer maintained (*) are considered obsolete.
- Other Files
- Definition
Radioss Example Guide
This manual presents examples solved using Radioss with regard to common problem types.
Radioss Verification Problems
This manual presents solved verification models.
Radioss Frequently Asked Questions
This section provides quick responses to typical and frequently asked questions regarding Radioss.
Radioss Theory Manual
This manual provides detailed information about the theory used in the Altair Radioss Solver.
Radioss User Subroutines
This manual describes the interface between Altair Radioss and user subroutines.

*MAT_001_FLUID (ELASTIC_FLUID)

LS-DYNA Input Interface KeywordDefines an isotropic, linear elastic material using Hooke’s law.

Format


(1)	(2)	(6)
MAT_001_FLUID or MAT_ELASTIC_FLUID
`mat_ID`	$ρ_{i}$	`K`
	`Pmin`

Definition


Field	Contents	SI Unit Example
`mat_ID`	Material identifier. (Integer)
$ρ_{i}$	Initial density. (Real)	$[\frac{kg}{m^{3}}]$
`K`	Fluid bulk coefficient. (Real)	$[Pa]$
`Pmin`	Cavitation pressure cut off. Default = -1.0*10²⁰ (Real)	$[Pa]$

Comments

This keyword maps to /MAT/LAW6 (HYDRO or HYD_VISC) and /EOS/LINEAR.
The option “_TITLE” can be added to the end of this keyword. When “_TITLE” is included, an extra 80 characters long line is added after the keyword input line which allows an entity title to be defined.