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Reference Guide
This manual provides a detailed list of all the input keywords and options available in Radioss.
New Keywords in 2025
New and modified features in Radioss.

Welcome
What's New
View new features for Radioss 2025.
Overview
Radioss^® is a leading explicit finite element solver for crash and impact simulation.
Tutorials
Discover Radioss functionality with interactive tutorials.
User Guide
This manual provides details on the features, functionality, and simulation methods available in Altair 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 2025
  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.
- 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  Keywords that are still supported, but no longer maintained (*) are considered obsolete.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
Example Guide
This manual presents examples solved using Radioss with regard to common problem types.
Verification Problems
This manual presents solved verification models.
Frequently Asked Questions
This section provides quick responses to typical and frequently asked questions regarding Radioss.
Theory Manual
This manual provides detailed information about the theory used in the Altair Radioss Solver.
User Subroutines
This manual describes the interface between Altair Radioss and user subroutines.

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New Keywords in 2025

New and modified features in Radioss.

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New Starter Keywords

/DFS/DETPOINT/SET - locates the detonation point defined in the node group and set lighting time for an explosive material law
/FUNCT_PYTHON - defines a function defined with Python script
/INISPHCEL/FULL - describes the initial state for a Smooth Particle Hydrodynamic (SPH)
/MAT/LAW169 (ARUP_ADHESIVE) - an elastoplastic connection material law with coupled damage and failure

Modified Starter Keywords

/CLOAD and /PLOAD - added new Itypfun flag
/DEF_SOLID, /PROP/TYPE6 (SOL_ORTH) and /PROP/TYPE14 (SOLID) - added new element distortion control flag, I_control

New Engine Keywords

/STATE/SPHCEL/FULL - describes the stress state for Smooth Particle Hydrodynamic (SPH)

New LS-DYNA Keywords

*INITIAL_STRESS_SOLID - initializes the strain for solid elements in the global coordinate system
*MAT_005 (SOIL_AND_FOAM) - defines an isotropic, elastic-plastic simple material model for representing soil, concrete, or crushable foam
*MAT_073 (LOW_DENSITY_VISCOUS_FOAM) - defines a visco-elastic low density foam tabulated material for solid elements
*MAT_111 (JOHNSON_HOLMQUIST_CONCRETE) - defines a material law that is based on the theory of Johnson-Holmquist-Cook model theory
*MAT_183 (MAT_SIMPLIFIED_RUBBER_WITH_DAMAGE) - defines an incompressible rubber material with uniaxial tensile/compression test results as input curve
*MAT_ADD_THERMAL_EXPANSION - used to add thermal expansion property for material

Obsolete Keywords

All Optimization Keywords