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Radioss Reference Guide
This manual provides a detailed list of all the input keywords and options available in Radioss.
Starter Input
This manual provides a list of all the model definition keywords and options available in Radioss.
General Controls
Block Format Keyword In this group, keywords are used to set default value, global parameter, analysis type, input/output print, damping and ALE and CFD treatment for the whole model. For default value, it is still possible to overwrite in each specific keywords.
Default Value
Keywords used to set the default value.
/DEFAULT/INTER/TYPE24
Block Format Keyword Defines default values for all /INTER/TYPE24.

Welcome
What's New
View new features for Radioss 2026.
Radioss Overview
Radioss is a leading explicit finite element solver for crash and impact simulation.
Tutorials
Discover Radioss functionality with interactive tutorials.
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.
  - 2D and 3D Analysis Options
  - Starter Keywords Syntax
    Block Format Keyword
  - Smooth Particle Hydrodynamics (SPH)
    The Smooth Particle Hydrodynamics method formulation is used to solve the equations of mechanics, when particles are free from a meshing grid.
  - Computational Fluid Dynamics (CFD)
  - General Controls
    Block Format Keyword In this group, keywords are used to set default value, global parameter, analysis type, input/output print, damping and ALE and CFD treatment for the whole model. For default value, it is still possible to overwrite in each specific keywords.
    - Formats
    - Default Value
      Keywords used to set the default value.
      - /DEF_SHELL
        Block Format Keyword Used to set default values for certain parameters in all shell properties, but options could still be changed in each property set input and in this case, the latter will prevail.
      - /DEF_SOLID
        Block Format Keyword Used to set default values for certain parameters in all solid properties and thick shells. The default values defined here will be overwritten by any values entered on the individual property input.
      - /DEFAULT/INTER/TYPE2
        Block Format Keyword Defines interfaces TYPE2 default values.
      - /DEFAULT/INTER/TYPE7
        Block Format Keyword Defines default value for TYPE7 interfaces.
      - /DEFAULT/INTER/TYPE11
        Block Format Keyword Defines default values for TYPE11 interfaces.
      - /DEFAULT/INTER/TYPE19
        Block Format Keyword Defines default values for TYPE19 interfaces.
      - /DEFAULT/INTER/TYPE24
        Block Format Keyword Defines default values for all /INTER/TYPE24.
      - /DEFAULT/INTER/TYPE25
        Block Format Keyword Defines default values for all /INTER/TYPE25.
      - /IMPLICIT
        Block Format Keyword This option allows different default values which are suitable for implicit calculations.
      - /SPHGLO
        Block Format Keyword Describes the SPH global parameters.
      - /STAMPING
        Block Format Keyword This option allows adapting error messages to stamping applications.
    - Computation
    - Input/Output
    - Damping
      Block Format Keyword In this group, keywords are used to set Rayleigh mass and stiffness damping coefficients, which apply to a set of nodes used to stabilize the results.
    - ALE and CFD
  - Nodes
    Block Format Keyword In Radioss, two node types are available. They use Cartesian coordinate to describe the position of each node.
  - Elements
    Block Format Keyword
  - Component and Parts Organization
    Block Format Keyword In this group, keywords are used to combine material and property information (/PART), assemble model (/SUBSET) or define a separate model (//SUBMODEL).
  - Interfaces
    Block Format Keyword Interfaces solve the contact and impact conditions between two parts of a model. Several interface types are available in Radioss and use different contact treatments.
  - Materials
  - Properties
    Block Format Keyword
  - Monitored Volumes (Airbags)
    Block Format Keyword Monitored volumes can be used to model an airbag, tire, tank, or any closed volume.
  - Constraints
    Block Format Keyword Radioss supports several different kinematic constraints, which are mainly used to impose acceleration, velocity, displacement or temperature in structure or constraint the moving of structure. They are mutually exclusive for each degree-of-freedom (DOF). Two kinematic conditions applied to the same node may be incompatible.
  - Load Cases
    Block Format Keyword In Radioss the following load cases are available. Stress/strain as initial state could be considered by modeling, as well as pressure, gravity, and thermal load.
  - Tools
    Block Format Keyword In this group, tools like transformation, frames, skews, and curve are introduced.
  - Groups(Sets)
    Block Format Keyword Keywords in this group are used to define how to select a group of node, part, elements, lines, or surfaces.
  - Adaptive Meshings
    Block Format Keyword Adaptive Meshing is used in metal forming to divide the element to better describe the geometry. /ADMESH/GLOBAL and /ADMESH/SET are not available for SPMD computation.
  - Output Database
    Block Format Keyword Time histories output for different element groups, section output, or gauge output are described in this group.
- 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
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.

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/DEFAULT/INTER/TYPE24

Block Format Keyword Defines default values for all /INTER/TYPE24.

Format


(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
/DEFAULT/INTER/TYPE24
Blank
		`I`_stf			`Irem_i2`		`I`_del
			`I`_edge
				`I`_gap0	`I`_pen0

Required Fields


(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
Blank
			`Inacti`
Blank

Definition


Field	Contents	SI Unit Example
`I`_stf	Interface stiffness definition flag. = 0 Set to 1000. = 2 Interface stiffness is the average of the main and secondary stiffness. = 3 Interface stiffness is the maximum of the main and secondary stiffness. = 4 Interface stiffness is the minimum of the main and secondary stiffness. = 5 Interface stiffness is the main and secondary stiffness in series. = 6 Interface stiffness is the minimum of the main and secondary stiffness with special adjustment to improve convergence for implicit solution. = 12 Nitsche method is used with the average of the main and secondary stiffness. = 13 Nitsche method is used with the maximum of the main and secondary stiffness. = 14 Nitsche method is used with the minimum of the main and secondary stiffness. = 1000 (Default) Interface stiffness is only based on the main side stiffness. (Integer)
`Irem_i2`	Flag for deactivating the secondary node, if the same contact pair (nodes/segment) has been defined in interface TYPE2. = 0 Set to 1. = 1 (Default) Secondary nodes in /INTER/TYPE2 tied contacts are removed from this contact. = 3 No change to secondary nodes.
`I`_del	Node and segment deletion flag. = 0 Set to 1000. = 1 When all the elements (4-node shells, 3-node shells, solids) associated to one segment are deleted, the segment is removed from the main side of the interface. It is also removed in case of explicit deletion using Radioss Engine keyword /DEL in the Engine file. Additionally, non-connected nodes are removed from the secondary side of the interface. = 2 When a 4-node shell, a 3-node shell or a solid element is deleted, the corresponding segment is removed from the main side of the interface. It is also removed in case of explicit deletion using Radioss Engine keyword /DEL in the Engine file. Additionally, non-connected nodes are removed from the secondary side of the interface. = 1000 (Default) No deletion. Note: Using `I`_del results in higher CPU cost.
`I`_edge	Edge definition flag. = 0 Set to 1000. = 1 Edge to edge contact is activated using the external border edges from `surf_ID`₁ and `surf_ID`₂ and sharp edges between contact segments. = 1000 (Default) No edge to edge contact. (Integer)
`I`_gap0	Gap modification flag for secondary shell nodes on the free edges. = 0 Set to 1000. = 1 Set gap to zero for the secondary shell nodes. = 1000 (Default) No change. (Integer)
`I`_pen0	Initial penetration detection flag. = 0 Set to 1000. = 1 Including self-impact in each part. = 1000 (Default) Excluding self-impact in each part. (Integer)
`Inacti`	Initial penetration flag. = -1 All initial penetrations are taken into account. = 0 Set to 1000. = 5 The main segment is shifted by the initial penetration value $P_{0}$ if $P \geq P_{0}$ , then $P' = P - P_{0}$ , where $P_{0}$ is the initial penetration. = 1000 (Default) Only tiny initial penetrations (1.0e-08) will be taken into account. (Integer)