Home
User Subroutines
This manual describes the interface between Altair Radioss and user subroutines.
Extended Material Laws
In Radioss, 99 material user laws can be defined for 3D and 2D solid elements, connection element, and 3D shell elements.

Welcome
What's New
View new features for Radioss 2024.
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.
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.
- Global User Window
  With Radioss, it is possible to define a global user window. This is the most general interface between Radioss and external code.
- Material Laws 29, 30, 31
  Up to 3 material user’s laws (law 29, 30 and 31) can be defined for 3D, 2D solid elements and 3D shell elements. User’s laws for beam or truss elements are not available.
- Extended Material Laws
  In Radioss, 99 material user laws can be defined for 3D and 2D solid elements, connection element, and 3D shell elements.
  - Starter Subroutine LECMUSERnn
    This subroutine reads the user law input data.
  - Engine Subroutine LUSERnn for Solid Elements
    This subroutine calculates the stress tenor versus the strain tensor, strain rate tensor, density, volume, internal energy, or user variables.
  - Solid Elements Examples
    An elastic material law is defined for solid elements.
  - Engine Subroutine LUSERnnC for Shell Elements
    This subroutine calculates the stress tensor versus the strain tensor, strain rate tensor, or user variables.
  - Shell Elements Examples
  - Additional Interface Routines for Solid and Shell Material Laws
- User Property Elements
  Up to 3 spring user properties (property number 29, 30, and 31) can be defined for spring and solid elements.
- User Sensors
  In Radioss, up to three types of user sensors can be defined.
- User Failure Models
  In Radioss up to 3 user’s failure models (USER1, USER2, and USER3) can be defined for shell and solid elements.
- Write in Output Files
  Some user subroutines do not pass the IOUT file descriptor and, thus, do not permit writing in a Radioss output file.
- Generate Radioss User Libraries
  Radioss user libraries are built on Windows and Linux with two different compilers: Intel Fortran or Gfortran.
- Initialize, Verify and Finalize
  The workflow in some user options may require initialization, verify during the run and finalize tasks in the Engine.
- Appendix

Extended Material Laws

In Radioss, 99 material user laws can be defined for 3D and 2D solid elements, connection element, and 3D shell elements.

User laws for beam or truss elements are not yet available.

To define a user law, two subroutines for each law must be provided. One must be linked with Radioss Starter and the other with Radioss Engine.

The Starter subroutine is called LECMUSERnn (where nn = 01, 02, 03, … 99) and reads material data and initializes material parameters
The Engine subroutine for solids is called LUSERnn (where nn = 01, 02, 03, … 99) and computes the solid element stress tensor at the integration point. The corresponding shell subroutine is called LUSERnnC (where nn = 01, 02, 03, … 99)

Note: All communication between Radioss and the User’s subroutines takes place within the argument list.