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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.
- Run Radioss
  The Radioss solver can be executed using different methods described here.
- Explicit Structural Finite Element Analysis
  In this section, available explicit features for different explicit analyses are presented.
  - Time Step
    An explicit is solved by calculating results in small time increments or time steps. The size of the time step depends on many factors but is automatically calculated by Radioss.
  - Finite Elements
  - Modeling Tools
  - Materials
    Different material tests could result in different material mechanic character.
  - Failure
  - Composites
    Composite materials consist of two or more materials combined each other. Most composites consist of two materials, binder (matrix) and reinforcement. Reinforcements come in three forms, particulate, discontinuous fiber, and continuous fiber.
    - Composite Material
      - LAW12 and LAW14
        Describes orthotropic solid material which use the Tsai-Wu formulation. The materials are 3D orthotropic-elastic, before the Tsai-Wu criterion is reached. LAW12 is a generalization and improvement of LAW14.
      - LAW25 (Tsai-WU and CRASURV)
        LAW25 is the most commonly used composite material in Radioss. It can be used with shell and solid elements. The two formulations available in LAW25 are the Tsai-Wu and CRASURV formulations.
      - LAW19 and LAW58 for Fabric
        Radioss has two material laws for modeling fabrics LAW19 and LAW58. LAW19 is an elastic orthotropic material and must be used with /PROP/TYPE9. LAW58 is hyperelastic anisotropic fabric material and must be used with /PROP/TYPE16.
    - Composite Modeling
      Composite modeling techniques used in Radioss.
    - Composite Properties
      Composites may be modeled with solid or shell element. Depending on the element type, the following properties can be used in Radioss to model a composite.
    - Composite Failure Model
  - Connections
  - Kinematic Constraints
    In Radioss, a kinematic condition is a nodal constraint applied to a set of nodes.
  - Interfaces
    Several interfaces are available in Radioss, this section deals with contact interfaces only. Each interface is distinguished with a type number.
  - Loads
  - Airbag Modeling
    Airbags are modeled as monitored volumes /MONVOL in several different ways.
  - Debugging Guidelines
  - Appendix
- Implicit Structural Finite Element Analysis
- Fluid and Fluid-Structure Simulation
  In this section, fluid and fluid-structure simulation is presented.
- 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.
- Multi-Domain Technique
  The objective of the Multi-Domain technique (also referred to as RAD2RAD) is to optimize the computing performances of large scale Radioss models.
- Design Optimization
  Optimization in Radioss was introduced in version 13.0. It is implemented by invoking the optimization capabilities of OptiStruct and simultaneously using the Radioss solver for analysis.
- Error Message Database
  This section is comprised of error messages in ascending numerical order.
- Engine Error Messages
- Warning Message Database
  This section is comprised of warning messages in ascending numerical order.
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.

View All Altair HyperWorks Help

LAW19 and LAW58 for Fabric

Radioss has two material laws for modeling fabrics LAW19 and LAW58. LAW19 is an elastic orthotropic material and must be used with /PROP/TYPE9. LAW58 is hyperelastic anisotropic fabric material and must be used with /PROP/TYPE16.

Coupling between warp and weft directions could be defined in this material law to reproduce physical interaction between fibers. Both material laws are often used for airbag modeling.

In LAW58, two methods are provided to define the stress-strain behavior.

Nonlinear function (fct_ID_i) curve to define the warp, weft and shear behavior
Young's modulus, soften coefficient B, straightening strain S_i and fiber bending modulus reduction factor Flex_i
In warp and weft direction:
$σ_{i i} = E_{i} ε_{i i} - \frac{(B_{i} ε_{i i}^{2})}{2} (i = 1, 2) when \frac{d σ}{d ε} > 0$
$σ_{i i} = \max_{ε_{i i}} (E_{i} ε_{i i} - \frac{(B_{i} ε_{i i}^{2})}{2}) (i = 1, 2) when \frac{d σ}{d ε} \leq 0$
For in-plane shear in initial state, use $G_{0}$ . Once $α$ (angle between wrap and weft) reaches $α_{T}$ (shear lock angle), then use G_T to describe the strengthening.
$τ = G_{0} \tan (α) - τ_{0}$ if $α \leq α_{T}$
$τ = \frac{G_{T}}{1 + \tan^{2} (α_{T})} \tan (α) + (G_{0} - \frac{G_{T}}{1 + \tan^{2} (α_{T})}) \tan (α_{T}) - τ_{0}$ if $α > α_{T}$

Figure 1.

For out-of-plane shear stress-strain is described with

$G_{s h}$ .

Figure 2.

For fabric, there is straight process at the beginning of tension. At this phase, fiber shows very soft, due to not being tightened yet.

Figure 3.

In LAW58, use Flex_i to describe this behavior:

$E_{f i} = F l e x_{i} * E_{i}$

After the fabric is tight (strengthening strain S_i is reached), then normal fiber elasticity E_i could be used.

Figure 4.