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.

The two beam elements available in Radioss are used on one-dimensional structures and frames. It carries axial loads, shear forces, bending and torsion
moments (contrary to the truss that supports only axial loads).

This spring is a simplification of spring TYPE13; in which the properties of the spring cross-section are considered
to be invariable with respect to Y and Z.

Under-integrated elements are very familiar in crash worthiness. In these elements, a reduced number of integration
points are used to decrease the computation time. This simplification generates zero energy deformation modes, called
hourglass modes.

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.

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.

Spring TYPE12 is used to model a pulley. When used in a seat belt model, it is
defined with three nodes.

Node 2 is located at the pulley, and a deformable rope is joining the three nodes (Figure 1). The spring
mass is distributed on the three nodes with ¼ at node 1 and node 3 and ½ at node 2.

A Coulomb friction can be applied at node 2, taking into account the angle between the two
strands. Without friction, forces are computed as:(1)

${\delta}_{1}$ is the elongation of strand 1-2 and ${\delta}_{2}$ of strand 2-3.

Time step is computed with the same equation that for spring TYPE4, but the stiffness is replaced
with twice the stiffness to ensure stability with high friction coefficients.

Note: The two strands have to be long enough to avoid node 1, or node 3 slides
up to node 2. Nodes 1 and 3 will be stopped at node 2, if there is a knot at nodes 1
and 3.

For further information, refer to the Radioss Theory
Manual.