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.
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.
When rupture is modeled and elements are expected to fail, it is important to deal with failed elements defined either
as a master segment, or as slave nodes.
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.
The default stiffness value computed by Radioss is often suitable to
avoid very high penetration, leading to the time step dropping. When contact occurs between
similar materials, there is no problem using the default stiffness; except when the
materials are different. For instance, when mild steel impacts soft foam, the default
stiffness may be too low to avoid a large penetration. When such contacts are willing to
occur, it is advised to first compute the ratio of the slave material stiffness over the
master material stiffness. If this ratio is greater than 100, a scale factor (Stfac)
equal to this ratio should be used to increase the interface stiffness.
Figure 1
shows contact between mild steel and soft foam. The ratio of stiffness is greater than 380,
in such a case where the master side is the soft side, the flag Stfac may
be set to 380 to avoid very high penetrations.