Soft Part against Hard Part

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 secondary material stiffness over the main 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. Impact Between Steel and Foam

Figure 1 shows contact between mild steel and soft foam. The ratio of stiffness is greater than 380, in such a case where the main side is the soft side, the flag Stfac may be set to 380 to avoid very high penetrations.