In such designs the gouging causes plastic deformation in the collapsing steering column, which helps to dissipate the kinetic energy of the crash event. The rigid sphere is given a constant velocity as it traverses the metal tube. Actual components use concentric metal tubes with metal balls between them, and the motion of the spheres is dictated by the geometry of the surrounding tubes. Despite this approximation, comparison with experiments suggests that the simplifications are valid. Contact is defined by specifying that the upper surface of the metal tube can contact the outer surface of the rigid ball.
Friction is included in the model.
8-node brick elements used to model the metal tube. Contours of plastic strain in tube. Plastic dissipation in tube.