About the Restitution Contact Model

To manage contacts, the model uses two equal and opposite impulses to generate unilateral contact forces between the colliding bodies, and to prevent penetration.

Impulses are computed on all contact points and take account of every force applied on the entire mechanism.

Since the model depends more on velocity than on depth penetration, the time step does not have a significant impact on the result. A Max Penetration is specified to ensure that the penetration does not exceed a certain value.

When possible, the solver can reduce the time step to guarantee the Max Penetration. The default value is 0.15mm.

The physical parameters of the materials are not taken into account during the simulation.

Following the contact, the relative velocity between the 2 colliding bodies is equal to the relative velocity between the 2 bodies before contact multiplied by the Restitution Coefficient.

The Restitution Coefficient calculates, along the line of impact, the ratio of speeds before and after the impact. Its value is always positive.

Value	Description
0	The bodies stop at the collision. The kinetic energy is fully absorbed.
Between 0 and 1	The pairs of bodies do not collide elastically. There is a loss of kinetic energy.
1	The pairs of bodies collide elastically. There is no loss of kinetic energy.
Superior to 1	Kinetic energy is generated.

Friction is the force resisting the relative motion of solid surfaces. It includes the static friction between nonmoving surfaces, and the kinetic friction between moving surfaces. The Restitution Contact Model is based on a friction law, the Coulomb friction model, which includes two friction coefficients:

• The static friction coefficient (optional): the friction between two nonmoving objects.
• The dynamic friction coefficient: the friction between moving surfaces.

The user can specify the velocity threshold for the static and the dynamic friction.