The effect of static friction behav

The effect of static friction behavior like Coulomb friction,viscous friction and the Sribeck effect are described using the Tustin model. Coulomb friction force is the force that acts in the direction opposite to the motion and the magnitude of this force is always a constant. Viscous friction force is the force between two layers in contact that is proportional to the sliding velocity relative to it. For most common situations at lower velocities the friction force decreases continuously with the increase in velocity. This is called Stribeck effect or Stribeck friction. Stiction is the maximum friction force that exists just before sliding.The applied force for describing static friction is shown in Fig. 5. In Fig. 6, it is clearly observed that when the applied force is less than the stiction the object does not move and there is no displacement. When the applied force is greater than stiction the object undergoes permanent displacement.When the object starts sliding the friction force starts decreasing until the sliding velocity is equal to the Stribeck velocity as shown in Fig. 7. The friction force reduces to the minimum value i.e. Coulomb friction force as shown in Fig.As the sliding velocity increases the friction force increases linearly with the applied force as shown in Fig. 8.The force at which the object undergoes the permanent displacement is called break away force. Static model assume that there is no displacement when the applied force is less than break away force.