Rubber Friction mechanism

In the design and development of rubber product such as tire , rubber seal , rubber automotive part , it is important to evaluate the contact load dependency of the friction coefficient. Mechanism of friction in rubber generates three different forms of friction: adhesion, deformation, and wear, which  adhesion force is the most influential component in rubber friction in dry conditions and low speed so that  adhesion friction is dominant for smooth contact at low speeds and dry conditions. Therefore increasing friction adhesion is possible by increasing the contact area of the product. Product samples that influence of the adhesion force is the industrial tire used in the warehouse where the floor is smooth and dry.

The hysteresis component of friction is caused by the bulk deformation of rubber material as it comes into contact with pavement asperities. Such deformation causes energy losses as rubber slides over the pavement surface. These energy losses are caused by the hysteretic.  In the case of contact between a rubber specimen and a rough hard surface , such as contact between tire and asphalt, the hysteresis component becomes dominate. 

The third major component of friction (cohesion losses) is caused by the wearing of rubber as it slides over the pavement surface. Pavement texture has an important role in the friction components—a recent study showed that higher pavement microtexture and macrotexture result in higher frictional properties. 

Energy tires : How to reduce rolling resistance (effect of speed)

The rolling resistance coefficient f generally increases with the speed V of the vehicle , at the beginning very slowly and then at an increased rate. The following expressions can be used

f = fo + KV

or

f = fo + KV^2

The value of fo and K must be measured on any particular tire . The speed at which the curve f(V) show a sharp bend upward is generally said to be the “critical speed of the tire” (Pic1) the critical speed is influenced by many parameter such as above that speed strong overheating take place; as most of increase of the rolling power is converted into heat. the increase of temperature can quickly cause the destruction of the tire itself ; the standing waves which propergate along the circumference of the tire from the contact zone are clearly visible. And it is of the factor which must be taken into account in the choice of the tire.

Pic1. Rolling resistance coefficient of tire