Rolling contact is a mechanical phenomenon involving rolling bodies like wheels or bearings that come into contact with each other, or surfaces like roadways. At the point where they meet, the relative velocity is zero. This underlies a wide range of mechanical processes, from the toothed gears used in cars to conveyor belts. Researchers study the physics behind rolling contact because it provides important information about how and when bearings fail. It is a special kind of mechanical wear.
In a simple example, two bearings can roll against each other to allow a joint to articulate and move. As they change position, they come into rolling contact. This point may have a relative velocity of zero, but the strain can be very high, because the force is concentrated there. Consequently, rolling contact fatigue tends to develop across the surfaces of the bearings. They can develop cracks, pitting, and other problems, depending on the amount of strain involved in the joint.
The level of friction present in rolling joints can depend on their design, how they are used, and the lubricants that may be added to smooth their movement. Low friction allows a joint to move more seamlessly and functionally, and can reduce strain on the components. It can also cause slipperiness, which may require a tradeoff. With cars, for example, some friction is necessary to help the wheels grip the road, while too much would slow the car down and make it difficult to handle.
Research on rolling contact joints looks at the kinds of conditions that need to be present for components or entire joints to fail. High pressure and high friction tend to increase the failure rate, as do harsh conditions. Dust storms, for example, can drive grit into joints that causes the bearings to wear down more quickly. This research helps engineers determine how to design bearings more effectively to create strong, reliable joints with minimal maintenance needs.
Forms of rolling contact have been in use among human populations for an extremely long time. One of the earliest forms of the bearing was the log roller, which allowed people to move massive objects by pushing them along arrays of logs. People laid out logs, set objects on top, and pushed them. As the logs turned under the objects, they forced them forward onto logs at the front of the cluster. Eventually, individual logs would pop out from underneath, and could be recycled by being placed at the front of the array again.