ABSTRACT
Great efforts have been committed to explore mechanisms of contact, lubrication, friction, and surface failures, and to develop updated theories and methods for engineering applications. Although huge successes and invaluable accomplishments have been achieved, many aspects of tribological interfaces still largely remain mysterious. Up to now, the contact-rubbing nature of the interfaces still prohibits direct observation of the true status of surface interactions. Understanding tribological interfaces is still one of the most difficult tasks in science and engineering for many years to come mainly due to the following reasons:
A tribological interface contains interactive surfaces of materials under contact and relative motion, where complicated phenomena occur, such as friction, asperity deformation, material removal due to wear, cracking, softening, and melting caused by temperature rise, vibration, noise, tribochemical reaction, electromagnetic charging, and even sparking, although sometimes certain types of phenomena may behave much stronger than others. One of the greatest complications is the mutual influence and inter-dependence of these phenomena, making the precise mathematical description very difficult.
Interfacial phenomena usually have multi-scale characteristics. The interface itself is a multi-scale system, where macroscopic contact and relative motion may provide conditions and environments for smaller scale activities. On the other hand, nanoscopic and microscopic phenomena may determine and propagate to macroscopic ones through complicated processes.
Interfacial phenomena often appear in the form of, or are strongly influenced by, multifields, which typically include at least mechanical and thermal fields, and, in many cases, tribochemical field as well.
Many phenomena involve complicated processes that are time dependent and subjected to variations or transitions from one status to another. Many processes are accompanied through energy dissipation. However, only friction-related dissipation has currently drawn a notable attention.
