ON MICROSCOPIC MECHANISMS OF FRICTION AND WEAR

Under normal sliding conditions encountered in engineering applications, the frictional force is generated by plowing of surfaces by wear particles, asperity deformation and adhesion. Of these three basic contributing factors, the plowing of the surfaces by wear particles is found to be the most important in most sliding situations. Careful experiments are attempted to eliminate the mechanical effects of friction in order to measure only the inherent friction due to adhesive forces between two sliding surfaces. However, it has been found that it is extremely difficult to eliminate microstructural changes caused by mechanical interactions at the microscopic scale. Experimental results obtained using extremely smooth silicon and sapphire surfaces are described to support the claim that permanent damages are present in most friction tests, which may ultimately contribute to the formation of wear debris, particles, and sheets. A plausible model for a microscopic friction and wear process is presented.