The contact characteristics of rough surfaces in line contact during running-in process

The contact parameters between mating surfaces during running-in process were investigated using a ring-on-block line contact device. The experimental and theoretical results indicate that both contact width and real contact area substantially increased during the running-in process. This increase in contact width might be the main reason that the line contact running-in process increases tribological performance between relative surfaces. During the process, the real contact area was multiplied and its variation can be evaluated by dimensionless correlation distance only for relatively close contact under lubrication conditions. The true friction power intensity (TFPI) is defined as the ratio between the friction power and the real contact area for two relative surfaces. Regardless of loads and roughness values, TFPI index value increases to a maximum with time and then decreases to a low stable value during the running-in process. The initial running-in stage is the key stage determining whether or not the run-in will fail for constant loading condition based on the variation of TFPI index. In general, the running-in for temperature needs a longer time to reach a stable condition than the running-in for wear. The results of skewness and fluid retention index show that the running-in process transforms the original surface into a beneficial surface having many small valleys to accommodate lubrication oil and protect relative surfaces, so that the oil-bearing capability of total valley volume per unit sampling area remains the same. (C) 2002 Elsevier Science B.V. All rights reserved.