Quantifying, Locating, and Following Asperity-Scale Wear Processes Within Multiasperity Contacts

Wear tests are inherently destructive and wear surfaces are often consumed before the worn volume can be detected with traditional methods. Elucidating the subtler features of incipient wear requires improvements in our ability to quantify, locate, and follow wear at the asperity scale. The topographic difference method provides a possible solution, but its use is limited by the difficulty in perfectly repositioning samples and the uncertain effect of imperfect repositioning on the wear measurement. This paper quantified the detection limits of the topographic difference method under the conditions of typical repositioning errors, surface topographies, and measurement approaches. With repositioning errors on the order of 2 μm, the raw/uncorrected topographic difference method reliably detected worn volumes as small as 10 μm3, which rivals the most sensitive macroscale wear measurements reported in the literature. Following virtual posttest realignment, wear volumes as small as 0.1 μm3 were detected. Using standard topographic difference methods in an interrupted wear test allowed us to map asperity-scale wear onto features of the unworn surface profile, observe a complex distribution of real contact areas, and follow the gradual removal of individual asperities with a resolution of 0.1 μm3. To our knowledge, these are the first direct observations of the asperity-scale wear process within a multiasperity macroscale contact.