Wear particles produced in repeated contact of aluminium with two pyramidal asperities are studied with image analysis. Four types of wear particles which reflect four different wear mechanisms can be identified with morphological parameters. Type 1 wear occurs only in two-asperity contact, and the particles had thin fibrous shape. Type 2 wear particles are small fragments produced at side ridges. Type 3 wear particles are from a wedge formed in front of the contact, and are of relatively thick, bulky shape. Type 4 wear is cutting caused by asperities with smaller tip angles, yielding chips of characteristic shapes. The criterion of identification based on the morphological parameters is applied to wear particles produced in a conventional ball-on-disk test, in which most particles are identified as Types 2 and 3 though Type 1 particles also exist. It is suggested that several additional processes, including stacking of loose particles within small gaps between sliding surfaces and adhesion of the particles on the surfaces, work to make wear more complex than those with two asperities.
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