The formation of spherical wear debris in fatigue cracks subject to mode II loading was investigated. Test pieces containing an inclined central slot and fatigue starter cracks, in both pure aluminium and mild steel, were loaded cyclically in compression. The test duration was varied under both lubricated and unlubricated conditions. In aluminium, spherical debris was formed after only 1000 cycles in unlubricated conditions. Lubricant suppressed spherical debris formation up to at least 250 000 cycles. Its mechanism of formation was found to be by plastic deformation and heavy wear of non-spherical primary wear debris in sockets or against ridges in the surface. Sphere formation was modelled using crack surfaces made from Plasticine modelling clay and subjected to alternating sliding displacements.
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|Published - 1982