Near surface microstructures developing under large sliding loads

The subsurface zones of copper developed during the application of large sliding loads were observed using TEM and SEM. Differences in microstructural development as a function of load and sliding velocity are assessed. The observed microstructural changes, such as the development of a dislocation substructure and a mechanically mixed layer, are used to estimate the stress and strain-state of the near surface zone during sliding. These estimates of local stress and strain were compared to the applied stresses to show that large stress concentrations develop at and below a sliding interface. Thus, the stresses which develop locally within the near surface zone can be many times larger than those predicted from the applied load and the friction coefficient. It is postulated that these stress concentrations arise from two sources: (1) asperity interactions and (2) local and momentary bonding between the two surfaces. These results are compared to various friction models.

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