NEAR-SURFACE MICROSTRUCTURES DEVELOPING UNDER LARGE SLIDING LOADS

The subsurface zones of copper developed during the application of lar ge sliding loads were observed using TEM and SEM, Differences in micro structural development as a function of load and sliding velocity are assessed, The observed microstructural changes, such as the developmen t of a dislocation substructure and a mechanically mixed layer, are us ed to estimate the stress and strain-state of the near surface zone du ring sliding, These estimates of local stress and strain were compared to the applied stresses to show that large stress concentrations deve lop at and below a sliding interface, Thus, the stresses which develop locally within the near surface zone can be many times larger than th ose predicted from the applied load and the friction coefficient, It i s postdated 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.