Early fatigue damage and residual stresses in polycrystalline copper: A scanning probe microscopy study

A distinction between material with and with no near surface compressive residual stresses in polycrystalline copper was observed by AFM. Fine scale surface features caused by slip upset were retarded by the near surface residuals. This ongoing research activity intends to provide more insight into localized surface damage produced under different cyclic load conditions. It is the authors' opinion that such fatigue findings are promising in assessing any fatigue initiation life model besides providing a better understanding of secondary stress effects. Accordingly, the following is concluded: (1) Thermal residual stress effects in polycrystalline copper fatigue were evaluated by atomic force microscopy. (2) Residuals estimated at 0.78σy resulted in a significant retardation of fine feature slip upset at a strain amplitude of 10-4 and 10000 cycles life. (3) For initiation of very small cracks on the order of 2-4 μm, the residual stress field effect was minor.