AFM characterization of the evolution of surface deformation during fatigue in polycrystalline copper

Atomic force microscopy (AFM) is a relatively new tool that readily provides high resolution digitized images of surface features. AFM is used here to study the development of slip bands and protrusions in strain controlled fatigue tests on polycrystalline copper at 0.161 and 0.255% strain amplitudes. The average slip band heights at failure for both strain amplitudes conditions are comparable. implying that the growth of slip bands saturates at a specific height. A parameter, is defined that is a measure of the local slip irreversibility at the surface and is applicable to any type of surface deformation feature, independently of the size of the fields of view. Thus, estimates of surface deformation developed in regions where fatigue crack nucleation is likely to occur can be obtained, from which a fatigue crack nucleation criterion is defined. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.