ABSTRACT REF NO: 1CF100904OR USE OF ATOMIC FORCE MICROSCOPY IN ASSESSING SURFACE DAMAGE DUE TO FATIGUE

Strain controlled fatigue tests were conducted on polycrystalline copper at ∆ε/2=0.161 % and 0.255% to various fractions of fatigue life. Scanning electronic microscope (SEM) and atomic force microscopy (AFM), a relatively new tool that readily provides high resolution digitized images of surface features, were used to describe and quantitatively characterize the evolution of surface deformation during fatigue. To quantify surface deformation, a parameter γirrev is defined that is a measure of the local slip irreversibility at the surface. This parameter applies to any type of surface deformation feature, is independent of the size of the fields of view and yields information on the distribution of surface strains over the specimen gage length. From this formalism, a criterion for crack nucleation is proposed using actual AFM surface strain measurements