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Abstract
The size effects and physical mechanisms governing small-scale mechanical behavior have important influences on the atomic force microscopy (AFM) measurement. Typically, high surface to volume ratio associated with the small-scale system leads to an appreciable surface force; such that the adhesion of AFM indenter to specimen should be taken into consideration for the nanoindentation and nanoscratch testing. In this work, a finite element method (FEM) model was developed to simulate the adhesive contact between spherical indenter and half-space, in which the adhesive stress is obtained based on the Lennard–Jones potential. Shallow indentation and scratching under different contact conditions were investigated with the proposed FEM model. For adhesion-included cases, the load drop events were found during the indent process, which is demonstrated as a manifestation of local plastic yielding caused by the adhesive stress in contact edge. Adhesion-included scratch load was found sharply increased in the beginning, and rapidly decreased once the scratch displacement reaches to a critical value. Such a predicted stick-slip behavior was interpreted as the rupture of adhesive bond with increasing of scratching distance.