The evolution of contact-induced deformation on the nanoscopic scale is of considerable interest in terms of both the scientific understanding of defect nucleation and the practical concern of contact damage resistance of a wide range of surfaces in engineering applications. Currently, experimental tools such as nano indentation, atomic force microscopy, and atomic-resolution transmission electron microscopy allow quantification of nanoscale deformation and damage induced by contact at surfaces. However, none of these methods allows for in-situ visualization of atomic-level deformation during contact loading, Recently, we have employed the Bragg-Nye bubble raft to studs in situ the conditions governing defect nucleation in fee crystals subjected to nanoindentation. Although there are inherent limitations to this two-dimensional model. we have Found useful parallels to the mechanisms of homogeneous defect nucleation and deformation in three-dimensional fcc crystals. Such observations have the potential to guide computational models based on molecular dynamics. In this paper, we compare the characteristics of defect nucleation and slip step formation under monotonic and cyclic normal indentation using the Bragg-Nye model. We identify the atomic-level surface roughening process arising from homogeneous and heterogeneous defect nucleation and cyclic slip under repeated indentation loading. These findings provide insights into the atomic level mechanisms of cyclic slip and surface roughening during contact fatigue. [References: 10]
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