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Title: Understanding pop-ins in spherical nanoindentation

In this study, pop-ins, or sudden displacement-bursts at constant load in a nanoindentation test, are typically attributed to the difficulty of setting up potent dislocation sources in the very small indentation zones in these experiments. Such displacement (and strain) bursts would intuitively indicate a sharp drop in stress during the pop-in event itself. However, spherical indentation stress-strain curves routinely exhibit a high and stable indentation stress value during the pop-in, and the indentation stresses decrease only after a further finite amount of additional indentation displacement has been applied. In order to understand this discrepancy, we utilize a combination of interrupted spherical indentation tests along with depth profiling of the residual indentation surfaces using in-situ atomic force microscopy (AFM) to study pop-ins. The AFM surface profile maps show that there is an asymmetric profile change over a limited region around the indentation contact area for a single pop-in; the asymmetry disappears upon further loading beyond the pop-in. A plausible sequence of physical processes (related to metal plasticity) occurring underneath the indenter during and immediately after the occurrence of the pop-in is proposed to explain these observations.
 [1] ;  [2] ;  [3] ;  [2]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  2. Empa, Swiss Federal Laboratory for Materials Testing and Research (Switzerland)
  3. Georgia Institute of Technology, Atlanta, GA (United States)
Publication Date:
Report Number(s):
Journal ID: ISSN 0003-6951; APPLAB
Grant/Contract Number:
W911NF-10-1-0409; AC52-06NA52396; Center for Integrated Nanotechnologies; Los Alamos National Laboratory Director�??s Postdoctoral Fellowship
Accepted Manuscript
Journal Name:
Applied Physics Letters
Additional Journal Information:
Journal Volume: 105; Journal Issue: 16; Journal ID: ISSN 0003-6951
American Institute of Physics (AIP)
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
Country of Publication:
United States
36 MATERIALS SCIENCE; atomic force microscopy; stress strain relations; elasticity; hardness; nanotechnology
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1224247