Understanding pop-ins in spherical nanoindentation
Abstract
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.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Oct 20, 2014
- Source ID
- 10.1063/1.4898698
Entities
People
- Jessica L. Riesterer
- Johann Michler
- Siddhartha Pathak
- Surya R. Kalidindi
Organizations
- Army Research Office
- Georgia Tech
- Los Alamos National Laboratory
- Swiss Federal Laboratories for Materials Science and Technology
- United States Department of Energy