INDENTATION AND ADHESION AT SMALL LENGTH SCALES - Nanoindentation with Biological Applications - page 24

and in separating the limits of indentation and adhesive contacts; the
characteristic values calculated here will be used below.

2. Contact Behavior Sensed by Instrumented Indentation

Let us consider the extremes of indentation and adhesive contact in
the context of the typical experimental ranges of the two instruments
used to measure load-displacement responses of contacting bodies:
Nanoindenters and atomic force microscopes. Instrumented indentation
testing, IIT, sometimes referred to as depth-sensing indentation (with
acronym DSI), enables the displacement of a probe to be measured along
with the load during contact with a test surface. The resistance of
the probe to elastic and plastic deformation is typically much greater
than that of the surface and IIT, as the name implies, is typically used
to measure indentation behavior. Indentation displacements < 1 μm,
measured with < 1 nm resolution, are typical and thus the technique is
well suited to measure contact responses at very small length scales and
is often referred to as “nanoindentation.”
A schematic diagram of a typical IIT device is shown in Fig. 2-1 . The
indenter consists of a very stiff frame supporting the probe and
surrounding a platform for the test surface. The probe contacts the
surface through an indentation column that defines an indentation axis.
The indentation apparatus controls the position of the probe along the
axis or the load applied through the column. The load and, more
importantly, the position of the probe, are measured remotely from the
contact, which occurs between the tip of the probe and the surface.
Hence, although the indentation load experienced by the tip-surface
contact is identical to that measured by the remote load cell (as the cell
and the contact are elements in series connected by the indentation
column), the displacement of the tip relative to the surface is not the
same as that imposed by the indenter on the probe as a whole and
measured by the remote displacement gauge. The imposed probe
displacement and the tip reaction displacement are related by the
stiffness of the indentation column between the tip and the gauge and the
tip-surface interaction stiffness. It is convenient to view the indentation
column between the tip and the gauge as a linear-elastic element with a