Theory 7
Agilent Nano Indenter G200 User’s Guide
7-30
Calculations Using Raw Displacement and Load Data
On Nano Indenter instruments, the following analyses are applied to the
raw displacement and load data in order to calculate:
•
Displacement into Surface: the penetration into the test surface,
h
, and
•
Load on the sample,
P
Reference to the Point of Contact
All load and displacement data acquired throughout the test are
referenced to the point at which the indenter first contacts the test
surface. Usually, the software does a good job of determining this point
automatically, but sometimes (especially on soft materials) the user
must “help” decide when contact occurred. This may be done using
several contact-sensitive parameters, one of which is the slope of the
load-versus-displacement data. That is, when contact occurs, a given
change in applied load produces a smaller change in displacement than
before contact. If the instrument has the CSM option, dynamic
contact-sensitive parameters may also be used.
Thermal Drift
This correction is unique to each indentation experiment and seeks to
adjust measured correction displacements to account for small amounts
of thermal expansion or contraction in the test material and/or
indentation equipment. Near the conclusion of the indentation
experiment, the indenter is held at a small constant load for at least 50
seconds. Displacement changes measured during this period are
attributed to thermal expansion or contraction in the test material or
indentation equipment, and a drift rate is calculated, in nm/sec, as shown
in
