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Express Test I
Agilent Nano Indenter G200 User’s Guide
H-12
on the test sample using the
method.
Express Test Tip Calibration
The Express Test Tip Calibration method is used to quickly determine
the indenter area function and frame compliance and is only available as
an Individual Method. This method is outlined in
Express Test, Varied Force
The purpose of the method is to use Express Test for rapid
characterization of Young's modulus and hardness as a function of
applied force and is only available as an Individual Method. The method
is especially suited for testing films on substrates because substrate
influence increases with increasing force. This method may also be used
to determine in situ frame stiffness.
Theory
Although the method can simply be used to evaluate the
force-dependence of properties, this method lends itself well to
determining
in situ
frame stiffness. Frame Stiffness is a scalar value (K
f
)
which models as a single spring all sources of deformation in the
hardware which are in series with the contact. Typical sources of such
deformation include: gantry, indenter shaft, tip holder, adhesive, puck,
puck holder, and translation stages. In indentation analysis, the frame
stiffness must be known in order to deduce the contact stiffness (S) from
the total measured stiffness (K). Contact stiffness is related to total
stiffness and frame stiffness by:
The form of this equation derives from the model of two springs in
series.
A value of frame stiffness is determined along with the area function on
fused silica, and this value is sufficient, so long as S << K
f
. But as the
value of S approaches the value of K
f
, it becomes increasingly important
to know K
f
well. This will often be the case for metals, because they
tend to have a high Young's modulus and a low hardness. To some
extent, K
f
is sample-dependent because every sample is mounted
1
S
---
1
K
----
1
K
f
-----
–
=