Theory 7
Agilent Nano Indenter G200 User’s Guide 7-24
Diagnostics
A critical parameter in evaluating system performance is Stiffness
Squared Over Load, S
2
/P. This parameter is proportional to the square
of modulus divided by hardness. It is a material property which is
independent of contact area and has units of stress; typically GPa is
used.
Square the elastic modulus from Equation 6 on page 7-4 and set b to 1:
(31)
then use H = P/A to yield
(32)
Thus:
(33)
For fused silica and Borofloat, the parameter S
2
/P should be constant
between the values of 640
and 710 GPa for all displacements greater
than 200
nm. Graphs with acceptable data are shown as follows:
•S
2
/P versus depth in Figure 7-17 on page 7-25.
• Elastic modulus versus depth in Figure 7-18 on page 7-25, where E
is between 70 and 75 GPa for all depths.
• Hardness versus depth in Figure 7-19 on page 7-26, where H is
between 9 and 10 GPa for all displacements greater than 200 nm.
E
r
2
H
--------
4
---
S
2
A
-----
A
P
---
4
---
S
2
P
-----
==
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