Theory 7
Agilent Nano Indenter G200 User’s Guide 7-32
Compensating for Deformation of the Load Frame
This type of analysis is common to nearly all mechanical tests. That is,
most of the measured displacement occurs in the test sample, but the
load frame (test fixtures, sample stage, gantry, and so on) is inevitably
deformed by some small amount. The load frame and sample may be
modeled as two springs in series, with stiffnesses K
f
and S, respectively,
as shown in
Figure 7-25.
Figure 7-25Dynamic model
Once this parameter is known, one may determine that part of the total
measured displacement that occurs in the load frame and correct the
displacement data for it. The displacement into the test equipment is
given by P/K
f
.
Compensating for the Force Exerted by the Support Springs
The raw load data must be compensated for the force exerted by the
springs that support the indenter shaft. The stiffness of the supporting
springs is determined at the factory and may be represented by K
s
.
Thus, the force exerted by the supporting springs depends on their
deflection, x, and is given by x • K
s
.
References
• Oliver, W. C., and Pharr, G. M. (1992). J. Mater. Res., 7, p. 1564.
• Hay, J. L., and Pharr, G. M. (2000). ASM Handbook for Mechanical
Testing and Evaluation, 8, p.232.
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