Continuous Stiffness Measurement A
Agilent Nano Indenter G200 User’s Guide A-13
Computing Parameters for Polymers
On polymers, the storage modulus and loss modulus are often of
interest.
The storage modulus, E’, is usually defined as:
(44)
The storage modulus, E’, is related to the elastic contact stiffness, S,
through the contact area. It has been suggested that the loss modulus,
E”, should be related to the contact damping coefficient, D
s
w, in an
analogous way; that is:
(45)
Although quite promising, this technique for measuring loss modulus
has yet to be rigorously tested on a variety of materials. Again, it must
be emphasized that the total measured damping is a combined response
from both the indentation equipment and the contact. Isolating the
material response has been the largest practical hindrance to
determining loss modulus by indentation. Relative to that of the contact,
the equipment damping is usually quite high, making it critical to
correctly account for its contribution. Thus far, the technique has been
applied only to materials that have relatively high damping.
The parameter tan d indicates the relationship between the loss and the
storage modulus, that is:
(46)
The higher tan d, the higher the mechanical losses in the material.
E
S
2 A
----------------=
E
D
s
2 A
-----------------------=
tan
E
E
------
D
s
S
----------==
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