Biomedical Engineering Reference
In-Depth Information
polymer + water
Metal (Pt) particle
S
Material stretching
(a) Positive strain
Center
Anode
r(S, t)
(b) No strain
+
+
Material
compression
−
(c) Negative strain
Cathode
(a)
(b)
FIGURE 2.11
A cantilever configuration (left) of the IPMNC (a) and an illustration of
positive/negative strains experienced in the operation mode of the IPMNC (b) in the cath-
ode/anode sides of the electrodes, respectively.
is in turn related to the maximum tensile
(positive) or compressive (negative) strains in the beam as
Note that the radius of curvature
ρ
h
2
ε
≅
(2.5)
ρ
where
is the thickness of the beam at the built-in end.
Note that in the actuation mode of the IPMNC, the tensile strain can be simply
realized, but difficult to isolate. In the negative strain (material compression) illus-
trated in figure 2.11(b), the metal particles become predominant so as to experience
much higher stiffness and modulus of elasticity than the ones in the positive strain
regime.
Thus, the mathematical description regarding the physics of the cantilever beam
of the IPMNC is somewhat challenging and should be addressed carefully. Obvi-
ously, experimental approaches are available and should be pursued.
Note in figures 2.12 and 2.13 that swelling is an important parameter to affect
the mechanical property; that is, swelling causes mechanical weakening while elec-
trical activation has a tendency to stiffen the material due to redistribution of ions
within the IPMNC.
The stress,
h
, by simply using Hooke's law,
assuming linear elasticity. (One can also consider other constitutive equations in
which the stress
σ
, can be related to the strain,
ε
in a nonlinear fashion—i.e., rubber
elasticity, which could be a future study.) It leads to
σ
can be related to the strain
ε
Mh
I
σ=
(2.6)
2
