Chemistry Reference
In-Depth Information
E
r
IS
10
90
Mol % Short
Figure 7.21:
The energy required for rupture
E
r
and the impact strength
IS
shown as a function of
composition for typical bimodal networks that are sufficiently brittle for such testing.
Elastomeric networks can be studied in pure shear by stretching a sheet
that has a large ratio of length to width, in the direction perpendicular to
the length. Pure shear is compared to simple shear by Treloar (ref. 124,
page 84). In shear measurements on some unimodal and bimodal net-
works of PDMS
263
the bimodal PDMS networks showed large upturns in
the pure-shear modulus at high strains that were similar to those reported
for elongation and biaxial extension.
Upturn
Upturn
Equibiaxial
extension or
compression
Elongation
1.0
α
-1
Figure 7.22:
Representative stress-strain isotherm for a bimodal elastomer in both uniaxial extension
(left side) and biaxial extension (right side).
