posted on 2022-01-12, 15:15authored byYuga Taniguchi, Thanh-Tam Mai, Masashi Yamaguchi, Katsuhiko Tsunoda, Kenji Urayama
The
Mullins effect is commonly observed in the mechanical properties
of elastomer/filler composites: The stress during unloading or second
loading is considerably lower than the first loading stress. We measured
the mechanical stresses and electrical conduction to investigate the
Mullins effect in carbon-black (CB)-reinforced elastomers under various
biaxial stretching. Imposing the small equibiaxial strain of 30% increases
the electrical surface resistivity in the deformed state by more than
3 orders of magnitude, indicating the breakdown of the initial conductive
percolated CB network. The resistivity of the relaxed unloaded states
(ρS), representing the degree of residual destruction
of the CB network, increases with the biaxial strain for small imposed
deformation. However, ρS saturates at large deformations,
indicating that the residual CB-network destruction does not increase
further. The mechanical dissipation factor (Δ; the ratio of
energy dissipation to input work) and ρS obtained
at various degrees and types of deformation can be described by a
single variable, i.e., the first invariant of deformation tensor.
This indicates that the orthogonal strains cause the residual damage
of the CB network and the internal mechanical damage.