Publication date: 22 September 2017
Source:Polymer, Volume 126
Author(s): Thanh-Tam Mai, Yoshihiro Morishita, Kenji Urayama
Anisotropy induced by stress-softening phenomena (Mullins effect) in filled elastomers has been intensively investigated using various stretching modes for pre-stretching. A sequence of two tensile experiments was conducted for the evaluation of the anisotropy: firstly the virgin specimens were pre-stretched by several modes, i.e., uniaxial, planar, unequal-biaxial and equibiaxial extensions, with various degrees of strain; secondly, the rectangular subsamples, which were cut out from the pre-stretched and relaxed specimens at various angles relative to the axis of the larger pre-strain (x-axis), were uniaxially stretched. The dependence of the energy dissipation on the direction and pre-strain was examined on the basis of the comparison of the uniaxial loading curves of the subsamples and virgin samples. The damage in the x-direction is governed only by the maximum stretch in the corresponding direction, and it is independent of the degree of the pre-strain in the other direction (y-direction). The damages in the directions unparalleled to the x-direction are influenced by the degrees of the pre-strains in both x- and y-directions, and they are well expressed as a sum of the quadratic effect of the pre-strain in the x-direction, and the linear effect of that in the y-direction. This feature of the cross-effect of strains on the damage is different from the feature of the strain cross-effect on stresses where the stresses in all directions are influenced by the imposed strains in the two directions. An increase in the anisotropy of the pre-strain field or filler content, and the introduction of a silane coupling agent increase the anisotropy of damage in the Mullins effect.
Graphical abstract
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