PSI - Issue 32

Kseniia A. Mokhireva et al. / Procedia Structural Integrity 32 (2021) 137–143 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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When the multi-walled carbon nanotubes are introduced into a highly filled with carbon black system, the material behaviour under sequential uniaxial cyclic loading is different in two mutually perpendicular directions (see Fig. 5). It is seen that the properties of the material change significantly after training along the OX-axis; obviously there occurs a reorientation of tubes in agglomerates along the loading axis. In the opposite direction, micro fractures are generated in the matrix at the nanotube surface. This induces a significant softening of the material in the perpendicular direction. After loading along both axes OX and OY, the material acquires new properties along the OX axis, since it softens strongly during deformation along both axes.

Fig. 5. Loading curves for cross-shaped specimens at 50% cyclic deformation caused by loading along two mutually perpendicular directions. Solid black line – loading along the OX-axis, dashed blue line – loading along the orthogonal OY-axis, solid red line – reloading along the OX axis. Filler: a) carbon black (43 phr) + original MWCNT (7 phr) and b) carbon black (43 phr) + purified MWCNT (7 phr). 4. Conclusion We have studied the formation of initial and induced anisotropies in elastomeric nanocomposites. For this purpose, we performed standard uniaxial experiments with the specimens cut along and across the calendering direction and complex successive cyclic tests with cruciform specimens loaded along each of two mutually perpendicular axes. In these experiments, materials containing fillers of various morphologies and different concentration were examined. Analysis of the obtained results shows that the technology for manufacturing nanocomposites can provide the uniform mechanical properties of all materials filled with spherical and layered particles. We have obtained interesting results for elastomers filled with nanotubes. During the preparation of nanocomposites filled with single-walled carbon nanotubes, the agglomerates are broken down, and the nanotubes are oriented in the matrix. The difference in the behaviors of the specimens cut along the calendaring direction and along the direction transversal to calendering is more pronounced when granular carbon black particles are added to this composite. However, no initial anisotropy was observed in the composites reinforced with multi-walled nanotubes. Therefore, it is necessary to take into account other factors which are responsible for the formation of the initial anisotropy of materials; in our case, this is the flexibility (the structural feature) of nanotubes. The strain-induced anisotropy was analyzed by investigating the behavior of cruciform specimens sequentially cyclic loaded along each axis by using the biaxial testing machine. In high-filled systems, the anisotropic phenomenon manifests itself even at a low elongation ratio (about λ =1.5); it is typical for nanocomposites filled with particles of all types. It has been found that the way of formation of the induced anisotropy in the nanocomposites depends on the filler morphology. For granular and layered fillers, the material loaded along one direction exhibits softening along this direction only. In the orthogonal direction, the specimen retains its original properties. The