Text

theses

The main focus of this thesis is on the constitutive modeling of two important classes of advanced functional materials, that is graphene-based nanocomposites and piezoelectric-piezomagnetic multiferroic composites. Along the way, several related issues with complex physical nature are essentially examined from a continuum-based viewpoint. Our study begins with the development of a homogenization scheme with several desirable features for determination of overall magneto-electro-elastic response of multiferroic composites containing periodic distribution of multi-inhomogeneities. The accuracy and applicability of proposed theory is verified through consideration of several examples of three-phase multiferroic composites with complex microstructures. Besides, the strong dependence of overall behavior of composites on the microstructure parameters, such as the interface condition, thickness, eccentricity and material properties of core inhomogeneities and their coating layers is well demonstrated. Through the second part of this investigation, we offer a robust analytical methodology to determine the magneto-electro-elastic scattered fields of a shear wave induced by a two-phase multiferroic inhomogeneity within a transversely isotropic piezoelectric or piezomagnetic medium. To put its wide range of applicability in perspective, the developed theory is applied to several descriptive examples with various degrees of complexities. The numerical results thoroughly illustrate the influence of material properties of constituent phases, the thickness and eccentricity of coating layer, and the frequency of propagating SH-wave on the scattered fields induced by the multiferroic fiber. In the third part of this thesis, we aim to uncover how the imperfect load transfer at the graphene–matrix interface can affect the time-dependent viscoelastic response of graphene/polymer nanocomposites. To this end, different interface models are formulated within the framework of Mori-Tanaka homogenization theory. Through consideration of different sets of experimental data we demonstrate that, by adopting the weakened interface models in our homogenization theory, the quantitative behavior of creep response of graphene/polymer nanocomposites can be well captured. In addition, both stress relaxation and stress–strain relations are also found to greatly depend on the interface condition. In the closing part of this investigation, the effective electrical conductivity and permittivity constants of graphene/polymer nanocomposites are examined via the effective-medium theory. To do so, the microcapacitor and electron tunneling activities are taken as two interfacial processes that depend on the volume concentration of graphene fillers, and can be well modeled in a phenomenological way. The proposed model is shown to be able to successfully recover the experimental data of nanocomposite samples in AC electrical settings.

ETD_7836

Ph.D.

Includes bibliographical references

by Roohollah Hashemi

doi:10.7282/T3VH5R92

ETD doctoral

The author owns the copyright to this work.