Loading...

Wave Propagation in Cubic Crystal Media within Surface Elasticity Theory

Behnoud, Paria | 2022

52 Viewed
  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 55819 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Mohammadi Shodja, Hossein
  7. Abstract:
  8. The aim of this work is to investigate the surface effects on SH wave propagation in ultra-thin layers with body-centered cubic single-crystal and face-centered cubic single-crystal structures, as well as Love and Rayleigh surface waves propagation in a single crystalline bcc half-space solid.Due to the wide application of wave propagation in science and technology, this issue has attracted the attention of many researchers and engineers. Wave propagation is used in surface science, coustoelectronics, and non-destructive evaluations.In this study, ultra-thin layers have thicknesses between 2 and 6 nm. For such layers, the physical and mechanical effects of surface are not negligible.It is clear that in a nanometer object, the ratio of the surface to the volume is high; therefore, the ratio of the number of surface atoms to the bulk atoms is high; hence, the necessity of considering the atomic layer of the surface as an influential part in the behavior of nano structures along with considering the bulk is unavoidable.The classical theory predicts the SS (0)-mode of shear wave propagation in the thin layer is nondispersive, but we see that all modes of SH wave propagation in ultra thin layer considering the surface effect are dispersive. Also by increasing of the thickness, the surface effects become negligible. In other words, if we apply the necessary assumptions to obtain the isotropic dispersion relations, then, by increasing the layer thickness, we see that our results become close to the classical theory results.In classical theory, the surface effects are not considered, and the medium is considered a homogeneous material; in contrast, in surface elasticity theory, the effects of the nano structure of cubic crystals are correctly modeled. It should be noted that the Love wave does not propagate in the classical half-space; however, by considering the surface effects in surface elasticity theory, the Love wave propagates in the half-spaces with dispersion characteristics. Also, unlike the classical theory, Rayleigh wave propagation in half space is dispersive by considering the surface effects.The detailed investigation of wave propagation and the detection of phenomena in nano structures that have a high surface-to-volume ratio using the classical theory of elasticity, in which the effects of size and surface are not considered, is not possible, and due to the weakness and shortcomings of classical theory, there is a need to use enriched theories of elasticity that consider the surface effect. For this purpose, it is necessary to use the surface elasticity theory in the proposed study to investigate the wave propagation in crystalline solids. We will show that wave dispersion strongly depends on the direction of wave propagation relative to the crystallography of the material. The innovation of this research is the investigation of wave propagation in cubic crystals by considering the surface effect based on the surface elasticity theory, which was ignored in classical theories
  9. Keywords:
  10. Surface Effect ; Cubic Crystals ; Wave Scattering ; Shear Wave Propagation ; Face-Centered Cubic Crystal ; Body-Centered Cubic Crystal ; Surface Wave Propagation ; Surface Elasticity

 Digital Object List

 Bookmark

No TOC