Sharif Digital Repository

The improved properties of nanocomposites are not achievable with conventional composites. Scale effect is one the most important parameters in the physical and mechanical properties of polymeric nanocomposites. One of the physical phenomena, which can be related to the scale effect, is the very large interface between the nanoparticles and the polymeric matrices. Motional behavior and conformation of polymeric chains change near the nanoparticles surfaces. Due to high interface of the nanoparticles with the polymeric matrices the amount of these types of changes in the polymeric chains are so large that can change the physical and mechanical properties of polymeric nanocomposites. In this... 

The investigation of interface residual stress and interface elastic moduli tensors plays a crucial role in enhancing the conventional theory of elasticity. These considerations allow us to account for size effects and eliminate nonphysical singularities near defects. The primary objective of this study is to comprehensively calculate interface energy, residual stress components, and interface elastic moduli tensors for various interfaces between non-magnetic fcc metals using density functional theory (DFT). We achieve this by performing ab initio DFT calculations to determine the interface energies for different coherent interfaces among these metals. Subsequently, these energies are... 

Excellent mechanical properties and high aspect ratio of carbon nanotubes have been the reason for extensive research on nanocomposites reinforced by this nanostructure, and recently metal matrix type of these nanocomposites, due to their advantages, have received great attention. Moreover, nanoporous materials are another type of nanostructured materials which due to their very high porosity have special applications in hydrogen storage, separating molecules, purification and energy absorption. Because of completely neglecting the details of nanoscale structure and not paying attention to the length scale, classical continuum mechanics methods are not precise enough for evaluating different... 

In this study, an analytical solution is presented for anti-plane scattering of Love waves by a surface-breaking crack normal to the free surface of an ultra-thin layer bonded to a semi-infinte medium within the surface/interface elasticity theory. The Fourier transform techniques are used to formulate the corresponding mixed-boundary value problem as a singular integral equation of the Cauchy type which is solved numerically. Mode III dynamic stress intensity factor at the crack tip, crack face and crack mouth opening displacements, the reflection coefficient at large distances from the crack face, and the stress field on the interface are computed and plotted for different valued of... 

In the framework of surface elasticity theory, the scattering of in-plane elastic waves by a multicoated nanofiber embedded in an elastic matrix is studied. Atoms near an interface experience a local environment different from it within the bulk. Going from macro to nano dimensions, surface to volume ratio increases significantly. Thus, on this scale it is important to consider the surface/interface properties as well as the bulk properties. In this dissertation, the surface/interface is modeled by a very thin layer in which the traction and displacement are discontinuous. Effects of surface/interface parameters on the dynamic stress concentration factor (DSCF) and scattering cross section... 

The aim of this study is to investigate the propagation of anti-plane shear waves in an elastic medium composed of periodic nanolayers (metamaterials) with deformable interfaces.Some of interesting properties of metamaterials are band-gaps and negative refraction angle.In nanolayered mediums the effect of interface becomes significant and classical continuum theory is not sufficient individualy. In this research by introducing 4 interface parameters and adding some equations to classical continuum theory, the possibilty of discontinuity of traction and displacement across the interface is provided and the effect of interface is considered. Then, a functional representing the energy of the... 

In recent years, carbon nanotubes have been the focus of considerable researches. Numerous investigators have reported remarkable physical and mechanical properties for this new form of carbon. In particular, the exceptional mechanical properties of carbon nanotubes, combined with their low density, offer scope for the development of nanotube reinforced composite materials. The potential for nanocomposites reinforced with carbon tubes having extraordinary specific stiffness and strength represent tremendous opportunity for application in this century and recently metal matrix type of these nanocomposites, due to their advantages, have received great attention. Classical theories of... 

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... 

This work focuses on developing a theoretical approach for the calculations of the surface elastic constants for (100) planes of fcc crystals. Using this method, the surface elastic constants, as well as the surface residual stress of the (100) planes of Al, Ag, Ni, Pt, and Cu fcc crystals, are evaluated using quantum calculations and VASP code. Surface effects are important in nanostructures and the considered metals are the most applicable ones in nanostructures especially in optic and electronic fields. For verification of the obtained values for surface elastic constants and residual stress, other surface parameters including the equilibrium lattice parameter, the energy per atom of the... 

Due to ignoring the effect of length scale and neglecting the details at nanosize, classical methods are not sufficiently accurate to determine the properties of nanostructured materials. More reliable results can be obtained, using surface elasticity theory. Lots of analytical, experimental and numerical investigations have been done on the effect of interphase on the mechanical properties of polymer nanocomposites whereas metal matrix nanocomposites are in the first stages of analytical and numerical researches and have attracted so much attention.
The main objective of this research is to investigate the effects of interphase as well as coating, on the mechanical behavior of metal...