Sharif Digital Repository

In this research, we have modeled nano-Beams using molecular dynamics. The scope of our study is FCC metals, therefore an appropriate inter-atomic potential for this kind of materials must be chosen. A multi-body long-range potential proposed by Sutton-Chen, which has been used in many physical investigations of FCC metals is applied in our study. Using conducted simulations, the different mechanical properties of material such as elastic modulus, shear modulus and poison's ratio are calculated. The results show that the elastic properties decrease with increase in nano cantilever size. ©2008 IEEE  

The aim of this research is to conduct atomistic investigations of physical interaction analysis of nanoscale objects manipulation. The system consists of tip, particle and substrate. The manipulation tool moves with a constant speed while pushing the particle in a desired direction. The focus of the research is on ultra-fine metallic nanoparticles. To perform this research, Nose-Hoover dynamics and Sutton-Chen interatomic potential will be used to investigate the behavior of the aforementioned system which is made from different transition metals. The effects of size, material type and temperature on the success of the process have been investigated by planar molecular dynamics. © 2008 IEEE... 

The competition and interaction of two edge cracks within the triangular lattice of an fcc material are addressed. We have also examined the effect of presence of a nanovoid in the vicinity of one of the crack-tips, on the competition of the cracks. An atomic scale finite element method (AFEM) [B. Liu, Y. Huang, H. Jiang, S. Qu, K.C. Hwang, The atomic-scale finite element method, Comput. Methods Appl. Mech. Eng. 193 (2004) 1849-1864], based on the Morse interatomic potential, is employed to explore the events in the (1 1 1) plane. Particular attention is given to the phenomenon of brittle-to-ductile transition (BDT) that occurs during crack propagation. © 2007 Elsevier B.V. All rights... 

Often, during fabrication of thin films on substrates, different types of defects may be introduced into the films. Recently, the determination of the elastic fields due to the self-assembly of quantum dots or strained islands in thin films has been of major concern. In the micromechanical studies, such strained islands are modeled by inclusions. This paper aims to develop a theory pertaining to the presence of nano-inclusions of various geometries within thin films having face centered cubic (fcc) structure. To this end, the notion of eigenstrain is combined with a many body inter-atomic potential suitable for fcc crystals. The interaction between atoms is modeled via Sutton-Chen (SC)... 

In this work a new method for analyzing nanostructured materials has been proposed to accelerate the simulations for solid crystalline materials. The proposed Structural Approximation Method (SAM) is based on Molecular Dynamics (MD) and the accuracy of the results can also be improved in a systematic manner by sacrificing the simulation speed. In this method a virtual material is used instead of the real one, which has less number of atoms and therefore fewer degrees of freedom, compared to the real material. The number of differential equations that must be integrated in order to specify the state of the system will decrease significantly, and the simulation speed increases. To generalize... 

In this paper, a novel temperature-dependent multi-scale method is developed to investigate the role of temperature on surface effects in the analysis of nano-scale materials. In order to evaluate the temperature effect in the micro-scale (atomic) level, the temperature related Cauchy-Born hypothesis is implemented by employing the Helmholtz free energy, as the energy density of equivalent continua relating to the inter-atomic potential. The multi-scale technique is applied in atomistic level (nano-scale) to exhibit the temperature related characteristics. The first Piola-Kirchhoff stress and tangential stiffness tensor are computed, as the first and second derivatives of the free energy... 

In this paper, the scattering of anti-plane shear waves in an infinite matrix containing a multi-coated nanofiber/nanotube is studied. Based on the fact that the surface to volume ratio for nano-size objects increases, the usual classical theories which generally neglect the surface/interface effects fail to provide reasonable results. Therefore, to analyze the problem the wave-function expansion method is coupled with the surface/interface elasticity theory. In order to provide some quantitative results through consideration of several examples, the knowledge of the relevant surface and/or interface properties of the corresponding constituent materials are required. For this reason, part of... 

The usual continuum theories are inadequate in predicting the mechanical behavior of solids in the presence of small defects and stress concentrators; it is well known that such continuum methods are unable to detect the change of the size of the inhomogeneities and defects. For these reasons various augmented continuum theories and strain gradient theories have been proposed in the literature. The major difficulty in implication of these theories lies in the lack of information about the additional material constants which appear in such theories. For fcc metals, for the calculation of the associated characteristic lengths which arise in first strain gradient theory, an atomistic approach... 

In the present work, characterization of the surface trenches and vacancies with Amplitude Modulation AFM (AM-AFM) using Molecular Dynamics (MD) is simulated and the effects of the tip shape on the resulting images are investigated. The simulated system includes a recently developed gold coated AFM probe which interacts with a sample including a surface trench or a single-atom vacancy. In order to examine the behavior of the above system, including different transition metals, a Molecular Dynamics (MD) simulation with Sutton-Chen (SC) interatomic potential is used. Special attention is dedicated to the study of tip geometry effects such as the tip apex radius, the tip cone angle, the probe... 

Classical continuum mechanics fails to give accurate solution near the crack tip, moreover, it implies that a solid is able to sustain an infinite stress at the Griffith-Inglis crack tips. Among other critical issues is the inability of the classical approach to sense the size effect. For these reasons, for more in-depth understandings and accurate behavioral predictions, it is essential to develop some atomistic methods which properly accounts, not only for the structure but also the long and short range atomic interactions effectively. In this work the interaction of inhomogeneity and crack under polynomial loading is simulated by using the many body Rafii-Tabar and Sutton potential... 

Continuum-based modeling of nanostructures is an efficient and suitable method to study the behavior of these structures when the deformation can be considered homogeneous. This paper is concerned about multiscale nonlinear tensorial constitutive modeling of carbon nanostructures based on the interatomic potentials. The proposed constitutive model is a tensorial equation relating the second Piola-Kirchhoff stress tensor to Green-Lagrange strain tensor. For carbon nanotubes, some modifications are made on the planar representative volume element (RVE) to account for the curved atomic structure resulting a non-planar RVE. Using the proposed constitutive model, the elastic behavior of the... 

This paper is devoted to the characterization of the surface defects using a recently developed AFM technique named as frequency and force modulation AFM (FFM-AFM). The simulated system includes a recently developed gold coated AFM probe which interacts with a sample including single-atom vacancy and impurities. In order to examine the behavior of the above system including different transition metals, molecular dynamics (MD) simulation with Sutton-Chen (SC) interatomic potential is used. Along this line, an imaging simulation of the probe and sample is performed, and the effects of the horizontal scan speed, the effective frequency set-point, the cantilever stiffness, the tip-sample rest... 

Mechanical properties of materials are an important factor in designing nanoscale systems. Several researches and experiments have shown that the mechanical properties of the nano-scale materials are different from those of bulk. One of the major reasons for this difference is that the ratio of surface to volume increases at the nano-scale, and the effects of free surfaces become very important. In this paper, we have measured the surface elastic constants of silicon crystalline structure using different interatomic potentials. The potentials employed here are EDIP (Environment-Dependent Interatomic Potential), Stillinger-Weber and Tersoff, and also different crystalline orientations are...