Ehsan Mohammadpour

Experimental and predicted mechanical properties of Cr1−xAIxN thin films, at high temperatures, incorporating in situ synchrotron radiation X-ray diffraction and computational modelling

Cr1−xAlxN coatings, synthesised by an unbalanced magnetic sputtering system, showed improved microstructure and mechanical properties for ∼14–21% Al content. In situ SR-XRD analysis indicated various crystalline phases in the coatings that included: CrN, AlN, α-Cr with small amounts of AlO2 and Al2O3 over the 25–700 °C range. Al doping improves resistance to crystal growth, stress release and oxidation resistance of the coatings. Al doping also enhances the coating hardness (H) from 29 to 42 GPa, elastic modulus (E) from 378 to 438 GPa and increased the resistance to deformation. First-principles and quasi-harmonic approximation (QHA) studies on bulk CrN and AlN were incorporated to predict the thermo-elastic properties of Cr1−xAlxN thin film coatings in the temperature range of 0–1500 °C. The simulated results at T = 1500 °C give a predicted hardness of H = ∼41.5 GPa for a ∼21% Al doped Cr1−xAlxN coating.

Electronic properties and stability phase diagrams for cubic BN surfaces

Abstract This contribution investigates structural and electronic properties as well as stability phase diagrams of surfaces of the cubic boron nitride (c-BN). Our calculated parameters for bulk c-BN agree reasonably well with both experimental and computed values available in the literature. Based on the energies of the three experimentally recognised phases of bulk boron, i.e. α-B36, β-B105 and γ-B28, we estimate enthalpy of formation of c-BN to be −2.8 eV. The c-BN(1 0 0) surface offers separate B and N terminations (denoted as c-BN(1 0 0)_B and c-BN(1 0 0)_N), whereas c-BN(1 1 1) and c-BN(1 1 0) are truncated with combinations of boron and nitrogen atoms (denoted as c-BN(1 1 1)_BN and c-BN(1 1 0)_BN). Optimised geometries of surfaces display interlayer displacements up to the three topmost layers. Downward displacement of surface boron atoms signifies a common geometric feature of all surfaces. Bulk c-BN and its most stable surface c-BN(1 0 0)_N possess no metallic character, with band gaps of 5.46 and 2.7 eV, respectively. We find that, only c-BN(1 0 0)_B configuration exhibits a metallic character. c-BN(1 1 0)_BN and c-BN(1 1 1)_BN surfaces display corresponding band gaps of 2.5 and 3.9 eV and, hence, afford no metallic property.

Finite Element Modeling of Nanotube Structures

This book presents a new approach to modeling carbon structures such as graphene and carbon nanotubes using finite element methods, and addresses the latest advances in numerical studies for these materials. Based on the available findings, the book develops an effective finite element approach for modeling the structure and the deformation of grapheme-based materials. Further, modeling processing for single-walled and multi-walled carbon nanotubes is demonstrated in detail.

A finite element model to investigate the Stress–Strain behavior of single walled carbon nanotube

This chapter describes a finite element (FE) method that is appropriate for the numerical prediction of mechanical behavior of different types of isolated Single walled carbon nanotube (SWCNT). The aim of this research is to develop a FE model based on the modified Morse interatomic potential to evaluate axial Young’s modulus of nanotubes. The novelty of the model lies on the use of ANSYS’s beam element with non-linear capability, i.e., element type BEAM188 is used to evaluate SWCNT‘s mechanical properties. In the present modeling work, an individual carbon nanotube (CNT) is simulated as a frame-like structure and the primary bonds between two nearest-neighboring carbon atoms are treated as 3D beam elements. The beam element properties are determined via the concept of energy equivalence between molecular dynamics and structural mechanics using modified Morse potential. The calculated mechanical properties show good agreement with existing works.

Thermo-mechanical properties of cubic titanium nitride

Abstract The equilibrium structure, elastic constants Cij and thermodynamic functions of cubic titanium nitride (TiN) were calculated within the temperature range of 0–3100 K and under a pressure range 0–60 GPa. Properties were computed using the generalised gradient approximations (GGA) exchange-correlation functional. Calculated mechanical properties (Elastic constants, Young’s modulus and shear modulus) and phonon spectra of TiN obtained via robust DFT-QHA algorithm, were generally in a good agreement with available experimental and theoretical analogous values. In particular, a well-examined quasi-harmonic approximation method implemented in the Gibbs2 code is utilised herein to provide accurate estimation of thermal expansion coefficients, entropies, heat capacity values (at different combinations of temperature/volume/pressure) and Debye’s temperature. Parameters calculated herein shall be useful to elucidate the superior performance of TiN at harsh operational conditions encompassing elevated temperatures and pressures pertinent to cutting machineries and surface coatings.

Non-linear Finite Element Analysis of Nanotubes

From proven chemical calculations [1], the harmonic functions provide a reasonable approximation to the potential energy of molecular systems in which the bond length is near its equilibrium position.

Nanotube Modeling Using Beam Element

Advances in computing technology have significantly increased the scientific interest in computer based molecular modeling of nano materials [1]. In order to perform any computational study on molecular properties, it is necessary to create a molecular model. In other words, it is essential to create an accurate model of atomic interactions at the first step. This model could be used to investigate the mechanical properties of a material near molecular length scales [2]. It can be derived by taking into account an appropriate crystal structure. Any technique that can produce a valid model for a given compound seems appropriate. Molecular modeling could be a useful tool at this stage. It is widely employed to determine molecular equilibrium structures. In addition, it could be used to design new materials with desirable properties [3]. These theoretical methods can be classified into two board branch which are ‘‘bottom up’’ and ‘‘top down’’. ‘‘Bottom up’’ is based on quantum/molecular mechanics including the classical MD and ab initio methods. In contrast, ‘‘top down’’ approach arose from continuum mechanics.

Mechanical Behavior of Carbon Nanotube-Reinforced Polymer Composites

Nanocomposite is a multiphase solid material where one of the phases has one, two or three dimensions of less than 100 nm, or structures having nano-scale repeat distances between the different phases that make up the material. In the broadest sense this definition can include porous media, colloids, gels and copolymers, but is more usually taken to mean the solid combination of a bulk matrix and nano-dimensional phase(s) differing in properties due to dissimilarities in structure and chemistry. The mechanical, electrical, thermal, optical, electrochemical, catalytic properties of the nanocomposite will differ markedly from that of the component materials [1–3].

Influence of Defects on the Strength of Graphene and Carbon Nanotube

As with every material, the presence of a crystallographic defect influences the material properties. Defects can occur in various forms with significant effect. With high levels of such defects can lower the tensile strength by up to 85 % [1]. In general, three types of defects are reported in the CNTs [2, 3].

Finite Element Modeling of Nanotubes

In order to develop a finite element model for a given nanotube, it is necessary to set few things. Geometry of the nanotube should be well understood. As discussed in the previous chapters, atomic coordinates in a nanotube structure should be determined. The atomic coordinates is the base of any atomic modeling. Bonding between atoms should be established with respect to the experimental observations. Chemical bonds will be replaced with a proper structural element. After creating the frame-like structure of the nanotube, we can apply boundary conditions and carry out the simulation process.