Showing papers by "Liangchi Zhang published in 2007"

An FEM investigation into the behavior of metal matrix composites: tool-particle interaction during orthogonal cutting

Abstract: An analytical or experimental method is often unable to explore the behavior of a metal matrix composite (MMC) during machining due to the complex deformation and interactions among particles, tool and matrix. This paper investigates the matrix deformation and tool–particle interactions during machining using the finite element method. Based on the geometrical orientations, the interaction between tool and particle reinforcements was categorized into three scenarios: particles along, above and below the cutting path. The development of stress and strain fields in the MMC was analyzed and physical phenomena such as tool wear, particle debonding, displacements and inhomogeneous deformation of matrix material were explored. It was found that tool–particle interaction and stress/strain distributions in the particles/matrix are responsible for particle debonding, surface damage and tool wear during machining of MMC.

Fabrication and application of polymer composites comprising carbon nanotubes.

Abstract: Carbon nanotubes are being used in place of carbon fibers in making composites due to their high strength, high aspect-ratio and excellent thermal and electrical conductivity. Although carbon nanotubes were discovered more than a decade ago, works on preparation of satisfactory composites reinforced by carbon nanotubes have encountered difficulties. This review will discuss some registered patents and relevant papers on the fabrication of carbon nanotube- polymer composites on improving material properties such as electrical conductivity, mechanical strength, and radiation detection which have a broad range of applications in nano-electronic devices, and space and medical elements.

Ballistic resistance capacity of carbon nanotubes

Abstract: Carbon nanotubes have high strength, light weight and excellent energy absorption capacity and therefore have great potential applications in making antiballistic materials. By examining the ballistic impact and bouncing-back processes on carbon nanotubes, this investigation shows that nanotubes with large radii withstand higher bullet speeds and the ballistic resistance is the highest when the bullet hits the centre of the CNT; the ballistic resistance of CNTs will remain the same on subsequent bullet strikes if the impact is after a small time interval.

Grinding-hardening with liquid nitrogen: Mechanisms and technology

Abstract: This paper studies an innovative development of a steel grinding–hardening technology using an inert cryogen—liquid nitrogen. It was found that phase transformations took place during grinding with the application of liquid nitrogen and resulted in hardened surface layer in a ground component. The layer had a fine laths martensite structure which gave rise to a remarkably high hardness. It was also shown that the treatment can produce superior surface integrity, with compressive surface residual stresses and without surface oxidation. Due to the inert nature of the liquid nitrogen, the grinding process becomes environmentally conscious.

Polishing of polycrystalline diamond by the technique of dynamic friction. Part 2: Material removal mechanism

Abstract: This paper investigates the material removal mechanisms of PCD using the dynamic friction polishing technique. Scanning electron microscopy, energy dispersive X-ray, X-ray diffraction and Raman spectroscopy were used to identify the mechanisms by analyzing the specimen surfaces and debris produced by polishing. It was found that the material removal occurred in a rather complex way, which can be a chemo-mechanical process, diffusion, oxidization and evaporation, or their combinations.

Polishing of polycrystalline diamond by the technique of dynamic friction, part 3: Mechanism exploration through debris analysis

Abstract: This paper investigates the mechanisms of material removal in dynamic friction polishing of polycrystalline diamond composites through the analysis of polishing-produced debris. The specimens used were PCD compacts composed of diamond and silicon carbide. In order to uncover the debris’ structure, high-resolution transmission electron microscopy (HRTEM), electron diffraction and electron energy loss spectroscopy (EELS) were used. Additionally, the density and the sp 2 to sp 3 ratio in the hybridized carbon materials of the debris were estimated from the EELS spectra. It was found that the debris were mainly of amorphous structure and consisted of different forms of carbon, silicon oxide/carbide, iron oxides, etc. The results show that during polishing, the diamond has transformed to nondiamond carbon, and silicon carbide to amorphous silicon carbide/oxide. r 2007 Elsevier Ltd. All rights reserved.

Carbon nanotube reinforced ceramic composites and their performance.

Abstract: Carbon nanotubes are considered as excellent reinforcements for improving the properties of ceramic composites. This paper reviews the reported techniques for the preparation of various ceramic coated CNTs, CNT-ceramic composites, CNT-ceramic composite coatings, etc. It is noted that a wide range of techniques have been used to fabricate these composites. Their characterisation has revealed that considerable improvements in electrical/thermal properties can be achieved, but only a few studies have demonstrated significant improvements in macro-scale mechanical properties of ceramics such as fracture toughness.

Micro-Indentation of Metal Matrix Composite - An FEM Investigation

Abstract: Micro-indentation has been widely used to evaluate the mechanical properties of materials. It has also been considered to be an important measure in the study of machinability of difficult-to-machine materials such as metal matrix composites (MMCs). Because of the complexity of deformation of an MMC and the interaction in the vicinity of contact zone between the indenter and work material, an analytical or experimental method is unable to predict the detailed deformation process. The present paper uses the finite element method to investigate the behavior of MMCs subjected to micro-indentation by a spherical indenter including the development of stress and strain fields in the MMCs during loading/unloading. Particle fracture, debonding and displacement, and inhomogeneous deformation of matrix material were explored and compared with the experimental results reported in the literature. The analysis also provides an insight for understanding the formation of residual stresses in machined MMC components.

Grind-hardening of steel surfaces: a focused review

Abstract: Surface hardening of steel components using grinding-induced heat seems to be a cost-effective technique for production. This paper provides a review focusing on the research effort on grind-hardening in the author's Laboratory for Precision and Nano-processing Technologies. The discussion includes the mechanisms of heating and cooling, microstructural changes in workpiece materials, surface integrity generation and wear and fatigue behaviour of ground components.

Upper limit of x in Ba6−3xNd8+2xTi18O54 new tungsten bronze solid solution

Abstract: In the present work, the upper limit of x in Ba 6−3 x Nd 8+2 x Ti 18 O 54 ceramics was determined by investigating the phase constitution as the function of composition and process conditions. For the compositions of x ≤ 0.75, the new tungsten bronze structure is stable and the single phase structure is easy to be obtained. While, the new tungsten bronze structure becomes unstable for compositions of x = 0.8, 0.9 and 1.0, where the new tungsten bronze major phase is generally detected together with some secondary phases. The excellent microwave dielectric characteristics are not only obtained at x = 0.67 but also obtained at 0.8 and 0.9.

Mechanical interaction between single-walled carbon nanotubes during the formation of a bundle

Abstract: This paper investigates the intertubular van der Waals interactions that produce the initial cross sectional distortion of single-walled carbon nanotubes during a bundle formation. By combining the analysis of molecular dynamics with the continuum mechanics, the distributions of the van der Waals forces were determined. The dependence of the load parameters, deformation variables and the lattice constant on the nanotube radius, was also investigated. It was found that the van der Waals forces are attractive and vary circumferentially in a harmonic manner. For the considered zigzag nanotubes of radius 7–14 A, the intensity of the van der Waals forces is radius-dependent and can be as large as 6–11 GPa in the channels of the bundle and 1–5 GPa at the closest points between the single-walled nanotubes.

The effect of interface chemical bonds on the behaviour of nanotube-polyethylene composites under nano-particle impacts

Abstract: This paper uses the molecular dynamics method to investigate the influence of chemical bonds on the mechanical behaviour of nanotube–polyethylene composites subjected to nano-particle impacts. In the analysis, carbon nanotubes (CNTs)were incorporated into the polyethylene (PE)matrix in two ways, with and without radical centres, so that the resulting nano-composites had two corresponding properties, i.e., with and without chemical bonds at the CNT–PE interfaces. A spherical diamond nano-particle was used to impact and penetrate into the composites with a high velocity. It was found that the interface chemical bonds play an important role in the composite reinforcement.

Optical Surface Finish of PCD Composites by Dynamic Friction Polishing

Abstract: This paper presents a cost-effective technique for achieving optical surface finish of thermally stable polycrystalline diamond (PCD) composites using dynamic friction polishing (DFP). The effect of polishing parameters on the material removal rate and surface characteristics of polished specimens were studied. The surface characterisation was carried out by optical microscopy, atomic force microscopy (AFM), scanning electron microscope (SEM) and its attached energy dispersive X-ray (EDX) analysis. It was found that optical surface finish of PCD with roughness Ra = 50 nm could be obtained efficiently with nearly a ten fold reduction in polishing time compared to the currently used method in industry.

Grinding force modelling: combining dimensional analysis with response surface methodology

Abstract: This paper describes a new technique for an empirical modelling of unit grinding force in surface grinding by combining dimensional analysis with Response Surface Methodology (RSM). The grinding experiment on K1045 steel (190 BHN) was carried out using conventional alumina wheels. The predictive grinding force model was developed in terms of spindle speed, work speed, depth of cut, width of cut and the strength of the work material. The adequacy of the model was judged by a variance analysis. Based on the response model, contours in the planes of investigated parameters were generated to predict the grinding conditions for a particular grinding force. The new technique can significantly reduce the number of experiments required for the force modelling and thereby is cost-effective.

Polishing of Diamond Composite Cutting Tools

Abstract: This paper presents an effective polishing technology for cutting tools made of thermally stable Polycrystalline Diamond Composites (PCDCs). The research includes: design and manufacture of a special polishing machine; temperature characterisation; comprehensive experimental and theoretical investigation of the material removal mechanism; and the selection of polishing parameters to achieve the required nanometric surface finish.

The Mechanical Properties of a Silicon Nanowire Under Uniaxial Tension and Compression

Abstract: This paper studies the mechanical properties of a silicon nanowire (SiNW) under uniaxial tension and compression with the aid of the molecular dynamics method. The three-bodied Tersoff potential is used to describe the silicon atomic interactions. It was found that under tension, SiNW exhibits rapid necking followed by a continuous unravelling of amorphous silicon atoms featuring a chain of single atoms. During compressive loading, the SiNW undergoes a large post-buckling deflection in its elastic regime. Irreversible deformation via amorphization only occurs in six localized zones before fracture.

Modelling the Free Vibration of Single-walled Carbon Nanotubes

Abstract: This paper proposes a two-dimensional elastic shell model to characterise the deformation of single-walled carbon nanotubes using in-plane stiffness, Poisson ratio, bending stiffness and off-plane torsion stiffness as independent elastic constants. It was found that the off-plane torsion stiffness of a single-walled carbon nanotube is not zero due to the off-plane torsion induced change in the {pi} - orbital electron density on both sides of the nanotubes. It was concluded that a three-dimensional elastic shell model of single-walled carbon nanotubes can be established with well-defined effective thickness.

A New Method for Stress and Deformation Analysis from Nano to Macro Dimensional Scales

Abstract: This paper presents a concurrent multiscale method for the stress analysis of solids using a coupled meshless and molecular dynamic analysis. A new transition algorithm using transition particles was employed to ensure the compatibility of both displacements and their gradients. The equivalent continuum strain energy density was obtained locally based on the atomic potential and Cauchy-Born rule, and hence plasticity can be easily handled in not only the atomic domain but also the continuum domain. Numerical examples demonstrated that the present multiscale technique has a promising potential of application to multiscale systems subjected to deformation.

Simulation of Chemically Bonded Nanotube-polyethylene Composites Subjected to Mechanical Loading

Abstract: Carbon nanotube polymer nano-composites are promising new materials with a combination of good mechanical, electrical and radiation detection properties. This paper reports the influence of covalent bonds at the carbon nanotube-polyethylene interface under different mechanical loading conditions. Interface covalent bonds were generated by incorporating carbon nanotubes into polyethylene matrix with radical centers on the polymer chains. The resulting nano-composite was then subjected to nano-impact and nano-sliding with the aid of molecular dynamics analysis. It was found that the load carrying capacity of the nano-composite was higher and the bending deformation of carbon nanotube was elastic. In addition, the covalent bonds at the interface were stable during the loading processes.