Papers by Author: Kausala Mylvaganam

Abstract: Unlike the traditional silicate glasses, borosilicate glasses behave differently because of the addition of boron atoms. Extensive studies have been carried out to understand the abnormal function of boron in glass network. However, it is not clear how the atomic structure of borosilicate glass changes under loading. This paper investigates the behaviour of borosilicate glass under uniaxial compression with the aid of ab initio simulations. Sodium borosilicate glass having 160 atoms and a mass density of 2.51 g/cm³ with composition 3Na₂O-B₂O₃-6SiO₂ were equilibrated first at 3500K, then at 2500K, 1500K, 1200K, 1000K, 825K and 625K. Structural analysis showed that at higher temperatures the sodium borosilicate liquid does not have a specific structure. At around 825 K (i.e. around T_g), boron network and silicon network form and remain stable even at a temperature of 625 K. When the supercooled sample at 825K was subjected to uniaxial compression, the stress along the compression direction first increases and then decreases with a change in boron structure, which could modify the behaviour of the borosilicate glass.

Abstract: This paper investigates the high speed nano-grooving on mono-crystalline copper by nano-end-milling and nano-peripheral-milling. The molecular dynamics method was used for simulation. The milling forces and grooving quality were analysed in detail. The comparison showed that peripheral-milling requires a higher force, but the milled groove has a better quality. Nevertheless, both the milled groove subsurfaces are free of major dislocations.

Abstract: Mono-crystalline silicon experiences various phase transformations under different loading conditions. This paper reveals, with the aid of molecular dynamics simulations, that scratching the silicon {001} surface along the [110] direction under a load of 0.8 µN or more would produce stable 5 coordinated body centered tetragonal (bct-5) silicon in the subsurface. By examining the effect of this bct-5 silicon on indentation, it was found that the resistant to deformation of bct-5 silicon is higher than a-Si but lower than diamond Si.

Abstract: This paper uses the molecular dynamics simulation to investigate the quality of nano-scale grooving on mono-crystalline copper by high-speed nano-milling and nano-cutting. The results reveal that nano-milling produces a high-quality nano-groove with smooth surfaces in comparison with a nano-cutting. It is also interesting to note that the machined workpiece subsurface can be free from dislocations.

Abstract: To improve the structural properties of engineering ceramics, carbon nanotubes have been used as a reinforcement phase to produce stronger ceramic matrix composites. This paper investigates the possible chemical bond formation between a carbon nanotube and alumina with the aid of quantum mechanics analysis. The cases with and without functionalizing the nanotubes were examined. The nanotubes were modeled by nanotube segments with hydrogen atoms added to the dangling bonds of the perimeter carbons. The cleaved ceramic (0001) surface was represented by an alumina molecule with the oxygen atoms on either end terminated with hydrogen. Methoxy radicals were used to functionalize the CNTs. The study predicts that covalent bonding between Al atoms on a cleaved single crystal alumina surface and C atoms on a nanotube are energetically favorable.

Abstract: This paper explores the effect of the depth-of-cut of an indenter on the phase transformations during nanoscratching on monocrystalline silicon on the Si(100) orientation. The analysis was carried out by molecular dynamics simulations. It was found that the depth-of-cut and the impingement direction of the indenter had a significant influence on the phase transformations in the initial impression region. At a relatively low depth-of-cut, only amorphous silicon was formed on the scratched surface. When the indenter impinged on a silicon surface with an angle, a bct5-Si crystalline phase in the initial impression region would emerge.

Abstract: This paper investigates the scale effect of indenter tip radius on the deformation of silicon under nanoindentation using molecular dynamics simulation. It was found that with larger diamond tips a six-coordinated silicon phase different from β-silicon on loading and a diamond like crystal beneath the indenter on unloading would appear as a result of the indentation stressing. This is a new phenomenon that has not been observed previously.

Abstract: This paper aims to provide an understanding of the intrinsic frictional behaviour of CNTs under contact sliding by eliminating the possible effects of CNT rolling and slipping. Two critical steps towards the mechanism exploration were carried out: (1) the development of a new deposition method for CNT film fabrication, which allows the manufacture of densely packed, highly entangled CNT films to be firmly bonded on solid substrates for contact sliding testing; and (2) the theoretical understanding of the frictional behaviour of CNTs using the molecular dynamics analysis. The investigation clarified the controversial arguments in the literature and concluded that CNT films can be used as a superior solid lubricant with an ultra-low coefficient of friction of around 0.01.

Abstract: This paper discusses the methods of promoting covalent bonds between polymer and carbon nanotubes to make high performance composites. Such methods involve attachment of chemical moieties (i.e. functional groups) to the sidewalls of carbon nanotubes, introduction of mechanical deformation on nanotubes, or generation of radicals on the polymer chains using free radical generators. The implementation of the latter method is demonstrated at both quantum mechanics and molecular dynamics levels.