Papers by Keyword: Pattern Formation

Abstract: Thermodynamic and diffusion models are given to describe morphological evolution of the reaction zone during diffusion-limited interaction between non-oxide Si-containing ceramics (SiC and Si₃N₄) and transition metals (Cr, Mo, Ti, Ni, Co, Pt). In the case of diffusion-controlled process in the ternary metal-ceramic systems, reaction phenomena can be rationalized using chemical potential diagrams. However, in some cases, a periodic layered morphology is found in the transition zone, which is not fully understood, and it is difficult to predict a priori. Silicide formation in systems based on dense Silicon Nitride and non-nitride forming metals can be explained by assuming a nitrogen pressure build-up at the contact surface. This pressure determines the chemical potential of Silicon at the interface, and hence, the product phases in the diffusion zone. Traces of Oxygen in the ambient atmosphere might affect the interaction in non-oxide ceramic/transition metal systems. The thermodynamic stability of the condensed phases in the systems where volatile species may form can be interpreted using predominant area-type diagrams.

Abstract: TRIP steel shows excellent mechanical properties such as greatly high strength, ductility and toughness by means of the appropriate combination of the strain-induced martensitic transformation (SIMT) behavior and the deformation behavior of each phase at crystal scale. In the past, the effect of grain size in the austenite on the deformation behavior of TRIP steel is investigated by introducing the grain size into a generalized model for the kinetics of SIMT. In order to validate the size-dependent kinetics modelling, it is necessary to simulate the deformation and SIMT behavior of the polycrystalline for the different grain size at the crystal scale. This study focuses on an investigation of SIMT behavior in polycrystalline TRIP steel by finite element simulation. The constitutive formula for monocrystalline TRIP steel including transformation strain in each variant system derived on the basis of the continuum crystal plasticity theory is applied. For the polycrystalline model, Voronoi tessellation is employed. The deformation behavior with a patterning process of martensitic phase in two different numbers of grains with initial crystal orientations for describing the deformation-related length scale is simulated under plane strain condition with two planar slip systems by a cellular automata approach.

Abstract: One of the basic collective behaviors of swarm robotic systems is flocking, which has been actively studied for more than a decade and mimics a natural phenomenon where a group of animals move together as a single entity. In flocking, each robot in the flock tries to adjust its velocity and align with other robots in the flock while maintaining a predetermined pattern (formation) and avoiding collisions with obstacle and other members of the flock. This paper presents an up-to-date review on the characteristics of flocking problems and tasks, as well as solution approaches to flocking problems. We have addressed flock characteristics from the formation type, robustness, leader-follower, information, and communication aspects. Also, various flocking tasks of exploration, motion planning and navigation, shepherding, covering, object transportation, and simultaneous object collection and shepherding are investigated. Also, a new categorization of approaches to flocking is presented, which contains Leader-Follower, Behavior-based, Control-based, Fault-Tolerant, and Hybrid approaches. Finally, a comparative table on the characteristics of flocking problems appeared in various works of the literature is presented.

Abstract: Patterned silicon oxide films were formed by a simple process using a dimethyl-silicone-oil as source and inks as patterning masks.After the coating of the ink, the dimethyl-silicone-oil was coated onto the substrate. The sample was heated at 150oC and ozone gas was irradiated. After the heat treatment with ozone gas, patterned silicon film was formed. The circle pattern with a diameter of 20 μm wassuccessfully formed.After the formation of the patterned silicon oxide film, the silicon oxide was hardly observed at the position where the ink coated.

Abstract: The elastic buckling of a biaxially pre-tensioned soft elastic film in proximity to a rigid contactor was studied. By a linear analysis, it was shown that the critical mode of buckling depended on the two in-plane principal stretches in the respective tensile directions, and the threshold of buckling only depended on the product of two principal stretches. Such a regular effect of pre-tension may be applied in the field of the generation of the precise surface patterns.

Abstract: The surface instability of trilayer films consisting of a fluid layer sandwiched in between the two thin elastomer capping layers was studied. The solid-liquid-solid sandwiched films will form well-defined periodic surface buckling spontaneously. In the present study, the flow of the sandwiched liquid layer was approximated by the theory of lubrication. The elastic capping films was modeled with the nonlinear theory of a thin plate. A linear stability analysis identified the growth rate and the critical wave number of the surface undulation of trilayer films. The analysis showed that applied deformation in the capping layers regulated the surface buckling and resulted in well-defined periodic surface corrugation with tunable wavelength. The result of this study may provide a mechanism to control the morphology of the films in a mechanical way.

Abstract: Interdiffusion in Zn/InSb system has been investigated under high (0.59×10⁶ G) and low (1 G) gravity conditions at 673, 593 and 573K, respectively. Samples annealed at 0.59×10⁶ G, 673K for 60 hours, indicated the formation of a periodic reaction layer structure. Since such structures can be formed in solid state reactions of ternary systems [, the effect of high gravitational field and high hydrostatic pressure (approximately 3kbar) in the formation of periodic patterns was investigated. Systematic investigations at ambient pressure and low gravitational field were carried out at 593 and 573 K in sandwich geometry. SEM and EDX analysis had shown that there are different phases between the initial components. Starting from the Zn side of the specimen there is a very thin single-phase with high (about 90%) In content. Next to it is a thin two-phase layer, containing mainly 50-50% InSb and some elongated Zn particles and then there is a thick phase with the composition of Zn₅In₂Sb₄ which is followed by a similar two-phase mixture (InSb+Zn) similar to the Zn side of the sample. Although the diffusion zone is not a well developed periodic structure, but every layer (clearly distinguishable form the others and was either a single-or multiphase layer) grows with the time.

Abstract: Despite the tremendous success of phase-field (PF) modelling in predicting many of the experimentally observed microstructures in solids, additional progress is required in order to apply it to predict microstructure evolution in real alloy systems. One way to achieve this is to couple thermodynamic and kinetic databases with PF model. In this work, we present phase-field simulations of spinodal decomposition in Fe-Cr alloy during thermal ageing and anisothermal heating. In the PF method, the local free energy is directly constructed using the CALPHAD method. During isothermal ageing, the morphology of decomposed phases consisted in an interconnected irregular shape for short ageing times, and a further ageing caused the change to a droplet like shape of the decomposed Cr-rich phase. The influence of heating rate on phase transformations is then simulated and compared with experimental results obtained by differential thermal analysis, carried out with heating rates in the range 0.5 °C.min^-1 to 15 °C.min^-1. The simulation results show that heating rate strongly influences the microstructure morphology.

Abstract: Coal floor water inrush is the reason that the deformation and failure of rock strata in floor is induced by mining stress, cracks gradually develop, grow and accumulate, catastrophe result in forming water inrush passages, finally floor water inrush occurs. Interactions of adjacent damage element and long range correlation in coal floor are simulated by pattern dynamics. The evolution process of floor cracks is simulated by the change of element state, and some criteria are given to judge if the floor will fracture with the change of element state. The obvious characteristics of evolution process of floor cracks are progressive, and cracks make order-disorder distribution at different scales that evolve into order distribution, and finally form water inrush passages.

Abstract: In this paper we present an extension of a mathematical model for the morphological evolution of metal electrodeposits – recently developed by some of the authors – accounting for mass-transport of electroactive species from the bulk of the bath to the cathode surface. The implementation of mass-transport effects is specially necessary for the quantitative rationalisation of electrodeposition processes from ionic liquids, since these electrolytes exhibit a viscosity that is notably higher than that of cognate aqueous solutions and consequently mass-transport control is active at all practically relevant plating rates. In this work we show that, if mass-transport is coupled to cathodic adsorption of ionic liquid species and surface diffusion of adatoms, it can lead to electrodeposit smoothing. This seemingly paradoxical theoretical result has been validated by a series of Mn electrodeposition experiments from aqueous baths and eutectic ionic liquids. The latter solutions have been shown to be able to form remarkably smoother coatings than the former ones. Mn electroplates have been proposed for Cd replacement and their corrosion protection performance seems comparable, but so far the required surface finish quality has not been achieved with aqueous electrolytes. Ionic liquids thus seem to provide a viable approach to aeronautic-grade Mn electroplating.