Papers by Keyword: Materials Processing

Abstract: Serious defects in the continuous casting of steel, including surface cracks and depressions, are often related to thermal mechanical behavior during solidification in the mold. A finite-element model has been developed to simulate the temperature, shape, and stress of the steel shell, as it moves down the mold in a state of generalized plane strain at the casting speed. The thermal model simulates transient heat transfer in the solidifying steel and between the shell and mold wall. The thermal model is coupled with a stress model that features temperature-, composition-, and phase dependent elastic-visco-plastic constitutive behavior of the steel, accounting for liquid, δ-ferrite, and γ-austenite behavior. Depressions are predicted to form when the shell is subjected to either excessive compression or tension, but the shapes, severity, and appearance differ with conditions. Cracks appearing without depressions are suggested to form in the lower ductility trough when the shell is colder but more brittle. The local thickness of the shell and austenite layer appears to have major effects as well. The model reveals new insights into the formation mechanisms and behavior of surface depressions and longitudinal cracks in the continuous casting process.

Abstract: . In order to fulfill the clinical requirements for strong, tough and stable ceramics for dental applications, we have designed and developed innovative Ceria-stabilized zirconia (Ce-TZP)-based composites. In particular, we have added two kinds of second phases to the Ce-TZP matrix: equiaxed a-Al₂O₃ grains, for increasing the hardness and the fracture strength, and elongated hexa-aluminates (both SrAl₁₂O₁₉ and CeMgAl₁₁O₁₉), to provide an additional toughening effect by crack deflection/bridging mechanisms. In order to carefully control the composition and the microstructure in those complex composite systems, we have used a novel surface-coating approach for the preparation of the nanostructured composite powders, which allows a perfect tailoring of the microstructural, morphological and compositional features of the composites. Once optimized the sintering cycle for each composite material, both composites reached full densification. Mechanical properties (Vickers hardness, flexural strength and fracture toughness) were evaluated, while the zirconia transformability was followed by means of an optical microscope during load-unload bending tests. The sensitivity to ageing was estimated by autoclave treatments. In spite of a remarkable different behavior – mainly in terms of stress-induced tetragonal to monoclinic zirconia transformability - both materials showed excellent mechanical properties as well as a negligible sensitivity to ageing, thus demonstrating their high potential for new reliable and safe devices for structural biomedical applications.

Abstract: The thickness of the plastic film is an important physical index to the production of plastic. The measurement reslut relates directly to the companies’ economic benefit. This paper mainly introduces the digital signal processing in the detection system of film thickness. Through a perfect processing, the system can improve its SNR and finally get a high precision. Firstly, the principle and scheme was presented. After that, this paper mainly introduces the hardware implementation of the system. It includes analog filter circuit, AD sampling and digital filter. With the experimental verification, the system realizes the measurement of the film thickness on-line which can get the precision of micrometer. At present, the equipment has aready put into use by some companies.

Abstract: In all process based in powder and in particular in the rotational moulding process, the major physical phenomenon during the flow of the powders is the sintering and grains growth. The sintering is the formation of only one particle starting from two or many particles under the effect of the temperature and the forces of surface tension. We interest in this study in particular at the mechanism of Polyvinylidene fluoride (PVDF) sintering. The results of this study can enable us to maximize our knowledge about sintering mechanism and enable us to determine parameters such as the speed of sintering for the optimization of the process.

Abstract: Microwave heating was discovered more than 60 years ago. And nowadays, it became popular for the use as domestic ovens. Microwave has also been utilized for the industrial processes, such as drying and roasting. On the other hand, there have been many applications of microwave, being investigated for materials' processing and environmental technologies. They are attempted to take advantage of some specific characteristics in microwave heating, which differs from that of the conventional one. Rapid heating, internal heating, selective heating are the features to be taken into consideration. Moreover, so-called "non-thermal effect" is the additional feature in which researchers are particularly interested. In this article, it is intended to describe fundamental aspects in microwave heating and introduce some selected topics of research projects performed in our research group. They include researches on fabrication of some functional materials and on handling industrial wastes etc. In this article, it is also intended to interpret the phenomena observed in these applications from the fundamental view points of electromagnetic wave interaction with materials.

Abstract: Through introduction of the principle and characteristics of electron beam machining technology, the application status and application instance of electron beam in research of materials science and materials processing in recent years were introduced in detail. The research situation of the previous various electron beam machining methods and applications was discussed, and the various research results were analyzed, thus concluded that the emphasis and advantages of the electron beam machining technology in the application of various materials.

Abstract: Microwave heating represents a modern technique to sintering the composites materials. The microwaves absorbance property of the materials is depending by the electrical permittivity of the materials. Researchers showed that the ceramic materials are suitable for sintering using microwave heating. The most important advantage of that sintering procedure is the reduced sintering time and temperatures. However, during the heating process these properties are changing and a pattern of the heating process cannot be established. The penetration depth of microwaves into materials depends on the electrical properties of them, and gives rise to a heat source. The electromagnetic wave absorption is responsible for the macro and micro structural changes in the materials morphology, and consequently for their electrical properties. Thermal runaway is one phenomenon which should be avoided during the microwave processing of the materials. The microwave heating consists in direct introduction of the energy in the volume of the material. If the absorbance properties of the material are increasing with temperature, than a critical phenomenon, called thermal runaway, appears during the heating process. This paper aims to study the thermal runaway of the BaCO₃ + Fe₂O₃ homogenous mixture and mechanical alloy in a mono-mode applicator, when the heat source is a microwave generator at 2,45 Ghz. A special mono-mode chamber has been designed with dimensions 140 x 140 x 70 mm and an active system for rotating the samples, in order to record the values of the temperature and to assure a uniform exposure of the samples to the high frequency electromagnetic field. The materials used in experiments were homogenous mixture of BaCO₃ + Fe₂O₃ which have been milled in a planetary ball mill for 5 and 20 hours. The experimental procedure consists in establishing the levels of the temperatures during the microwave heating process when the thermal runaway appears. These experiments have been done for fixed levels of microwave injected power from 0 1250 W. Numerical simulation for different heating conditions (microwave power, heating time, position of the samples inside the chamber) has been performed in order to elaborate a predictable mathematical model for continuous microwave heating and avoiding the thermal runaway of the homogenous mixture.

Abstract: Surface flexible rolling method, using two integral working rolls as the forming tool, can achieve fast, flexible and continuous manufacturing of three-dimensional sheet metal parts. This paper introduces the basic principle of surface flexible rolling and discusses the numerical simulation results when the working rolls are bended as circular arcs. The stability indicates the forming effect to some extent and the flow type of the metal can be deduced from stability analysis. To integrate and analyze the simulation results by means of reverse engineering. The analysis results show that the forming process is stable and the effect of surface flexible rolling is fine. It also indicates that inhomogeneous deformation and accumulation occurs during the process. The numerical simulation and experimental results demonstrate that the surface flexible rolling is a feasible and effective way to form three-dimensional sheet metal parts.

Abstract: A strong gravitational field causes the changes in composition and structure through sedimentation or displacement of atoms in multi-component condensed matter. We have developed a high-temperature ultracentrifuge to generate a strong acceleration field of even over 1 million (1x10⁶) G, and, for the first time succeeded in realizing the sedimentation of the constitutive solute atoms and aeven isotope atoms in solids or liquids. The changes in composition and crystalline state of various alloys, polymers, and other substances have been investigated. Recently, we started the experiments on compounds and semiconductors with the aims of new materials synthesis and semiconductor control. The chemical reaction, crystal structure change have been found for metallic compound (Bi₃Pb₇), or covalent compounds (Y₁Ba₂Cu₃O_7-x, TiO₂, etc.). The impurity control was also examined in semiconductor. In this article, the recent progress and the future prospects for materials processing are described.

Abstract: The internal flow and level fluctuation of liquid metal exposed to linear electromagnetic stirring are mainly induced by the electromagnetic force. As a result, it is necessary to estimate the electromagnetic force amplitude generated by electromagnetic stirrers. The Maxwell's equations were simplified on some reasonable assumption so as to estimate the electromagnetic force amplitude in this study. During the electromagnetic force analysis, the characters of the electromagnetic force in liquid metal exposed to a linear electromagnetic stirrer were determined at the same time.