Particle distribution and interfacial reactions of Al–7%Si–10%B<Subscript>4</Subscript>C die casting composite

Aluminum–boron carbide particle reinforced composite is an advanced material which can be used in applications such as neutron-shielding components, aircraft, and aerospace structures. In the microstructural characterization of an Al–7%Si–10%B₄C die casting, attention is particularly focused on particle distribution and interface reaction products between B₄C particles and the aluminum matrix. The quantitative analysis results show that, in a cross-section of the cast part, more particles concentrate in the center and fewer particles are present in the wall regions. Moreover, some particle segregation bands have been observed. The mechanisms of the particle migration are proposed to describe the phenomenon. However, the average particle fraction in any cross-section of the cast part is almost the same. A barrier layer consisting of several sublayers was detected on the surface of B₄C particles. Using electron diffraction in selected areas, it is found that these sublayers are composed of Al₃BC crystals, TiB₂ crystals, Si crystals, and coarse stick-shaped TiB₂ particles. In addition, it is observed that Si plays an important role in the formation of a dense barrier layer. The barrier layer can limit B₄C decomposition and improve B₄C stability in the aluminum melt.     

Composite group vector space method for estimating melting and boiling point of pure organic compound

Composition Group Vector Space (CGVS) method for estimating melting and boiling point T _m , T _b of organic compound has been proposed, and the principle of this method has been elucidated. The models for estimating T _m , T _b have been established and the numerical values of relative parameters have been presented. The average percentage deviations of T _m , T _b estimation are 7.53 and 1.58, respectively, which show that the present method demonstrates significant improvement in applicability to predict the above properties, compared to conventional group methods.     

A Simple Quasi-2D Numerical Model of a Thermogage Furnace

A simple quasi-2D model for the temperature distribution in a graphite tube furnace is presented. The model is used to estimate the temperature gradients in the furnace at temperatures above which contact sensors can be used, and to assist in the redesign of the furnace heater element to improve the temperature gradients. The Thermogage graphite tube furnace is commonly used in many NMIs as a blackbody source for radiation thermometer calibration and as a spectral irradiance standard. Although the design is robust, easy to operate and can change temperature rapidly, it is limited by its effective emissivity of typically 99.5–99.8%. At NMIA, the temperature gradient along the tube is assessed using thermocouples up to about 1,500°C, and the blackbody emissivity is calculated from this. However, at higher operating temperatures (up to 2,900°C), it is impractical to measure the gradient, and we propose to numerically model the temperature distributions used to calculate emissivity. In another paper at this conference, the model is used to design an optimized heater tube with improved temperature gradients. In the model presented here, the 2-D temperature distribution is simplified to separate the axial and radial temperature distributions within the heater tube and the surrounding insulation. Literature data for the temperature dependence of the electrical and thermal conductivities of the graphite tube were coupled to models for the thermal conductivity of the felt insulation, particularly including the effects of allowing for a gas mixture in the insulation. Experimental measurements of the temperature profile up to 1,500°C and radial heat fluxes up to 2,200°C were compared to the theoretical predictions of the model and good agreement was obtained.     

Ontologies and reasoning techniques for (legal) intelligent information retrieval systems

An application of Narrative Knowledge Representation Language (NKRL) techniques on (declassified) ‘terrorism in Southern Philippines’ documents has been carried out in the context of the IST Parmenides project. This paper describes some aspects of this work: it is our belief, in fact, that the Knowledge Representation techniques and the Intelligent Information Retrieval tools used in this experiment can be of some interest also in an ‘Ontological Modelling of Legal Events and Legal Reasoning’ context.     

An anti-plane crack perpendicular to the weak/micro-discontinuous interface in a bi-FGM structure with exponential and linear non-homogeneities

Treated was an anti-plane crack perpendicular to the interface of an exponential-type FGM strip bonded to another linear-type FGM substrate with infinite thickness. Through Fourier integral transform, the problem was reduced as a Cauchy singular integral equation, which was further solved numerically by the Lobatto–Chebyshev collocation method. Based on the numerical solution, the effects of the geometrical and physical parameters on the stress intensity factor (SIF) were analyzed and the following conclusions were obtained: (a) A notable discrepancy between the interface-perpendicular crack and the interfacial one is that, to reduce the weak-discontinuity of interface or to make the interface micro-discontinuous will not necessarily decrease the SIF of the former, but will surely decrease that of the latter. (b) When a crack tip is situated very near to the interface (or free surface), its SIF will be high and totally dominated by the interface (or free surface). (c) To increase the stiffness of the FGM on one side of the interface is beneficial to preventing the crack on the other side from growing toward the interface. Besides, some practical suggestions were further given for material design in the field of composites.     

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