Flow patterns and re-melting during filling of a large composite casting

Abstract

The filling and remelting of an industrial scale composite casting has been simulated to investigate the effect of fluid flow patterns in the liquid metal on the remelting of the shell material of the composite casting. In the composite casting under investigation, an outer shell material is first cast inside a large cylindrical mould, which is then assembled to additional mould parts, and the core material is poured into the shell/mould assembly. During casting of the core, a thin layer of the shell material re-melts and mixes with the core material producing a bonding layer of intermediate composition. Obtaining the optimum re-melting and thus intermediate bonding zone between the shell and core is critical to producing high quality rolls. The present numerical model employs the volume of fluid method and an enthalpy-porosity technique to couple the filling of the core material and re-melting of the shell material. The interface between the solid and liquid phases is tracked and can be used as a guide to examine the extent of remelting and, to some degree, mixing of the shell and core material. Simulations have shown that the circulation loops that form in the liquid metal pool significantly affect the amount of shell material that remelts.     

Oxidation of γ-TiAl Intermetallic Coated with Electrodeposited Nickel-La2O3 Composite Films

A coating of nickel withLa₂O₃ particles waselectrodeposited on the surface of -TiAl toimprove its high-temperature oxidation resistance. Theexperimental results showed that contrary to theoxidation of bare specimens, the electrodepositedNi-La₂O₃ composite-coated onesexhibited much better resistance to both isothermal andcyclic oxidation in air at 1000 and 900°C. For theoxidation of the Ni-La₂O₃ composite-coated -TiAl EPMA/EDX microanalyses revealed that after the composite film had beenthoroughly oxidized, a La₂O₃-richNiO layer close to the gas-scale interface and twoalumina-rich layers, with one beneath the NiO layer and the otheradjacent to the -TiAl matrix, were produced inthe scale. The results indicated that the preferentiallyformed La₂O₃-doped NiO layerretarded the growth of rutile and favored the formation of twoalumina-rich layers. The mechanism of the effect of theelectrodeposited Ni-La₂O₃composite on the oxidation behavior of -TiAl isdiscussed in detail.     

SOLUTION OF DIFFERENT HOLES SHAPE BORDERS OF FIBRE REINFORCED COMPOSITE PLATES BY INTEGRAL EQUATIONS

Accurate boundary conditions of composite material plates with different holes are founded to settle boundary condition problems of complex holes by conformal mapping method upon the nonhomogeneous anisotropic elastic and complex function theory. And then the two stress functions required were founded on Cauchy integral by boundary conditions. The final stress distributions of opening structure and the analytical solution on composite material plate with rectangle hole and wing manholes were achieved. The influences on hole-edge stress concentration factors are discussed under different loads and fiber direction cases, and then contrast calculates are carried through FEM.     

26—THE FLOW OF LIQUID FROM A JET THROUGH A COMPRESSIBLE POROUS LAYER. PART I: ANALYSIS OF METHODS OF APPLYING A LIQUID TO FLOW THROUGH A POROUS LAYER

The volumetric rates of flow of a fluid through holes and porous layers when a uniform fluid pressure is applied are compared. An analysis is made of the comparative rates of flow of fluid through holes and porous layers when the application is by uniform pressure and by jets. It is shown that the fluid pressure near a hole located in a porous layer is less than the over-all applied pressure and that this accounts for less flow through the layer near the hole than occurs when the fluid is applied by a jet.     

The Specific Heat of Hygroscopic Textiles

A comparison between the qualities of open-end- and ring-spun yarns produced from Egyptian cottons is reported. Yarns of different counts and twist factors were produced on both the BD 200 open-end-spinning machine and a conventional ring-spinning machine, and their quality was studied by determining their strength, uniformity, and number of imperfections. The quality of open-end-spun yarn relative to that of ring-spun yarn is expressed in terms of the relative quality factor.

It is shown that the percentage reduction in strength of open-end-spun yarns compared with that of ring-spun yarns can be minimized by spinning them to coarser counts from shorter cottons. This is attributed to the different interactions between the fibre properties and the mechanism of yarn formation when different types of cotton are used.

It is also shown that the relative quality of open-end-spun yarns can be considerably increased by spinning them to coarser counts from Ashmouni cotton. The quality of open-end-spun yarn can exceed that of ring-spun yarn when Ashmouni cotton is spun to a linear density exceeding 30 tex.

It is concluded that the BD 200 open-end-spinning machine cannot be recommended for spinning fine yarns from long-staple Egyptian cottons.     

Microstructural study of super Ni laminated composite/1Cr18Ni9Ti steel dissimilar welded joint

Abstract

Super Ni laminated composite and 1Cr18Ni9Ti stainless steel were welded by the tungsten inert gas process with the Cr25–Ni13 filler alloy. The microstructure, element distribution and phase formation near the fusion zone were evaluated by standard technique. Results indicated the formation of four main regions: the fusion transition region on the 1Cr18Ni9Ti steel side, the fusion transition region on the super Ni laminated composite side, a columnar crystal weld region and the weld centre region. The microstructure on either side of the weld was characterized by strong directionality and changed from columnar austenite to equiaxed austenite in the weld centre. A Ni, Fe and Cr element transition region, about 30 μm wide, was formed at the fusion zone on the super Ni side. The phase formed into welded zone was composed mainly of austenite, δ-Fe, γ-Ni(Cr, Fe) and FeNi intermetallic compounds.     

Effects of SnO on growth and physical properties of BSCCO whiskers

Abstract

Superconductor whiskers doped with SnO have been fabricated by annealing a melt quenched (Bi₂Sn₁)-223 precursor using suitable heat treatment cycles. Approximately 5 μm thick, 90 μm wide and 5 mm long whiskers were fabricated, and their physical, electrical and magnetic properties were investigated. Crystallisation activation energies of glass phase fabricated were calculated to be 390 kJ mol^–1 using Kissinger method based on the differential thermal analysis data. The T _c value of the whiskers was found to be 94 K from M–T measurement. The magnetisation of whiskers before superconducting transition increased with decreasing temperature, and after superconducting transition, the magnetisation of whiskers decreased, from positive to negative, due to the diamagnetic nature of superconductivity. The change on magnetisation dependence of applied magnetic fields (M–H) showed that whiskers have paramagnetic–diamagnetic multiphase structure.     

Thermal properties of paraffin/graphite composite phase change materials in battery thermal management system

Abstract

The thermal properties of paraffin/graphite composite phase change materials for power nickel metal hydride batteries were experimentally investigated. Two different modes for heat dissipation were designed in this experimental study: air cooling and cooling with phase change materials. Paraffin/graphite composite phase change thermal energy storage materials were prepared and tested by differential scanning calorimetry. It appeared that the battery thermal management system with phase change materials had better performance than air cooling, especially when the scale of paraffin/graphite composite material approximates 4:1.     

A review of materials degradation in utility scale wind turbines

Abstract

This paper presents a comprehensive review of the state of knowledge of materials used in the major wind turbine components of both land based and offshore wind turbines. The paper is divided into the following seven major sections: utility scale wind turbine design overview; current state of wind turbine technology; review of degradation of materials used in wind turbines; a summary of materials degradation service experience; condition monitoring overview; review of materials based research and development for wind turbines; a summary of missing knowledge and future materials challenges. The review points out that the most important degradation mechanism is fatigue which limits the life, reliability and performance of current wind turbines. As even larger machines are built in the future, with pressures to cut weight and cost, continued materials research and development, as summarised in this paper, is warranted. This critical assessment and review of materials based degradation should be of interest to a wide range of technical energy specialists including those from manufacturers, research and development centres, end users (i.e. electric power generation companies) and financiers and insurers.     

Key experimental parameters in steam oxidation testing and their impact on interpretation of experimental results

Abstract

The acceptance of materials for extended duration, safety critical power generation applications usually requires several stages of testing and data generation. Simple, short term exposures under nominally constant atmospheres and temperatures can eliminate materials that are grossly unsuitable, but do not differentiate between materials that have broadly acceptable properties. To better differentiate between candidate materials it is desirable to tailor laboratory tests such that they more closely replicate in service conditions. In terms of components that are exposed to steam oxidation degradation mechanisms, this means replicating the steam conditions with an aim of producing oxide scale morphologies similar to that seen in service. Key experimental parameters have been identified, including water chemistry, pressure, steam delivery and flowrate, and a series of steam exposure tests on ferritic (P92), austenitic (Esshete 1250) and superalloy (IN740) material conducted to evaluate their effect on degradation rate and oxide scale morphology. The oxidation rate of the austenitic, and to a lesser extent the ferritic, material was found to be sensitive to the level of dissolved oxygen in the feed water, low (10 ppb) dissolved oxygen levels producing an increase in oxidation rate. The propensity to spall was also found to be reduced at low dissolved oxygen concentrations. In addition, the steam pressure and steam delivery method were shown to affect the oxidation rate and scale morphology for these materials.