Wear of hardfacing white cast irons by solid particle erosion

The response of three commercial weld-hardfacing alloys to erosive wear has been studied. These were high chromium white cast irons, deposited by an open-arc welding process, widely used in the mineral processing and steelmaking industries for wear protection. Erosion tests were carried out with quartz sand, silicon carbide grit and blast furnace sinter of two different sizes, at a velocity of 40 m s-1 and at impact angles in the range 20° to 90°. A monolithic white cast iron and mild steel were also tested for comparison. Little differences were found in the wear rates when silica sand or silicon carbide grit was used as the erodent. Significant differences were found, however, in the rankings of the materials. Susceptibility to fracture of the carbide particles in the white cast irons played an important role in the behaviour of the white cast irons. Sinter particles were unable to cause gross fracture of the carbides and so those materials with a high volume fraction of carbides showed the greatest resistance to erosive wear. Silica and silicon carbide were capable of causing fracture of the primary carbides. Concentration of plastic strain in the matrix then led to a high wear rate for the matrix. At normal impact with silica or silicon carbide erodents mild steel showed a greater resistance to erosive wear than these alloys. © 1995.

The elastic-plastic indentation response of a columnar thermal barrier coating

Thermal barrier coatings with a columnar microstructure are prone to erosion damage by a mechanism of surface cracking upon impact by small foreign particles. In order to explore this erosion mechanism, the elastic indentation and the elastic-plastic indentation responses of a columnar thermal barrier coating to a spherical indenter were determined by the finite element method and by analytical models. It was shown that the indentation response is intermediate between that of a homogeneous half-space and that given by an elastic-plastic mattress model (with the columns behaving as independent non-linear springs). The sensitivity of the indentation behaviour to geometry and to the material parameters was explored: the diameter of the columns, the gap width between columns, the coefficient of Coulomb friction between columns and the layer height of the thermal barrier coating. The calculations revealed that the level of induced tensile stress is sufficient to lead to cracking of the columns at a depth of about the column radius. It was also demonstrated that the underlying soft bond coat can undergo plastic indentation when the coating comprises parallel columns, but this is less likely for the more realistic case of a random arrangement of tapered columns. © 2009 Elsevier B.V.

Characterisation and simulation of asphalt road surfaces

Accurate simulation of rolling-tyre vibrations, and the associated noise, requires knowledge of road-surface topology. Full scans of the surface types in common use are, however, not widely available, and are likely to remain so. Ways of producing simulated surfaces from incomplete starting information are thus needed. In this paper, a simulation methodology based solely on line measurements is developed, and validated against a full two-dimensional height map of a real asphalt surface. First the tribological characteristics-asperity height, curvature and nearest-neighbour distributions-of the real surface are analysed. It is then shown that a standard simulation technique, which matches the (isotropic) spectrum and the probability distribution of the height measurements, is unable to reproduce these characteristics satisfactorily. A modification, whereby the inherent granularity of the surface is enforced at the initialisation stage, is introduced, and found to produce simulations whose tribological characteristics are in excellent agreement with the measurements. This method will thus make high-fidelity tyre-vibration calculations feasible for researchers with access to line-scan data only. In addition, the approach to surface tribological characterisation set out here provides a template for efficient cataloguing of road textures, as long as the resulting information can subsequently be used to produce sample realisations. A third simulation algorithm, which successfully addresses this requirement, is therefore also presented. © 2011 Elsevier B.V.

SRY基因进化的研究现状

国家自然科学基金重点项目及中国科学院重大项目资助。

Colourless adaptively modulated optical OFDM transmitters using SOAs as intensity modulators.

The wavelength dependent transmission performance of adaptively modulated optical OFDM (AMOOFDM) signals is investigated, for the first time, over optical amplification- and chromatic dispersion compensation-free IMDD SMF systems using semiconductor optical amplifiers (SOAs) as intensity modulators. A theoretical SOA model describing both optical gain saturation and gain spectral dynamics is developed, based on which optimum SOA operating conditions are identified for various wavelengths varying in a broad range of 1510 nm- 1590 nm. Results show that, SOA intensity modulators operating at the identified optimum conditions enable the realization of colourless AMOOFDM transmitters within the aforementioned wavelength window. Such transmitters are capable of supporting >30 Gb/s signal transmission over 60 km SMFs.

Effect of bend orientation on life and puncture point location due to solid particle erosion of a high concentration flow in pneumatic conveyors

An investigation into predicting failure of pneumatic conveyor pipe bends due to hard solid particle impact erosion has been carried out on an industrial scale test rig. The bend puncture point locations may vary with many factors. However, bend orientation was suspected of being a main factor due to the biased particle distribution pattern of a high concentration flow. In this paper, puncture point locations have been studied with different pipe bend orientations and geometry (a solids loading ratio of 10 being used for the high concentration flow). Test results confirmed that the puncture point location is indeed most significantly influenced by the bend orientation (especially for a high concentration flow) due to the biased particle distribution and biased particle flux distribution. © 2004 Elsevier B.V. All rights reserved.