Yat Choy Wong

Effect of magnetic cluster and magnetic field on polishing using magnetic compound fluid (MCF)

Using the magnetic compound fluid (MCF) developed by one of the authors in this paper, we performed polishing under various intensities of steady and fluctuating magnetic fields. We determined the optimal intensity of both types of magnetic field in order to produce the most effective polishing effect. The optimal intensity is related to the produced magnetic clusters in the MCF.

Hydrodynamic profiling and grit blasting of low-carbon steel surfaces

Abstract The surface preparation by hydrodynamic profiling and grit blasting of low-carbon steel specimens is investigated. Roughness measurements and SEM imaging show that hydrodynamic profiling forms a surface profile with a high roughness and without surface contamination. In contrast, grit-blasted specimens show grit residues embedded in the substrate surface. The debris collected after hydrodynamic profiling show a rounded shape suggesting that the material is removed due to low-cycle fatigue. The debris produced by grit blasting appear in the shape of platelets and flow-type chips suggesting a mixture of micro-cutting and forging–extrusion. The influence of stand-off distance, exposure time, and flow speed on the profiling process are also studied. The results identified the optimum operational conditions for hydrodynamic profiling. Fatigue by impacting fluid drops is suggested to be the dominant material failure mode. However, results of a comparative calculation of the incubation drop impact frequency suggests that fatigue is accompanied by energy-dissipative processes.

A review on porous negative electrodes for high performance lithium-ion batteries

Today’s lithium(Li)-ion batteries (LIBs) have been widely adopted as the power of choice for small electronic devices through to large power systems such as hybrid electric vehicles (HEVs) or electric vehicles (EVs). However, it falls short of meeting the demands of new markets in the area of EVS or HEVs due to insufficient energy density, poor rate capability, and low cyclic life. Introduction of porous electrode materials represents one of the most attractive strategies to dramatically enhance battery performance such as capacity, rate capability, cycling life, and safety. In this paper, the applications of porous negative electrodes for rechargeable lithium-ion batteries and properties of porous structure have been reviewed. Porous carbon with other anode materials and metal oxide’s reaction mechanisms also have been elaborated. The purpose of this review is to give a broad overview of the recent scientific researches and developments of porous negative electrodes and indicate future trends in anode development of porous materials as a replacement for graphite in LIBs.

Overblasting effects on surface properties of low-carbon steel

The influence of overblasting on surface properties of low-carbon steel was investigated. In detail, surface roughness, contact angle, Vickers-hardness, degree of surface contamination, and pull-off strength were evaluated. It was shown that overblasting had notable effects on the surface properties. Most importantly, the surface roughness was significantly reduced, and the microhardness of the substrate increased. Also, overblasting increased surface wettability. The influence on the pull-off strength of applied coating systems was only marginal.

Experimental investigation of the effect of the MPL (magnetic polishing liquid) on surface finishing

We investigated the polishing effect of magnetic polishing liquid (MPL) made of abrasive particles and a newly developed magnetic responsive fluid, magnetic compound fluid (MCF) as intelligent or smart fluid. By applying steady and fluctuating magnetic fields, we investigated the polishing effects of the magnetic fields, varying the kinds of polishing material and the components of the MPL. In order to explain the cause of the experimental results, we investigated the apparent viscosity of the MCF and MPL, and used microscopic to investigate behavior of the particles in the MCF and MPL. We clarified the mechanisms governing the polishing effects through the use of a model based on the observation of the particles.

Optimising parameters for meaningful measurement of residual strain by neutron diffraction in self-pierce riveted joints

Abstract The aim of this work is to examine the uncertainties involved in measuring residual strain and their dependence on both the gauge volume of the neutron beam and the acquisition time in self-pierce riveted (SPR) joints while using the neutron diffraction technique. The main challenge involved dealing with the very small dimensions of SPR joints and developing optimum instrument configuration that allowed faster and/or more accurate stress measurement in SPR while maintaining the same time resolution required for the millimetre scale of the problem. Two different gauge volumes were used (0·125 and 1·0 mm3), and two different measuring directions were chosen in order to examine the rotational accuracy of the sample table. All measurements were conducted in steel‐steel joints. Even though small sizes were involved, meaningful results were obtained and measurement errors were reduced by optimising the instrument parameters.

Residual stress profiles in riveted joints of steel sheets

Abstract The residual stress profiles in two different self-piercing riveted (SPR) joints were characterised using the neutron diffraction technique. The joints were produced using semi-tubular steel rivets and carbon steel sheets of different thicknesses and hardnesses. The residual stress in the sheet material inside the bore of the rivet was compressive at the centre and the stress became tensile away from the centre. The stresses found in the semi-tubular rivet were compressive, with a lower magnitude in the rivet head compared with those in the rivet leg. For the SPR joints examined, the compressive residual stress in the rivet leg was greater for the thin joint than the thick joint, and this was due to the higher force gradient encountered during the rivet flaring stage. The originality of this work was to relate the residual stress profile to the physical event that occurred during the SPR process.

Evaluation of Residual Stress in SPR Joint by Neutron Diffraction

The feasibility of measuring residual stresses in Self-Pierce Riveted (SPR) joints by neutron diffraction was evaluated in this study. Despite the small dimensions involved, meaningful results were obtained. It was observed that residual stress in the rivet head was higher in the centre and lower at the edge. For the SPR joints examined, the maximum value of residual stress evaluated was 550MPa, compressive and occurred in the rivet leg. Stresses in material adjacent to the rivet wall and at a distance of three times the rivet radius from the rivet axis were not significant. The results are discussed with respect to the physical events involved during SPR.

The role of metallurgical solid state phase transformations on the formation of residual stress in laser cladding and heating

There are two major types of solid state phase transformations in metallic materials; the formation of second phase particles during heat treatments, and the transformation of the matrix from one crystalline packing arrangement to another during either heating or cooling. These transformations change the spacing between adjacent atoms and can thus influence the residual stress levels formed. The heating and cooling cycles of materials processing operations using lasers such as cladding and melting/heating, can induce phase transformations depending on the character of the material being processed. This paper compares the effects of the different phase transformations and also the influence of the type of laser processing on the final residual stress formed. The comparisons are made between laser clad AA7075, laser clad Ti-6Al-4V and laser melted nickel-aluminium bronze using neutron diffraction and the contour method of measuring residual stress.

Effect of Joining Process on the Coatings of Self-Piercing Rivets

In this study, effects of laser assisted self-pierce riveting (LSPR) as a mechanical joining technique were investigated on the coatings of self- piercing rivets. Zn-Sn and Al plated rivets were used to join magnesium sheets by LSPR. Microstructure, surface topography and roughness of the rivet’s coatings were characterized by optical microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and surface profilometry. A comparison of results before and after joining process showed that under joining conditions, Zn-Sn coating was deformed during riveting process and its thickness and microstructure varied along the rivet shank, while Al coating remained unchanged and no effects of riveting process was detected.