Sumsun Naher

SIMULATION OF THE STIR CASTING PROCESS

Abstract Non-homogeneous particle distribution is one of the greatest problems in casting metal matrix composites (MMCs). To optimise some of the parameters for uniform particle distribution for batch compocasting the present simulation studies were conducted. The simulation involves visualisation experiments. In the visualisation experiments liquid and semisolid aluminium are replaced by other fluids with similar characteristics. SiC reinforcement particulate similar to that used in aluminium MMCs was used in the simulation fluid mixtures. Scaled-up stirring experiments were carried out in a transparent crucible with the percentage of reinforcement material being varied. Optimum conditions for photographing flow patterns were established. The dependence of the photography conditions (shutter speed, aperture control, lighting), particles dispersion and settling times and vortex height on stirrer geometry and speed was found. Results are discussed in terms of their applicability to MMC production.

Association between essential trace and toxic elements in scalp hair samples of smokers rheumatoid arthritis subjects

The incidence of rheumatoid arthritis (RA) has been increased among people who possess habit of tobacco smoking. In the present study, zinc (Zn), copper (Cu), manganese (Mn), lead (Pb) and cadmium (Cd) were determined in scalp hair samples of smokers and nonsmokers RA patients, residents of Dublin, Ireland. For comparison purposes scalp hair samples of age and sex matched healthy smokers and nonsmokers were also analyzed. The concentrations of understudied elements were measured by inductive coupled plasma atomic emission spectrophotometer, prior to microwave assisted acid digestion. The validity and accuracy of methodology was checked using certified reference material (NCS ZC 81002b) and by the conventional wet acid digestion method on the same certified reference material and on real samples. The mean hair Zn, Cu and Mn contents were significantly lower in smokers and nonsmokers RA patients as compared to healthy individuals (p=0.01-0.001). Whereas the concentrations of Cd and Pb were significantly higher in scalp hair samples of RA patients of both group (p<0.001). The referent smokers have high level of Cd and Pb in their scalp hair samples as compared to those had not smoking tobacco (p<0.01). The ratio of Cd and Pb to Zn, Cu and Mn in scalp hair samples was also calculated. The Cd/Zn ratio was higher in smoker RA patients with related to nonsmoker RA and referents. This study is compelling evidence in support of positive associations between toxic elements, cigarette smoking, deficiency of essential trace elements and risk of arthritis.

Effect of micro-channel geometry on fluid flow and mixing

Understanding the flow fields at the micro-scale is key to developing methods of successfully mixing fluids for micro-scale applications. This paper investigates flow characteristics and mixing efficiency of three different geometries in micro-channels. The geometries of these channels were rectangular with a dimension of; 300 lm wide, 100 lm deep and 50 mm long. In first channel there was no obstacle and in the second channel there were rectangular blocks of dimension 300 lm long and 150 lmwide are placed in the flow fields with every 300 lm distance attaching along the channel wall. In the third geometry, there were 100 lm wide fins with 150_ angle which were placed at a distance of 500 lm apart from each other attached with the wall along the 50 mm channel. Fluent software of Computational Fluid Dynamics (CFD) was used to investigate the flow characteristics within these microfluidic model for three different geometries. A species 2D model was created for three geometries and simulations were run in order to investigate the mixing behavior of two different fluid with viscosity of water (1 mPa s). Models were only built to investigate the effect of geometry, therefore only one fluid with similar viscosity was used in these models. Velocity vector plots were used in the CFD analysis to visualise the fluid flow path. Mass fractions of fluid were used to analyse the mixing efficiency. Two different colours for water were used to simulate the effect of two different fluids. The results showed that the mixing behaviour strongly depended on the channel geometry when other parameters such as fluid inlet velocity, viscosity and pressure of fluids were kept constant. In two geometries lateral pressure and swirling vortexes were developed which provided better mixing results. Creation of swirling vortexes increased diffusion gradients which enhanced diffusive mixing.

Comparative metal distribution in scalp hair of Pakistani and Irish referents and diabetes mellitus patients

BACKGROUND The essential metals, chromium (Cr), magnesium (Mg), manganese (Mn) and zinc (Zn), are necessary for many metabolic processes and their homeostasis is crucial for life. The toxic metals, cadmium (Cd) and lead (Pb), have no beneficial role in human metabolism. The aim of this study was to investigate the levels of Cd, Cr, Mg, Mn, Pb, and Zn in scalp hair samples of type 2 diabetes mellitus patients of both genders, ages ranging from 30 to 50 y, and belong to urban areas of Ireland and Pakistan. For comparison purposes, age matched non-diabetic subjects of both countries were selected as referents. METHODS The concentrations of metals in scalp hair samples were measured by inductively coupled plasma atomic emission spectrophotometer and atomic absorption spectrophotometer after microwave-assisted acid digestion. The validity and accuracy of the methodology were checked by conventional wet-acid-digestion method and using certified reference materials. RESULTS The mean values of Cd and Pb were significantly higher in scalp hair samples of both Pakistani and Irish diabetic patients as compared to referents of both countries (P<0.001). In contrast, lower Cr, Mg, Mn, and Zn (P<0.01) concentrations were detected in scalp hair derived from patients with type 2 diabetes versus healthy subjects of both countries. CONCLUSION This study showed that, increased toxic elements and decreased essential elements are associated with diabetes mellitus. Therefore, these elements may play a role in the development and pathogenesis of diabetes mellitus.

In vitro fibroblast and pre-osteoblastic cellular responses on laser surface modified Ti-6Al-4V.

The success of any implant, dental or orthopaedic, is driven by the interaction of implant material with the surrounding tissue. In this context, the nature of the implant surface plays a direct role in determining the long term stability as physico-chemical properties of the surface affect cellular attachment, expression of proteins, and finally osseointegration. Thus to enhance the degree of integration of the implant into the host tissue, various surface modification techniques are employed. In this work, laser surface melting of titanium alloy Ti-6Al-4V was carried out using a CO2 laser with an argon gas atmosphere. Investigations were carried out to study the influence of laser surface modification on the biocompatibility of Ti-6Al-4V alloy implant material. Surface roughness, microhardness, and phase development were recorded. Initial knowledge of these effects on biocompatibility was gained from examination of the response of fibroblast cell lines, which was followed by examination of the response of osteoblast cell lines which is relevant to the applications of this material in bone repair. Biocompatibility with these cell lines was analysed via Resazurin cell viability assay, DNA cell attachment assay, and alamarBlue metabolic activity assay. Laser treated surfaces were found to preferentially promote cell attachment, higher levels of proliferation, and enhanced bioactivity when compared to untreated control samples. These results demonstrate the tremendous potential of this laser surface melting treatment to significantly improve the biocompatibility of titanium implants in vivo.

Permeability of rapid prototyped artificial bone scaffold structures

In this work, various three-dimensional (3D) scaffolds were produced via micro-stereolithography (µ-SLA) and 3D printing (3DP) techniques. This work demonstrates the advantages and disadvantages of these two different rapid prototyping methods for production of bone scaffolds. Compared to 3DP, SLA provides for smaller feature production with better dimensional resolution and accuracy. The permeability of these structures was evaluated experimentally and via numerical simulation utilizing a newly derived Kozeny-Carman based equation for intrinsic permeability. Both experimental and simulation studies took account of porosity percentage, pore size, and pore geometry. Porosity content was varied from 30% to 70%, pore size from 0.34 mm to 3 mm, and pore geometries of cubic and hexagonal closed packed were examined. Two different fluid viscosity levels of 1 mPa · s and 3.6 mPa · s were used. The experimental and theoretical results indicated that permeability increased when larger pore size, increased fluid viscosity, and higher percentage porosity were utilized, with highest to lowest degree of significance following the same order. Higher viscosity was found to result in permeabilities 2.2 to 3.3 times higher than for water. This latter result was found to be independent of pore morphology type. As well as demonstrating method for determining design parameters most beneficial for scaffold structure design, the results also illustrate how the variations in patients blood viscosity can be extremely important in allowing for permeability through the bone and scaffold structures.

Evaluation of Essential Trace and Toxic Elements in Scalp Hair Samples of Smokers and Alcohol User Hypertensive Patients

The incidence of hypertension has been associated to cigarette smoking and consumption of alcohol. In the present study, trace and toxic elements were determined in scalp hair of patients diagnosed with hypertension who are smokers and habitual alcohol drinkers living in Dublin, Ireland. These results were compared with age- and sex-matched healthy, nonsmokers, nondrinking controls. The concentrations of trace and toxic elements were measured by inductively coupled plasma atomic emission spectrophotometer after microwave-assisted acid digestion. The validity and accuracy of the methodology were checked using certified reference material (NCS ZC 81002b) and by the conventional wet acid digestion method on the same certified reference material and on real samples. The recovery of all the studied elements was found to be in the range of 97.5%–99.7% in certified reference material. The results of this study showed that the mean values of cadmium, copper, iron, nickel and lead were significantly higher in scalp hair samples of both smoker and nonsmoker hypertensive patients than referents (P < 0.001); whereas, the concentration of zinc was lower in the scalp hair samples of hypertensive patients of both genders. The deficiency of zinc and the high exposure of trace and toxic metals as a result of cigarette smoking and alcohol consumption may be synergistic with risk factors associated with hypertension.

Laser Surface Modification of Tool Steel for Semi-Solid Steel Forming

This paper presents an analysis of the effect of CO2 laser processing parameters on the surface modification and heat treatment of steels. The CO2 laser and sample movement process parameters are presented. The controlled operation of these in conjunction with each other is required to obtain better surface hardness and structure. H13 tool steel samples were rotated at high speeds to keep exposure times below 0.3s. Laser processed samples were analysed using EDX spectroscopy, optical microscopy, Vickers and Martens micro-hardness testing, and X-ray diffraction (XRD). Results show how the hardness profile through the surface is related to the laser treatment and resultant microstructures. Increased surface hardness was noted due to a complete microstructural transformation to an amorphous state in the glazed samples. The usefulness of such coatings on tool steels, in conjunction with other thermal barriers, for the forming of semi-solid steel alloys is presented.

Thermal Simulation of Laser Surface Modification of H13 Die Steel

In this study, the effects of laser parameters on the properties of glazed die steel were investigated. A Rofin DC-015 diffusion-cooled CO2 slab laser with 10.6 µm wavelength was used. Die steel sample surfaces were prepared with a 3 µm roughness and chemically treated to improve CO2 laser wavelength absorbance. One set of processing parameters were processed through the thermal simulation program and correlated with physical results determined from actual test samples. Set processing parameters were 1138 W peak power, 2900 Hz PRF, 24% duty cycle and 261 mm/s traverse speed. Scanning Electron Microscopy (SEM) micrographs and micro-hardness properties of the affected surface were measured. An analytical mathematical model of the heat field generated in the laser glazing process was used to predict the nominal temperature distribution in the surface and dimensions of melt pool. A thermal model using point source surface energy inputs was used to predict the thermal profiles in the die steel. This allowed estimation of the depths of microstructurally altered regions. For higher energy absorbance, the depth of the glazed surface increased from 20 μm to 40 μm. At high nominal heating to cooling rate ratios, high micro-hardness values were recorded.

Laser surface modification of H13 die steel using different laser spot sizes

This paper presents a laser surface modification process of AISI H13 tool steel using three sizes of laser spot with an aim to achieve reduced grain size and surface roughness. A Rofin DC‐015 diffusion‐cooled CO2 slab laser was used to process AISI H13 tool steel samples. Samples of 10 mm diameter were sectioned to 100 mm length in order to process a predefined circumferential area. The parameters selected for examination were laser peak power, overlap percentage and pulse repetition frequency (PRF). Metallographic study and image analysis were done to measure the grain size and the modified surface roughness was measured using two‐dimensional surface profilometer. From metallographic study, the smallest grain sizes measured by laser modified surface were between 0.51 μm and 2.54 μm. The minimum surface roughness, Ra, recorded was 3.0 μm. This surface roughness of the modified die steel is similar to the surface quality of cast products. The grain size correlation with hardness followed the findings corre...