Automated Control of Laser System for Micro-Machining
PhD Student: Shadi Karazi
This work is targeted on the development of an automated laser machining process with high dimensional accuracy and pre-defined process costing. This work includes analysis of the dimensions and cost prediction modelling of Nd:YVO4 laser internal micro-channel fabrication in PMMA and internal laser processing of polycarbonate for the purpose of microfluidic device fabrication. In order to achieve these project goals, ANN and DoE dimensional measurement comparison and cost comparison with CO2 and Nd:YVO4 laser systems have been performed. Full implementation of closed loop control with sub-micrometer linear positional accuracy with encoder feedback has been implemented. In particular, the automation for the alser firing and sample positioning is controlled using FPGA. Advanced understanding gained of the operational procedure and software for the Nd:YVO4 system enabled change of the control unit into Compact-Rio Programmable Automation Controller (PAC), which is completed in LabVIEW code controlling in closed loop mode three dimensional positioning stages using high resolution encoders of sub-micron resolution. Completed full automation of this process in LabVIEW code is in progress. Current and future work includes dimensional accuracy, precision and repeatability measurements for the designed system; and related optimisation of geometry of micro-channels for the production of microfluidic and lab-on-a-chip devices to be used in chemical/analytical applications and in separation science.
Effect of the temporal thermal field on quality of semi-solid metal formed components
PhD Student: Asnul Ahmad
Superior mechanical properties are needed for numerous applications in semi-solid metal (SSM) formed components. The outstanding mechanical properties such as wear resistance, high strength and stiffness rely on the microstructural feature produced from ultra-fine grain size. This grain size normally depended on the optimum processability of SSM. However, SSM cast components tends to contain residual porosity, which is extremely detrimental to performance. In this work, the important process of semi-solid metal forming will be investigated to provide improved quality parts. These parts should have reduced porosity and improved microstructural features including ultra-fine granularity and homogenous distribution of strengthening precipitates and alloy micro-elemental composition. The effects of the time-temperature pre-processing route for required microstructure development will in particular be analyzed. Resulting properties from quality improvement such as increased strength, hardness, and stiffness will be investigated.
Laser Surface Modification of Steels
PhD Student: Syarifah Nur Aqida Binti Syed Ahmad (PhD 2011)
The presented work is an investigation of the laser surface modification of H13 tool steel using pulse laser processing mode. Initial screening experimental designs conducted lead to more optimised detailed designs. A carbon dioxide (CO2) laser system with 10.6 μm wavelength was used. In the experimental designs investigated three different sizes of laser spot used were 0.4, 0.2 and 0.09 mm diameter. The other controlled parameters were laser peak power, pulse repetition frequency and pulse overlap. The laser processing was constantly assisted by in line argon gas at 0.1 MPa pressure. H13 samples were roughened and chemically etched prior processing to improve the surface absorbance at the CO2 laser wavelength. Laser processed samples were prepared for metallographic study and were characterised for physical and mechanical properties. The metallographic study and chemical composition analysis were conducted using scanning electron microscope integrated with energy dispersive x-ray spectroscopy. The crystallinity and phase detection of the modified surface were conducted using an XRD system with Cu Kα radiation and wavelength of 1.54 Å. The surface profile was measured using stylus profilometry measuring systems. The hardness properties of the modified surface were measured by micro-Vickers diamond indentation. A customized thermal fatigue system was used to investigate the effect of surface roughness on the modified surface fatigue properties. A modified surface grain with an ultrafine size of less than 500 nm was observed to be achievable. A modified surface depth which ranged between 35 and 150 µm was developed on the laser processed H13 samples. A reduction of crystallinity was noticeable for the modified H13 surface which was related to the more random distribution of crystallites after laser processing. A minimum modified H13 average surface roughness, Ra, of 1.9 µm was achieved. Another important finding was that at different settings of laser parameters, the modified H13 surface exhibited a range of hardness between 728 and 905 HV0.1. A relationship between thermal simulations findings (heating and cooling rates) and hardness results was established for further understanding of the effects of the laser parameters. These findings are significant to the establishment of surface hardening techniques for wear resistance and thermal barrier coating applications.
Parametric impact characterisation of a solid sports ball, with a view to developing a standard core for the GAA sliotar
PhD Student: Fiachra Ciarán Collins (PhD 2011)
The main aim of this research was to characterise the dynamic impact behaviour of the sliotar core. Viscoelastic characterisation of the balls was conducted for a range of impact velocities. Modern polymer balls exhibited strain-rate sensitivity while traditional multi-compositional balls exhibited strain dependency. The non-linear viscoelastic response was defined by two values of stiffness, initial and bulk stiffness. Traditional balls were up to 2.5 times stiffer than the modern types, with this magnitude being rate-dependent. The greater rate of increase of traditional ball stiffness produced a more non-linear COR velocity-dependence compared to modern balls. The dynamic stiffness results demonstrated limited applicability of quasi-static testing and spring-theory equations. Analysis of ball deformation behaviour demonstrated that centre-of-mass displacement and diameter compression were not consistently equivalent for all ball types. The contribution of manufacturing conditions to ball performance was investigated by conducting extensive prototyping experiments. Manufacturing parameters of temperature, pressure and material composition were varied to produce a range of balls. Polymer hardness affected stiffness but not energy dissipation, with increased hardness increasing ball stiffness. The nucleating additive influenced ball liveliness, with increased additive tending to reduce ball liveliness, but this effect was sensitive to polymer grade. Numerical analysis was conducted to simulate the impact response of the ball using three mathematical models. The first model was shown to replicate ball behaviour to only a limited degree, despite being used previously with reported success for other ball types. The second model exhibited a reasonable representation of ball impact response that was universally applicable to all tested ball types; however, the accuracy in terms of predicting force-displacement response was not as high as required for broad range implementation. The third model exhibited significantly better accuracy in simulating ball response. The model-generated force values from this model exhibited a 95% agreement with the experimental data.
Investigation of Semi-Solid Metal Processing Route
Mian Wajid Ali Shah (MEng 2006)
Two main objectives were complete during this work. One was the design and construction of a high temperature capillary viscometer and the second was the modelling of semi-solid metal flow with a view to aiding the design and providing data for comparison purposes. The high temperature capillary viscometer has been constructed and has been used for preliminary testing. This device will be used to measure the viscosity of semi-solid metals under high temperature and shear rate conditions, similar to those found in industry. The capillary viscometer is a single point system that can be used to calculate the viscosity by measuring the flow rate and pressure difference between the two end of the capillary tube as the viscosity directly proportional to the pressure drop and inversely proportional to the flow rate. Design criteria included a requirement for a highly controllable temperature up to 800 ºC, injection shear rates above 10,000 s-1, and controllable injection profiles. A 2D, two phase theoretical unsteady state model using a computational fluid dynamics (CFD) software FLUENT was developed. This was used to evaluate the viscosity of semi-solid metals passing through the designed capillary viscometer at injection speeds of 0.075, 0.5, and 1 m/s. The effects of fractions solid (fs) of the metal from 0.25 to 0.50 were also investigated. Strong correlations between these parameters and the resulting viscosity were noted for the power law viscosity equations which were used to develop the Fluent models.
Examination of the Stir-Casting Method to Produce Al-SiC Composites
PhD Student: Sumsun Naher (PhD 2004)
This work examined the influence of processing parameters on the production of Al-SiC metal matrix composites (MMC) by batch compocasting process. Processing parameters investigated include stirring speed, stirring time, stirrer geometry, stirrer position, metal fluid temperature (viscosity). Room temperature (25±C) visual simulations, computer simulations and validation Al-SiC MMC production tests were performed. In the visual and computer simulations, water and glycerol/water were used to represent liquid and semi-solid aluminium respectively. The effects of viscosities of 1, 300, 500, 800 and 1000 mPas and stirring speeds of 50, 100, 150, 200, 250 and 300 rpm were investigated. A 10 vol. % reinforced SiC particulate, similar to that used in the aluminium MMC's, was used in the visualisation and computational tests. The visualisation tests were carried out in a transparent glass beaker. The computational simulation was performed with Fluent (CFD software) and an add on package MixSim. This consisted of a 2D axisymmetric multiphase time dependent simulation of the production route using an Eulerian (granular) model. The dependence of particle dispersion times, settling times and vortex height on stirring geometry and stirrer speed was found. A blade angle of 60 degrees was found better for the °at blade stirrer, to obtain uniform particulate dispersions quickly. From these tests a stirring speed of 150 rpm for water-SiC and 300 rpm for the glycerol/water-SiC system were found to be necessary in order to obtain a uniform distribution of the SiC. A viscosity increase from 1 mPas (for liquid metal) to 300 mPas (for semi-solid metal) was found to have a tremendous effect on the SiC dispersion and settling times. However, a further increase from 300 mPas to 1000 mPas had negligible effect on this time. A significant part of the work consisted of the design, construction and validation of a specialised quick quench compocaster for this high temperature processing method. This machine consisted of a stirrer with four 60 degree angled flat blades and a crucible in a resistance heated furnace chamber. An actuator was integrated to this rig to enable quick quenching of the processed mixture. This device was used to produce Al-SiC composites. Generally, good agreement was found between the visualisation, computational and validation experimental results.
Computer Application in Electro-Mechanical Systems
Meftah Ibrahim (MEng 2004)
There are many different Rapid Prototyping (RP) technologies available which have been developed to large-scale use, mainly in the last decade. Today’s commercially available rapid prototyping systems work with different techniques using paper, waxes, photocurable resins, polymers and new metal powders. This project is concerned with one type of rapid prototyping technology, namely fused deposition modelling, which was initially commercialised in 1991. A new version of the fused deposition modelling system using wax has been designed and used in this work. The present project describes the basic system design, and the method of wax deposition. The FDM machine builds the part by extruding semi-molten material through a heated nozzle in a prescribed pattern onto a platform. The extrusion jet is mounted on a X-Y table which is controlled by a computer system. In conjunction with the automated control of the plunger mechanism and the depositor position, accurate models were produced. Single layers of wax were built up one on top of the other to produce two-dimensional and three-dimensional objects. The characteristics of the wax were also analysed in order to optimise the model production process. These included wax phase change temperature, wax viscosity and wax droplet shape during processing
Application of Activity Based Costing for Optimisation of Irish Engineering based SMEs
Micro-Fluidic Chip Based Platforms for Liquid Chromatographic Separations
PhD Student: Aymen Ben Azouz
Over the last five years, two laser micro-machining processes which allow for the production of channels and voxels with repeatable micrometre level resolution have been developed within the Separation Science Cluster research group at Dublin City University. A focus of this work is the utilisation of tailored materials for the separation of target biomolecules. Preliminary work has illustrated that novel capillary mixing and surface channel morphologies that can be generated with a view to enhancing separation capabilities. This work will focus on applying the available micro-manufacturing facilities to develop surface and channel geometries that will provide enhanced separation and characterisation for biological systems. The application of these systems will be along the lines of the ‘lab-on-a-chip’ approach for biological diagnostic purposes. Devices fabricated with this developed technology will be utilised in this project for micro-fluidic lab-on-a-chip applications. The objective of this project will be the use experimental design, optimisation and modelling techniques to enable a direct link between the laser processing parameters and the channel micro and nano-scale features and the ability to utilise this information for enhanced separations within these micro-fabricated channels. Specific work outputs include: Improved channel designs and surface morphology for separation science; Monolithic based pumps and extraction phases within an integrated chip; and Separation of selected and extracted target bio-molecule on integrated chip.
Generation and control of temporary temperature gradients and longitudinal profiles along LC capillary columns through the use of Peltier arrays and infra-red thermal imaging
PhD Student: David Collins
A new direct contact platform for capillary column precise temperature control, based upon the use of individually controlled sequentially aligned Peltier thermoelectric units has been developed. The platform provides rapid temperature control for capillary and micro-bore liquid chromatography columns, and allows simultaneous temporal and spatial temperature programming. The operating temperature range of the platform is between 15 and 200 °C, for each of ten aligned Peltier units, with a ramp rate of approximately 400 °C/min. The system has been evaluated for a number of non-standard capillary based sensing modes, such as the direct application of temperature gradients with both linear and non-linear profiles, including both static column temperature gradients and temporal temperature gradients, the formation of in-capillary monolithic stationary phases with gradient polymerisation through precise temperature control, and the fabrication of monolithic phases within micro-fluidic channels (on-chip). This device can be used in conjunction with standard and plot column chromatography systems.
Electrohydrodynamic Focusing in 2 Dimensional Planar Microfluidic Devices for Pre-concentration of Low Abundance Analytes
PhD Student: Tomasz Piasecki (2011)
This work concerns the electrohydrodynamic focusing (EHDF) and photon transmission to aid the development of species pre-concentration and identification. EHDF is an equilibrium focusing method for ions, based on establishing a balance between the hydrodynamic and electric forces, what allow that the ion in question will become stationary. In this research a novel approach of using a 2-dimensional planar microfluidic device is presented with an open 2D-plane space instead of conventional microchannel system. Such devices can allow pre-concentration of large volume of species and are relatively simple fabricated. In this research results of newly developed simulations using COMSOL Multiphysics® 3.5a are presented. Results from these models were compared to experimental results to validate the determined flow geometries and regions of increased concentration. The developed numerical microfluidic models were compared with previously published experiments and presented high correspondence of the results. Basing on these simulations a novel ship shapes were investigated to provide optimal conditions for EHDF. The experimental results using this chip exceeded performance of the model. A novel mode, named lateral EHDF, when test substance was focused perpendicularly to the applied voltage was observed in the fabricated microfluidic chip. As detection and visualisation is a critical aspect of such species pre-concentration and identification systems. Numerical models and experimental validation of light propagation and light intensity distribution in 2D microfluidic systems is presented. The developed numerical mode of the light propagation was successfully verified experimentally both in the aspect of the actual light path through the system and the intensity distribution giving results that may be interesting for the optimisation of photo-polymerisation systems as well as for the optical detection systems employing capillaries.
Computational Control of Laser Systems for Micro-Machining
PhD Student: Ahmed Issa (PhD 2007)
Depending on the geometry, the microfabricated structures have applications in telecommunications, microfluidics, micro-sensors, data storage, glass cutting and decorative marking applications. The relations of Nd:YVO4 and CO2 laser system parameter settings to the dimensions and morphology of microfabricated structures were examined in this work. Laser system parameters investigated included power, P, pulse repetition frequency, PRF, number of pulses, N, and scanning speed, U. Output dimensions measured included equivalent voxel diameter as well as microchannel width, depth and surface roughness. A 3D microfabrication system was developed using the Nd:YVO4 laser (2.5 W, 1.604 µm, 80 ns) to fabricate microstructures inside polycarbonate samples. Microstructure voxels ranged from 48 to 181 µm in diameter. Tight focusing was also achieved with this system using a microscope objective lens to produce smaller voxels ranging from 5 to 10 µm in soda-lime glass, fused silica and sapphire samples. The CO2 laser (1.5 kW, 10.6 µm, minimum pulse width of 26 µs) was used to fabricate microchannels in soda-lime glass samples. The cross-sectional shapes of the microchannels varied greatly between v-shape grooves, u-shaped groves and superficial ablated regions. Microchannels dimensions varied greatly also with widths ranging from 81 to 365 µm, depths ranging from 3 to 379 µm and surface roughness between 2 to 13 µm being produced depending on the settings. The microchannel dimensions were studied in terms of the laser processing parameters using the response surface methodology (RSM) with the design of experiments technique (DOE). The collected results were used to study the effect of the process parameters on the volumetric and mass ablation rates. Moreover, a thermal mathematical model of the process was also developed in order to aid understanding of the process and to allow channel topology prediction a priory to actual fabrication.
Development of a Laser Based Surface Profilometer Using the Principle of Optical Triangulation
David Collins (MEng 2005)
The metrology industry is constantly looking for new ways to accurately and quickly inspect and digitise surface topographies including the calculation of surface roughness parameters and generating point clouds (a collection of 3-dimensional points which describe a surface or surfaces) for modelling or reverse engineering purposes. Many types of profilometer systems currently exist and the past decade has seen the rise in popularity of optical based systems, however most optical profilometers are expensive to purchase and to maintain. The development of optical profilometers can also be exceptionally complex depending on the type of system and its fragility may not make it suitable for most workshop or factory floor applications. This project covers the development of a profilometer using the principle of optical triangulation. The developed system has a scanning table area of 200 by 120 millimetres and a vertical measurement range of five millimetres. The position of the laser sensor above the target surface also has an adjustable range of 15 millimetres. A control program was developed to automatically scan user selected part and surface areas. This new system was characterised in terms of dimensional accuracy. The maximum cosine error of the system was measured at 0.07°. Dynamic accuracy of the system was measured at 2μm in the Z-axis (height) and at approximately 10μm in the X and Y axes. Good dimensional correlation between scanned parts (coins, screws, washers, and fibre optic lens moulds) were achieved. Testing of the system will be also discussed, including the limitations of the profilometer and possible improvements to the system.
Development and Characterisation of a Novel Optical Surface Defect Detection System
Mohammad Abu Hana Mustafa Kamal (MEng 2005 )
The objective of this project was to develop and characterise a novel optical high-speed online surface defect detection system. The inspection system is based on the principle of optical triangulation and provides a non-contact method of determining 3D profile of a diffuse surface. Primary components of the developed system consist of a diode laser, CCf15 CMOS camera, and two PC controlled servomotors. Control of the sample movement, image capturing, and generation of 3D surface profiles was programmed in LabView software. Inspection of the captured data was facilitated by creating a program to virtually present the 3D scanned surface and calculate requested surface roughness parameters. The servomotors were used to move the sample in the X and Y directions with a resolution of 0.05 m. The developed non-contact online surface-profiling device allows for quick high-resolution surface scanning and inspection. The developed system was successfully used to generate automated 2D surface profiles, 3D surface profiles and surface roughness measurement on different sample material surfaces. This automated inspection facility has a X-Y scanning area capacity of 12 by 12 mm. In order to characterise and calibrate the developed profiling system, were compared to surface profiles measured by the system were compared to optical microscope, binocular microscope, AFM and Mitutoyo Surftest – 402 measurement of the same surfaces.
Development of a Laser Scanning Thickness Measurement Inspection System
S. M. Mahfuzul Haque (MEng 2004)
The quality specifications for products and the materials used in them are becoming ever more demanding. The solution to the many visual inspection quality assurance (QA) problems is the use of automatic in-line surfaces inspections systems. These need to achieve uniform product quality at high throughput speeds. As a result, there is a need for systems that allow 100% in-line testing of materials and surfaces. To reach this goal, laser technology integrated with computer control technology provides a useful solution. In this work, A high speed, low cost, and high accuracy non-contact laser scanning inspection system was developed. The system is capable of measuring the thickness of solid, non-transparent objects using the principle of laser-optical triangulation. Measurement accuracies and repeatabilities to the micrometre level were achieved with the developed system.
Development of a laser based inspection system for surface defect detection
Mohammed Belal Hossain Bhuian (MEng 2002)
The objective of this project was to design and develop a laser based inspection system for the detection of surface defects and to assess its potential for high-speed online applications. The basic components of this inspection system are a laser diode module as illumination source, a random access CMOS camera as detector unit, and an XYZ translation stage. Algorithms were developed to analyse the data obtained from the scanning of different sample surfaces. The inspection system was based on optical triangulation principle. The laser beam was incident obliquely to the sample surface. Differences in surface height were then taken as a horizontal shift of the laser spot on the sample surface. This enabled height measurements to be taken, as per the triangulation method. The developed inspection system was first calibrated in order to obtain a conversion factor that would render a relationship between the measured spot shift on the sensor and the vertical displacement of the surface. Experiments were carried out on different sample material surfaces: brass, aluminium and stainless steel. The developed system was able to accurately generate three-dimensional topographic maps of the defects presented to it in the work. A spatial resolution of approximately 70 µm and a depth resolution of 60 µm were achieved. Characterisation of the inspection system was also performed by measuring the accuracy of distances measured.
Development of high-speed fibre-optical laser scanning system for defect recognition
Abdulbaset Abuazza (PhD 2002)
High-speed fibre optic laser scanning systems are being used in automated industrial manufacturing environments to determine surface defects. Recent methods of surface defect detection involve the use of fibre-optic light emitting and detection assemblies. This thesis deals with the design and development of a new high-speed photoelectronic system. In this work, two sources of emitting diode were examined, LED (light emitting diode) and laser diode. A line of five emitting diodes and five receiving photodiodes were positioned opposite each other. Data capture was controlled and analysed by PC via LabVIEW software. The system was used to measure the dimensions of the surface defects, such as holes (1 mm), blind holes (2 mm) and notches in different materials. The achieved results show that even though this system was used mainly for 2D scanning, it may also be operated as a limited 3D vision inspection system. This system furthermore showed that all the metal materials examined were able to reflect a signal of the infrared wavelength. A newly developed technique of using an angled array of fibres allowed an adjustable resolution to be obtained with the system, with a maximum system resolution of approximately 100 µm (the diameter of the collecting fibre). The system was successfully used to measure various materials surface profile, surface roughens, thickness, and reflectivity. Aluminium, stainless steel, brass, copper, tufnol, and polycarbonate materials were all capable of being examined with the system. The advantages of this new system may be seen as faster detection, lower cost, less bulky, greater resolution, and flexibility.
Generic system development for marine environmental sensing
Design build and test a novel system for integration and deployment of emerging environmental sensor technologies. Particularly for the application of faecal bacteria monitoring
Alteration of Micro and Nanostructures of Silicon Solar Photovoltaic Panels for Enhanced Energy Provision
PhD Student: David Moore
One of the main engineering problems that society faces in today’s world is that of sustainable energy supply. The time has come when it is imperative that society needs begins to rely heavily on renewable energy sources. The sun provides the earth with free energy; however, current methods of harnessing this energy as electricity have some limitations. In terms of photovoltaic cells, the main problem is the lack of efficiency for harvesting the solar energy. Laser micromachining is commonly used for creating interconnects between active layers (for example glass substrate, hydrogenated silicon, and zinc oxide layers) in photovoltaic cells. It is also known that if the surface area of the solar cell can be increased, by micromachining for example that more power can be generated. Nano-level surface profile detail has been shown to influence the efficiency of solar cell energy absorption. The aim of the current work is to investigate the benefits of tailoring the solar cell micron, nano and meso-scale structure such that increased power provision can be attained. Variation of the process parameters for this micro and nano-structuring will allow investigation of their influence over surface topology. Cells will be tested for energy produced under experimentally controlled levels of electromagnetic light exposure. A direct link will be made between the cell efficiencies and the surface textures.
Application of Metal Matrix Composite of CuSiC and AlSiC as Electronics Packaging Materials
PhD Student: Mohabattul Zaman Bnsbukhari
Metal Matrix Composite (MMC) is rapidly becoming prime candidates as structural materials in engineering as well as in electronic application. Aluminium (Al) and Copper (Cu) reinforced by SiC is used in various industries due to its excellent thermo-physical properties such as low coefficient of thermal expansion (CTE), high thermal conductivity and improved mechanical properties such as higher specific strength, better wear resistance and specific modulus. Recently, these MMCs with high ceramic contents have become another focus for thermal management applications in electronic packaging. Normally, in packaging power devices, Aluminium (Al) or Copper (Cu) has been used as a heat sink or baseplate for attaching ceramic substrates that carry the chips and the associated lead structures. The large difference in coefficient of thermal expansion (CTE) between the ceramic and Aluminium or Copper is a drawback, as it results in a less reliable package and also restricts the size of the ceramic substrate that can be attached to the baseplate.
Looking at this drawback, there is now an opportunity for new materials to be developed, study and characterize in order to meet the prescribed requirements of thermally enhanced materials. With an improve properties in thermal conductivity as well as in coefficient of thermal expansion (CTE), MMCs of CuSiC and AlSiC are now the possible solution for electronic packaging industry. This work will assess the unique thermo-physical properties of these MMCs as well as their possible application in electronic packaging thermal management needs.
Inhibition of weld corrosion for carbon steel pipelines within an aggressive environment
PhD Student: Ali Abdunnabi Abdurrahim
Oil companies have experienced considerable corrosion in weld zones of oil and gas industry systems made of carbon and low alloy steel. In CO2 containing environments corrosion failures are often explained by varying tenacity of protective corrosion scales adhesion on different carbon steel microstructures. Localised corrosion of weld metal (WM) and heat affected zone (HAZ) has mostly been explained by galvanic effects caused by both differences in alloy content and microstructure. An investigation of microstructural features of parent metal (PM), WM and HAZ was carried out to understand microstructural effects on the corrosion behaviour of welded joints of low carbon steel. Corrosion testing within a 3.5% NaCl solution saturated with CO2 under deoxygenated condition at room temperature (20±2 ˚C), with pH of 4.0±0.3 was examined. Characterisation of the corrosion behaviour was carried out by electrochemical techniques of open circuit potential, potentiodynamic polarization sweep and linear polarization resistance as well as general metallographic characterisation performed using optical microscopy. The main morphological phases found were acicular ferrite, retained austenite, and martensite/bainite structures in WM. These were less prevalent in the HAZ. Significantly different electrochemical behaviour and corrosion rates have been found within the PM, WM and HAZ.
Improvement of Efficiency in a Submersible Pump Motor
James Wall (MEng 2008)
The work covered in this project had the aim of improving the electrical efficiency of a submersible pump. The requirement for the pump manufacturing industry to move in this direction has increased recently with the introduction of new EU legislation making it a requirement that new higher efficiency levels are met across the industry. In this work, the use of the cooling jacket to keep the solenoid region of the pump cool was analysed and improvements in design suggested. Specifically, the fluid flow and heat transfer in the current pump cooling jacket was characterised. Improvement in the cooling jacket design would give better heat transfer in the motor region of the pump and hence result in a higher efficiency pump, with reduced induction resistance. For this work, a dry pit installation pump testing system was added to the side of an already existing 250 m3 test tank facility. This enabled high speed camera tracking of flow fields and thermal imaging of the pump housing. The flow fields confirmed by CFD analysis allowed alternate designs to be tried, tested and compared for maintaining as low an operating temperature as possible. The original M60-4 pole pump design experienced a maximum pump housing outside temperature of 45 °C and a maximum stator temperature of 90 °C. Analysis of various model designs showed which designs would be more useful for higher efficiency systems and which should not be used. In particular, an integrated cooling coil design was shown to provide no improvement over the original design. Increasing the number of impeller blades from four to eight reduced the running temperature, measured on the housing, by seven degrees Celsius.
Software development for wireless data collection for road traffic monitoring
High Speed Laser Processing of Metallic Alloys for Biomedical Applications
PhD Student: Evans Chikarakara
Combining high power densities and reduced exposure time on metal processing induce surface microstructural changes. Obtaining the optimum combination of laser process parameters and cooling rates is crucial in altering the grain structure and producing improved tribological properties on the surface of the material. The primary aim of this study is to investigate the effects of rapid pulsed laser processing on the tribological properties of commercially available metallic biomaterials. This work is concentrated on the laser surface modification of AISI 316L stainless steel and Ti-6Al-4V. A 1.5kW pulsing CO2 laser is used to investigate the effects of varied laser process parameters and resulting surface microstructure and morphology. Cylindrical samples rotating perpendicular to the laser irradiation direction were used with laser irradiance, exposure time, energy fluence, and pulse width being varied. Characterisation was undertaken using SEM, EDX, stylus roughness measurement and XRD analysis. A surface temperature prediction model was also implemented to set the initial experimental process parameters. A process mapping investigation was then carried out to determine a range of specific laser processing parameters that melt the surface of the steel. A strong correlation between irradiance, residence time, depth of processing and roughness of processed samples has been established. High depth of altered microstructure and increased roughness were linked to higher levels of both irradiance and residence times. Energy fluence and surface temperature models were used to predict levels of melting occurring on the surface through the analysis of roughness and depth of processed region. As the laser beam interaction time increased, the surface roughness of the steel increased for the various pulse energy levels examined. While the structure of the surface was seen to retain a conventional crystal arrangement, grain orientation changes were observed in the laser processed region.
Analysis and Characterisation of the Strain Behaviour of Tissues and the Implications for Scaffold Design
During this project several different scaffold geometries were designed and Finite Element Analysis was carried out to understand the mechanical properties of bone structures, their role in tissue development, maximum stress and strain distribution in the scaffolds. Apart from the CAD designed scaffold structures, computed tomography (CT) scans of trabecular bone samples were collected. These designs allowed prototypes to be built and tested as well as FEA of these structures to be performed. Micro-strain mechanical measurements were taken from the manufactured scaffolds and the femoral head trabecular bone samples, and these results were compared to those obtained for the same structures form the FEA work. Mechanical properties were seen to depend on the designed pore shape (architecture), pore size (120, 340 and 600 µm) and loading conditions (with or without loading blocks). Examination of these parameter variations on 8mm3, 22.7mm3 and 1000mm3 porous scaffolds were conducted to fully examine their influence on stress distribution. The experimental and model results have suggested that the geometrical design of the structure plays a significant role in the stress distribution and highlights the great possibilities for scaffold design to enhance bone regeneration. Overall the pore size was seen to be more important than the porosity level in determining the overall maximum stress level. The porosity level however is also important in determining the osteoconductivity of the scaffold structure. By increasing the porosity levels from 30% to 70% with the same pore sizes, the maximum stress values increased dramatically.
The pore size of the scaffold is also important for the fabrication method. To date all of the rapid prototyping methods have certain limitations. Although more versatile the conventional manufacturing, more complicated and smaller structures may often not be manufactured. Most of these technologies are not nominally currently capable of consistent production of pores sizes below 500µm. The results for the 600µm pore size in this work are therefore most relevant to the manufacturing capabilities of current rapid manufacturing technologies. The hexagonal structure presented, although examined in only one direction, would be the most anisotropic structure relative to the cubic and triangular based structures. The cubic and triangular structures are relatively isotropic compared to the hexagonal structure. Anisotropy is important in considering the osteoconductivity of designed scaffolds. Stress distribution and pore size location affect the remodelling processes and different loading conditions may change the maximum stress values and its location. The dominant loading direction should encourage pore sizes and distribution to allow cells growth into the larger pores as well as providing nutrients and building material. Another interesting finding from this work from examination of the strut cross sectional stress distribution was that larger values of stress were recorded at the surface of the struts compared to the centres. In this work the pore size, porosity level and loading methods have been shown to be strongly correlated with the stress levels experienced in the structures. These findings indicated the ability to design a strut architecture within which the stress levels can be varied to a larger degree at the strut surfaces such that cellular attachment and growth can be promoted.
Production of Hard Tissue Scaffolds Using Three-Dimensional Printing Method
Tamás Dávid Szűcs (MEng 2008)
Synthesised bone replacement scaffolds provide the possibility to individually tailor properties, overcome limited donor availability and improve osteointegration. The aim of bone tissue engineering is to provide solutions to these problems by making available high quality transplants that can be supplied in larger quantities. In these applications both the internal and external geometry of the scaffold are very important since they have significant effect on mechanical properties, permeability and cell proliferation. Rapid Prototyping technologies allow the use of customised materials with predetermined and optimised geometries to be fabricated with good accuracy. This work investigates the ability of the 3D printing technology to manufacture intricate bone scaffold geometries from biocompatible calcium phosphate based materials. Initial investigations with the proprietary materials showed that predicted directional mechanical behaviour can be realised. Practical measurements investigating the directional mechanical properties of the manufactured samples showed trends identical with the results of the Finite Element Analysis (FEA). The ability of 3D Printing technology to fabricate tissue engineering scaffold geometries made of biocompatible calcium phosphate cements was also demonstrated in this work. Scaffolds were manufactured by printing aqueous sodium phosphate dibasic solution on the powder bed consisting of a homogeneous mixture of dicalcium phosphate and calcium hydroxide. The wet-chemical reaction of precipitation took place in the powder bed of the 3D Printer. Solid specimens were manufactured in order to measure the bulk compressive mechanical properties of the fabricated Calcium Phosphate Cement (CPC). The average elastic modulus for the so produced parts was 3.59 MPa, and the average compressive strength was 0.147 MPa. Sintering resulted in significantly increased compressive properties (E = 9.15 MPa, σy = 0.483 MPa), but it decreased the specific surface area of the material. As a result of sintering, the calcium phosphate cement decomposed to β-Tricalcium Phosphate (β-TCP) and Hydroxyapatite (HA) as confirmed by Thermogravimetric Analysis and Differential Thermal Analysis (TGA/DTA) as well as with X-Ray Diffraction (XRD). The obtained mechanical properties are not sufficient for high load bearing implants, where the required strength in ranging between 1.5 -150 MPa and compressive stiffness is above 10 MPa. However further post processing such as infiltration with biodegradable polymers may allow these structures to be used for scaffold applications.
Effect of Vibration on the Shear Strength of Impacted Bone Graft in Revision Hip Surgery
Stephen A.M. Brennan (MCh 2008)
Aims: Studies on soil mechanics have established that when vibration is applied to an aggregate, it results in more efficient alignment of particles and reduces the energy required to impact the aggregate. Our aim was to develop a method of applying vibration to the bone impaction process and assess its impact on the mechanical properties of the impacted graft.
Phase 1: Eighty bovine femoral heads were milled using the Noviomagus bone mill. The graft was then washed using a pulsed lavage normal saline system over a sieve tower. A vibration impaction device was developed which housed two 15V DC motors with eccentric weights attached inside a metal cylinder. A weight was dropped onto this from a set height 72 times so as to replicate the bone impaction process. A range of frequencies of vibration were tested, as measured using an accelerometer housed in the vibration chamber. Each shear test was then repeated at four different normal loads so as to generate a family of stress-strain curves. The Mohr-Coulomb failure envelope from which the shear strength and interlocking values are derived was plotted for each test.
Phase 2: Experiments were repeated with the addition of blood so as to replicate a saturated environment as is encountered during operative conditions.
Phase 1: Graft impacted with the addition of vibration at all frequencies of vibration showed improved shear strength when compared to impaction without vibration. Vibration at sixty Hertz was displayed the largest effect and was found to be significant.
Phase 2: Graft impacted with the addition of vibration in a saturated aggregate displayed lower shear strengths for all normal compressive loads than that of impaction without vibration.
Conclusions: Civil engineering principles hold true for the impaction bone grafting procedure. In a dry aggregate the addition of vibration may be beneficial to the mechanical properties of the impacted pellet. In our system the optimal frequency of vibration was 60 Hz. In a saturated aggregate the addition of vibration is detrimental the shear strength of the aggregate. This may be explained by the process of liquefaction.
Design of a Dynamic Balance Assessment System
John Considine (MEng 2007)
The aim of this work was to design, build and test a system that could perturb a test subject standing upon it in order to assess their ability to react to these changes. This would be achieved by rapidly tilting the surface on which the person was standing and then returning it to the horizontal position. From this it could be determined whether the test subject was able to maintain a state of balance or how long it took them to return to that state of balance. This state of balance would be determined by measuring the subject’s postural sway. Their natural postural sway was measured using a foot pressure profile plate to determine how much deviation there was during testing. This system was also designed to be more versatile and affordable than what is currently available commercially, as while these machines are important for studies they are not in common use at present due to their cost. The newly developed system presented in this thesis, has been used to move test subjects up to 100kg in weight.
A Study of the Implementation of Virtual Instrumentation in University Laboratory Environments
Philip Smyth (MEng 2007)
In this work six engineering and physical science laboratory experiments were developed to enhance the learning experience for students. This was achieved by instrumenting and creating virtual instruments for these experiments. The use of virtual instrumentation is directly compared with traditional laboratory teaching techniques and pedagogical principles from which both methods have developed from are discussed. Previous work utilising Computer Based Learning (CBL) in similar projects relating to this work have been used to evaluate some of the benefits of virtual instrumentation, especially those relating to increased student interest, memory retention, understanding and ultimately performance in laboratory reports. The virtual experiments discussed in this study are redesigned versions of traditional style experiments and hence a direct comparison of newer CBL techniques to traditional style laboratories was undertaken. There was no change in concepts being between the two versions of the experiments; the only difference was in the methodology of presentation. The effectiveness of these CBL techniques was assessed by looking at the performance of students using virtual instrumentation against that of other students from the same class undertaking the traditional mode of the experiments. All students were assessed by report submission, multiple choice questions relating to their experiment and questionnaires. The results of this study were also compared to other related studies within the field of CBL.