- Research Professor specialising in surface metrology and its applications. Particular interests in Additive Manufactu... moreResearch Professor specialising in surface metrology and its applications. Particular interests in Additive Manufacturing metrology, Biometrology, metrology for Forensic Ballistics,. Council Member of the European Society for Precision Engineering(Research Professor specialising in surface metrology and its applications. Particular interests in Additive Manufacturing metrology, Biometrology, metrology for Forensic Ballistics,. Council Member of the European Society for Precision Engineering)edit
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The great success of cemented total hip replacement to treat patients with end-stage osteoarthritis and osteonecrosis has been well documented. However, its long-term survivorship has been compromised by progressive development of aseptic... more
The great success of cemented total hip replacement to treat patients with end-stage osteoarthritis and osteonecrosis has been well documented. However, its long-term survivorship has been compromised by progressive development of aseptic loosening, and few hip prostheses could survive beyond 25 years. Aseptic loosening is mainly attributed to bone resorption which is activated by an in-vivo macrophage response to particulate debris generated by wear of the hip prosthesis. Theoretically, wear can occur not only at the articulating head—cup interface but also at other load-bearing surfaces, such as the stem—cement interface. Recently, great progress has been made in reducing wear at the head—cup interface through the introduction of new materials and improved manufacture; consequently femoral stem wear is considered to be playing an increasingly significant role in the overall wear of cemented total hip replacement. In this review article, the clinical incidences of femoral stem wear...
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Research Interests: Engineering, Mechanical Engineering, Materials Science, Machining, Manufacturing Engineering, and 7 moreDiamond Turning, Industrial and Manufacturing Engineering, Engineering and manufacturing science, Surface Metrology, Coordinate Measuring Machine, Machine Tool, and Automatic Control and Systems Engineering
ABSTRACT Although cemented total hip replacement has long been recognized as a situation that can lead to wear, the wear generated on the femoral stem has not been well documented, especially with regard to how this wear is initiated and... more
ABSTRACT Although cemented total hip replacement has long been recognized as a situation that can lead to wear, the wear generated on the femoral stem has not been well documented, especially with regard to how this wear is initiated and propagated. This present work aimed to further investigate this issue based on a comprehensive study on surface morphology of the femoral stem and the bone cement, which were collected from seven in vitro wear simulations. It was shown that the wear locations on the stem surface compared well with the results of retrieval studies, and the boundaries of the worn areas matched well the edges of the micropores present in the bone cement surface. This indicated that the micropores could potentially contribute to the generation of femoral stem wear. In addition, metallic debris was detected around the micropores from the simulation with increased loading cycles. However, no evidence of macro-cracks was observed across the cement mantle in spite of the presence of micro-cracks initiated at the edge of the micropores. This study demonstrated a possible cause for progression of femoral stem wear and it may have an important bearing on the long term durability of cemented hip prosthesis.
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Cemented total hip replacement has been performed worldwide to treat patients with osteoarthritis and osteonecrosis, with aseptic loosening as its primary reason for revision. It has been indicated that the stem-cement interfacial... more
Cemented total hip replacement has been performed worldwide to treat patients with osteoarthritis and osteonecrosis, with aseptic loosening as its primary reason for revision. It has been indicated that the stem-cement interfacial porosity may contribute to the early loosening of cemented hip prosthesis. In addition, it is generally accepted that the micropores in bone cement surface and in the bulk material are detrimental to the mechanical integrity of bone cement and act as stress concentrators, resulting in generation of fatigue cracks in the cement mantle. Furthermore, it was demonstrated that the micropores also play an important part in initiation and propagation of fretting wear on polished femoral stems. Taking this into consideration, a detailed review of the potential significance of the micropores in bone cement and the methods that could be employed to reduce porosity is given in this article. It was considered that modern cementing techniques are clinically beneficial and should be applied in surgery to further improve the survivorship of cemented total hip replacement.
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It has been reported that bone cement correlates with survivorship of cemented total hip replacement. However, little research has been published to investigate the influence of bone cement type on production of fretting wear on the... more
It has been reported that bone cement correlates with survivorship of cemented total hip replacement. However, little research has been published to investigate the influence of bone cement type on production of fretting wear on the femoral stem. In the present study, we performed six in vitro wear simulations using the same type of femoral stem (polished Exeter V40™) and three different bone cements (Simplex P, Palacos R, and CMW 3). Fretting wear was consistently reproduced on the stem surface and the wear locations compared well with the results of retrieval studies. Selected 3D surface parameters were utilised to quantitatively evaluate fretting wear and no significant difference was identified in terms of fretting wear severity between these simulations. The bone cements were all badly damaged in those sites contacting the fretting wear areas on the femoral stem. Additionally, there were plenty of wear debris present on the cement surface, and the energy dispersive X-ray analysis confirmed that it was just cement particles for Simplex P bone cement, whilst it included metallic particles for Palacos R and CMW 3 bone cements. This preliminary study shed some light on the influence of bone cement type on production of fretting wear on the femoral stem surface but further research is needed to gain a better understanding on this issue.
Research Interests: Mechanical Engineering, Materials Science, Biomedical Engineering, Fretting, Medicine, and 15 moreSoil Cementation, Humans, Clinical Biomechanics, Femur, Rd, Cement, Bone Cement, Friction, Biomimetic materials, Surface Properties, Bone Cements, TJ, Materials Testing, Cementation, and In Vitro Techniques
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Research Interests: Engineering, Materials Science, Optics, Image Processing, Microstructure, and 15 moreMachining, Digital Image Processing, Micromachining, Data acquisition, Dislocation, Fast Tool Servo, Dislocations, Groove, Microstructures, Data Processing, Microlens, Digital Image, Microlens array, Parametric analysis, and Pattern analysis
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Research Interests: Engineering, Optics, Metrology, Interferometry, TS, and 2 moreWavelength and Production Line(Wavelength and Production Line)
(Wavelength and Production Line)
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In additive manufacturing (AM), especially for advanced powder fusion machines, it is of high importance to develop an in situ inspection system to monitor the printed surface and pre-print powder bed as the build cycle proceeds.... more
In additive manufacturing (AM), especially for advanced powder fusion machines, it is of high importance to develop an in situ inspection system to monitor the printed surface and pre-print powder bed as the build cycle proceeds. Consequently, high resolution, high precision and fast detection measurement systems need to be investigated, as such optically based measurement systems can provide feedback for manufacturing process optimisation. Fringe projection technology has a great advantage in the measurement of topography in such environments. The implementation of a fringe projection system requires that the system is pre-calibrated in order to obtain high measurement resolution and repeatability. This paper presents a simple calibration method for an AM-based in situ fringe projection system using a phase-depth calibration model. If a calibration plate with certificated marks is used, however, the texture of the plate will affect the measured phase accuracy. A simple calibration ...
Research Interests: Mechanical Engineering, Computer Science, Additive Manufacturing, Control and Optimization, Calibration, and 7 moreIndustrial and Manufacturing Engineering, Machines, Repeatability, Fringe Projection, Electrical And Electronic Engineering, Automatic Control and Systems Engineering, and Institutional Collaboration
Electron Beam Metal Additive Manufacturing (EBAM) has been developed over recent years because of its advantages in manufacturing internal features and complex structures with relatively high productivity. The process proceeds by layer by... more
Electron Beam Metal Additive Manufacturing (EBAM) has been developed over recent years because of its advantages in manufacturing internal features and complex structures with relatively high productivity. The process proceeds by layer by layer melting and re-solidification of metal powder utilising an electron beam energy source. Following solidification of the build layer, the surface becomes ‘shiny’ with high reflectivity which makes in-process inspection of the surface of the build layer using fringe projection, difficult. To address this issue, a novel intelligent fringe projection technique using a support-vector-machine (SVM) algorithm is proposed to measure the 3D topography of high dynamic range surfaces on a layer by layer basis within the EBAM machine. To facilitate the SVM implementation a range of EBAM manufactured surfaces are utilised as samples for training and classification. The training measurements are based on different exposure times and saturated pixels are ut...
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ABSTRACT This paper describes assumptions, aims, methodology, content and consortium make up of a European project (SAM-EMU) founded under the Erasmus Lifelong Learning Programme. The project has developed learning materials in the field... more
ABSTRACT This paper describes assumptions, aims, methodology, content and consortium make up of a European project (SAM-EMU) founded under the Erasmus Lifelong Learning Programme. The project has developed learning materials in the field of evaluation of measurement uncertainty. It is available in the form of a multimedia web based course, which has many advantages. This format is commonly accepted as a good way to prepare an EU wide vocational training vehicle. The course is available in English. (c) 2011 Elsevier Ltd. All rights reserved.
Research Interests: Engineering, Mechanical Engineering, Applied Mathematics, Condensed Matter Physics, Education, and 10 moreLifelong Learning, Statistical Analysis, Vocational Training, Measurement, Coordinate Measurements, Statistics and Probability, Elsevier, E Learning, Measurement Uncertainty, and Uncertainty of Measurements
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The long term stabilization and durability of cemented total hip replacement (THR) depends on not only the bulk properties of the components but also the interfaces through which they interact. The stem-cement interface has been... more
The long term stabilization and durability of cemented total hip replacement (THR) depends on not only the bulk properties of the components but also the interfaces through which they interact. The stem-cement interface has been consistently considered as a weak link in the stem-cement-bone system, being a transitional zone between two materials with significantly different mechanical properties. Previous research concerning this interface has been limited to investigation of interfacial shear strength through in vitro test and finite element analysis (FEA). Until now, a deep insight into the contact characteristics at this interface, especially the interaction between femoral stems with various surface finishes and bone cement, has not been established. In addition, it is still an area of debate whether a permanent fixation can be achieved by utilizing a matt femoral stem, and furthermore it is another matter of concern that a matt femoral stem would cause much more damage to the c...
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Inherent to the somewhat uncontrolled nature of the additive process, the surfaces of metal powder bed fusion additively manufactured components tend to be very rough. Large isolated ‘bumps’, as one of the major defect features, are often... more
Inherent to the somewhat uncontrolled nature of the additive process, the surfaces of metal powder bed fusion additively manufactured components tend to be very rough. Large isolated ‘bumps’, as one of the major defect features, are often present due to partially melted particles attached to the surface. An enhanced watershed segmentation method is proposed to separate these ‘bump’ features from the underlying surface texture such that the ‘bumps’ and underlying surface can be quantitatively analysed. The results show that the amplitude roughness parameters of the underlying surface are significantly less than the un-segmented surface and spatial roughness parameters differ between two surfaces. Characterising the extracted underlying surface and ‘bumps’ independently allows better correlation between surface measurements and additive system performance and hence aids in process optimization.
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Traditionally, quantitative measurement of surface texture has been carried out using contacting stylus instruments yielding purely 2-dimensional topographical information. Recently, there has been a great expansion in this field through... more
Traditionally, quantitative measurement of surface texture has been carried out using contacting stylus instruments yielding purely 2-dimensional topographical information. Recently, there has been a great expansion in this field through developments in ...
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This presentation reports on the latest development taking place within the EU funded NanoMend project. The aim of the project is to develop integrated process inspection, cleaning, repair and control systems for thin films on flexible... more
This presentation reports on the latest development taking place within the EU funded NanoMend project. The aim of the project is to develop integrated process inspection, cleaning, repair and control systems for thin films on flexible photo voltaic films based on CIGS (Copper Indium Gallium Selenide CuInxGa(1-x)Se2). Flexible PV films are fabricated on polymer film by the repeated deposition, and patterning, of thin layer materials using roll-to-roll processes, where the whole film is approximately 3um thick prior to final encapsulation. Take up of such devices, especially for building integrated applications BIPV, is hampered by long-term degradation of efficiency due to water ingress through the barrier layer defects to the CIGS modules causing electrical shorts and efficiency drops. To address this problem a thin (~40nm) barrier coating of Al2O3 usually provides the environmental protection for the PV cells. The highly conformal aluminium oxide barrier layer is produced by atomi...
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Producing components using metal additive manufacturing processes, such as powder bed fusion, presents manufacturing and measurement challenges, but also significant opportunities. The as-built surface may include overhanging (re-entrant)... more
Producing components using metal additive manufacturing processes, such as powder bed fusion, presents manufacturing and measurement challenges, but also significant opportunities. The as-built surface may include overhanging (re-entrant) features not intentionally included in the design, but that aid in component functionality. In addition, the AM process presents opportunities to design and manufacture re-entrant features intentionally. Re-entrant features increase the specific surface area and, in addition, produce mechanical locking to the surface. These features may be intended to improve surface performance in areas such as biological cell attachment, coating adhesion, electrical capacitor and battery plate design, fluid flow and material cooling. Re-entrant features may prove difficult or impossible to measure and characterise using conventional line-of-sight instrumentation. The correct measurement of these surfaces is vital for functional optimisation. This paper reports on the measurement of re-entrant features using X-ray computed tomography and the extraction of actual surface area information (including re-entrant surfaces) from sample AM surfaces. The proposed new parameter, Sdr prime , is discussed. This parameter is intended to relate directly to surface function. Sdr prime is the percentage of additional surface (including re-entrant surfaces) contributed by the texture as compared to a plane the size of the measurement area. In addition to Sdr prime , the actual surface area is discussed, together with the percentage of re-entrant surface. The errors produced using line-of-sight instruments and height map parameter generation per ISO 25178-2 are discussed. Measurement results for EBM and SLM additively manufactured components will be presented.
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Assessing functional performance is the most important stage of any component verification. Mechanical properties can be evaluated by means of destructive testing which can be both expensive and lengthy in addition to loss of the original... more
Assessing functional performance is the most important stage of any component verification. Mechanical properties can be evaluated by means of destructive testing which can be both expensive and lengthy in addition to loss of the original component under test. It is therefore advantageous where possible to utilise non-destructive techniques that can achieve the same or similar outcomes through collection of three-dimensional data that can then be used in simulation to determine functionality. Such non-destructive methods are essentially density-and porosity-based testing methods. Additive manufacturing allows for the creation of complex geometrical features that are often defined based on function. Optimisation of AM component geometry based on functionality allows for the specification of components that have features that cannot be mapped efficiently to current GPS standards. In addition, the integrity of complex optimised AM structures that may lie on a critical stress or heat path must be assessed and any elements of unmelted powder must be detected. This study details the development of a Ti6AL4V artefact built using an Arcam Q10 electron beam-melting machine (EBM). Defects of between 50 and 500 microns in diameter were then machined into the surface of the artefact using a CNC machine equipped with nano-drills and end mills. Once this was achieved, the defects were characterised using focus variation interferometer. Virgin Ti6AL4V powder was added to fill 50% of the defects and then the artefact was measured using a Nikon XTH225 industrial CT. This was used to analyse the relative size and location of the defects and assess the capability of the inspection process to both assess the size of pores of this size and to detect the powder-filled defects based on different X-ray detector magnifications. To reduce the number of process variables, all the measurement process parameters, such as filament current, acceleration voltage and X-ray filtering material and thickness, were kept constant. The acquired data processing, surface determination process and defect analysis was carried out using VgStudio Max (Volume Graphics, Germany). The focus of the study is on providing best practice regarding the selection of inspection parameters to accurately perform defect detection.