Ultrasonic inspection is the primary method of Non-Destructive Evaluation (NDE) for the detection of planar flaws in engineering components. In recent years phased array technology has been adopted for use in NDE following success in related fields, such as medical and sonar applications. Phased array technology provides increased flexibility relative to single element monolithic transducers and the development of controlling hardware with large numbers of parallel channels has allowed the use of large phased arrays able to focus at long range, and offer increased performance. Full Matrix Capture (FMC) is a method of recording data using a phased array transducer that allows image reconstruction to be performed for any inspection technique than could be deployed using delay laws applied to the transmit voltage pulses applied to the array and receiving amplifiers. FMC technology provides a step change in inspection flexibility, and also provides the opportunity to take advantage of imaging techniques that are not practical to implement using phased arrays in the conventional way. However, existing inspection calibration procedures defined in standards do not allow these benefits to be fully realised. This thesis reports the development of a calibration framework designed for FMC based inspection for both rigid and conformable wedge mounted arrays. A large part of this work has been the development of acceptance limits on transducer performance variations. The developments of these limits have required a significant amount of modelling work, often using a Monte Carlo approach. To accommodate this, modelling tools have been developed to investigate the effect of array element directivity, sensitivity, and relative phase on system performance. For conformable phased arrays the effect of surface profile measurement accuracies has also been assessed. The developed calibration framework includes the tools necessary to monitor transducer performance throughout an inspection, with minimum impact on inspection duration. A means of calibrating imaging tools against known reflectors, in accordance with established industrial practice, has also been produced.

There is increasing use of Unicondylar or Unicompartmental Knee Replacements (UKR), especially following publication of good survival data and a trend towards ‘minimally invasive surgery’. The UKR preserves one of the femoral condyles and its meniscus, plus both of the cruciate ligaments. Therefore, the knee functions more normally following UKR than after Total Knee Replacement (TKR). However, the odds for failure of the UKR are higher than the TKR, and a principal reason is loosening of the tibial and femoral components. There is a need for the development of more reliable UKR fixation designs. The overall aim of this research was to understand fixation of UKR and make recommendations for improvement to designers and surgeons. Since the Oxford mobile-bearing UKR is most widely used in the UK, it was used as the benchmark in this study. To assess initial fixation, in-vitro bone-constructs were prepared from ten cadavers implanted with the Oxford mobile-bearing UKR and tested for bone strain and bone-implant interface motion with the implants fixed using first cementless and then cemented methods. Cementless fixation produced higher proximal tibia strain and bone-implant displacement than cemented fixation. Peak bone strain increased with reduced bone density, such that the lowest density specimen fractured when implanted with the cementless UKR. To assess long-term fixation, an in-vivo prospective follow-up study of 11 Oxford UKR patients was developed and conducted for one-year, taking measurements of bone density using Dual X-Ray Absorptiometry (DXA) scanning. The average bone resorption under the tibial implant was found to be low; while it was higher under the femoral component and very high under the tibial intercondylar eminence. The fixation of the Oxford UKR implant was considered to be adequate at 1-year. Finite Element (FE) simulation techniques were reviewed and developed to simulate the UKR knee for investigation of bone strain, bone-implant interface micromotion and bone remodelling to assess initial and long-term fixation performance. Computer simulations of the tibiae and femora of 2 patients and 4 cadaveric specimens (obtained from the in-vivo and in-vitro studies) were developed and validated for bone strain, bone-implant interface micromotion and bone remodelling. Comparative multi-specimen computational studies were conducted to understand how particular design features affected fixation. Good fixation was indicated for cementless UKRs when implanted in dense bone, but bone strains were very high in low density tibia. Cementation of the implants spread the loads more evenly and reduced bone strains. The cementless tibial implant caused less bone resorption (compared to the cemented equivalent) but the difference in the femur was small. Bone resorption was highest at the anterior tibia and posterior to the femoral peg. Bone density was an important factor in the fixation performance of implant design features. Less bulky fixation features reduced bone resorption, provided that the underlying bone was sufficiently dense to maintain bone strains below the failure limit of bone. For patients with dense bone, fixation could be improved with shorter tibial keels and less stiff femoral implants. For patients with low density bone, fixation could be improved with cementation and bone resection that avoids creating stress-raisers.

The removal of contamination particles from silicon wafers is critical in the semiconductor industry. Traditional cleaning techniques encounter difficulties in cleaning micro and nanometer-sized particles. A promising method that uses acoustically-driven micro-bubbles to clean contaminated surfaces has been reported. However, little is understood about the microscopic interaction between the micro-bubble and particle. This thesis explores the mechanism underlying the ultrasonic cleaning using micro-bubbles at the micrometer scale. The investigation was carried out from the perspective of bubble dynamics near a surface and bubble-particle interaction. Prior to contributing to the particle removal, micro-bubbles normally need to be transported to a target surface. The motion of a bubble was analyzed based on a force balance model for single and multi-bubble translations respectively. A good agreement is found between the observed bubble movement trajectories and the theoretical predictions. After arriving on a surface, a micro-bubble starts to disturb the flow field near the boundary through its oscillation. The characteristics of the flow field are closely related to the bubble oscillation modes. The influence of a wall on the change of bubble oscillation mode during its translation toward the boundary was studied. The relationship between bubble oscillation modes and the corresponding microstreaming around the bubble was established. The experimental results of bubble oscillation modes and the flow motion are quantitatively in good agreement with the simulation results. From a mechanic point of view, a possible ultrasonic cleaning mechanism is explained by exploring the relationship between different torques that are exerted on micro and sub-micrometer-sized particles. This estimation provides a qualitative insight into the ultrasonic cleaning process at a moderate pressure amplitude. The experimental investigation of the complicated particle detachment process requires improved test equipment to be developed in the future.

Human-machine interfaces (HMI) provide a communication pathway between man and machine. Not only do they augment existing pathways, they can substitute or even bypass these pathways where functional motor loss prevents the use of standard interfaces. This is especially important for individuals who rely on assistive technology in their everyday life. By utilising bioacoustic activity, it can lead to an assistive HMI concept which is unobtrusive, minimally disruptive and cosmetically appealing to the user. However, due to the complexity of the signals it remains relatively underexplored in the HMI field. This thesis investigates extracting and decoding volition from bioacoustic activity with the aim of generating real-time commands. The developed framework is a systemisation of various processing blocks enabling the mapping of continuous signals into M discrete classes. Class independent extraction efficiently detects and segments the continuous signals while class-specific extraction exemplifies each pattern set using a novel template creation process stable to permutations of the data set. These templates are utilised by a generalised single channel discrimination model, whereby each signal is template aligned prior to classification. The real-time decoding subsystem uses a multichannel heterogeneous ensemble architecture which fuses the output from a diverse set of these individual discrimination models. This enhances the classification performance by elevating both the sensitivity and specificity, with the increased specificity due to a natural rejection capacity based on a non-parametric majority vote. Such a strategy is useful when analysing signals which have diverse characteristics, false positives are prevalent and have strong consequences, and when there is limited training data available. The framework has been developed with generality in mind with wide applicability to a broad spectrum of biosignals. The processing system has been demonstrated on real-time decoding of tongue-movement ear pressure signals using both single and dual channel setups. This has included in-depth evaluation of these methods in both offline and online scenarios. During online evaluation, a stimulus based test methodology was devised, while representative interference was used to contaminate the decoding process in a relevant and real fashion. The results of this research provide a strong case for the utility of such techniques in real world applications of human-machine communication using impulsive bioacoustic signals and biosignals in general.

The objective of this study is to quantify the effect of low amplitude cyclic stresses, such as those induced by environmental condition fluctuations and transportation, on multilayer paint systems found in works of art. A model was developed to establish criteria for damage, which take into account viscoelastic fatigue, and to establish safe rates of change for environmental parameters. To establish the methodology, the investigation focused on modern paintings executed in mixed media. In particular, acrylic gesso grounds with superimposed alkyd paint layers on canvas were investigated, which have been found to be vulnerable to stresses and delamination. Data from uniaxial testing of free-standing paint films were used to determine the constitutive properties of the paint. The effects of temperature, strain rate and age on the tensile properties were investigated. Results from peel tests, performed to determine the energy release rate of the interface between the paint and gesso layers, are reported. The peel tests were modelled using Finite Element Analysis with cohesive zone elements at the interface in a commercial finite element software Abaqus. The value of the maximum traction in the traction-separation law was determined by comparing numerical and experimental peel loads and the cohesive energy was determined using an established analytical method. The cohesive zone properties determined from the peel tests, and the calibrated constitutive model for the alkyd paint, were used in a separate finite element model of a coating on a primed canvas substrate subjected to combined cyclic hygrothermal and static mechanical loadings typically experienced by fine art paintings; interface separation was controlled by an irreversible cohesive zone model that includes damage accumulation due to cyclic loading. Fatigue crack initiation times in years, and crack propagation rates, are predicted under various conditions including ordinary and extreme histories that paintings may experience in museum and conservation settings.

Modern tribological coatings often possess a multilayered structure, where the properties of each layer can be chosen to optimise the tribological performance of the coating. Such structure can offer advantages over a single layer coating in terms of improved coating durability and reduced contact friction and wear. The behaviour of such complex contacts cannot be fully analysed with current contact models, especially when real surface roughness is considered. Therefore, there is a need for an improved contact analysis model that is able to predict the contact behaviour and sub-surface stresses for real rough multilayered contacts. The work presented in this thesis provides a complete three-dimensional numerical model for non-conformal multilayered real rough surface contacts, which offers a powerful tool for analysis and optimisation of such coated contacts. The model can be used to predict the contact pressure distribution and deformations as well as sub-surface stress field due to applied normal and tangential loads. The contacting bodies are modelled to have an arbitrary geometry, possessing real rough surfaces thus avoiding any assumptions about asperity distribution or shape. The model is based on linear elastic theory and utilises the influence coefficients approach to solve for contact pressures and deformations in a rough contact. The influence coefficients are obtained by utilizing Fourier transforms to solve the Navier’s generalized equation for displacement and stress fields, for an imposed set of boundary conditions pertinent to a multilayered contact. An iteration scheme is set up to obtain the full distribution of pressure and displacement for a rough contact given the applied normal loading, friction coefficient and material properties. The model is validated by comparing its predictions for a set of carefully chosen cases to those obtained with existing analytical and numerical solutions. Results are presented to illustrate the capabilities of the model and its potential applications. These results illustrate how the contact performance, in terms of surface and sub-surface stress, can be enhanced by carefully selecting the properties of each of the layers in a complex multilayered coating. Such enhancements could lead to improved durability and efficiency of machine components, such as rolling element bearings.

No description available.

High intensity focused ultrasound (HIFU) enables highly localised, non-invasive tissue ablation, and its efficacy in the treatment of a range of cancers, including those of the kidney, prostate and breast has been demonstrated. HIFU offers the ability to treat deep-seated tumours locally, and potentially bears fewer side effects than more established treatment modalities such as resection, chemotherapy and ionising radiation. There remain, however, a number of significant challenges which currently hinder its widespread clinical application. One of these challenges is the need to transmit sufficient energy through the ribcage to ablate tissue at the required foci whilst minimising the formation of side lobes and sparing healthy tissue. Ribs both absorb and reflect ultrasound strongly. This sometimes results in overheating of bone and overlying tissue during treatment, leading to skin burns. Successful treatment of a patient with tumours in the upper abdomen therefore requires a thorough understanding of the way acoustic and thermal energy is deposited. In this thesis, an approach which predicts the acoustic field of a multi-element HIFU array scattered by human ribs, the topology of which was obtained from CT scan data, has been developed, implemented and validated. It is based on the boundary element method (BEM). Dissipative mechanisms were introduced into the propagating medium, along with a complex surface impedance condition at the surface of the ribs. A reformulation of the boundary element equations as a constrained optimisation problem was carried out to solve the inverse problem of determining the complex surface normal velocities of a multi-element HIFU array that best fitted a required acoustic pressure distribution in a least-squares sense. This was done whilst ensuring that an acoustic dose rate parameter at the surface of the ribs was kept below a specified threshold. The methodology was tested at an excitation frequency of 1 MHz on a spherical section multi-element array in the presence of human ribs. It was compared on six array-rib topologies against other methods of focusing through the ribs, including binarised apodisation based on geometric ray tracing, phase conjugation and the DORT method (décomposition de l’opérateur de retournement temporel). The constrained optimisation approach offers greater potential than the other focusing methods in terms of maximising the ratio of acoustic pressure magnitudes at the focus to those on the surface of the ribs whilst taking full advantage of the dynamic range of the phased array.

Hydroxyapatite (HA) coated titanium (Ti) based dental and orthopaedic implants are widely utilised owing to their bone-bonding capability. However, the longevity of such implants is restricted by poor HA-Ti interfacial adhesion. In contrast, alternative coating materials such as titania (TiO2) and zirconia (ZrO2) have superior mechanical properties but are generally bioinert. Therefore, the performance of coated implants has been optimised by combining highly bioactive HA with mechanically superior TiO2 or ZrO2. This thesis investigated the deposition of novel electrosprayed bioceramic films with enhanced bioactivity and mechanical properties. Sol-gel derived TiO2 and ZrO2 nano-particles were synthesized using a range of precursors and solvents whereas nano-sized HA was synthesized by precipitation. Composite suspensions with a range of HA:TiO2 and HA:ZrO2 compositions were prepared by mixing. The liquid physical properties such as electrical conductivity and surface tension were affected by suspension composition which in turn influenced the electrospray process. Film morphology was dependent on deposition parameters such as needle-to-substrate distance and suspension flow rate as well as post deposition annealing. The in vitro bioactivity was generally enhanced by post deposition annealing temperature and was further improved by the presence of HA. However, the TiO2/HA composite films were more bioactive than the ZrO2/HA composite films. The mechanical integrity of the electrospray films was assessed by scratch testing. The scratch hardness improved with an increase in the post deposition annealing temperature and declined with an increase in HA content. Furthermore, the scratch resistance was affected by materials composition and was in the order ZrO2>TiO2>HA. The scratch resistance was further enhanced by the deposition of HA-based bi-layer and functionally graded films with a comparable in vitro response to the electrosprayed HA films. Thus the electrospray process is a promising route for the deposition of bioceramic composite films for biomedical applications.

The velocity potential theory has been adopted to investigate the two-dimensional vortex shedding problems in marine hydrodynamics. The theory can find its applications to the lifting body problems such as a hydrofoil advancing near the free surface, the flow passing through an orifice of a damaged compartment, the vortex shedding at sharp edges of a marine structure. Since the viscosity of the fluid is assumed to be confined within a thin boundary layer along the surface of the structure, the fluid flow can be described by velocity potential theory. Literature review on vortex shedding has been presented. The development of relevant theories and their applications have been discussed. The challenges and suitable methodologies are investigated. When the steady motion and small amplitude unsteady motion of a hydrofoil advancing near free surface is considered, a flat vortex sheet is introduced and imposed behind the trailing edge; linear free surface conditions are imposed to study the free surface effects. Free surface Green functions, which satisfy free surface boundary conditions, are adopted to account for the free surface effects which are found to be highly significant. To study the non-linear effects of body surface boundary condition and vortex wake when the attack angle or the motion amplitude becomes moderately large, we introduce a time stepping scheme. The vortices shed from the trailing edge are approximated by introducing point vortex. The non-linear effects of body surface condition and vortex wake are investigated. Further studies on the submerged foil and surface piercing structures with vortex shedding are presented; efforts are made to investigate the non-linear wave-body interaction problems with vortex shedding. The non-linear free surface and non-linear vortex wake are found to have significant effects on the fluid flow and the hydrodynamic force.