Experimental techniques for investigating lubricated, compliant contacts

The study of Tribology between soft or compliant surfaces is not well understood despite its importance to many biological and engineering applications, ranging from synovial joints to rubber o-ring seals. It has also been shown that the science of Tribology and lubrication in compliant contacts is an important factor in the sensory perception and functionality of skin, hair and the oral cavity, and so has an immediate application of the design of consumer products such as skin creams, hair conditioners and foodstuffs. This thesis aims to improve our understanding of thin film lubrication between soft, deformable surfaces under light loading and low-pressure conditions. The primary focus of the thesis is the development of techniques by which to measure the film thickness between compliant surfaces, from the nano- to the micro-scale. Several experimental techniques currently exist for measuring film thickness in hard, metallic contacts and these are widely employed in Tribology research of engineering systems. However they require considerable modification to be applicable to compliant contacts. This thesis describes the development of two such techniques; · a optical interferometric technique; for measuring nano-scale thicknesses in compliant contacts; · a laser induced fluorescence technique; developed to enable measurement of lubricant thickness of relatively thick films in compliant contacts

Holography: A survey

The development of holography and the state of the art in recording and displaying information, microscopy, motion, pictures, and television applications are discussed. In addition to optical holography, information is presented on microwave, acoustic, ultrasonic, and seismic holography. Other subjects include data processing, data storage, pattern recognition, and computer-generated holography. Diagrams of holographic installations are provided. Photographs of typical holographic applications are used to support the theoretical aspects

Label-free mapping of near-field transport properties of micro/nano-fluidic phenomena using surface plasmon resonance (SPR) reflectance imaging

My doctoral research has focused on the development of surface plasmon resonance (SPR) reflectance imaging technique to detect near-field transport properties such as concentration, temperature, and salinity in micro/nano fluidic phenomena in label-free, real-time, and full-field manner. A label-free visualization technique based on surface plasmon resonance (SPR) reflectance sensing is presented for real-time and full-field mapping of microscale concentration and temperature fields. The key idea is that the SPR reflectance sensitivity varies with the refractive index of the near-wall region of the test mixture fluid. The Fresnel equation, based on Kretschmann’s theory, correlates the SPR reflectance with the refractive index of the test medium, and then, the refractive index correlates with the mixture concentration or temperature. The basic operation principle is summarized and the laboratory-developed SPR imaging/analyzing system is described with the measurement sensitivity, uncertainties and detection limitations of the implemented SPR reflectance imaging. Total five proposed uses of SPR reflectance imaging technique are presented: (1) micromixing concentration field development of ethanol penetrating into water contained in a micro-channel, (2) full-field detection of the near-wall salinity profiles for convective/diffusion of saline droplet into water, (3) full-field and real-time surface plasmon resonance imaging thermometry, (4) correlation of near-field refractive index of nanofluids with surface plasmon resonance reflectance, and (5) unveiling hidden complex cavities formed during nanocrystalline self-assembly

VUV 157nm F₂ laser irradiation of micro- and nano-scale particles

Micro- and nanoscale particles have recently become the focus of a great deal of research interest due to their wide-ranging potential in a number of applications.This thesis concerns the interaction of small particles with the 157nm wavelength vacuum ultraviolet, VUV, emission from a molecular fluorine gas, F₂, laser. The laser system is introduced and an overview of laser ablation of polymers is presented.Small particles of different materials and sizes, supported on polymeric substrates, are irradiated at a wavelength of 157nm. The silica particles are transparent to the 157nm radiation, which leads to a lens effect. The polystyrene, silicon carbide and silver particles are opaque to the 157nm radiation, leading to a substrate-shielding effect.The lens effect results in the focussing of the incident laser beam into a hotspot at the interface between the particle and the substrate. The enhancement leads to the removal of substrate material underneath the particle to form a dimple on the surface of the substrate. The substrate-shielding effect leads to the removal of the substrate material around the opaque particle while the underlying material is left behind. This forms a polymeric support structure, with the seeding particle attached to the top. The shape of the seeding particle dictates the shape of the support structure, for example spherical particles seed composite conical structures and cylindrical particles seed linear prismatic structures. The polystyrene and silver particles are seen to undergo shape and size transformations as a result of laser irradiation. This is discussed in terms of mass loss through heating.Finite Element Method modelling is used to investigate and support the experimental results.Fluorescent polystyrene particles are also irradiated at a wavelength of 157nm. They retain their fluorescence after irradiation and exhibit Whispering Gallery Mode resonances, ideal for high-sensitivity sensing applications and Lab-on-a-Chip microreactors

Investigation of Line-Scan Dispersive Interferometry for In-Line Surface Metrology

Advanced manufacturing techniques enable ultra-precision surfaces to be fabricated with various complicated and large-area structures. For instance, the cost-effectiveness of Roll-to-Roll (R2R) manufacturing technology has been widely demonstrated in industries making high volume as well as large-area foil products and flexible electronics. Evaluation of these fine surfaces by an expensive trial-and-error approach is unadvisable due to the high scrap rate. Therefore quality control using in-line metrology of the functional surface plays an important role in the success of employing R2R technology by enabling a high product yield whilst guaranteeing high performance and a long lifespan of these multi-layer products. This thesis presents an environmentally robust line-scan dispersive interferometry (LSDI) technique that is suitable for applications in in-line surface inspection. Obtaining a surface profile in a single shot allows this interferometer to minimise the effect of external perturbations and environmental noise. Additionally, it eliminates the mechanical scanning and has an extended axial measurement range without the 2π phase ambiguity problem by dispersing the output of the spectrometer onto the camera. Benefiting from high-speed camera, general-purpose graphics processing unit and multi-core processor computing technology, the LSDI can achieve high dynamic measurement with a high signal-to-noise ratio and is effective for use on the shop floor. Two proof-of-concept prototypes aimed at different applications are implemented. The cylindrical lens based prototype has a large lateral range up to 6 mm and can be used for characterisation of additively manufactured surface texture, surface form and surface blemish. The second prototype using a 4X microscope objective with a diffraction limited lateral resolution (~ 4 µm) is aiming at characterisation of surface roughness, micro-scale defects, and other imperfections of the ultra-precision surfaces. System design, implementation, fringe analysis algorithms and system calibrations are presented in detail in this thesis. Their performances are evaluated experimentally by measuring several standard step heights as well as Al2O3 coated polyethylene naphthalate (PEN) films. The measurement results acquired using both prototypes and a commercial available instrument (Talysurf CCI 3000) align with each other acceptably. This shows that the developed metrology sensors may potentially be applied to production lines such as R2R surface inspection where only defects present on the surface are concerned in terms of quality assurance. Implementation of these prototypes offers an attractive solution to improve manufacturing processing and reliability for the products in ultra-highprecision engineering

Interferometric study of porous metal bearings

Imperial Users onl

Interferometric Metrology Using Reprogrammable Binary Holograms

Interferometric methods for surface metrology have been widely used for many years due to their speed, accuracy and versatility. It is frequently necessary however to produce a known comparison reference surface to minimise the optical path difference and hence enhance the dynamic range. An alternative to this is to use a computer generated hologram to act as the reference wave, or to correct a spherical reference wave to match a highly aspheric optic in order to achieve a null test. This thesis shall present a novel method of producing such holograms through the use of a binary ferroelectric liquid crystal on silicon spatial light modulator (FLCOS SLM) rather than using the more common lithographically produced plates. One of the primary advantages this could introduce is the ability for arbitrarily reprogrammable holograms to be created upon demand rather than needing to produce a series of holographic plates, saving both time and money in the testing of surfaces. We present results characterising the ability of a FLCOS SLM to produce increasingly large Zernike aberrations as well as quantifying the resulting errors, before using the device to reduce interferometric fringe density allowing us to measure aberrated optics and reveal low amplitude surface variations on the scale of 0.045 waves RMS

Visualisation and quantification of the defects in glass-fibre reinforced polymer composite materials using electronic speckle pattern interferometry

Non-destructive testing (NDT) of glass-fibre reinforced polyester (GRP) composite materials has been becoming increasingly important due to their wide applications in engineering components and structures. Electronic Speckle Pattern Interferometry (ESPI) has promising potential in this context because it is a non-contact, whole-field and real-time measurement system. This potential has never been fully exploited and there is only limited knowledge and understanding available in this area. This reality constrains the wide popularity and acceptance of ESPI as a novel NDT technique. Therefore it is of considerable importance to develop an understanding of the capability of ESPI with respect to damage evaluation in GRP composite materials. The research described in this thesis is concerned with an investigation into the applicability of ESPI in the NDT of GRP composite materials. Firstly, a study was carried out to determine excitation techniques in terms of practicality and effectiveness in the ESPI system. Three categories of defects were artificially introduced in GRP composite materials, namely holes, cracks and delaminations each with different geometrical features. ESPI was then employed to evaluate the three kinds of defects individually. It has been found that cracks and holes on back surfaces can be defined when the technique is used in conjunction with thermal excitation. Internal Temperature Differential (ITD) induced fringe patterns were more efficient than External Thermal Source (ETS) induced fringe patterns with regard to detecting the presence of holes and cracks. In the case of delamination, ESPI was found to be capable of detecting the damage when used in combination with mechanical excitation originating from a force transducer hammer. The geometrical features and magnitudes of delaminations were also established as being quantifiable. The validation of ESPI as an NDT technique was carried out in an attempt to establish a better understanding of its suitability and have more confidence in its applications. Four damaged specimens were Subjected to ESPI examination in conjunction with visual inspection, ultrasonic C-scan and sectioning techniques. The geometrical features and magnitudes of damage evaluated using ESPI showed a good correlation with those evaluated by conventional techniques. Poor visibility and readability is an inherent problem associated with ESP! due to an overlapping between the noise and signal frequencies. An improvement of image quality is expected in an attempt to achieve a wide acceptance of ESPI as a novel NDT technique. It has also been demonstrated that this problem can be tackled using optical phase stepping techniques in which optical phase data can be extracted from the intensity fringes. A three-frame optical phase stepping technique was employed to produce the "wrapped" and "unwrapped" phase maps which are capable of indicating internal damage with high visibility and clarity. Finally ESPI was practically employed to evaluate damage in GRP composites introduced by quasi-static and dynamic mechanical loading. It was found that ESP! was capable of monitoring the progressive damage development of specimens subjected to incremental flexural loading. The initial elastic response, damage initiation, propagation and ultimate failure of specimens were clearly characterised by the abnormal fringe pattern variations. In a similar manner, ESPI was employed to evaluate the low velocity falling weight impact induced damage. A correlation was established between the magnitude of damage and the impact event parameters as well as the residual flexural properties

Holography

Holography - Basic Principles and Contemporary Applications is a collection of fifteen chapters, describing the basic principles of holography and some recent innovative developments in the field. The book is divided into three sections. The first, Understanding Holography, presents the principles of hologram recording illustrated with practical examples. A comprehensive review of diffraction in volume gratings and holograms is also presented. The second section, Contemporary Holographic Applications, is concerned with advanced applications of holography including sensors, holographic gratings, white-light viewable holographic stereograms. The third section of the book Digital Holography is devoted to digital hologram coding and digital holographic microscopy

Holographic instrumentation applications

Investigating possibilities and limitations of applying holographic techniques to aerospace technolog