101 research outputs found
On the characterisation of periodic patterns in tessellated surfaces
No full textTessellated surfaces are a class of structured surfaces where texture has been engineered to reproduce a periodic pattern, specifically designed to meet a functional requirement. Despite having gained considerable acceptance in industrial production, tessellated surfaces still pose considerable challenges in terms of their metrological verification. The small scale of the dominant texture features requires the application of instruments typical of surface metrology; however, the computation of conventional surface texture parameters generally is not sufficient to capture the geometric properties and regularity aspects, which are fundamental for a complete characterisation of the pattern. In the work reported here, the characterisation of a periodic texture pattern is approached as a dimensional metrology problem, where the aim is the determination of target dimensional and geometric properties directly mapped to the design specifications. To illustrate the approach presented in this paper a specific test case, involving laser textured dimpled patterns designed to reduce friction in bearing applications, has been selected. This test case is used to highlight the many issues and critical aspects involved in the characterisation of tessellated surface
Development of a traceability route for areal surface texture measurements
No full textModern manufacturing industry is beginning to benefit from the ability to control the three dimensional, or areal, structure of a surface. To underpin areal surface manufacturing, a traceable measurement infrastructure is necessary. In this thesis a practical realisation of areal surface traceability is presented, which includes the development of: a primary in-strument, methodologies for using the primary instrument to calibrate material measure-ment standards used as standard transfer artefacts, and the process of transferring this traceability to industrial users of stylus and optical instruments.
The design of the primary instrument and its complex measurement uncertainty model are described, including detailed analysis of the input parameters of the uncertainty model and their effect on the co-ordinate measurements of the instrument.
The development of the process of transferring the areal traceability to industrial users lead to a set of metrological characteristics applicable to all areal surface topography measuring instruments. The set of metrological characteristics, now included into international stand-ards, comprise of: measurement noise, flatness deviation, amplification, linearity and squareness, and resolution. Despite the differences in operation of the various types of in-strument, the idea behind this set of metrological characteristics is based on the fact that these instruments produce three dimensional data sets of points, which is a new approach in the field. Metrological characteristics are quantities that can be measured directly, gener-ally using calibrated material measures. The development of standard methodologies for calibrating the metrological characteristics, and the explicit relationship between the metro-logical characteristics and the measurement uncertainty associated with the co-ordinate measurements provided by the instrument is presented. Many of the techniques described in this thesis are now being discussed for inclusion into international standards
Characterisation of structured surfaces and assessment of associated measurement uncertainty
No full textThis thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonRecently, structured surfaces, consisting of deterministic features designed to produce a
particular effect, have shown promise in providing superior functional performance for a
range of applications including: low friction surfaces, hydrophobic surfaces and optical
effects.
Methods have been developed to characterise such structured surfaces. The most
widely used characterisation methods are based on segmenting the surface in feature and
background regions and then determining the geometrical properties of those features.
However, further work is needed to refine these characterisation techniques and provide
associated uncertainties.
This thesis considers the effect of various segmentation control parameters such as
thresholds on the final geometric parameters. The effect of varying filter size is also considered.
These considerations should help in selecting a suitable characterisation method
for future projects.
Additionally, uncertainty in the characterisation should be estimated in order to give
an indication of the accuracy of the assessment. However, no previous work has assessed
uncertainty in the dimensional properties of structured surfaces. Therefore, this thesis
presents two methods to characterise the uncertainty in the geometric characteristics of
structured surfaces.
First, the measurement reproducibility is used, which can be determined by repeated
measurement of a feature. However, measurement reproducibility cannot account for all
sources of uncertainty and cannot assess any bias in the measurements.
Therefore, a second method based on assessment of the metrological characteristics of
the instrument is considered. The metrological characteristics estimate errors produced
by the instrument in a way that can easily be measured. Monte Carlo techniques are then
used to propagate the effects of the metrological characteristics and their uncertainties
into the final measurement uncertainty. For the example used, it was found that the results
using the metrological characteristics were in good agreement with the reproducibility results. From these results, it is concluded that the choice of segmentation method, control parameters and filtering can all significantly effect the characterisation of features on a structured surface, often in unexpected ways. Therefore, care must be taken when selecting these values for a specific application. Additionally, two methods of determining the uncertainty of the structured surfaces were considered. Both methods are valid and produce similar results. Using the measurement reproducibility is simple to perform, but requires many measurements and cannot account for some uncertainty sources such as those due to the instrument amplification factors. On the other hand, the use of metrological characteristics can account for all significant sources of uncertainty in a measurement, but is mathematically more complex, requiring Monte Carlo simulations to propagate the uncertainties into the final characteristics. Additionally, other artefacts than the sample being measured are required to determine the metrological characteristics, which may be an issue in some cases
The possibility of performing FEA analysis of a contact loading process fed by the MD simulation data
No full textMeasurement Uncertainty Associated With Profilometry Of Tooth Wear In Vitro.
No full textMeasurement Uncertainty Associated With Profilometry of Tooth Wear In VitroAustin RS 1, Giusca C 2, Leach R 2, Festy F 3, Dunne S 1, Moazzez R 4, Bartlett DW 5.1 Department of Primary Dental Care, King's College London Dental Institute, London Bridge, SE1 9RT 2 Higher Research Scientist, National Physical Laboratory, Hampton Rd, Teddington, Middlesex, UK, TW11 0LW 2 Principal Research Scientist, Mass & Dimensional Group, Engineering Measurement Division, National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW 3 Department of Biomaterials Science, King's College London Dental Institute, London Bridge, SE1 9RT 1 Department of Primary Dental Care, King’s College London Dental Institute, King’s College Hospital Denmark Hill, London. SE5 9RW 4 Department of Conservative Dentistry, King’s College London Dental Institute, London Bridge, SE1 9RT 5 Department of Fixed and Removable Prosthodontics, King’s College London Dental Institute, London Bridge, SE1 9RT.AbstractObjectives: To identify and quantify all possible sources of measurement uncertainty associated with a tooth wear measurement system. To carry out an analysis of uncertainty in accordance with international guidelines. To analyse the relative merits of tooth wear outcome parameters. Methods: An analysis of uncertainty associated with the use of a white light confocal profilometer (XYRIS 4000 WL, TaiCaan Technologies Ltd., Southampton, UK) in combination with custom designed software (ImageJ v1.42q, Rasband, W. S., U. S. National Institutes of Health, Bethesda, Maryland, USA) for measuring tooth wear in vitro, was carried out following the principles outlined in the ISO Guide to the Expression of Uncertainty in Measurement. Uncertainty budgets were compiled by summating the variances of each potential source of uncertainty and the effect of the measurement of tooth wear was considered. The relationship between step height and volume loss of enamel after erosion; erosion-abrasion and erosion-attrition was then examined.Results: The main contribution to the uncertainty budget was from a flatness deviation (max 0.49 µm), whereas the contributions from noise, non-linearity, sample shrinkage during dehydration and software errors were negligible. Despite the flatness error, the overall combined uncertainty was < 6 %, even when measuring a simulated depth of wear of 0.3 µm. Investigation of the use of step height and volume loss outcome parameters suggested that for erosion and erosion-abrasion the preferred outcome measure should be step height loss and for erosion-attrition the preferred outcome measure should be volume loss.Conclusion: The uncertainty analysis quantitatively expressed of the comprehensive effect of the likely degree of uncertainty introduced during tooth wear measurement. This allows users to gauge how ‘fit for purpose’ a measurement system is in order that the results of tooth wear research can be readily understood and properly interpreted.<br/
Lithium monolayers on single crystal C(100) oxygen-terminated diamond
No full textThin lithium layers on oxygenated C(100) boron-doped diamond have been observed using x-ray photoemission spectroscopy. Conductive boron-doped diamond was oxygen- terminated using an ozone cleaner. Lithium was evaporated onto the oxygen-terminated C(100) surface and an as-grown hydrogen terminated surface to a thickness of approximately 50 nm. After washing with deionised water, significant lithium signal is still detected on oxygenated diamond, but not on hydrogenated diamond, indicating a strongly bound lithium-oxygen surface layer is formed, as predicted by recent theoretical modeling
Exploring graphene formation on the C-terminated face of SiC by structural, chemical and electrical methods
No full textThe properties of epitaxial graphene on the C-face of SiC are investigated using comprehensive structural, chemical and electrical analyses. By matching similar nanoscale features on the surface potential and Raman spectroscopy maps, individual domains have been assigned to graphene patches of 1-5 monolayers thick, as well as bare SiC substrate. Furthermore, these studies revealed that the growth proceeds in an island-like fashion, consistent with the Volmer-Weber growth mode, illustrating also the presence of nucleation sites for graphene domain growth. Raman spectroscopy data shows evidence of large area crystallites (up to 620 nm) and high quality graphene on the C-face of SiC. A comprehensive chemical analysis of the sample has been provided by X-ray photoelectron spectroscopy investigations, further supporting surface potential mapping observations on the thickness of graphene layers. It is shown that for the growth conditions used in this study, 5 monolayer thick graphene does not form a continuous layer, so such thickness is not sufficient to completely cover the substrate
Considerations on the proposed linear theory of surface measurement for coherence scanning interferometers
No full textIt was suggested in [Appl. Opt. 52, 3662 (2013) [CrossRef(external)] ] that the result of a measurement via coherence scanning interferometry could be viewed as the convolution of a point spread function of the instrument and an open surface in 3D space that lies at the air/material interface over a portion of the object’s surface. Further, it was suggested that by measuring certain objects, such as ones that are very close to spherical, and whose surface is known to a sufficient level of accuracy, that a point spread function for the instrument could be determined from the measurement result. We conclude that the approximations used in this calculation do not give sufficient accuracy to allow this to be achieved, and that the truncation of the surface function from the closed surface surrounding the object is not defined sufficiently well in order to give a unique solution to the problem. The physical justification for the truncation of the surface in this manner is also questione
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