Dissertations / Theses on the topic 'Fibre processing'
To see the other types of publications on this topic, follow the link: Fibre processing.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Fibre processing.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Korte, Sandra. "Processing-Property Relationships of Hemp Fibre." Thesis, University of Canterbury. Mechanical Engineering, 2006. http://hdl.handle.net/10092/1175.
Full textAbstract:
There is great interest in the plant Cannabis sativa (hemp) as a source of technical fibres for the reinforcement of polymers in composite materials due to its high mechanical properties. As a natural fibre hemp also offers biodegradabilty and is therefore an inexpensive and renewable alternative to glass fibres However, the environmental benefits of natural fibres cannot be fully exploited if the manufacturing of their composites involves polluting processing steps. Unfortunately, there is still a lack of environmetally sustainable processing methods yielding technical fibres of sufficient quality. Enzyme application as a biotechnological processing method is a good candidate for this aim and is therefore actively investigated at present. In this work the effects of a range of enzymes on the morphological, compositional and mechanical properties of hemp was investigated. The enzymes were firstly characterised and then applied to hemp fibre for differing periods of time. After visual inspection, a set of fibre samples were selected and subjected to further analysis by Fourier-Transform Infrared Spectroscopy (FTIR), tensile testing and scanning electron microscopy (SEM). The commercial formulation Pectinex® Ultra-SL emerged as the most efficient in terms of treatment time and fibre quality. The effectiveness of treatments was further investigated by developing a novel experimental method that correlates the adhesion forces measured by atomic force microscopy (AFM) on the fibre surface to the properties of the fibres or composites. In order to identify correlations between the adhesion forces and fibre or composite properties, hemp fibre was subjected to four distinctly different treatments to obtain significant differences between fibre properties. The fibres and composites were then analyzed using a combination of FTIR, tensile testing, 3-point bend testing, dynamic mechanical analysis (DMA) and SEM. Based on this comprehensive dataset the AFM data was correlated using the software SPSS. The information derived from AFM (adhesion forces and surface topology) was useful in the clarification of fibre modifications evoked by the treatments.
2
Islam, Mohammad Saiful. "The Influence of Fibre Processing and Treatments on Hemp Fibre/Epoxy and Hemp Fibre/PLA Composites." The University of Waikato, 2008. http://hdl.handle.net/10289/2627.
Full textAbstract:
In recent years, due to growing environmental awareness, considerable attention has been given to the development and production of natural fibre reinforced polymer (both thermoset and thermoplastic) composites. The main objective of this study was to reinforce epoxy and polylactic acid (PLA) with hemp fibre to produce improved composites by optimising the fibre treatment methods, composite processing methods, and fibre/matrix interfacial bonding. An investigation was conducted to obtain a suitable fibre alkali treatment method to: (i) remove non-cellulosic fibre components such as lignin (sensitive to ultra violet (UV) radiation) and hemicelluloses (sensitive to moisture) to improve long term composites stability (ii) roughen fibre surface to obtain mechanical interlocking with matrices (iii)expose cellulose hydroxyl groups to obtain hydrogen and covalent bonding with matrices (iv) separate the fibres from their fibre bundles to make the fibre surface available for bonding with matrices (v) retain tensile strength by keeping fibre damage to a minimum level and (vi) increase crystalline cellulose by better packing of cellulose chains to enhance the thermal stability of the fibres. An empirical model was developed for fibre tensile strength (TS) obtained with different treatment conditions (different sodium hydroxide (NaOH) and sodium sulphite (Na2SO3) concentrations, treatment temperatures, and digestion times) by a partial factorial design. Upon analysis of the alkali fibre treatments by single fibre tensile testing (SFTT), scanning electron microscopy (SEM), zeta potential measurements, differential thermal analysis/thermogravimetric analysis (DTA/TGA), wide angle X-ray diffraction (WAXRD), lignin analysis and Fourier transform infrared (FTIR) spectroscopy, a treatment consisting of 5 wt% NaOH and 2 wt% Na2SO3 concentrations, with a treatment temperature of 120oC and a digestion time of 60 minutes, was found to give the best combination of the required properties. This alkali treatment produced fibres with an average TS and Young's modulus (YM) of 463 MPa and 33 GPa respectively. The fibres obtained with the optimised alkali treatment were further treated with acetic anhydride and phenyltrimethoxy silane. However, acetylated and silane treated fibres were not found to give overall performance improvement. Cure kinetics of the neat epoxy (NE) and 40 wt% untreated fibre/epoxy (UTFE) composites were studied and it was found that the addition of fibres into epoxy resin increased the reaction rate and decreased the curing time. An increase in the nucleophilic activity of the amine groups in the presence of fibres is believed to have increased the reaction rate of the fibre/epoxy resin system and hence reduced the activation energies compared to NE. The highest interfacial shear strength (IFSS) value for alkali treated fibre/epoxy (ATFE) samples was 5.2 MPa which was larger than the highest value of 2.7 MPa for UTFE samples supporting that there was a stronger interface between alkali treated fibre and epoxy resin. The best fibre/epoxy bonding was found for an epoxy to curing agent ratio of 1:1 (E1C1) followed by epoxy to curing agent ratios of 1:1.2 (E1C1.2), 1: 0.8 (E1C0.8), and finally for 1:0.6 (E1C0.6). Long and short fibre reinforced epoxy composites were produced with various processing conditions using vacuum bag and compression moulding. A 65 wt% untreated long fibre/epoxy (UTLFE) composite produced by compression moulding at 70oC with a TS of 165 MPa, YM of 17 GPa, flexural strength of 180 MPa, flexural modulus of 10.1 GPa, impact energy (IE) of 14.5 kJ/m2, and fracture toughness (KIc) of 5 MPa.m1/2 was found to be the best in contrast to the trend of increased IFSS for ATFE samples. This is considered to be due to stress concentration as a result of increased fibre/fibre contact with the increased fibre content in the ATFE composites compared to the UTFE composites. Hygrothermal ageing of 65 wt% untreated and alkali treated long and short fibre/epoxy composites (produced by curing at 70oC) showed that long fibre/epoxy composites were more resistant than short fibre/epoxy composites and ATFE composites were more resistant than UTFE composites towards hygrothermal ageing environments as revealed from diffusion coefficients and tensile, flexural, impact, fracture toughness, SEM, TGA, and WAXRD test results. Accelerated ageing of 65 wt% UTLFE and alkali treated long fibre/epoxy (ATLFE) composites (produced by curing at 70oC) showed that ATLFE composites were more resistant than UTLFE composites towards hygrothermal ageing environments as revealed from tensile, flexural, impact, KIc, SEM, TGA, WAXRD, FTIR test results. IFSS obtained with untreated fibre/PLA (UFPLA) and alkali treated fibre/PLA (ATPLA) samples showed that ATPLA samples had greater IFSS than that of UFPLA samples. The increase in the formation of hydrogen bonding and mechanical interlocking of the alkali treated fibres with PLA could be responsible for the increased IFSS for ATPLA system compared to UFPLA system. Long and short fibre reinforced PLA composites were also produced with various processing conditions using compression moulding. A 32 wt% alkali treated long fibre PLA composite produced by film stacking with a TS of 83 MPa, YM of 11 GPa, flexural strength of 143 MPa, flexural modulus of 6.5 GPa, IE of 9 kJ/m2, and KIc of 3 MPa.m1/2 was found to be the best. This could be due to the better bonding of the alkali treated fibres with PLA. The mechanical properties of this composite have been found to be the best compared to the available literature. Hygrothermal and accelerated ageing of 32 wt% untreated and alkali treated long fibre/PLA composites ATPLA composites were more resistant than UFPLA composites towards hygrothermal and accelerated ageing environments as revealed from diffusion coefficients and tensile, flexural, impact, KIc, SEM, differential scanning calorimetry (DSC), WAXRD, and FTIR results. Increased potential hydrogen bond formation and mechanical interlocking of the alkali treated fibres with PLA could be responsible for the increased resistance of the ATPLA composites. Based on the present study, it can be said that the performance of natural fibre composites largely depend on fibre properties (e.g. length and orientation), matrix properties (e.g. cure kinetics and crystallinity), fibre treatment and processing methods, and composite processing methods.
3
Leedumrongwatthanakun, Saroch. "Quantum information processing with a multimode fibre." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS526.
Full textAbstract:
Le transport à haut débit de données à travers des fibres optiques grâce au multiplexage spatial est en pratique limité par la diaphonie modale. Au lieu de considérer ce couplage modal comme une limitation, nous exploitons ici ce mélange de modes comme une ressource. Nous mettons en oeuvre un réseau optique linéaire programmable basé sur le concept de design photonique inverse, exploitant les techniques de mise en forme du front d’onde. Nous démontrons la manipulation d’interférences quantiques à deux photons sur divers réseaux linéaires, comprenant des degrés de liberté spatiaux et de polarisations. En particulier, nous vérifions expérimentalement la « zero transmission law » dans des interféromètres de Fourier et de Sylvester, permettant de quantifier le degré d’indiscernabilité d’un état d’entrée. De plus, grâce à la possibilité de mettre en oeuvre un réseau non unitaire, nous mettons en évidence l’anti-coalescence de photons dans toutes les configurations de sortie, et réalisons une expérience d’absorption cohérente. Nous démontrons ainsi l’aspect reconfigurable de l’implémentation de tels réseaux optiques linéaires dans des fibres multimodes. De plus, nous étudions les propriétés statistiques du speckle à un et à deux photons générés à partir de divers états d’entrée, après propagation dans une fibre multimode. Ces propriétés statistiques du speckle peuvent être utilisées pour extraire des informations sur la dimensionnalité, la pureté et l’indiscernabilité d’un état quantique inconnu, permettant ainsi leur classification. Ce travail met en évidence le potentiel du contrôle de front d’onde en milieux complexes pour le traitement quantique de l’informationTransport of information through a multimode optical fibre raises challenges when one wants to increase the data traffic using many spatial modes due to modal cross-talk and dispersion. Instead of considering those complex mixing of modes as a detrimental process, in this dissertation, we harness its mode mixing to process quantum optical information. We implement a reconfigurable linear optical network, a fundamental building block for scalable quantum technologies, based on an inverse photonic approach exploiting the technology of wavefront shaping. We experimentally demonstrate manipulation of two-photon quantum interference on various linear optical networks across both spatial and polarization degrees of freedom. In particular, we experimentally show the zero-transmission law in Fourier and Sylvester interferometers, which are used to certificate the degree of indistinguishability of an input state. Moreover, thanks to the ability to implement a non-unitary network, we observe the photon anti-coalescence effect in all output configurations, as well as the realization of a tunable coherent absorption experiment. Therefore, we demonstrate the reconfigurability, accuracy, scalability and robustness of the implemented linear optical networks for quantum information processing. Furthermore, we study the statistical properties of one-and two-photon speckles generated from various ground-truth states of light after propagating through a multimode fibre. These statistical properties of speckles can be used to extract information about the dimensionality, purity, and indistinguishability of an unknown input state of light, therefore allowing for state classification. Our results highlight the potential of complex media combined with wavefront shaping for quantum information processing
4
Mahmood, Amjed Saleh. "Processing-performance relationships for fibre-reinforced composites." Thesis, University of Plymouth, 2016. http://hdl.handle.net/10026.1/4181.
Full textAbstract:
The present study considers the dependence of mechanical properties in composite laminates on the fibre architecture. The objective is to characterise the mechanical properties of composite plates while varying the fibre distribution but keeping the constituent materials unchanged. Image analysis and fractal dimension have been used to quantify fibre distribution and resin-rich volumes (RRV) and to correlate these with the mechanical properties of the fibre-reinforced composites. The formation, shape and size of RRV in composites with different fabric architectures is discussed. The majority of studies in literatures show a negative effect of the RRV on the mechanical behaviour of composite materials. RRV arise primarily as a result of (a) the clustering of fibres as bundles in textiles, (b) the stacking sequence, and/ or stacking process, (c) the resin properties and flow characteristics, (d) the heating rate as this directly affects viscosity and (e) the consolidation pressure. Woven glass and carbon/epoxy fabric composites were manufactured either by the infusion or the resin transfer moulding (RTM) process. The fractal dimension (D) has been employed to explore the correlation between fabric architecture and mechanical properties (in glass or/ carbon fibre reinforced composites with different weave styles and fibre volume fraction). The fractal dimension was determined using optical microscopy images and ImageJ with FracLac software, and the D has been correlated with the flexural modulus, ultimate flexural strength (UFS), interlaminar shear strength (ILSS) and the fatigue properties of the woven carbon/epoxy fabric composites. The present study also considers the dependence of fatigue properties in composite laminates on static properties and fibre architecture. Four-point flexural fatigue test was conducted under load control, at sinusoidal frequency of 10 Hz with amplitude control. Using a stress ratio (R=σmin/σmax) of 0.1 for the tension side and 10 for the compression side, specimens were subjected to maximum fatigue stresses of 95% to 82.5% step 2.5% of the ultimate flexural strength (UFS). The fatigue data were correlated with the static properties and the fibre distribution, in order to obtain a useful general description of the laminate behaviour under flexural fatigue load. The analysis of variance (ANOVA) technique was applied to the results obtained to identify statistically the significance of the correlations. Composite strength and ILSS show a clear dependence on the fibre distribution quantified using D. For the carbon fabric architectures considered in this study, the fatigue properties of composite laminates have significant correlations with the fibre distribution and the static properties of the laminates. The loss of 5-6 % in the flexural modulus of composite laminates indicates an increasing risk of failure of the composite laminates under fatigue loads. The endurance limits, based on either the static properties or the fibre distribution, were inversely proportional to the strength for all laminates.
5
Pini, Niccolò. "Development and processing of novel Active Fibre Composites /." Zürich : ETH, 2006. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=16904.
Full text
6
Svanberg, Maria. "Effects of processing on dietary fibre in vegetables." Lund : Dept. of Applied Nutrition and Food Chemistry, Lund Institute of Technology, Lund University, 1997. http://books.google.com/books?id=EcZtAAAAMAAJ.
Full text
7
Doroudiani, Saeed. "Microcellular wood-fibre thermoplastic composites, processing-structure-properties." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq41016.pdf.
Full text
8
Penty, Richard Vincent. "Novel optical fibre Kerr devices for signal processing." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.291606.
Full text
9
Millar, D. S. "Digital signal processing for coherent optical fibre communications." Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1333248/.
Full textAbstract:
In this thesis investigations were performed into digital signal processing (DSP) algorithms for coherent optical fibre transmission systems, which provide improved performance with respect to conventional systems and algorithms. Firstly, an overview of coherent detection and coherent transmission systems is given. Experimental investigations were then performed into the performance of digital backpropagation for mitigating fibre nonlinearities in a dual-polarization quadrature phase shift keying (DP-QPSK) system over 7780 km and a dual-polarization 16- level quadrature amplitude modulation (DP-QAM16) system over 1600 km. It is noted that significant improvements in performance may be achieved for a nonlinear step-size greater than one span. An approximately exponential relationship was found between performance improvement in Q-factor and the number for required complex multipliers. DSP algorithms for polarization-switched quadrature phase shift keying (PS-QPSK) are then investigated. A novel two-part equalisation algorithm is proposed which provides singularity-free convergence and blind equalisation of PS-QPSK. This algorithm is characterised and its application to wavelength division multiplexed (WDM) transmission systems is discussed. The thesis concludes with an experimental comparison between a PS-QPSK transmission system and a conventional DP-QPSK system. For a 42.9 Gb/s WDM system, the use of PS-QPSK enabled an increase of reach of more than 30%. The resultant reach of 13,640 km was, at the time of publication, the longest transmission distance reported for 40 Gb/s transmission over an uncompensated link with standard fibre and optical amplification.
10
Alam, Shaif-ul. "Advanced fibre circuitry for all-optical signal processing." Thesis, University of Southampton, 2000. https://eprints.soton.ac.uk/15501/.
Full textAbstract:
This thesis presents results of new types of fibre lasers and oscillators as well as a new all-fibre nonlinear modulator with nearly instantaneous response time. The development of a simple and stable, passively mode-locked source of picosecond pulses is described in chapter 2. Here the mode locking of the laser was obtained by using the combined effect of frequency-shifted feedback and a nonlinear amplifying loop mirror. The new cavity configuration allowed tuning of the laser continuously over 25 nm of the erbium gain bandwidth by using a bulk diffraction grating. The shortest reported pulse width (1.2 ps) from this type of laser has been demonstrated. A complete characterisation of the laser, including its mode locking build-up time, is presented. Cascaded nonlinearity in quadratic nonlinear materials is the basis in realising nonlinearity free optical amplifiers. Experimental results on cascaded nonlinearity in a periodically poled lithium niobate sample are presented in chapter 3. A nonlinear phase shift of more than 1.5p was obtained from only a 4 mm long sample due to its large effective nonlinear refractive index coefficient (~1 x 10-13 cm2/W). Experiments on the nonlinear phase shift compensation in an optical fibre and amplifier are presented in chapter 4. Phase shift compensation of more than 1.5p has been successfully demonstrated. Chapter 5 presents theoretical investigations on the modulation of optical signals using the stimulated Raman scattering (SRS) process in silica fibre. Numerical results reveal that to modulate signals in this scheme it is necessary to consider other competing nonlinear effects such as cascaded SRS, modulation instability etc. actively. Signal modulation as fast as 250 - 300 GHz can be realised using this intensity modulator. Chapter 6 describes the experimental results on the modulation of optical signal using SRS in optical fibre. With this Raman intensity modulator, bit-by-bit modulation of 10 Gbit/s simulated data stream has been demonstrated. An extinction ratio (modulation depth) of more than 15 dB was realised. The proposed intensity modulator can also be used as a time domain scalpel and can create a dark pulse in a bright background.
11
Hsu, Che-Yuan. "Experimental determination of fibre orientation distribution and prediction of stiffness in short fibre-reinforced thermoplastics." Thesis, University of Nottingham, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243399.
Full text
12
Farries, Pamela Mary. "Processing and properties of fibre reinforced silicon carbide composites." Thesis, Imperial College London, 1998. http://hdl.handle.net/10044/1/11355.
Full text
13
Nagel, Ulf. "The processing and characterisation of recycled glass fibre composites." Thesis, University of Strathclyde, 2016. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=27388.
Full textAbstract:
The widespread use of glass fibre reinforced polymers (GFRP) over the last decades has led to an increasing amount of waste and a demand for recycling solutions. Mechanical, chemical and thermal GFRP recycling processes have been developed in academia but the commercialisation of GFRP recycling processes has proven to be difficult. The value of recycled glass fibres is low because their strength is usually reduced during recycling processes. Thermal recycling processes involve the exposure of GFRP waste to elevated temperatures to degrade the polymer matrix and extract the glass fibres. The room temperature strength of the glass fibres and organic sizings are degraded during thermal recycling processes which leads to a lower composite performance when the recycled fibres are processed into composites. The main objective of this thesis was to develop composites based on thermally recycled glass fibres that can compete with as received fibre composites. Polypropylene (PP) was chosen as matrix material because of its processability and its widespread use. First, an understanding of the structure performance relationship of glass fibre PP (GF/PP) composites was established and gaps in existing literature were studied. The addition of maleic anhydride grafted PP (MAPP) to injection moulded GF/PP composites correlated with an increase of the ultimate mechanical properties (tensile strength, strain at break) but too high MAPP contents resulted in a reduction of the ultimate mechanical composite properties and the composite modulus. The optimum MAPP content was observed to depend on the glass fibre content. The composite tensile test data was used to analyse the microstructural composite properties. It was concluded that the analysis of the composite tensile data based on the Kelly-Tyson model can be used as a screening tool to detect general trends of the interfacial adhesion between glass fibres and PP matrix. However, micromechanical tests like the microbond tests are still required for more detailed studies of the interfacial adhesion because the composite tensile properties are often affected by a number of interacting factors. Glass fibres were thermally degraded before composite processing to simulate a thermal recycling process. Thermal gravimetric analysis and microbond tests showed that all investigated commercial sizings degraded at thermal recycling temperatures. The ultimate mechanical composite properties were reduced when the glass fibres were thermally degraded. The drop of the composite performance was attributed to a reduction of the glass fibre strength and a low interfacial adhesion between fibres and PP. Most of the interfacial adhesion between thermally degraded glass fibres and PP was recovered when the MAPP content was optimised. However, the composite performance was still low compared to as received glass fibre composites because of the low fibre strength. It was concluded that the post treatment of thermally recycled glass fibres should include the regeneration of the fibre strength and the reactivation of the fibre surface functionality in order to increase the reinforcement potential of the fibres. Aminopropyltriethoxy silane (APS) and sodium hydroxide (NaOH) were applied to the thermally degraded glass fibres. Approximately 70 % of the tensile strength loss of injection moulded GF/PP composites was recovered when thermally degraded glass fibres were post treated with APS. Micromechanical analysis suggested that the APS regenerated glass fibres experienced similar stresses as the as received fibres. The increase of the glass fibre stress could not solely be explained by an increase of the interfacial adhesion between fibres and matrix. It was proposed that the APS treatment also led to an increase of the maximum glass fibre strength in the injection moulded composites. Thermally degraded glass fibres tend to form a fluffy mat during the NaOH treatment and could not be processed via extrusion compounding and injection moulding. A glass mat thermoplastic (GMT) process was set up over the course of this PhD to process NaOH treated glass fibres. The treatment of the thermally degraded glass fibres with NaOH led to an increase of the composite tensile strength. The increase of the composite tensile strength was correlated with an increase of the glass fibre strength. The APS treatment of the thermally degraded glass fibres also led to an increase of GMT composite tensile strength but the increase was lower compared to the injection moulded GF/PP composites. It was speculated that the effect of APS on the strength of thermally degraded glass fibres might be gauge length dependent. The optimum treatment of thermally recycled glass fibres might therefore depend on the final fibre length in the composite. An APS treatment might be suitable for injection moulded composites with glass fibres shorter than 1 mm while the NaOH treatments might be required for composites with longer fibres. To the author’s knowledge the work presented in this thesis shows for the first time that the reinforcement potential of thermally degraded glass fibres can be regenerated without hydrogen fluoride. Thus, this work might be a step towards the development of an economically viable GFRP recycling process.
14
Watkins, L. R. "Optical fibre communications : signal processing to accommodate system impairments." Thesis, Bangor University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.279143.
Full text
15
Khandaker, Iman Ibrahim. "Optical fibre sensors for the optimization of plasma processing." Thesis, University of Liverpool, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318236.
Full text
16
Smith, Paul. "Structural preform design for low cost composites processing." Thesis, University of Nottingham, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263424.
Full text
17
Popescu, Carmen Rodica. "Processing and characterisation of SiC-fibre reinforced Cu-matrix composites." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=971275645.
Full text
18
McEwen, Gordon John. "Colour image processing for textile fibre matching in forensic science." Thesis, Queen's University Belfast, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336101.
Full text
19
Fernandes, Monteiro Sampaio Sandra Cristina. "Wet processing of fibre blends containing pre-harvest retted flax." Thesis, De Montfort University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414922.
Full text
20
Chan, Tsang Hung. "Digital signal processing in optical fibre digital speckle pattern interferometry." HKBU Institutional Repository, 1996. http://repository.hkbu.edu.hk/etd_ra/269.
Full text
21
Ezbiri, A. "Passive signal processing techniques for miniature fibre fabry-perot interferometric sensors." Thesis, Cranfield University, 1996. http://dspace.lib.cranfield.ac.uk/handle/1826/11243.
Full textAbstract:
This thesis describes new signal processing techniques applicable to miniature low finesse Fabry-Perot interferometric sensors. The principle of operation behind the techniques presented resides in the use of the axial modes from a single multimode laser diode to produce a series of phrase shifted interferometric outputs in conjunction with the path imbalance of the sensor microactivity.
22
Bland, Jonathan H. "The rheology and processing of glass mat thermoplastics." Thesis, University of Newcastle Upon Tyne, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363537.
Full text
23
Rangie, Massod. "The processing and thermal stability of PMR based carbon fibre composites." Thesis, University of Sheffield, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265586.
Full text
24
Kaya, Cengiz. "Processing and properties of alumina fibre-reinforced mullite ceramic matrix composites." Thesis, University of Birmingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.633209.
Full textAbstract:
The present study examines the feasibility of fabricating Saffil alumina fibre-reinforced mullite matrix composites via a single-infiltration EFD process, and/or EFD plus pressure filtration. An in-situ EFD cell was developed in order to produce fibrereinforced composites. This cell is able to record the weight gain during EFD, i.e., in real time, thus providing information to establish the exact EFD kinetic model. The critical issues in preparing an aqueous based mullite precursor (suitable for EFD) from nano-size boehmite and fumed silica particles were discussed. It has also been shown that dense, homogeneous green mullite composition and sintered mullite microstructures can be prepared successfully only by controlling the short-range particle-particle interactions of the dissimilar particle species within the suspension. A reaction bonded mullite (RBM) slurry containing alumina and silicon carbide powders was developed in order to obtain zero-shrinkage RBM after sintering. Saffil alumina fibre mats pre-coated with mullite using EFD were infiltrated with RBM slurry using PF. By these means, high green density ( 64.5 % TD) and sintered density (94.6 % TD) were achieved. Room and high temperature 4-point bend behaviour of the monolithic and fibrereinforced CMCs were examined. 30 vol % fibre addition increased both the strength and toughness of the monolithic mullite at room and high temperature. At room temperature, a maximum 4-point bend strength (-500 MPa) was obtained from a fibrereinforced RBM composite having a weak mullite interface between the fibre and the mullite matrix. Both monolithic and fibre-reinforced mullite components produced here were able to keep the similar strength from room temperature up to 1300 °C. A slight decrease was observed at 1400 °C whilst a dramatic strength decrease occurred at 1500 °C, as fibre grain growth occurs at this temperature. Debonding, fibre pull-out, bridging, load transfer and crack deflection mechanisms are found to be responsible for the high strength and toughness. The state-of-damage in Saffil alumina fibre-reinforced RBM CMCs subjected to cyclic fatigue was investigated by means of acoustic emission (AE) monitoring and dynamic forced resonance (FR) techniques. FR measurements showed that as the number of cycles is increased, the Young's modulus decreases, whereas the internal friction increases. The sharp increase in Q" 1 as the number of cycles is increased is evidence for the development of significant microstructural damage, such as matrix cracking and delamination, resulting in the creation of new internal surfaces within the composite.
25
Cosgrave, Joseph Anthony. "Acoustic-optic monitoring of electrical power equipment using chromatic signal processing." Thesis, University of Liverpool, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263845.
Full text
26
Hu, Yiqun. "Digital Spatial Domain Multiplexing technique for optical fibre sensor arrays." Thesis, University of Southampton, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245041.
Full text
27
Niewczas, Pawel. "Implementation of a Faraday Effect based optical current transducer using digital signal processing techniques." Thesis, University of Strathclyde, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.248515.
Full text
28
Villanueva, German Reyes. "Processing and characterisation of the mechanical properties of novel fibre-metal laminates." Thesis, University of Liverpool, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399209.
Full text
29
Gunay, Volkan. "Sol-gel processing of fibre reinforced glass and glass-ceramic matrix composites." Thesis, University of Sheffield, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399683.
Full text
30
Munian, A. C. "Pineapple dietary fibre and the effects of processing on its functional properties." Master's thesis, University of Cape Town, 2006. http://hdl.handle.net/11427/11738.
Full textAbstract:
Includes bibliographical references.The waste streams from the pineapple canning industry are a valuable source of carbohydrates, in particular dietary fibre (DF) and neutral sugars. In addition, the waste is a suitable source of antioxidants, enzymes such as bromelin and flavours. Since this waste (core and peel) is currently sold at minimal cost to cattle farmers for use as cattle feed or compost, alternative uses of the material with commercial potential was investigated.
31
Chow, Wing Keung. "Applications of digital signal processing to real-time optical fibre holographic interferometry." HKBU Institutional Repository, 1992. https://repository.hkbu.edu.hk/etd_ra/18.
Full text
32
Ning, Bo. "Investigation of fibre protection and water saving in the wet processing of textiles." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/investigation-of-fibre-protection-and-water-saving-in-the-wet-processing-of-textiles(87379354-1316-4051-a17e-bc195687e379).html.
Full textAbstract:
The aim of this research was to minimize the damage of textile fibres (wool and cotton), in the wet processing, such as bleaching and dyeing, and also seek to reduce fresh water usage during these processes. Typically bleaching of textiles involves the application of oxidative and reductive whitening agents. However a detrimental side-effect is a reduction in their strength. Therefore the approach to developing robust processes is to optimize the chemical treatments and incorporate protective agents in to the treatment baths. This study has demonstrated the application of fibre protective agents were successful in maintaining fabric strength, as defined by flat abrasion, without affecting the improvement in fabric whiteness for both wool and cotton. While the protective mechanism for wool is probably based on restricting damage to the cell membrane proteins and minimizing internal lipid loss, the protective effect on cotton is less certain. Colouration of wool requires elevated temperatures through boiling of aqueous treatment baths or steaming after printing. In this study the effect of blank dyeing of wool fabrics was examined and the extent of hydrothermal damage and yellowing established. In addition the potential effect of fibre protective agents, such as protein hydrolysates and formaldehyde-based agents, were assessed and their benefits in terms of fabric tensile strength, colour, mechanical properties related to fabric handle, and abrasion resistance determined. It was demonstrated that both protective agents offer fibre protection as individual additives and co-applicants. Fresh water is a vital component in the processing of textiles. However water is a scarce commodity and the need for efficient use of it is important. Therefore in this study the use of simulated seawater as an alternative processing medium for bleaching and colouration was evaluated. It was found alkaline hydrogen peroxide bleaching of wool and cotton could be performed successfully in the seawater and benefits in terms of good whiteness and improved abrasion resistance achieved. Building on the previous fibre protection study the incorporation of Byco C into the salt water bleach bath was evaluated and flat abrasion strength benefits again demonstrated. In this research a modified paper-based filter was be used as the “clean” industrial textile water effluent. Initially the filter paper based on poultry feathers was evaluated. The keratinous byproduct/waste material offers a cheap potential source of fibre and was successfully converted into paper. The strength and dye adsorption properties of the papers filters were assessed and it was observed that the important wet strength was considerably improved by the application of a cationic reactive polymer. Novel C30-modified PVP based nanofibres were force spun and as evaluated as a dye absorbent for Direct and Disperse dyes. The nanofibre web offered significant potential for absorbing the comparable non-polar disperse dyes.
33
Sadek, Mohammad. "Modeling biofibre (hemp) processing using the discrete element method (DEM)." Food & Process Engineering Institute Division of ASABE, 2011. http://hdl.handle.net/1993/18484.
Full textAbstract:
The main objective of the research was to understand hemp processing at different stages through numerical simulations. Processing of hemp materials involves breaking the hemp into different sizes of particles and separating those particles into fractions of different sizes. Numerical models were developed using the discrete element method (DEM) to simulate hemp processing using a hammermill and separations of different hemp particles using a 3D vibratory screen-type separator. The models were implemented using a commercial DE code, the Particle Flow Code in Three Dimension (PFC3D). In the models, virtual hemp, hemp fibre and core were defined using clusters of PFC3D basic spherical particles which are connected by the PFC3D parallel bonds. The microproperties (e.g. particle stiffness and friction coefficient, and bond stiffness and strength) of these particles were calibrated. For calibrations, virtual tests were performed using PFC3D for hemp stem, fibre, and core. Those virtual tests included direct shear tests of fibre and core particles, tensile tests of fibre, and compression tests of hemp stems. The microproperties of these particles were calibrated through comparing results from the virtual tests with results from laboratory tests or literature data. Those calibrated particle microproperties were used in the PFC3D models developed for simulating the hammermill for hemp processing and the 3D vibratory separator for particle separation. These two machines were constructed using various PFC3D walls and lines, and had the main features and operational conditions as the real machines. The hammermill model was able to predict the power requirement of hammermill and particle dynamic behaviours (kinetic and strain energies) within the hammermill. The separator model was capable of predicting the separation efficiency of the 3D vibratory separator for separations of different hemp particle mixtures. The behaviour of the models reflected the real behaviour observed experimentally. The model results were reasonably good as compared with literature data and the test results. The models developed have the potential to simulate many other dynamic attributes of hemp particles with the machines. This study has laid a solid foundation for future studies of biomaterial-machine interactions using the DEM.
34
Virk, Amandeep Singh. "Numerical models for natural fibre composites with stochastic properties." Thesis, University of Plymouth, 2010. http://hdl.handle.net/10026.1/517.
Full textAbstract:
Natural fibres are increasingly being considered as the reinforcement for polymer matrix composites as they are perceived to be sustainable being a renewable resource. However, they suffer from higher variability in mechanical properties and concerns about their long-term durability in a moist environment. In this study the physical properties of the jute fibres were characterised, the fibre length distribution was determined and the fibre cross-section was analysed using digital images. It was observed that the true fibre area followed a log-normal distribution. The fibre area distribution for different geometrical shapes was estimated and the error in the estimated area of assumed fibre cross-section was also determined to assess the applicability of the assumed cross-section. The mechanical properties of the jute technical fibres from a single batch from South Asia were determined; fibre tensile tests were carried out at ten different gauge lengths between 6 mm and 300 mm and the Young’s modulus, strain to failure and ultimate tensile strengths were determined individually. A strong correlation was observed between the fibre strength/fracture strain and fibre gauge length. It was found as the gauge length increases the fibre strength/fracture strain drops. The fibre failure (Strength/Strain) was modelled using Weibull distribution and three statistical models were developed to relate the fibre strength/fracture strain to the fibre gauge length. Examination of tensile test data reveals that the coefficient of variation (CoV) for failure strain is consistently lower than the CoV for fracture stress (strength), as the failure strain is weakly influenced by the fibre cross-section. Hence, failure strain is the more consistent failure criterion and it is recommended to use failure strain as the key design criterion for natural fibre composites in order to improve reliability in the design of these materials. Different authors have tried to model natural fibre reinforced polymer elastic modulus using micromechanical models and have suggested that further study should include fibre angle and length distribution factors to improve the micromechanical prediction. This thesis further seeks to validate a novel methodology for the prediction of the tensile modulus and strength of natural fibre composites through careful consideration of each of the parameters in the rule of mixtures along with consideration of the statistical variation inherent in reinforcements extracted from plants. The tensile modulus and strength of jute fibre reinforced composites manufactured from well characterised fibres was measured experimentally. Six well established micromechanical models were used to predict the composite elastic modulus. Two micromechanical models were used to predict composite strength. For both mechanical properties, the inclusion of a fibre area correction factor to account for the non-circular cross-section of the fibre resulted in an improved prediction of the respective mechanical properties.
35
Saunders, R. A. "Compression and microstructure of glass fibre fabrics in the processing of polymer composites." Thesis, University of Surrey, 1997. http://epubs.surrey.ac.uk/842832/.
Full textAbstract:
The compression of typical glass fibre woven fabrics, namely plain, twill, satin, and noncrimped stitch-bonded fabric, was studied experimentally by performing a series of mechanical tests on dry and resin impregnated assemblies of fabrics. This was followed by microstructural studies of corresponding laminates cured under different degrees of compression. The experiments included investigations on the effects of applied pressure, speed of compression, fabric orientation, number of plies and different resin systems on fibre volume fraction,Vf, of the compressed assembly. It was found that the compression of dry fabrics followed a power-law relationship between pressure and Vf where the power law index, b, was determined to be approximately equal to 10.3, 9.8 and 9.1 for assemblies consisting of plain, twill and 5 harness satin weaves, respectively. A mathematical analysis was performed for the viscoelastic compression of resin impregnated assemblies of fabrics and a model was developed incorporating the deformation of the fibre network and resin flow through the reinforcement. A methodology was devised for the geometrical representation of plain weaves in the microstructural analysis of cured laminates. The microstructural studies then provided data for the area and geometrical parameters of the yam cross-section; the mean amplitude, wavelength and phase angle of the yarn waveform and the distance between plies at different compression pressures. Cross-sections of laminates with each of the considered fabrics were compared in terms of fibre area fractions, porosity and void content, for the different compression pressures. The aim for the microstructural analysis was to elucidate the mechanism of compression and to follow the development of fibre and pore structure under different degrees of compression. It was concluded that the compression of resin impregnated woven fabrics could be considered as a combination of four modes of deformation; (a) the elimination of a resin rich interlayer between adjacent layers of fabric; (b) the nesting of layers of fabric by slipping while under compression; (c) the deformation of the yam waveform which results in the reduction of thickness of individual plies and (d) the compression and deformation of the cross-sections of individual yarns.
36
Wu, Jiali. "Fabrication and characterisation ceramic matrix continuous fibre reinforced composites by sol-gel processing." Thesis, University of Sheffield, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387765.
Full text
37
Gerges, Awad Samir. "Novel fibre-optic-based interferometric sensors exploiting coherent and low-coherence signal processing techniques." Thesis, University of Kent, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236854.
Full text
38
Witten, Neil. "The melt inpregnation of continuous fibre tows in the processing of thermoplastic matrix composites." Thesis, University of Newcastle Upon Tyne, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294808.
Full text
39
Lee, Ju Han. "All-optical nonlinear signal processing devices and their applications within fibre-optic communication systems." Thesis, University of Southampton, 2003. https://eprints.soton.ac.uk/42436/.
Full textAbstract:
This thesis is concerned with research into the development of a range of all-optical fibre based nonlinear devices for optical communication applications. The research can he divided into two main themes. The first concerns the use nf superstructured fibre Bragg grating technology together with fibre based nonlinear devices to improve the overall system performance in both OCDMA and OTDM systems. The second theme area concerns the use of highly nonlinear holey fibre within a range of nonlinear signal processing devices and an analysis of the perfomance of these devices from a system context. A range of nonlinear devices based on a holey fibre is demonstrated. Holey fibre has a nonlinearity around 10-100 times greater than conventional fibre. The use of a short (8.7 m), highly nonlinear holey fibre based optical switch is presented and shown to provide enhanced code recognition quality in a SSFBG based OCDMA system. The use of a short (75 m), highly nonlinear holey fibre to obtain strong L+-band Raman amplification and SRS based signal modulation is also demonstrated. The use of HF within Brillouin based devices is next considered. Both stimulated and spontaneous Brillouin scattering effects are investigated. The observed high SBS lasing threshold is found to be mainly due to reduction in the effective gain coefficient caused by structural non-uniformity along the HF length. A 5.8 m length of HF is then used to achieve tuneable WDM wavelength conversion based on XPM and it is experimentally demonstrated that HF with normal GVD should be used for this sort of device in order to eliminate the coherence degradation related intensity noise observed in experiments employing anomalously dispersive HF. Finally, a FWM based wavelength converter using a 15 m, highly nonlinear HF with a high SBS threshold is presented. The high SBS threshold is achieved by applying structural variation to the HF along its length during the fabrication process
40
Dressler, Sven. "Simulation of Fibre Pull-out Using a Graphics Processing Unit Accelerated Discrete Element Model." Diss., University of Pretoria, 2020. http://hdl.handle.net/2263/75931.
Full textAbstract:
The combination of brittle material with ductile fibres can produce competent composites. The fibres transmit tensile forces across cracks that form in the brittle matrix at relatively low tensile strains. The fibre reinforcing, therefore, acts to both increase the maximum stress a structural section can support and improve the post maximum stress behaviour from brittle to ductile failure. An essential aspect of defining the effectiveness of fibre reinforcing is resolving the behaviour of the interface between the fibre and the matrix as the load being transmitted between the matrix and fibre increases.
The interface behaviour for simple fibres is understood analytically, and several models exist that can predict the stresses in the interface. Numerical models using finite element methods (FEM) have been used to investigate this problem in a more general way. FEM, being inherently a description of a continuum, does not elegantly describe the debonding process that occurs during the debonding of fibres from the surrounding matrix. Discrete Element Methods (DEM) describe continuous and discontinuous materials as the interaction between multiple independent particles and are well suited for modelling fracture and evolving contacts.
For this study two different DEM contact models are compared to investigate the model complexity that is required to describe fibre/matrix interface stresses and debonding accurately. A simple model (a linear spring model that only transmits normal and tangential forces) and a more complex model (parallel bonds which transmit normal and tangential forces, moments, and torsion) were used. Two stages of fibre pull-out were modelled independently using a GPU accelerated DEM simulator developed by the author: a fully bonded stage and the de-bonding stage. It was found that both models were able to simulate all stages when compared to analytical solutions. No improvement to the model behaviour was evident from using a complex contact model; for this reason, a simpler, faster contact model should be used to analyse this problem.
The DEM code is written relying heavily on the Numba module which allows the compilation of Python syntax for execution on a GPU. Non-reversible bond damage is simulated, and each bond must, therefore, be stored and bond damage updated at each time step. The implementation of collision detection, particle force determination and equation of motion integration written for execution on GPU are discussed. The data structure and memory use are described. The method used to apply boundary conditions is described. The performance of the developed code is investigated by comparison with similar codes, using Numpy and Numba Python modules, written for serial execution on CPU only. It was found that the developed code was 1000 times faster than the Numpy+Python implementation and 4 times faster than the Numba+Python implementation for force determination and equation of motion integration. Collision detection was 900 times faster compared to Numpy+Python but performed slower compared to Numba+Python.Dissertation (MEng)--University of Pretoria, 2020.
Mechanical and Aeronautical Engineering
MEng
Unrestricted
41
Pentney, John Michael. "A hard wired image processor for a scintillating fibre detector of elementary particles." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334178.
Full text
42
Brown, Trevor Junior. "Time division multiple access/code division multiple access for the optical local access network." Thesis, Manchester Metropolitan University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243716.
Full text
43
Zhang, Kuiwei. "Surface roughness and displacement measurements using a fibre optic sensor and neural networks." Thesis, Brunel University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246145.
Full text
44
Mitchell, Thomas A. "Machine vision techniques for inspection of dry-fibre composite preforms in the aerospace industry." Thesis, Brunel University, 1995. http://bura.brunel.ac.uk/handle/2438/7118.
Full textAbstract:
This thesis presents the results of a three year investigation into machine vision techniques for in-process automated inspection of dry-fibre composite preforms. Efficient texture analysis based techniques have been developed, tested, and implemented in a prototype robotic assembly cell. Industrial constraints have been considered in the development of all the algorithms described. A single channel texture analysis model is described which can successfully segment images containing only a few textures. The model is based on convolution of the image with small kernels optimised for the task, and is elegant in the sense that it is computationally simple and easily realisable in low cost hardware. A new convolution kernel optimisation algorithm is described. It is demonstrated that convolution kernels can also be optimised to perform as edge operators in simple textured images. A novel boundary refinement algorithm is described which reduces the inspection errors inherent in texture based boundary estimates. The algorithm takes the form of a local search, using the texture estimate as a guiding template, and selects edge points by maximising a merit function. Optimum parameters for the merit function are obtained using multiple training images in conjunction with simple function optimisation algorithms.
45
Bergquist, Jørgen, and Helge Titlestad. "Analysis of fibre cross sections : Developing methods for image processing and visualisation utilising the GPU." Thesis, Norwegian University of Science and Technology, Department of Computer and Information Science, 2006. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-9466.
Full textAbstract:
Modern graphics processing units, GPUs, have evolved into high-performance processors with programmable vertex and pixel shaders. With these new abilities a new subfield of research, dubbed GPGPU for General Purpose computing on the GPU has emerged, in areas as oil exploration, processing of sound effects, neural networks, cryptography and image processing. As the GPUs functionality and performance are still increasing, more programmers are appealed by their computational power. To understand the performance of paper materials a detailed characterisation of the fibre cross-sections is necessary. Using scanning electron microscopy, SEM, fibres embedded in epoxy are depicted. These images have to be analysed and quantified. In this master thesis we explore the possibility of taking advantage of todays generation of GPUs performance when analysing digital images of fibre cross-sections. We implemented common algorithms such as the median filter, the SUSAN smoothing filter and various mathematical morphology operations using the high-level shader language OpenGL Shader Language, GLSL. When measured against equivalent image processing opreations run on the CPU, we have found our GPU solution to perform about the same. The operations run much faster on the GPU, but due to overhead of binding FBOs, intialising shader programs and transfering data between the CPU and the GPU, the end result is about the same on the GPU and CPU implementations. We have deliberatly worked with commodity hardware to see what one can gain with just replacing the graphics card in the engineer's PCs. With newer hardware the results would tilt heavily towards the GPU implementations. We have concluded that making a paper fibre cross-section analysis program based on GPU image processing with commodity hardware is indeed feasible, and would give some benefits to the user interactivity. But it is also harder to implement because the field is still young, with immature compilers and debugging tools and few solid libraries.
46
Li, Kun. "Laser micro-processing of silicon using nanosecond pulse shaped fibre laser at 1 μm wavelength." Thesis, University of Cambridge, 2012. https://www.repository.cam.ac.uk/handle/1810/245313.
Full textAbstract:
Processing of Si in the semiconductor and solar cell industry has been dominated by the Diode Pumped Solid State (DPSS) Ultraviolet (UV) laser. Recent advances in laser source technology have produced fibre lasers with Master Oscillator Power Amplifier (MOPA) architectures that offer high repetition rates, high operational efficiencies, and pulse modulation controls exceeding those of typical Q-switched DPSS lasers. The aim of this research is to investigate 1 μm fibre laser machining of Si with a view to identifying the influential laser parameters for optimum processing of high quality, high efficiency micro drilling and surface texturing applications. A secondary aim is to develop a greater understanding of the laser material interactions and material removal mechanism when using fast rise-time nanosecond laser pulse envelopes. The IR fibre laser was able to perform percussion drilling and single pulse machining on the polished Si over a range of intensities up to 1.22 GW/cm2. With the optimum parameters, the micro-sized holes generated by the IR laser have a well defined edge, no heavy recast and no cracks. With a pulse shape of fast rise time (<7.5 ns for a 10-90% rise in signal), a high front peak power zone (approaching 14 kW) and an energetic long tail (40-180 ns), the absorption coefficient of Si at IR wavelength increased dramatically with time and temperature due to the fact that the liquid Si has a metal like absorption behavior. As a result, Si was quickly melted and the rest of pulse energy was able to remove the liquid Si effectively. The machining process left a limited amount of resolidified melt droplets and vapor condensates, which could be washed off ultrasonically. The drilling process was energy efficient when melt expulsion dominated the machining mechanism (0.08-0.2 mJ pulse energy depending on the pulse durations). The low energy pulse (~0.2 mJ) can achieve similar depth as the high energy pulse (~0.7 mJ), so high repetition rates of 100 kHz can be used to instead of 25 kHz, resulted in high processing speed. In addition, by comparing the single pulse machining with the state of the art UV laser, the IR fibre laser machined deeper features and better surface finish in the pulse energy region of >0.07 mJ. With the pulse shaping capability, the material properties can be varied and the wavelength factor can be minimized. The results suggest that applications like microvia drilling can now be carried out with the more flexible and low cost IR fibre laser. The increased repetition rates of fibre laser can increase production speed to satisfy the needs of drilling ~10 thousands holes per second, required by the modern semiconductor and solar cell production. The shortened optical penetration length of 1 μm wavelength laser on Si with increasing temperature and sufficient thermal diffusion length resulted from the asymmetrical fibre laser pulse and the dynamic properties of Si produced a thick liquid layer. A one-dimensional heat conduction model based on the surface heating source predicted that this superheated liquid layer was able to stay above 4706 K (0.905 times the thermal critical temperature 5200 K of Si) for longer than 70 ns to induce explosive boiling. This proposed material removal mechanism was also confirmed by the shadowgraph images, showing particulates ejection lasting up to ten microseconds after the laser pulse. The estimated hole depth based on the explosive boiling alone were different from the measured ones at varying peak power densities (<1.22 GW/cm2) but fixed pulse duration (200 ns), since Si was removed by a mixture of mechanisms. With varying pulse durations (40-200 ns) but fixed peak power density (~0.63 GW/cm2), the estimated depth based on the explosive boiling was in close agreement with the measured ones (6% difference on average). The SEM images at this power density showed a micron- /submicron-sized debris field, which was also observed with the explosive boiling in the past. Although the improved quality of Si machining was demonstrated with the 1 μm MOPA based fibre laser, the setup of this system was only applicable to surface texturing, blind holes and through holes of less than 100 μm in depth. Further research is required to demonstrate the capability of more energetic pulse with higher peak power and large pulse duration range to explore more machining options.
47
Venugopal, Saranya. "Synthesis and processing of sub-micron hafnium diboride powders and carbon-fibre hafnium diboride composite." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/12532.
Full textAbstract:
A vehicle flying at hypersonic speeds, i.e. at speeds greater than Mach 4, needs to be able to withstand the heat arising from friction and shock waves, which can reach temperatures of up to 3000oC. The current project focuses on producing thermal protection systems based on ultra high temperature ceramic (UHTC) impregnated carbon-carbon composites. The carbon fibres offer low mass and excellent resistance to thermal shock; their vulnerability is to oxidation above 500oC. The aim of introducing HfB2, a UHTC, as a coating on the fibre tows or as particulate reinforcement into the carbon fibre preform, was to improve this property. The objectives of this project were to: i) identify a low temperature synthesis route for group IV diborides, ii) produce a powder fine enough to reduce the difficulties associated with sintering the refractory diborides, iii) develop sol-gel coating of HfB2 onto carbon fibre tows iv) improve the solid loading of the particulate reinforcement into the carbon fibre preform, which should, in turn, increase the oxidation protection. In order to achieve the above set objectives, fine HfB2 powder was synthesized through a low temperature sol gel and boro/carbothermal reduction process, using a range of different carbon sources. Study of the formation mechanism of HfB2 revealed an intermediate boron sub-oxide and/or active boron formation that yielded HfB2 formation at 1300oC. At higher temperatures the formation of HfB2 could be via intermediate HfC formation and/or B4C formation. Growth mechanism analysis showed that the nucleated particles possessed screw dislocations which indicated that the formation of HfB2 was not only through a substitution reaction, but there could have been an element of a precipitation nucleation mechanism that lead to anisotropic growth under certain conditions. The effect of carbon sources during the boro/carbothermal reduction reaction on the size of the final HfB2 powders was analysed and it was found that a direct relation existed between the size and level of agglomeration of the carbon sources and the resulting HfB2 powders. A powder phenolic resin source led to the finest powder, with particle sizes in the range 30 to 150 nm. SPS sintering of the powder revealed that 99% theoretical density could be achieved without the need for sintering aids at 2200oC. Sol-gel coatings and slurry impregnation of HfB2 on carbon fibres tows was performed using dip coating and a 'squeeze-tube' method respectively. Crack free coatings and non-porous matrix infiltration were successfully achieved. The solid loading of the fine HfB2 into the carbon fibre preform was carried out through impregnation of a HfB2 / phenolic resin/acetone slurry using vacuum impregnation. Although the sub-micron Loughborough (LU) powders were expected to improve the solid loading, compared to the commercially available micron sized powders, due to the slurry made from them having a higher viscosity because of the fine particle size, the solids loading achieved was consequently decreased. Optimisation of the rheology of the slurry with LU HfB2 still requires more work. A comparison of the oxidation and ablation resistance of the Cf-HfB2 composites prepared with both commercial micron sized HfB2 powder and Loughborough sub-micron sized HfB2 powder, each with similar level of solid loading, was carried out using oxyacetylene torch testing. It was found that the composite containing the finer, Loughborough powders suffered a larger erosion volume than the composite with the coarser commercial powders indicating that the former offered worse ablation and oxidation resistance than the latter. A full investigation of the effect of solids loading and particle size, including the option of using mixtures of fine and coarse powders, is still required.
48
Blaese, Diego. "Processing and characterization of monoclinic-zirconia fibre-matrix interfaces in dense matrix alumina-alumina composites." reponame:Repositório Institucional da UFSC, 2013. https://repositorio.ufsc.br/handle/123456789/107283.
Full textAbstract:
Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2013.Made available in DSpace on 2013-12-05T23:42:12Z (GMT). No. of bitstreams: 1 318449.pdf: 2754019 bytes, checksum: d73daae4512a7cb151813f0d7e905cae (MD5) Previous issue date: 2013
Interfaces fibra-matriz tem um papel muito importante no desempenho de compósitos de matriz cerâmica. Sendo a interação entre fibra e matriz for muito forte, o compósito se comportará como uma cerâmica monolítica, e sendo muito fraca, o compósito perderá sua integridade estrutural e suas propriedades interlaminares. Zircônia monoclínica (não-estabilizada) tem mostrado ser uma boa alternativa na produção de interfaces fibra-matriz para compósitos cerâmicos à base de alumina devido à sua baixa interação química durante a sinterização e também devido ao fenômeno de microtrincamento causado pela transformação tetragonal-monoclínica durante o resfriamento. Interfaces porosas à base de zircônia monoclínica, as quais apresentam baixa tenacidade devido à sua porosidade e microtrincamento, haviam sido usadas no passado para criar interfaces com baixa interação entre fibras de safira e matrizes de alumina. Neste sistema, as interfaces se mostraram quimicamente estáveis mesmo acima de 1300 °C. Compósitos tenazes à base de alumina haviam sido fabricados com zircônia monoclínica como interface. Entretanto, a porosidade da matriz era ? 13%, o que dificulta a interpretação dos resultados, pois as propriedades mecânicas do compósito não podem ser claramente atribuídas às propriedades da zircônia monoclínica. Neste trabalho, compósitos-modelo com matriz densa e fibras individuais de alumina foram produzidos. A interface fibra-matriz foi produzida através de recobrimento por dip-coating das fibras em suspensões cerâmicas de zircônia monoclínica. Diferentes tamanhos de partícula foram utilizados no processo de dip-coating com o objetivo de variar a porosidade e assim, as propriedades das interfaces. A tensão de cisalhamento interfacial foi determinada através do teste de pushin nas fibras. O fenômeno de deflexão de trincas foi avaliado através de trincas criadas por indentação Vickers e o fenômeno de pullout das fibras através de observações nas superfícies de fratura. Propriedades como tenacidade à fratura, dureza e módulo de elasticidade da matriz e interface foram avaliadas para determinar os parâmetros de deflexão de trincas propostos por He e Hutchinson.
Abstract : Fibre-matrix interface properties play an important role on the performance of ceramic matrix composites. Being the fibre-matrix interaction too strong, the composite will behave such as a monolithic ceramic and being too weak, the composite will lose its structural integrity and its interlaminar properties. Monoclinic (unstabilized) zirconia has shown to be a suitable alternative for the production of fibre-matrix interfaces for alumina ceramic matrix composites due to its low chemical interaction during sintering and due to the microcracking phenomenon caused by the tetragonal-monoclinic transformation during cooling. Porous oxide coatings of monoclinic zirconia, which have low toughness because of their porosity and microcracking, have been used in the past to achieve debonding between sapphire fibres and alumina matrices and were to be chemically stable with sapphire above 1300 °C. Tough alumina matrix composites have been fabricated using monoclinic zirconia as fibres coating. However the matrix porosity was = 13%, which makes it difficult to interpret the results, because the toughness cannot be unambiguously attributed to the properties of the unstabilized zirconia interfaces. In this work, model composites with dense alumina matrix and single alumina fibres were fabricated. The fibre-matrix interface was produced via dip-coating single fibres in monoclinic zirconia suspensions. Different particle sizes were used for the dip-coating in order to vary the coating porosity. The interfacial sliding stress was determined via a modified fibre pushin test. The crack deflection behaviour was analysed from cracks created via Vickers indentations and the fibre pullout via surface fracture observations. Properties such as fracture toughness, hardness and elastic modulus for the interface and matrix were also evaluated in order to determine the crack deflection parameters established by He and Hutchinson.
49
Li, Xin. "Eddy current techniques for non-destructive testing of carbon fibre reinforced plastic (CFRP)." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/eddy-current-techniques-for-nondestructive-testing-of-carbon-fibre-reinforced-plastic-cfrp(e8aa9a3f-108d-49a4-9f32-2e6118195898).html.
Full textAbstract:
AbstractThis thesis describes research on the use of eddy current techniques for nondestructivetesting of carbon fibre reinforced plastic (CFRP). The research hasinvolved bulk conductivity testing, fibre direction characterization and 3D FEMmodeling of the CFPR and eddy current probes geometry. In the conductivity testing,how the sample thickness, fibre volume content and fibre conductivity affects thesignal from the eddy current has been evaluated. Eddy current testing shows gooddirectionality as CFRP is an anisotropic material, thus is very suitable to characterizethe fibre orientation. Direction sensitive probes have been developed and tested toreveal information about the fibre direction and layer. Computer FEM software hasbeen used to analyze the magnetic field inside the sample and probes. Specific probegeometries have been designed depending on the electrical properties of thecomposites and testing requirement. The experiment, simulation and analysis resultsshow very good agreement. However, when the measuring frequency increases, noisesand parasitic capacitance inevitably become significant and have a negative influenceon the results. Improvements and further research are proposed which are believed tomake eddy-current techniques a more feasible and efficient measurement method, willcontribute to the development and maintenance of light weight CFRP composites.
50
Silva, Duarte Nuno Rodrigues da. "Image processing methodology for assessment of drilling induced damage in CFRP." Master's thesis, Faculdade de Ciências e Tecnologia, 2013. http://hdl.handle.net/10362/9866.
Full textAbstract:
Dissertação para obtenção do Grau de Mestre em
Engenharia MecânicaComposite material components are produced in a near final shape. Machining operations such as drilling are often indispensable, namely for joining of structures. This process introduces damage along the periphery of the hole. Different methods to reduce this induced damage were developed. However, difficulties arise when comparing them since delamination is irregular in shape and in size. The delamination factor and the adjusted delamination factor quantify the damage but none achieved full acceptance since no international standards have been set. The aim of this work is to develop an image processing methodology associated with digital radiography that is capable of assessing the drilling induced damage in CFRP, being easily reproducible and allowing comparison of different drilling approaches. The subtraction of pre and post drill radiographies defined the target image to reach. In the image processing the threshold was found to be the most influential variable causing significant changes to the delamination factors. A new approach to the delamination factor is proposed in order to characterize the drilling induced damage. This approach allows the minimization of the quantified damage for the most irregular delamination shapes while equalling the current delamination factors for regular (crown like) damages.