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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
81

Flexible formwork for concrete structures

Orr, John January 2012 (has links)
Concrete, our most widely used construction material, is a fluid that offers the opportunity to economically create structures of almost any geometry. Yet this unique fluidity is seldom capitalised on, with concrete instead being cast into rigid prismatic moulds to create high material use structures with large carbon footprints. Our rate of concrete consumption means that cement manufacture alone is estimated to account for some 5% of global Carbon Dioxide emissions. This dissertation shows that by replacing conventional orthogonal moulds with a flexible system comprised primarily of high strength, low cost fabric sheets, the fluidity of concrete can be utilised to create structurally optimised concrete structures. Flexible formwork therefore has the potential to facilitate the change in design and construction philosophy that will be required for a move towards a less material intensive, more sustainable, construction industry. Optimisation and design processes developed in this thesis show that material savings of up to 40% are possible in flexibly formed concrete beams. Full scale structural testing of these processes is undertaken to verify the flexural and shear behaviours of non-prismatic elements. This is supported by further experimental and theoretical investigations into the durability of concrete cast in a permeable, flexible mould. Detailed analysis is provided alongside practical guidance for designers. Coupled with innovation in design and analysis techniques, flexible formwork is shown to provide a globally accessible method for the construction of low carbon, materially efficient and architecturally interesting concrete structures. Recognising the impact construction has on the environment, design philosophies centred around the need to put material where it is required are becoming increasingly desirable. This can now be achieved by replacing rigid formworks with systems comprised of flexible sheets of fabric. This is a step change in the way we think about our new concrete structures.
82

Study on the communication strategy to increase the awareness of fabric Hanji in Swedish market

Eunyoung, Kyoung January 2011 (has links)
Environmental sustainability is the most important issues in today’s business. They alsoinfluenced the fashion industry and elicit demand for eco-friendly clothes. Although thedemand for sustainable products is rapidly growing, quite few of sustainable materials areknown in fashion industry. Therefore, the thesis investigates one potential sustainable fabric,fabric Hanji and suggests strategies to improve awareness of the fabric in Swedish marketwhich has potential for being a huge market for the sustainable fabrics.The thesis studies characters of Swedish general market as well as fashion market andalso surveys consumer behaviour related to Hanji and Korean fashion’s image. As a result,the thesis figures out that unawareness of Korean fashion and Korean negative image arechallenges for Hanji business to be known Swedish consumers although Swedish market hasvarious attractive features. Based on the results, this thesis provides two methods to increasethe awareness of the fabric—providing the fabric for student designers and holdingworkshops for senior consumers.The two suggestions are definitely an important and meaningful start to introduce fabricHanji to the market. In addition, they will inspire those who are trying to market the fabric. / Program: Magisterutbildning i fashion management med inriktning modemarknadsföring
83

A comparison of absorption methods

JÖNSSON, EMMA January 2013 (has links)
This report is an attempt to find an absorption method that is more suitable for IKEA. Several different methods and standards from around the world are compared to see their pros and cons. The methods are compared both theoretically and practically. The practically comparison is made in a round robin were 14 different fabric is tested in three different methods. Two of the methods in the round robin are compared against each other and the result from a home test to see if the methods can show what the customer experience. The results from the round robin is used to recommend a proper method and requirement level that suit IKEA the best, based on their demands and requirements. / Program: Magister i textilteknologi
84

Engineering design of composite military helmet shells reinforced by continuous 3D woven fabrics

Min, Shengnan January 2016 (has links)
The present research aims at engineering design of military helmet shells with continuous 3D woven fabric reinforcements for improved protection at a lighter weight and a reduced cost. The research was carried out using both the experimental and numerical methods. The results proved that the designed 3D woven wadded through-the-thickness angle interlock (TTAI) fabrics can be successfully moulded as continuous reinforcements for the doubly curved military helmet shells; therefore, costs in pattern cutting in the current composite helmet making process are eliminated. An improved ballistic performance was also demonstrated in the continuously reinforced composite structures. The wadding yarns added into the conventional TTAI fabrics enhanced the mechanical properties along the warp direction significantly. Improved composite in-plane isotropy was achieved by using the wadded TTAI fabrics as reinforcements. The locking angle method was modified based on the deformation behaviour of TTAI fabrics and was used to predict and evaluate the mouldability of both conventional and wadded TTAI structures. Mouldability factor, defined from the locking angle, assists the design and selection of continuous reinforcements that are of the appropriate mouldability. The mouldability limit of a PASGT (Personnel Armour System for Ground Troops) helmet shell was determined as 25.54. Thus, TTAI fabrics with mouldability factor no larger than this value are capable of continuously reinforcing the doubly curved shape. Ballistic tests and post-mortem examinations through ultrasonic C-scan and X-ray computed tomography (CT) demonstrated the advantages of the continuously reinforced composite in energy absorption. Up to 19.3% more of the kinetic energy was absorbed by the continuously reinforced panel through generating a delamination volume that was twice as large as that of the discontinuously reinforced one, and the delamination damages were distributed over a wider area. Under the same level of fabric mouldability and composite areal density, the panels reinforced with fewer plies of heavier fabrics performed better. The wadded TTAI reinforced composite panel demonstrated the optimal ballistic resistance by showing a 25.5% thickness increase and 55.3% penetration through the thickness. The 3D wadded fabric and 2D plain weave fabric continuously reinforced flat panels presented an equivalent ballistic performance. Meanwhile, further numerical analyses were conducted based on the digitally obtained geometry of a PASGT helmet. Although the ballistic limits varied from location to location, an equivalent ballistic limit of the helmet shell was noticed for the PASGT shell when compared to its flat counterparts. The military helmet shells reinforced by 3D wadded TTAI fabrics continuously offer improved ballistic performance. This is attributed to the preserved reinforcement continuity and the enhanced through-the-thickness properties. The research provides a novel reinforcing strategy for the construction of future composite military helmet shells.
85

Experimental investigation of a model forming fabric

Gilchrist, Seth 11 1900 (has links)
Paper making involves three fabrics: forming, pressing, and drying. The forming fabric is responsible for sheet forming, the initial dewatering of a low concentration pulp suspension into a wet sheet of paper. In the process of forming, topographical and hydrodynamic marks can be transferred from the drainage media (the forming fabric) to the sheet produced. An experimental investigation of a model forming fabric was performed to identify the geometric parameters having the largest influence on hydrodynamic wire mark. The data were also compared with the numerical simulations of Huang. To simplify the problem, justifiable engineering simplifications were made. The second phase (the fibres) was removed and the machine-direction filaments were neglected. This reduced the problem to investigation of flow through a bank of dissimilar cylinders. It was desired to find the most important geometrical parameter to reduce flow non-uniformity in the paper side flow field. Particle image velocimetry, pressure drop and flow visualization tests were conducted to investigate the flow through the array of cylinders. It was found that with a cylinder surface separation of 0.75$\times$ the paper side cylinder diameter the pressure drop tended toward the sum of the rows, and the paper side flow field was nearly identical to the paper side row only flow field, regardless of the backing side cylinder dimensions and configuration. It was seen that when the pressure drop through the bank of cylinders was equal to the sum of the rows' pressure drops the paper side flow field was the same as the paper side row only flow field. As such, pressure drop can act as an indication of when the machine side row will not affect the paper side flow field.
86

Experimental investigation of a model forming fabric

Gilchrist, Seth 11 1900 (has links)
Paper making involves three fabrics: forming, pressing, and drying. The forming fabric is responsible for sheet forming, the initial dewatering of a low concentration pulp suspension into a wet sheet of paper. In the process of forming, topographical and hydrodynamic marks can be transferred from the drainage media (the forming fabric) to the sheet produced. An experimental investigation of a model forming fabric was performed to identify the geometric parameters having the largest influence on hydrodynamic wire mark. The data were also compared with the numerical simulations of Huang. To simplify the problem, justifiable engineering simplifications were made. The second phase (the fibres) was removed and the machine-direction filaments were neglected. This reduced the problem to investigation of flow through a bank of dissimilar cylinders. It was desired to find the most important geometrical parameter to reduce flow non-uniformity in the paper side flow field. Particle image velocimetry, pressure drop and flow visualization tests were conducted to investigate the flow through the array of cylinders. It was found that with a cylinder surface separation of 0.75$\times$ the paper side cylinder diameter the pressure drop tended toward the sum of the rows, and the paper side flow field was nearly identical to the paper side row only flow field, regardless of the backing side cylinder dimensions and configuration. It was seen that when the pressure drop through the bank of cylinders was equal to the sum of the rows' pressure drops the paper side flow field was the same as the paper side row only flow field. As such, pressure drop can act as an indication of when the machine side row will not affect the paper side flow field.
87

Robust repair methods of primary structures in composite

Ramström, Marcus, Gungner, Mattias January 2013 (has links)
A request of material change when performing repairs on composite parts of SAABs JAS 39 Gripen has lead to the initiation of this project. The aim is to create a quicker and more robust repair method. The requested method of repair is to use a direct-cured repair patch made of CFRP fabric instead of CFRP tape and to mount the patch with a scarf joint, see Figure 1.1. The fabric patch should then provide a robust quasi-isotropic repair, where the operator not is dependent of complete design data such as ply-directions etc. Today tape repairs are made on tape laminate and fabric repairs made on fabric laminate. The new method is to repair tape laminate with a fabric patch. This project will evaluate the possibility of implementing this method. The work started with a literature study to find out how repairs in composite parts of the airframe are being performed today. SAABs in-house analytical tools were then used to try to predict the results and examine some of the details in the questions at issue. Finite element models were then constructed to simulate a previous physical test program conducted to validate a repair method using a step joint and a direct-cured repair patch. If the FE models could show similar results as the physical tests the results from the FE models then can be assumed to be credible. The results of this project indicate that the change from fabric to tape in the repair patch can be done without disturbing the load path of a quasi isotropic composite laminate. Fabric repairs in orthotropic composite plates results in a knock-down of about 40%. The use of a scarf joint instead of a step joint should also work well as the repair patches show similar strains in the centre of the patches. The difference between step joint and scarf joint is the strain near the edge of the patch. It increases with scarf joint and it may lead to an earlier fibre failure in the repair patch. Results from the analysis of the bonded joint indicate that a scarf joint yields in a lower and more evenly distributed shear stress than the step joint. This indicates that the bonded joint in the step joint will reach failure earlier then the scarf joint.
88

The Evolution and Trends of Taiwan¡¦s Knitting fabric Industry

Lee, Yu-lin 30 August 2011 (has links)
Knitting fabric industry is a particular branch with obviously industrial cluster in textile industry, having the sufficient resources of raw materials, the rapid mobility of productivity, the mature dyeing and finishing technologies, the extensive experience in international trade, though having the complicated process to the variable products, has developed a completed supply chain of its own. In which closely the composition of the medium or small or even micro enterprise to create the competitive strengths on the whole industry, brings up Taiwan being a major exporting country of knitting fabric worldwide. From the evolution of environment, of market demanding, of trading partners, and the future trends, thru the in-depth interviewing with the representative figures and the experts of the industry, government, academia, R&D, in this research to investigate & analyze their points of view and suggestions for the reference of the field. The research results show, at the supply end, Taiwan has become an ODM manufacturer but not just OEM maker. At the product end, the environment protection and carbon reducing are now strictly requiring on the manufacturing of functional and fashionable hi-tec products. At marketing end, the vertical consolidation among supply chains and the name brands retailers, traders, garment factories, fabric converters, up to yarn mills, the supply chain integrate and the strategic alliance to the new products developing to cause the big bigger, in quick response to the trends now a day the fast fashion and short life cycle with meager profits. To position on the innovational products to meet consumer¡¦s demands, create demanding to create profits.
89

Formulation and simulation of impact dynamics for multilayer fabrics with various weaves

Shimek, Moss Evan 03 February 2012 (has links)
The high strength, light weight, and flexibility of fabric protection systems makes them the preferred solution for a number of ballistic applications. Examples include body armor, fan blade containment for jet engines, and orbital debris shielding. In general, these protection systems employ plain woven fabric, most suitable for flat or gently curved geometries. Highly curved surfaces, such as personnel extremities, may be more effectively protected using fabrics of different weaves. This dissertation presents the first numerical model developed to simulate ballistic impacts into plain, harness satin, twill, and basket weave fabrics. It extends previous work on hybrid particle-finite element methods developed for fabric modeling. The extended formulation closely replicates the tensile load response and contact-impact dynamics of highly flexible yarns, by generalizing the kinematic model and density interpolation used in previous work. The formulation has been validated in three dimensional simulations of impact experiments conducted to investigate the effects of weave type on fabric ballistic performance. / text
90

Semiconductor nanowires : from a nanoscale system to a macroscopic material

Holmberg, Vincent Carl 03 March 2014 (has links)
Semiconductor nanowires are one-dimensional nanoscale systems that exhibit many unique properties. Their nanoscale size can lead to defect densities and impurity populations different than bulk materials, resulting in altered diffusion behavior and mechanical properties. Synthetic methods now support the large-scale production of semiconductor nanowires, enabling a new class of materials and devices that use macroscopic quantities of nanowires. These advances have created an opportunity to fabricate bulk structures which exhibit the unique physical properties of semiconductor nanowires, bridging the properties of a nanoscale system with macroscopic materials. High aspect ratio germanium nanowires were synthesized in supercritical organic solvents using colloidal gold nanocrystal seeds. The nanowires were chemically passivated inside the reactor system using in situ thermal hydrogermylation and thiolation. The chemical stability of the passivated nanowires was studied by exposure to highly corrosive and oxidative environments. Chemical surface functionalization of germanium nanowires was investigated by covalently tethering carboxylic acid groups to the surface, as a general platform for the further functionalization of nanowire surfaces with molecules such as polyethylene glycol. Surface functionalization with dopant-containing molecules was also explored as a potential route for doping nanowires. In addition, static charging was exploited in the development of an electrostatic deposition method for semiconductor nanowires. In situ transmission electron microscopy experiments were conducted on gold-seeded germanium nanowires encapsulated within a volume-restricting carbon shell. A depressed eutectic melting temperature was observed, along with strong capillary effects, and the solid-state diffusion of gold into the crystalline stem of the germanium nanowire, occurring at rates orders of magnitude slower than in the bulk. Copper, nickel, and gold diffusion in silicon nanowires were also investigated. The rate of gold diffusion was found to be a strong function of the amount of gold available to the system. Finally, germanium nanowires were found to exhibit exceptional mechanical properties, with bending strengths approaching that of an ideal, defect-free, perfect crystal, and strength-to-weight ratios greater than either Kevlar or carbon fiber. Macroscopic quantities of nanowires were used to fabricate large sheets of free-standing semiconductor nanowire fabric, and the physical, morphological, and optical properties of the material were investigated. / text

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