Academic literature on the topic 'Light-sheets'

Neste trabalho é realizada a avaliação do desempenho solar e luminoso de chapas metálicas com diferentes padrões de perfurações empregados para proteção solar na envoltória das edificações. Foram ensaiadas experimentalmente as transmitâncias solar e luminosa em diversos ângulos de incidência de chapas metálicas, chapas expandidas e telhas metálicas, com ou sem pintura, planas ou com conformação espacial. Avaliou-se a relação entre a transmitância e % de perfuração da amostra para incidência da radiação em variadas alturas e azimutes solares, comparou-se o comportamento solar e luminoso de cada amostra e entre amostras com características semelhantes. As normas ASTM E972 Standard Test Method for Solar Photometric Transmittance of Sheet Materials Using Sunlight e ASTM E1084 Standard Test Method for Solar Transmittance (Terrestrial) of Sheet Materials Using Sunlight foram adotadas para medições de campo das amostras. Os resultados mostram que, para todas as amostras, as transmitâncias solar (TS) e luminosa (TL) na perpendicular se assemelham a % de perfuração da amostra; para ângulos diferentes da normal há uma redução conforme a altura solar diminui e que quanto maior for o furo em relação à espessura, menor será a redução. TS/TL decresce conforme a altura solar diminui, exceto para as telhas. Em relação à variação de azimute, para chapas perfuradas sem acabamento ou pintadas, os valores de TS e TL se mantêm praticamente iguais, enquanto que para chapas expandidas e telhas os valores variam. Para as amostras pintadas, TS e TL das amostras com cores claras são maiores do que das amostras com cores médias que por sua vez são maiores do que as amostras com cores escuras. A partir destes resultados e da elaboração da ficha de aplicação dos resultados para variados ângulos, no âmbito do projeto de arquitetura, contribui-se para o emprego apropriado deste tipo de material, além de complementar informações técnicas pouco disponíveis no mercado. Além disso, os dados medidos em campo podem servir de validação para modelagem computacional para uma variação maior de ângulos, e na avaliação de ambientes projetados ou construídos, os dados coletados, em especial os ângulos diferentes da incidência normal, podem ser usados em simulação energética ao longo do ano.<br>This research focuses on the evaluation of solar and optical performance of metal sheets with different patterns of perforations used as shading devices in the building\'s envelope. Solar and light transmittance were experimentally tested at normal and off-normal incident angles of samples of perforated metal sheet, expanded metal sheets and perforated tile, with or without painting, flat or volumetric shape. The relationship between % perforation of sample and transmittance for off normal angle incidence (height and azimuth) was evaluated. Solar and optical results were correlated for each sample. Samples with similar characteristics such as perforation, painting, hole dimension were compared. ASTM E 972 Standard Test Method for Solar Photometric Transmittance of Sheet Materials Using Sunlight and ASTM E 1084 Standard Test Method for Solar Transmittance (Terrestrial) of Sheet Materials Using Sunlight were adopted for field measurements of the samples. The results show that for all samples, the solar transmittance (TS) and light (TL) perpendicular to the sample is similar to % perforation; for off normal angles there is a reduction as the solar altitude decreases and that the higher the hole relative to thickness, the smaller the reduction. TS / TL decreases as solar height decreases, except for the tiles. Regarding the change in azimuth for perforated sheets with or without painting, the values of TL and TS remains practically the same, whereas for expanded metal and tiles values vary. For the painted samples, TS and TL bright color of the samples are higher than the intermediate color samples which are in turn higher than the samples of dark colors. From the results achieved and with the development of the application table to diferente incident angles, within the architecture field, these results provide information for the appropriate use of such material, plus some additional technical information available in the market. Furthermore, the data measured in the field can serve as validation for computational modeling to a wider range of angles, and also it could be used in buildings\' energy simulations.

Refill Friction Stir Spot Welding (RFSSW) is a new solid-state joining technology, which is suitable for joining similar and dissimilar overlap sheets connections, particularly in aluminium and magnesium alloys. This welding method is expected to have wide applications in joining of body parts in the automotive industry. In the present study, RFSSW has been used to join 1.0 mm gauge sheets of two material combinations: similar AA6111-T4 automotive aluminium alloy joints and a dissimilar aluminium AA6111-T4 to magnesium AZ31-H24 alloy combinations. The performance of the joints was investigated in terms of the effect of the welding parameters (including tool rotation rate, sleeve plunge depth, and welding time etc.) to improve current understanding and allow optimisation of the process for short welding-cycles when joining similar and dissimilar light alloys. The results of the investigations on similar AA6111 welds showed the ability to use a wide window of process parameters that resulted in joints with a successfully refilled keyhole and flat weld surface, even when using a welding time as short as 0.5 s. The joints in the as-welded condition showed strengths as high as 4.2 kN, when using welding parameters of 1500 rpm, 1.0 mm with a range of welding times from 0.55 to 2.0 s. All joints showed a nugget pull-out failure mode when using a sleeve plunge depth of 0.8 mm or more, as a result of increasing the joint area. The strength of the joints further improved and reached peak loads of 5.15 and 6.43 kN after natural and artificial ageing, respectively, for welds produced using optimised welding parameters of a 2500 rpm tool rotation rate, a 1.5 s welding time and a 1.0 mm plunge. This improvement in strength resulted from the improvement in the local mechanical properties in the HAZ and other regions, which results from a minimal HAZ due to the rapid weld cycle and the re-precipitation of GPZs and clustering on natural ageing, or β on artificial ageing. A modification to the RFSSW process was developed in this project to solve the problems faced when dissimilar welding Mg to Al. This modified process involved adding a final brief pin plunge stage to consolidate refill defects and it was successful in producing nearly defect-free joints with improved mechanical properties, using a wide range of the process parameters. The average peak load of the joints increased with increasing tool rotation rate, to reach a maximum value at 2500 rpm due to eliminating the weld defects by increasing the material plasticity. However, increasing the tool rotation rate further to 2800 rpm led to a decrease in the average peak failure load due to eutectic melting at the weld interface. The optimum welding condition was thus found to be: 2500 rpm, 1.0 s, and 1.0 mm, which gave an average peak failure load of 2.4 kN and average fracture energy of 1.3 kN.mm. These values represent an improvement of about 10 % and 27 %, respectively, compared to welds produced with the conventional RFSSW process, and about 112 % and 78 % of the Mg-Mg similar joints produced using the same welding conditions. A FE model developed in this project was successful in increasing understanding of the behaviour of the RFSSW joints when subjected to lap tensile-shear loading. The stress and strain distribution in the modelled samples showed that the highest concentration occurring in the region of the confluence of the SZ with the two sheets. With increasing extension, these regions of highest stress and strain propagated to the outer surfaces of the two sheets and then annularly around the weld nugget. This annular ring of high strain concentration agreed well with the failure path and results in the full plug pull-out fracture mode shown by the experimentally tested samples. The predicted force-extension curves showed high agreement with the experimental results, especially when including the effect of the hook defect and correction of compliance in the experimental results.

Over the past few decades, the study of field distribution at the geometrical focus of a lens (PSF) has gained a huge research interest in field ranging from Nanolithography to microscopy. The central theme of this thesis is to study the intricate details of the field distribution through theoretical modelling, computational studies and experimentation. Specifically, spatial filtering techniques have been proposed to understand and manipulate the field distribution for demanding applications. Based on the findings during the theoretical modelling and computational studies we have proposed light sheet based optical lithography technique. Optical lithography (Photolithography) has emerged as an efficient tool for the fabrication of micro/Nanostructures. It uses photon energy to create patterns on the substrate coated with a photosensitive material. The photochemical reactions which are necessary for the fabrication are spatially confined by the 3D extent of the field distribution. Hence the knowledge of field distribution plays a very crucial role in photolithography. State of the art techniques in optical lithography such as, two photon direct laser writing lithography, interference-based lithography techniques and STED Nano-lithography have made optical lithography a highly sought-after technique for the fabrication of micro/Nanostructures. Specifically, two photon direct lithography is used for making complex 3D structures. Interference based lithography techniques are used for fabricating 1D, 2D and 3D periodic Nanostructures whereas, STED Nano-lithography is capable of fabricating diffraction unlimited structures. The first chapter provides an overview of all the keywords and concepts used in photolithography. A brief summary of the emergence of the field is provided along with the development of different optical lithography techniques. The discovery of photopolymerization process and invention of various photoresist systems has helped in the development of photolithography. These techniques have made physics, chemistry and biology accessible to Nano-scale level. An introduction to photoresist systems and them brief classification is given in this chapter. In addition, we have also provided a brief description to recent techniques in photolithography that is widely used for micro/nanofabrication. Understanding these techniques helps us in identifying the novelty of the proposed lithography technique. A brief introduction is given to understand the field distribution/ point spread function (PSF) that provides the foundation for the entire thesis. In the second chapter, we describe the vectoral model for theoretically understanding the PSF for a spherical lens geometry. This is predominantly since the existing lithography techniques relay on spherical lens geometry. In view of demanding applications, the illumination PSF is tailored by employing spatial filtering techniques. We intend to employ spatial filter in order to add new features to lithography and expand its reach. For example, introduction of spatial filter at the back aperture of an objective lens produce a Bessel like beam which is generally used for applications that requires greater depth of focus. Bessel beams have self-reconstructing property which helps to achieve a greater depth of focus in scattering mediums. The extent of the PSF along the axial direction (z-direction) is 2-3 times greater when compared to the lateral extent. Hence the resolution along z-direction is 2-3 times worse when compared to its lateral counterpart. 4 geometry is generally employed to improve the axial resolution in spherical lens system. But this technique suffers from side-lobes that can cause artefacts. In order to reduce side lobes, we employed spatial filter in a 4_ geometry. A detailed description of these techniques is given in chapter 2. These techniques may add new features to Nano-lithography techniques and bring new applications in Nano-biology and Nanophysics. Chapters 3, 4 and 5 of the theses are dedicated to light-sheet based lithography for the fabrication of micro/Nanostructures. We begin by studying the field distribution at the geometrical focus of a cylindrical lens system. Unlike a spherical lens system, cylindrical lens system has a one-dimensional focusing property that results in a sheet of light. light-sheets are known for their selective plane illumination capabilities. They are widely used in bioimaging and optical microscopy. The intricate details about the field distribution are studied using the vectoral theory for cylindrical lens system. We have conducted experiments to validate the vectoral theory for cylindrical lens. _2 test revealed a good _t between experiment and theoretically obtained values. Like spatial filtering techniques in spherical lens geometry, we have carried out spatial filtering in cylindrical lens geometry to add new functionalists/ features in lithography. It is shown that the introduction of spatial filter at the back aperture of the cylindrical lens has resulted in the generation of multiple light-sheets. Spatial filter structures the incident wave front that is focused by the cylindrical lens thereby resulting in a distinct field distribution at and near the focal plane. The theory behind the generation of multiple light-sheets is discussed in chapter 3. We have demonstrated the generation of multiple light-sheets through computational simulations and experiment. Multiple light-sheets have the capability of illuminating multiple planes of the specimen simultaneously. The experimental results are discussed in chapter 3. Chapter 4 describes the fabrication of periodic micron structures using multiple light sheets. We have used a photoresist mixture which is sensitive to visible light. UV- Vis absorption spectroscopy was used to determine the sensitivity of the photoresist mixture. The photochemistry was studied using a 532 nm continuous laser. We could control the periodicity and the feature size by changing the spatial filter parameters. This technique is hoped to be a single shot fabrication technique for generating high aspect ratio periodic micron structures over a large area. In chapter 5, we have proposed and experimentally demonstrated the generation of periodic Nanostructures using counter propagating coherent light-sheets. The technique involves two opposing cylindrical lenses. When these lenses illuminate the common geometrical focus with a coherent beam of light a constructive interference takes place between two counter propagating light-sheets. The resulting interference structures can be captured on a substrate coated with the photoresist. Selective plane illumination nature of light-sheets is exploited to carry out patterning in the desired plane of a positive photoresist. A mathematical equation is derived that describes the field distribution at and around the common geometrical focus of two opposing cylindrical lens system. Before carrying out the fabrication, we have studied the field distribution in depth through computational simulations. Th periodicity is found to be half the wavelength of illumination light, whereas feature size is found to be approximately one fourth of the wavelength. This clearly indicates that sub-diffraction limited features can be generated using the proposed technique. The remaining part of this chapter describes the fabrication processes for the commercially available photoresist, S1813. This technique can be used for the fabrication of Nano-channels. Interesting applications are in bio-molecular research and protein analysis. Nano-channels are widely used in the detection and analysis of biomolecules such as DNA, proteins and ions. The ability to carve 2D periodic Nanostructures has a great potential for future technology development. Multiple beam interference lithography is most widely used technique for the fabrication of 2D and 3D periodic Nanostructures. In this technique, parameters (like amplitude and polarization angle) of the individual beam and the angle between the beams control the interference pattern. Choosing the right set of parameters for the individual beam is highly challenging. Phase mask lithography can produce desired beams from a single source. But these experiments are highly complex and requires expertise. Processes involved in the fabrication of phase mask are exigent. Chapter 6 describes the fabrication of 2D periodic Nanostructures. We have integrated spatial filtering technique with 2_ illumination to generate of 2D periodic Nanostructures. Theoretical and computational studies show that multiple light-sheets can be generated using an amplitude binary filter. Interference of counter propagating multiple light sheets result in a 2D periodic intensity distribution at the common geometrical focus which can be used for the fabrication of 2D periodic Nanostructures. This technique can be a stepping stone towards the fabrication of nanoelectromechanical systems (NEMS), fabrication of metamaterials and photonic crystals. Finally, we conclude the thesis with a brief description on the contribution of the thesis and the future scope of the research work.

AbstractFiber-reinforced plastics (FRP) are increasingly popular in light weight applications such as aircraft manufacturing. However, most production processes of thin-walled FRP parts to date involve the use of expensive forming tools. This especially hinders cost-effective production of small series as well as individual parts and prototypes. In this paper, we develop new possible alternatives of highly automated and die-less production processes based on a short review of current approaches on flexible thin-walled FRP production. All proposed processes involve robot guided standard tools, similar to incremental sheet metal forming, for local forming of the base materials. These include woven glass fiber fabrics which are locally impregnated with thermoset resin and cured using UV-light, woven commingled yarns made out of glass fibers and thermoplastic fibers which are locally heated and pressed, as well as pre-consolidated thermoplastic organo sheets which require selective heating for forming. General applicability of the processes is investigated and validated in practical experiments.

We demonstrate a new holographic technique which projects target 3D scenes constructed from parallel multi-sheets oriented perpendicular to the hologram plane. Our holograms provide high axial resolution and realistic depth perception for AR/VR applications.