Development of a high efficiency thin silicon solar cell

A key to the success of this program was the breakthrough development of a technology for producing ultra-thin silicon slices which are very flexible, resilient, and tolerant of moderate handling abuse. Experimental topics investigated were thinning technology, gaseous junction diffusion, aluminum back alloying, internal reflectance, tantalum oxide anti-reflective coating optimization, slice flexibility, handling techniques, production rate limiting steps, low temperature behavior, and radiation tolerance

Design and Characterization of an Adhesive for T-Joint Composite

With the increase in composites usage in aeronautical structures and with it, the use of Carbon-Fiber Reinforced Polymers (CFRP), there was also an increase in the use of diverse types of joints, being one of the most common the T-joints. The bonding method that has gained a lot of attention is the adhesive bonding, but its optimization requires an understanding of its behavior with different types of service conditions. In this work, the aeronautical structural adhesive film SEAL® EA451 U150 was characterized at 3-point bending using different strain-rates, stress relaxation and creep behavior. The adhesive was subjected to different temperatures while immersed in water and the degradation of properties (mechanical and viscoelastic) were evaluated. Finally, this adhesive was used in T-joints and Stiffener Pull-Off Tests (SPOT) were conducted in order to understand the effect of exposure to temperature and moisture on the failure mode. The results show that: the mechanical properties in 3-point bending of the adhesive depend on the service conditions: -it was observed that the ultimate stress strength and the elastic modulus increase with the strain-rate; - for a load of 60 % of the ultimate stress strength after 180 minutes the stress decrease is inferior to 10 %. After suffering environmental degradation, the adhesive decreases its ultimate stress strength (from 109 to 62 N) and decreases its maximum strain (from 3.4 to 1.8 %), T-joints in SPOT have a progressive failure mode (non-abrupt) and when subjected to environmental degradation present a reduction of maximum load of ~8%, but with an increase of ~18 % in deformationCom o aumento do uso de compósitos em estruturas aeronáuticas, em particular matrizes poliméricas reforçadas com fibras de carbono (CFRP), também aumenta o uso de diversos tipos de juntas, sendo uma das mais comuns as juntas em T. O sistema de união com maior interesse são os adesivos estruturais, mas a otimização do seu uso requer a compreensão do seu comportamento em diferentes condições de solicitação. Neste trabalho, o adesivo estrutural aeronáutico na forma de filme SEAL® EA451 U150, foi caracterizado à flexão em 3 pontos usando diferentes velocidades de ensaio, à relaxação de tensões e à fluência. O adesivo foi exposto a temperaturas de 20ºC, 40ºC e 80ºC, imerso em água e a degradação das propriedades mecânicas (estáticas e viscoelásticas) foram avaliadas. Finalmente, este adesivo foi usado em juntas em T e foram realizados ensaios de arrancamento (SPOT) por forma a compreender o efeito da exposição à temperatura e humidade nos mecanismos de ruína dominantes. Os resultados mostram que: as propriedades mecânicas em flexão em 3 pontos do adesivo dependem das condições de solicitação: -observou-se que a resistência mecânica (tensão) e o módulo de elasticidade aumentam com a velocidade de ensaio; -para uma carga de 60 % da tensão de rutura após 180 minutos a redução de carga é inferior a 10 %. Após a degradação ambiental verifica-se que o adesivo perde resistência (de 109 para 62 N) e diminui a deformação (de 3,4 para 1,8 %). As juntas em T nos ensaios SPOT têm um mecanismo de ruína progressivo (não abrupto) e quando sujeitas a degradação ambiental apresentam uma redução na carga máxima de ~8 %, mas um aumento na deformação de ~18 %

Joining Methods For Continuous Fiber Reinforced Thermoplastic Composites In Structural Applications

Continuous fiber reinforced thermoplastic (CFRTP) composites have been proposed as an alternative to metals in structural applications. CFRTP composites can be used to create structures that are lighter weight, have better resistance to environmental factors, and have the potential to be recycled. However, one of the main challenges to CFRTP composites is connections between structural members. The goal of this thesis is to investigate the feasibility of joining CFRTP composites to both similar and dissimilar materials through literature review, coupon testing, design of a structural joint, and a small scale laboratory prototype of the joint. To achieve this goal the following steps were implemented. 1) Conduct a literature review to determine the state of the art in joining methods, optimal thermoplastic materials to use, and appropriate computer modeling techniques for joints. 2) Perform coupon level testing to obtain standard mechanical properties of the thermoplastic materials, and to characterize material joining methods. 3) Design a structural CFRTP composite joint. 4) Test a small scale prototype of the joint for design validation. Two joining methods were selected to be examine: adhesive bonding and mechanical fastening. Carbon fiber-Polyphenylene sulfide (PPS) unidirectional composite tape was selected to consolidate plates with quasi-isotropic layups. Lap shear joints were examined using experimental evaluations. The experiments serve to characterize the mechanical properties required for structural design using the proposed joining methods: adhesive bonding strength and fastener bearing strength. In addition, a comprehensive program of standard tests for material characterization of the CFRTP composite were conducted to generate properties for structural analysis. A structural model of a connection in a bridging structure was developed using finite element analysis. Lastly, a prototype of the joint was constructed and tested

Fabric and Soft Materials Composites for Bio-Inspired Adhesives and Prosthetics

Adhesives have long been designed around a trade-off between adhesive strength and releasability. Within this spectrum, specialized materials have been designed to maximize adhesive ability for a given application. To overcome this trade-off, a new adhesive paradigm is required. Biologically inspired adhesives have been of interest over the past two decades, because organisms are seen using their adhesive pads to achieve high adhesive forces, while maintaining releasability and reusability. Many biological organisms possess microscopic fibrillar features on their toe-pads, which enables climbing. While much effort has been spent attempting to mimic these features, ultimately high force capacities have not been achieved. Recently, a new framework has been introduced which states that a specific surface morphology is not necessary for creating high force capacity, easy release adhesives. This framework states that for shear adhesives to achieve high force capacity, the ratio of contact area to compliance in the loading direction, A/C, must be increased. In this thesis we focus on expanding this framework to quantitatively understand both compliance and area, for a wide range of adhesive materials and geometries, and across a wide range of substrates with varying roughness. To increase the functionality of high strength, reusable adhesives, we have developed a new adhesive configuration which supports normal loading as well as shear loading. Finally, we expand to a new field, biological prosthetic materials, and develop fabric-based composites which are extremely tough, strong, and flexible, while containing water. The foundation of the work presented in this thesis is based upon an analytical model developed to calculate the compliance of fabricated adhesives (Chapter 2). Combining this knowledge with the previously developed scaling theory allows a high degree of accuracy in calculating force capacity. While this method works well for smooth surfaces such as glass, it assumes that the nominal pad area is equal to the true area of contact, which is not true on rough surfaces. A model is developed to calculate the true area of contact based on surface roughness and adhesive materials properties (Chapter 3). The results of this model demonstrate that there is an optimum pad modulus for any given surface roughness to achieve maximum stress capacity. In some situations, high strength and easy release adhesives are required in normal loading situations. We develop a new adhesive configuration which enables shear adhesives to support normal loads (Chapter 4). This method results in a six-fold increase in normal force capacity. This provides tolerance in adhesives applications, greatly improving the commercial utility of these adhesives. Finally, we use techniques learned from the fabrication of adhesives to develop composites from polyampholyte gels and glass fiber fabrics (Chapter 5). These materials exhibit enhanced properties over the controls, including extremely high toughness and strength, while maintaining flexibility and containing water. A general mechanism is explained that results in these improved properties, opening up opportunities to develop enhanced composites from fabrics and soft materials in other fields

Composite structural materials

A multifaceted program is described in which aeronautical, mechanical, and materials engineers interact to develop composite aircraft structures. Topics covered include: (1) the design of an advanced composite elevator and a proposed spar and rib assembly; (2) optimizing fiber orientation in the vicinity of heavily loaded joints; (3) failure mechanisms and delamination; (4) the construction of an ultralight sailplane; (5) computer-aided design; finite element analysis programs, preprocessor development, and array preprocessor for SPAR; (6) advanced analysis methods for composite structures; (7) ultrasonic nondestructive testing; (8) physical properties of epoxy resins and composites; (9) fatigue in composite materials, and (10) transverse thermal expansion of carbon/epoxy composites

Evaluation of a metal fuselage frame selectively reinforced with filamentary composites for space shuttle application

The development of metal structures reinforced with filamentary composites as a weight saving feature of the space shuttle components is discussed. A frame was selected for study that was representative of the type of construction used in the bulk frames of the orbiter vehicle. Theoretical and experimental investigations were conducted. Component tests were performed to evaluate the critical details used in the designs and to provide credibility to the weight saving results. A model frame was constructed of the reinforced metal material to provide a final evaluation of the construction under realistic load conditions

Producing High Concentrations of Hydrogen in Palladium via Electrochemical Insertion from Aqueous and Solid Electrolytes

Metal hydrides are critical materials in numerous technologies including hydrogen storage, gas separation, and electrocatalysis. Here, using Pd-H as a model metal hydride, we perform electrochemical insertion studies of hydrogen via liquid and solid state electrolytes at 1 atm ambient pressure, and achieve H:Pd ratios near unity, the theoretical solubility limit. We show that the compositions achieved result from a dynamic balance between the rate of hydrogen insertion and evolution from the Pd lattice, the combined kinetics of which are sufficiently rapid that operando experiments are necessary to characterize instantaneous PdHx composition. We use simultaneous electrochemical insertion and X-ray diffraction measurements, combined with a new calibration of lattice parameter versus hydrogen concentration, to enable accurate quantification of the composition of electrochemically synthesized PdHx. Furthermore, we show that the achievable hydrogen concentration is severely limited by electrochemomechanical damage to the palladium and/or substrate. The understanding embodied in these results helps to establish new design rules for achieving high hydrogen concentrations in metal hydrides.Comment: 38 page

Study Of Processing Parameters In Manufacturing Of Flat Glass-Epoxy Composite Laminates Using Vacuum Bagging Oven Curing

The effective manufacturing process for aircraft structural parts made from composite laminate usually involved autoclave prepreg material manufactured via vacuum bagging pre-forming and autoclave. Though, autoclave involves high capital, running cost and extortionate residual stress. Vacuum bagging only (VBO) pre-forming process with oven curing is the closest out-of-autoclave (OoA) method shifts from autoclave. Thus, this study focuses on the vacuum bagging pre-forming process in oven cure using the autoclave. This work involved revising the design of experiment (DOE) to design the possible experiments to be conducted in a systematic approach. The effects of vacuum bagging process of layup technique (debulking) and vacuum bagging configurations (edge breather, intensifier and mould release type) towards void content and mechanical properties of laminate produced were investigated using analysis of variance (ANOVA). The physical quality analysis is also performed to evaluate the thickness variation and abnormalities throughout the laminate. The abnormalities percentage of the produced laminate was studied using the image processing algorithm of ultrasonic C-scan image. To assess the relationship between void and inter-laminar shear strength (ILSS), scanning electron micrograph analysis was employed. It was concluded that the ILSS and tensile strength were reflected directly to the void content and void dimension which were also sensitive to the processing parameters

National Educators' Workshop: Update 1989 Standard Experiments in Engineering Materials Science and Technology

Presented here is a collection of experiments presented and demonstrated at the National Educators' Workshop: Update 89, held October 17 to 19, 1989 at the National Aeronautics and Space Administration, Hampton, Virginia. The experiments related to the nature and properties of engineering materials and provided information to assist in teaching about materials in the education community