Advanced Materials for Exploration Task Research Results

The Advanced Materials for Exploration (AME) Activity in Marshall Space Flight Center s (MSFC s) Exploration Science and Technology Directorate coordinated activities from 2001 to 2006 to support in-space propulsion technologies for future missions. Working together, materials scientists and mission planners identified materials shortfalls that are limiting the performance of long-term missions. The goal of the AME project was to deliver improved materials in targeted areas to meet technology development milestones of NASA s exploration-dedicated activities. Materials research tasks were targeted in five areas: (1) Thermal management materials, (2) propulsion materials, (3) materials characterization, (4) vehicle health monitoring materials, and (5) structural materials. Selected tasks were scheduled for completion such that these new materials could be incorporated into customer development plans

Visualisation of shielding gas flows during high-value manufacture

This thesis is a collection of experimental and theoretical analyses of the behaviour of inert gases during material processing. The approach taken is the use of a combination of schlieren imaging and numerical simulations to understand the physical mechanisms associated with the gas flows in each process. The visualisations carried out experimentally were used to validate the models, while the models aided in the interpretation of the imaged refractive index gradients. For gas metal arc welding (GMAW), the variation of Ar input flowrate with varying torch angle, standoff and joint type was investigated. Magnetohydrodynamic (MHD) models of the arc and electrodes showed that air entrainment was determined by the interplay between the momentum in the shielding gas stream and the inwards pull of Lorentz forces which develop within the plasma jet. Good agreement was found between the images and model, showing that gas coverage decreased at values below 9 l/min. Torch angle and standoff were shown to not significantly influence coverage. Similar coverage was found to occur in bead on plate and fillet welds under the same conditions. Further experiments using flux-cored, gas shielded arc welding (FCAW-G) and 80% Ar / 20% CO2 gas allowed good quality welds to be deposited with flowrates as low as 3 l/min. These results supported the use of flow controllers in production welding units at BAE systems Govan, leading to cost savings and reduced environmental impact by locking the gas flowrate to 12 l/min. A study of gas tungsten arc welding (GTAW) using alternating Ar and He shielding gases as a method of arc pulsing was also investigated. The effects of pulsing frequency and input flowrate were investigated. When pulsing, it was found that alternating the gases resulted in He constriction close to the arc region due to the preceding Ar pulse. Comparison of weld macrographs showed that He can be used more efficiently through alternating technique compared to a premixed gas with the same He content. The schlieren system was used to analyse the flow of Ar from a trailing shield device and plasma arc welding (PAW) torch in the context of wire-arc additive manufacture (WAAM). Flow characterisation with changes in standoff and welding configuration showed that air entrainment can be minimised when using a trailing shield. However, increasingly tall parts were insufficiently covered due to interactions between fast jets from the torch and shielding gas streams. MHD modelling of the torch allowed the characterisation of heat transfer and O2 levels with varying input current or over different geometrical features. The final study in this thesis concerns the fluid-particle interactions in laser powder-bed fusion (LPBF). High-speed direct and schlieren imaging showed that differences in laser plume orientation arise from different process settings, even under the same energy input. It was shown that the denudation of the powder bed was caused by drag forces acting on particles, due to atmospheric gas flow induced by the plume. Numerical modelling was in good agreement with the experiments, indicating that evaporative phenomena are an integral part of the heat and mass transfer in LPBF

Hydrogen production from polymeric organic solids via atmospheric pressure nonthermal Plasma

The potential of using hydrogen as a sustainable energy carrier is attributed to its high energy density and its utilization without CO$_2$ emissions. Existing technologies mainly produce hydrogen thermochemically via natural gas reforming or electrochemically through water splitting. Organic solid feedstocks rich in hydrogen, such as biomass and plastic waste, are under-utilized for this purpose. Approaches based on low-temperature atmospheric pressure plasma powered by renewable electricity could lead to the production of green hydrogen more viably than current approaches, leading to sustainable alternatives for upcycling plastic and biomass waste. This doctoral research dissertation focuses on the production of hydrogen from solids via atmospheric nonthermal plasma. First, two low-temperature atmospheric pressure plasma reactors, based on transferred arc (transarc) and gliding arc (glidarc) discharges and depicting complementary operational characteristics, are designed, built, and characterized to produce hydrogen from low-density polyethylene (LDPE) as a model plastic waste. Experimental results show that hydrogen production rate and efficiency increase monotonically with increasing voltage level in both reactors. Despite the reactors' markedly different modes of operation, their hydrogen production performance metrics are comparable.Comment: arXiv admin note: substantial text overlap with arXiv:2210.1136

Plasma Science and Technology

Plasma science and technology (PST) is a discipline investigating fundamental transport behaviors, interaction physics, and reaction chemistry of plasma and its applications in different technologies and fields. Plasma has uses in refrigeration, biotechnology, health care, microelectronics and semiconductors, nanotechnology, space and environmental sciences, and so on. This book provides a comprehensive overview of PST, including information on different types of plasma, basic interactions of plasma with organic materials, plasma-based energy devices, low-temperature plasma for complex systems, and much more

Characterization and stabilization of atmospheric pressure DC microplasmas and their application to thin film deposition

Ph.D., Mechanical Engineering -- Drexel University, 200

Plasma-material interaction and electrode degradation in high voltage ignition discharges

Erosion of material caused by electrical discharges takes place in many technical applications. Particularly, in spark plugs, the durability is mainly determined by the electrode erosion caused by ignition discharges. A better understanding of the wear mechanisms will help in developing new electrode materials with enhanced resistance against spark erosion. In this work, different aspects of the complex interaction between the plasma of the ignition discharge and the electrode are investigated based on experimental observations and simulations. The discharge mode behavior is quantitatively analyzed with regard to the arc and glow phase fractions for different electrode materials and conditions of pressure and gas. The influence of these parameters on the discharge is discussed. This work especially focuses on the formation of microscopic erosion craters on the electrode surface. Their morphology and microstructure are characterized by means of FIB/SEM dual beam techniques. The depth of modifications and the extent of the molten region are determined. To complete these experimental observations, thermal analysis of the crater formation is performed using analytical models and FEM simulations. Characteristic values of time, power density and current involved in the crater formation are estimated. These values are related to the electrical characteristic of the spark, and the effects of the discharge phases on the electrode surface degradation are discussed.Die Erosion von Materialien, die von einer elektrischen Entladung hervorgerufen wird, tritt in zahlreichen technischen Anwendungen auf. Auch die Lebensdauer einer Zündkerze wird durch die von den Zündentladungen verursachte Erosion an Elektrodenmaterialien maßgeblich bestimmt. Ein besseres Verständnis der Verschleißmechanismen ist von großer Bedeutung, um maßgeschneiderte Werkstoffe mit verbessertem Funkenerosionsverhalten zu entwickeln. In dieser Arbeit werden verschiedene Aspekte der komplexen Wechselwirkung zwischen dem Plasma der Zündentladung und der Elektrode anhand von experimentellen Beobachtungen und Simulationen erforscht. Das Entladungsverhalten (Bogen- und Glimmanteil) wird für verschiedene Elektrodenwerkstoffe, Gas-, und Druckbedingungen quantitativ untersucht. Die Morphologie und Mikrostruktur von Erosionskratern werden mit Hilfe von FIB/REM Dual-Beam-Techniken charakterisiert. Die mikrostrukturellen Veränderungen des Materials unterhalb der Oberfläche und insbesondere der Schmelzbadgröße werden bestimmt. Zur Ergänzung der experimentellen Beobachtungen, wird eine thermische Analyse der Kraterbildung mittels analytischen Modellen und FEM-Simulationen durchgeführt. Charakteristische Werte des Kraterbildungsprozesses wie z.B. die Wärmezufuhr, der Strom, und die Wechselwirkungsdauer werden bestimmt und in Bezug auf die verschiedenen Phasen der Zündentladung diskutiert

Frontiers in Atmospheric Pressure Plasma Technology

Atmospheric pressure plasma discharges have grown rapidly in importance in recent decades, due to the ease in handling and operation, plus their eco-friendly applications, for agriculture, food, medicine, materials and even the automotive and aerospace industries. In this context, the need for a collection of results based on plasma technologies is justified. Moreover, at the international level, the increased number of projects that translated to publications and patents in the multidisciplinary field of plasma-based technology gives researchers the opportunity to challenge their knowledge and contribute to a new era of green services and products that society demands. Therefore, this book, based on the Special Issue of “Frontiers in Atmospheric Pressure Plasma Technology” in the “Applied Physics” section of the journal Applied Sciences, provides results on some plasma-based methods and technologies for novel and possible future applications of plasmas in life sciences, biomedicine, agriculture, and the automotive industry.This book, entitled “Frontiers in Atmospheric Pressure Plasma Technology”, consists of 8 research articles, 2 review articles and 1 editorial. We know that we are only managing to address a small part of what plasma discharge can be used for, but we hope that the readers will enjoy this book and, therefore, be inspired with new ideas for future research in the field of plasma

Investigation on the effect of low-pressure plasma treatment on the adhesion properties of different carbon-fiber-reinforced-polymer materials for structural adhesive bonding

This three-part study, developed with the collaboration of the Istituto Italiano di Tecnologia (IIT), reports a systematic and quantitative evaluation of the effects induced by various low-pressure plasma (LPP) treatments on the adhesive properties of Carbon Fiber Reinforced Polymer (CFRP) substrates. In particular, Part A of this work was focused on the surface activation of CFRP substrates, made via traditional vacuum-bag technique, which was performed using several combinations of LPP parameters. From the comparison with conventional pre-bonding preparations, it was possible to quantify the effectiveness of LPP in increasing the performance of adhesively-bonded CFRP joints. Further measurements of roughness and wettability were performed, and analyses via x-ray photoelectron spectroscopy (XPS) were also carried out, allowing identification of the morphological, physical and chemical phenomena involved in the treatments. Then, a quantitative evaluation of the aging behavior of the adhesively-bonded joints was the topic of the subsequent Part B. Four significant sets of LPP-treatment conditions were selected, and then subjected to accelerated temperature-humidity aging. To assess the durability of the CFRP-adhesive system under severe aging conditions, tensile shear strength (TSS) testing and wedge cleavage test (WT) were performed in parallel. The experimental findings showed that LPP treatment of the CFRP substrates results in increased short-term quality of the adhesive joint as well as in enhancement of its durability even under severe aging conditions. The last part of the work (Part C) was inspired by the recent developments in additive technologies for the manufacturing of structural thermoplastic-composite parts. In this context, the mechanical and failure behavior were investigated of continuous carbon-fiber (CCF) composite materials built via Fused Filament Fabrication (FFF) technology when used as substrates for bonded joints. Notably, the experiments were focused on verifying how the additively-manufactured substrates respond to adhesive bonding when the interface interactions are increased by preparing the surface with LPP treatment. This approach allowed detection of those criticalities that might limit the application of adhesive bonding to 3D-printed composite parts, with respect to that observed using traditional CFRP materials

Ignition Systems for Gasoline Engines : 4th International Conference, December 6 - 7, 2018, Berlin, Germany

In addition to increasing electrification, forecasts show a worldwide increase in the number of gasoline engines being produced. Rising industrialization will likely lead to 120 million new registrations, at least 75% of them for vehicles based on combustion engines, by the year 2030. Ambitious climate targets will remain a chimera as long as the gasoline engine is not adapted to help significantly reduce carbon emissions. In addition to the requirements of the established markets, we must be prepared for new challenges in emerging economic regions in particular. Engines require greater optimization while remaining sufficiently robust to meet the demands of use all around the world. In addition to the Miller combustion cycle, the industry needs engines that employ strongly charge-diluted combustion to achieve efficiencies significantly above 40%. Instrumental in this will be ignition processes with great potential to shift ignition limits. The question we have to ask ourselves is how can ignition systems help further boost the efficiency of the combustion engine? Together with the participants we discussed this key question during the 4th International Conference on Ignition Systems for Gasoline Engines