Elasto-plastic shock waves in high-velocity compaction of spherical metal particles are the focus of this thesis which consists of four papers (A-D). The compaction process is modeled by a discrete element method while using elastic and plastic loading, elastic unloading and adhesion at contacts. Paper A investigates the dynamic compaction of a one-dimensional chain of homogenous particles. The development of the elasto-plastic shock waves, its propagation and influence on the compaction process are examined. Simulations yield information on the contact behavior, velocity of the particle and its deformation during dynamic compaction. Effects of changing loading parameters on the compaction process are also discussed. Paper B addresses the non-homogeneity in a chain having; particles of different sizes and materials, voids between the particles and particles with/without adhesion between them. Simulations show transmission and reflection of elasto-plastic shock wave during compaction process. The particle deformation during incident and reflected shocks and particle velocity fluctuations due to voids between particles are simulated. The effects of adhesion on particles separation during unloading stage are also discussed. Paper C develops a simulation model for a high-velocity compaction process with auxiliary pistons, known as relaxation assists, in a compaction assembly. The simulation results reveals that the relaxation assists offer; smooth compaction during loading stage, prevention of  the particle separation during unloading stage and conversion of  higher kinetic energy of hammer into particles deformation.  Furthermore, the influence of various loading elements on compaction process is investigates. These results support the findings of experimental work. Paper D further extends the one-dimensional case of Paper A and B into two-dimensional assembly of particles while adding friction between particles and between particles and container walls. Three particular cases are investigated including closely packed hexagonal, loosely packed random and a non-homogenous assembly of particles of various sizes and materials. Consistent with the one-dimensional case, primary interest is the linking of particle deformation with the elasto-plastic shock wave propagation. Simulations yield information on particle deformation during shock propagation and change in overall particles compaction with the velocity of the hammer. The force exerted by particles on the container walls and rearrangement of the loosely packed particles during dynamic loading are also investigated. Finally, the effects of presence of friction and adhesion on both overall particles deformation and compaction process are simulated. / QC 20110311

abstract: The interior of Earth is stratified due to gravity. Therefore, the lateral heterogeneities observed as seismic anomalies by seismologists are extremely interesting: they hold the key to understand the composition, thermal status and evolution of the Earth. This work investigates seismic anomalies inside Earth’s lowermost mantle and focuses on patch-like ultra-low velocity zones (ULVZs) found on Earth’s core-mantle boundary (CMB). Firstly, all previous ULVZ studies are compiled and ULVZ locations on the CMB are digitized. The result is a database, which is publicly available online. A key finding is that there is not a simple mapping between the locations of the observed ULVZs and the large low velocities provinces (LLVPs). Instead, ULVZs are more likely to occur near LLVP boundaries. This spatial correlation study supports a compositionally distinct origin for at least some ULVZs. Next, the seismic structure of the basal mantle beneath the Central America is investigated. This region hosts present and past subducted slabs, which could have brought compositionally distinct oceanic basalt all the way down to the CMB. The waveform distortions of a core-reflected seismic phase and a forward modeling method are used to constrain the causes of the CMB structures. In addition to ULVZ structures, isolated patches of thin zones with shear velocity increased by over 10% relative to background mantle are found for the first time. Ultra-high velocity zones (UHVZs) are interspersed with ULVZs and could be caused by subducted mid-ocean ridge basalt (MORB) that undergoes partial melting and melt segregation. Fe-rich partial melt of MORB can form ULVZs, and silica polymorphs (SiO2) and calcium-perovskite (CaPv) rich solid residue can explain the UHVZs. Finally, large-scale heterogeneities in the lowermost mantle are investigated using S waveform broadening observations. Several basal layer models are case-studied via synthetic calculations. S wave arrivals received at a distance larger than 80˚ in a global dataset from large earthquakes between the years 1994 and 2017 are examined and S waveform broadenings are documented. This approach exploits large distance data for the first time, and therefore is complementary to previous studies in terms of sampling locations. One possible explanation of S waveform broadening is velocity discontinuity inside the D″ layer due to the temperature controlled Bm-pPv phase transition. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2020

Swerea KIMAB has invested in a new and improved thermal spray technique, High Velocity Air-Fuel (HVAF). This has recently been introduced to the market given that the technical properties, costs and performance of the technique is still not thoroughly investigated and covered. An examination of these areas was therefore necessary to examine appropriate uses for the new technology. The investigation aimed to indicate how the new technology compares with established technologies in some areas in terms of performance and cost but also if there are any entirely new applications that the technology enables. In addition, there is also considerable uncertainty what the market for the new technology looks like today, and what it can be developed into. The market of thermal spraying is limited today. This entails that there is a great interest to investigate the preferences and equirements companies have to consider when choosing this new technology in favour of an ld one. It is also of great interest to investigate what skills and support companies’ requests in order to venture into this new technology. The aim with the work was to answer two research questions What are possible business cases for the HVAF technology from a technical as well as an economical point of view? What initiatives are necessary to get more companies and applications into the thermal spray business? The methods used for the master thesis were empirical studies, benchmarking, interviews, a survey and logical discussions. The report presents an overall knowledge bank for the most commonly used thermal spray technologies, compared with regards to characteristics and cost. As a result of the new features that the HVAF technology offers suitable application areas for the technology were identified through the work, such as high temperature corrosion protection. As a result of the survey the work also identified the general lack of knowledge about thermal spraying as the main obstacle to get more companies into using the technology. / Swerea KIMAB har nyligen investerat i en förbättrad teknik för termisk sprutning, High Velocity Air-Fule (HVAF). HVAF-tekniken har nyligen introducerats på marknaden och de tekniska egenskaperna har därmedinte undersökts grundligt eller jämförts med genskaperna för befintliga termiska spruttekniker. Arbetets syfte var att belysa hur och var den nya HVAFtekniken kan konkurrera med etablerade tekniker på områden i form av prestanda och kostnad. ndersökningen syftade även till att utreda om den nya tekniken kan medföra helt nya applikationsområden. En genomgång av befintliga tekniker var till en början nödvändig för att i slutändan kunna identifiera lämpliga användningsområden för HVAF-tekniken. Det finns en stor osäkerhet kring hur marknaden för HVAF ser ut idag, och hur den kan komma att utvecklas. Själva marknaden för termisk sprutning är i dagsläget begränsad, vilket innebär att det finns ett stort intresse kring att undersöka vilka önskemål och krav företag ställer på HVAF-tekniken för att den skall kunna konkurrera på marknaden. Utöver tidigare nämda delar av arbetet syftade det även till att identifiera vilka kunskaper och vilket stöd företagen önskar vid en eventuell övergång till termisk sprutning generellt. Följande forskningsfrågor har besvarats i arbetet. Vilka nya användningsområden möjliggör HVAF-tekniken för sett ur en teknisk och ekonomisk synvinkel? Vilka initiativ är nödvändiga för att öka användandet av termisk sprutning inom industrin? Empiriska studier, benchmarking, intervjuer och en enkätundersökning var de metoder som användes för arbetet. I rapporten presenteras en övergripande kunskapsbank för de vanligaste termiska sprutteknikerna, vilken omfattar en jämförelse av egenskaper och kostnader. Lämpliga användningsområden för HVAF-tekniken har identifierades och presenteras i rapporten. exempelvis som skydd mot höga temperaturer, korrosion och abrasion. Allmän brist på kunskap om termisk sprutning har identifierats som det främsta hindret mot ökad användning av tekniken i dagsläget.

To enhance material performance at different length scales, this study strives to develop a reliable analytical and computational tool with the help of internal state variables spanning micro and macro-level behaviors. First, the practical relevance of a nonlocal damage integral added to an internal state variable (BCJ) model is studied to alleviate numerical instabilities associated within the post-bifurcation regime. The characteristic length scale in the nonlocal damage, which is mathematical in nature, can be calibrated using a series of notch tensile tests. Then the same length scale from the notch tests is used in solving the problem of a high-velocity (between 89 and 107 m/s) rigid projectile colliding against a 6061-T6 aluminum-disk. The investigation indicates that incorporating a characteristic length scale to the constitutive model eliminates the pathological mesh-dependency associated with material instabilities. In addition, the numerical calculations agree well with experimental data. Next, an effort is made rather to introduce a physically motivated length scale than to apply a mathematical-one in the deformation analysis. Along this line, a dislocation based plasticity model is developed where an intrinsic length scale is introduced in the forms of spatial gradients of mobile and immobile dislocation densities. The spatial gradients are naturally invoked from balance laws within a consistent kinematic and thermodynamic framework. An analytical solution of the model variables is derived at homogenous steady state using the linear stability and bifurcation analysis. The model qualitatively captures the formation of dislocation cell-structures through material instabilities at the microscopic level. Finally, the model satisfactorily predicts macroscopic mechanical behaviors - e.g., multi-strain rate uniaxial compression, simple shear, and stress relaxation - and validates experimental results.

A uniaxial High-Velocity Compaction (HVC) process for polymer powder using a cylindrical, hardened steel die and a new technique with relaxation assist was tested with a focus on the compactibility characteristics and surface morphology of the compacted materials using various heights of relaxation assist device with different compacting profiles. Relaxation assist device was presented as a new technique to reduce springback, pull-out phenomenon and to improve the compaction process. The basic phenomena associated with HVC are explained and the general energy principle is introduced to explain pull-out phenomenon during the decompacting stage. In this study, polyamide-11 powders with different particle size distributions have been compacted with the application of different compaction profiles, e.g. different energies and velocities. It was found that the relative green density is influenced more by the pre-compacting (primary compaction step) than by the post-compacting (secondary compaction step). Experimental results for different compaction profiles were presented showing the effect of varying the opposite velocity during the decompacting stage and how to improve the homogeneous densification between the upper and lower surface and the evenness of the upper surface of the compacted powder bed by using relaxation assists, and the influences of the relaxation assist device on the process characteristics. It was found that the relaxation assist improves the compaction of the polymer powder by locking the powder bed in the compacted form. In addition, the relative times of the compacting stage, decompacting stage and the reorganisation of the particles can be controlled by altering the height of the relaxation assist. It was found that the high-velocity compaction process is an interruption process and that the delay times between the pressure waves can be reduced by increasing the height of the relaxation assist device. Furthermore, the first gross instantaneous springback and the total elastic springback are reduced. Two bonding strain gauges and a high-speed video camera system were used to investigate the springback phenomenon during the compaction process. Scanning electron microscopy (SEM) and image computer board Camera (IC-PCI Imaging Technology) were used to the study the morphological characteristics, the limit of plastic deformation and particle bonding by plastic flow at contact points, and pull-out phenomena. / QC 20100506

Mass spectrometers have proven to be vital to understanding the Solar System and the planets within it. Spacecraft containing mass spectrometers have been sent to numerous remote places and have determined important information about the atmospheric composition of Venus, Earth, Mars, Jupiter, and Saturn, along with other celestial bodies. Such results have shown a variety of small neutral molecules, such as CH4 NH3, H2O, CO2, and CO, neutral radicals such as atomic O, H, and N, and a host of small ions, such as H+, N+, and NH4+. Closed ion source inlets, which allow for the detection of these small neutral molecules, contain a spherical antechamber that allows the neutrals to thermalize with the walls of the chamber through many successive collisions before they are introduced into the ionization region of the spacecraft mass spectrometer. These collisions, however, energetically excite neutral molecules and lead to many chemical changes, such as racemization, ionization, or even dissociation. When these changes occur, smaller neutrals can be produced, even if they were not in the original sample from the atmosphere or surface. As a result, the determination of the true composition of an atmosphere or a surface is cast into doubt. Herein is given a brief description of mass spectrometry in space research and how the closed ion source has greatly assisted this process. Dissociation and other chemical changes caused by the high velocity impacts that occur in closed source antechambers is also addressed. A theoretical approach to understanding such dissociative processes that occur after high energy collisions in closed source antechambers is described and undertaken. Chapter 2 describes a proof-of-concept study using hexane as a representative molecule and determines the velocity at which widespread dissociation of hexane molecules is likely to occur in closed source antechambers. This same theoretical process is then utilized in Chapter 3 with many more members of the n-alkane family to probe what effect molecular weight has on the amount of dissociation. Alkanes of both higher and lower molecular weight than hexane (C6H14) are used to show the effect as a function of molecular weight. In all cases, it was found that the velocity at which half of the incoming neutral n-alkane molecules dissociate is roughly the same for all molecular weights studied. This result is then applied to current and future space research through a proposed hardware solution, which will reduce the amount of dissociation and a discussion of how this effect may be seen in the results obtained from future mission instruments. Lastly, future work with different molecular weights and with successive collisions (the second, third, fourth, etc.) is described. This future work will further expand the present study to show how different functional groups, which may be partly responsible for higher-than-expected levels of NH3 and CO2, are affected after a high velocity, high energy impact.

No description available.

No description available.

Pour prémunir les structures spatiales d'impacts hyper-véloces, le secteur aérospatial est continuellement à la recherche de matériaux toujours plus performants. Dans cette optique, les verres métalliques massifs se présentent comme de potentiels éléments de blindages spatiaux. De récentes études ont mis en exergue une meilleure résistance à la pénétration de ces matériaux comparativement aux blindages actuels. Les impacts par lanceurs permettent d'étudier et caractériser le comportement sous chocs des matériaux. Cependant, les vitesses des projectiles se retrouvent actuellement limitées à 10 km/s, correspondant aux niveaux d'impacts hyper-véloces les plus modérés. Pour s'affranchir de cette limitation, il est possible de se tourner vers les lasers de puissance. Ces dispositifs permettent de générer des ondes de choc dont les niveaux de pression et de vitesse de déformation sont supérieurs aux lanceurs. Les travaux menés ont permis d'étudier et de caractériser le comportement et l'endommagement de plusieurs verres métalliques ternaires ZrCuAl sous choc laser. Plusieurs campagnes expérimentales ont été réalisées sur les installations du Laboratoire pour l'Utilisation des Lasers Intenses (LULI2000 et ELFIE). Une partie de l'équation d'état des nuances étudiées a été obtenue à la fois par choc laser et compression isentropique. Les processus d'endommagement, l'influence des vitesses de déformation et de composition sur la rupture ont été étudiés. Pour des régimes de vitesse de déformation supérieurs de trois ordres de grandeur à ceux disponibles dans la littérature, il a été mis en évidence que les verres métalliques étudiés présentaient une limite à la rupture cinq à dix fois supérieure. / Space industry is always searching for efficient materials to protect space structures from high-velocity impacts. In this context, bulk metallic glasses appear as suitable elements of space debris shielding assemblies. Recent studies revealed a higher tolerance to impact of metallic glasses compared to materials currently used in shield assemblies. Gas-gun and powder launchers are usually used to study and characterize the dynamic and shock behaviour of materials. However, projectiles velocities are currently limited to 10 km/s, corresponding to the lowest high-velocity impacts levels. To overcome this limitation, one may consider shock waves induced by high-power laser facilities, whose pressure and strain rate levels can exceed those induced by canons. Hence, this work enabled to study and to characterize the dynamic and damage behaviours of several compositions of ternary ZrCuAl bulk metallic glasses subjected to shock waves induced by laser irradiation. Several experimental campaigns have been conducted on various laser facilities of the Laboratoire pour l'Utilisation des Lasers Intenses (LULI2000 and ELFIE). A part of the equation of state of the studied compositions was established using both shock waves and quasi-isentropic compressions. Damage processes and the composition and strain rate effects on fracture were also studied. For strain rate levels higher of three or more orders of magnitude than those available in the literature, it was shown that studied bulk metallic glasses displayed a five to ten times higher dynamic tensile limit.

Fibre reinforced composites have higher specific strength and stiffness in comparison to metals. However, composites are susceptible to impact damage resulting in degradation of mechanical properties especially compression strength. Numerous studies have been conducted to improve the impact damage tolerance of composite laminates using modified resin systems, thermoplastic matrices, 3-D fibre architectures and through thickness reinforcement. This work is primarily focussed on incorporating non dissolvable polypropylene fibres (PP) in a thermoset matrix for improving the damage tolerance. Commingling and wrapping techniques have been investigated. PP fibres have been incorporated at the preform stage and hence do not adversely affect the viscosity of the resin during infusion. The healing effect of PP fibres on impact damaged composite laminates when heating is introduced has also been studied. High velocity impact test results showed that using commingled glass/PP fibres increased the total energy absorption of composite laminates by 20% due to the extensive plastic deformation of the PP fibres and through the use of toughening mechanisms in the form of resin cracking and delamination. It has been found that PP fibres provide protection to the glass fibres during low velocity impact loading, so fewer fibre breakages occur which lead to improved residual properties compared with pristine glass laminates. Compression after impact (CAI) tests showed that the residual strength as a percentage of non-impacted strength increased with percentage of PP fibres used. For impact of 20-50J, glass/epoxy laminates retained 32 45% of their compressive strength while laminates with 7%, 13% and 18% PP fibres retained 37 50%, 42-52% and 43-60% of their compressive strength, respectively. It was also observed that glass/PP woven laminates had better compressive strength retention (62 83%) than the glass/PP non-crimp laminates (37-50%). Composite laminates with high-modulus PP fibres (Innegra) exhibited higher residual compression strengths in comparison to laminates with lower modulus PP fibres. For 15-50J impact, glass/Innegra laminates showed residual compression strength of 50 63% in comparison to 39-60%; laminates without thermoplastic fibres exhibited 33 43% residual compression strength. Modulus of thermoplastic fibres appears to be important at higher energy levels. Healing of damaged commingled laminates produced a significant reduction in the damage area and a corresponding increase in CAI strength after heating at 200ºC; CAI strength of healed laminates is about 85% of undamaged samples in comparison to 60% for non-healed samples. A novel micro-wrapping technique, developed in this work, demonstrated significant reduction in damage area (46%) in comparison to the commingling method. Core wrapped laminates had higher residual strength (43-60%) than glass laminates (33-43%). Better PP distribution in core-wrapped composites helped to decrease the PP rich areas and the impact damage did not propagate easily in comparison to commingled composites. However due to the reduction in damage area, impact energy absorption in core wrapped laminates was lower than for commingled.