FABRICATION, CHARACTERIZATION, AND IRRADIATION OF AN AUSTENITIC OXIDE DISPERSION STRENGTHENED STEEL SUITED FOR NEXT GENERATION NUCLEAR APPLICATIONS

As nuclear energy systems become more advanced, the materials encompassing them need to perform at higher temperatures for longer periods of time. In this Master’s thesis we experiment with an oxide dispersion strengthened (ODS) austenitic steel that has been recently developed. ODS materials have a small concentration of nano oxide particles dispersed in their matrix, and typically have higher strength and better extreme temperature creep resistance characteristics than ordinary steels. However, no ODS materials have ever been installed in a commercial power reactor to date. Being a newer research material, there are many unanswered phenomena that need to be addressed regarding the performance under irradiation. Furthermore, due to the ODS material traditionally needing to follow a powder metallurgy fabrication route, there are many processing parameters that need to be optimized before achieving a nuclear grade material specification. In this Master’s thesis we explore the development of a novel ODS processing technology conducted in Beijing, China, to produce solutionized bulk ODS samples with ~97% theoretical density. This is done using relatively low temperatures and ultra high pressure (UHP) equipment, to compact the mechanically alloyed (MA) steel powder into bulk samples without any thermal phase change influence or oxide precipitation. By having solutionized bulk ODS samples, transmission electron microscopy (TEM) observation of nano oxide precipitation within the steel material can be studied by applying post heat treatments. These types of samples will be very useful to the science and engineering community, to answer questions regarding material powder compacting, oxide synthesis, and performance. Subsequent analysis performed at Queen’s University included X-ray diffraction (XRD) and inductively coupled plasma optical emission spectrometry (ICP-OES). Additional TEM in-situ 1MeV Kr2+ irradiation experiments coupled with energy dispersive X-ray (EDX) techniques, were also performed on large (200nm+) non-stoichiometric oxides embedded within the austenite steel grains, in an attempt to quantify the elemental compositional changes during high temperature (520oC) heavy ion irradiation.

Self-healing thermal annealing: surface morphological restructuring control of GaN nanorods

With advances in nanolithography and dry etching, top-down methods of nanostructuring have become a widely used tool for improving the efficiency of optoelectronics. These nano dimensions can offer various benefits to the device performance in terms of light extraction and efficiency, but often at the expense of emission color quality. Broadening of the target emission peak and unwanted yellow luminescence are characteristic defect-related effects due to the ion beam etching damage, particularly for III–N based materials. In this article we focus on GaN based nanorods, showing that through thermal annealing the surface roughness and deformities of the crystal structure can be “self-healed”. Correlative electron microscopy and atomic force microscopy show the change from spherical nanorods to faceted hexagonal structures, revealing the temperature-dependent surface morphology faceting evolution. The faceted nanorods were shown to be strain- and defect-free by cathodoluminescence hyperspectral imaging, micro-Raman, and transmission electron microscopy (TEM). In-situ TEM thermal annealing experiments allowed for real time observation of dislocation movements and surface restructuring observed in ex-situ annealing TEM sampling. This thermal annealing investigation gives new insight into the redistribution path of GaN material and dislocation movement post growth, allowing for improved understanding and in turn advances in optoelectronic device processing of compound semiconductors.

Initiation and early crack growth in VHCF of stainless steels : Experimental and theoretical analysis

Mechanical fatigue is a failure phenomenon that occurs due to repeated application of mechanical loads. Very High Cycle Fatigue (VHCF) is considered as the domain of fatigue life greater than 10 million load cycles. Increasing numbers of structural components have service life in the VHCF regime, for instance in automotive and high speed train transportation, gas turbine disks, and components of paper production machinery. Safe and reliable operation of these components depends on the knowledge of their VHCF properties. In this thesis both experimental tools and theoretical modelling were utilized to develop better understanding of the VHCF phenomena. In the experimental part, ultrasonic fatigue testing at 20 kHz of cold rolled and hot rolled stainless steel grades was conducted and fatigue strengths in the VHCF regime were obtained. The mechanisms for fatigue crack initiation and short crack growth were investigated using electron microscopes. For the cold rolled stainless steels crack initiation and early growth occurred through the formation of the Fine Granular Area (FGA) observed on the fracture surface and in TEM observations of cross-sections. The crack growth in the FGA seems to control more than 90% of the total fatigue life. For the hot rolled duplex stainless steels fatigue crack initiation occurred due to accumulation of plastic fatigue damage at the external surface, and early crack growth proceeded through a crystallographic growth mechanism. Theoretical modelling of complex cracks involving kinks and branches in an elastic half-plane under static loading was carried out by using the Distributed Dislocation Dipole Technique (DDDT). The technique was implemented for 2D crack problems. Both fully open and partially closed crack cases were analyzed. The main aim of the development of the DDDT was to compute the stress intensity factors. Accuracy of 2% in the computations was attainable compared to the solutions obtained by the Finite Element Method.

Descripción de resultados de la reconstrucción de placa plantar en inestabilidad de la segunda articulación metatarsofalángica

Objetivo: Describir los desenlaces funcionales, complicaciones postoperatorias, dolor y satisfacción de un grupo de pacientes con diagnóstico de inestabilidad de segunda articulación metatarsofalángica y lesión de la placa plantar, que fueron intervenidos quirúrgicamente para su reconstrucción en el Hospital Universitario de cuarto nivel Fundación Santa Fé de Bogotá, en el periodo comprendido entre Enero de 2010 hasta Diciembre de 2015. Métodos: Estudio descriptivo de corte transversal que evalúa desenlaces funcionales, dolor y satisfacción para un grupo consecutivo de pacientes con diagnóstico de inestabilidad de la segunda articulación metatarsofalángica que fueron intervenidos quirúrgicamente mediante reconstrucción de la placa plantar entre Enero de 2010 a Diciembre de 2015 en el Hospital Universitario Fundación Santa fe de Bogotá. Resultados: El procedimiento se realizó a 39 pacientes (40 MTF), encontrando mejoría en dolor, función y satisfacción. El dolor postoperatorio paso de severo a leve en el 80% de los pacientes, 67.5% de los pacientes presentaron prueba de aprehensión positiva, 85% alineamiento adecuado, el reporte de escala de AOFAS postoperatoria fue de 87, y los resultados fueron satisfactorios en un 94.5%. La principal complicación con la cirugía fue la extensión residual del dedo operado (22.5%). Conclusiones: La reconstrucción de la placa plantar en casos de inestabilidad metatarsofalángica ha demostrado tener resultados satisfactorios, en el presente estudio encontramos mejoría respecto a dolor, función y satisfacción posterior a la realización del procedimiento. Sin embargo puede presentar complicaciones como extensión residual del dedo o elevación, rigidez y recidiva.

Luxación esternoclavicular posterior

Paciente masculino de 24 años, ingresa a urgencias por trauma contundente en clavícula derecha durante accidente de tránsito. Presenta dolor en articulación esternoclavicular que se exacerba con la movilización del hombro y disfagia. Al examen físico, leve depresión del extremo medial de la clavícula y limitación de los arcos de movimiento del hombro. Las imágenes confirmaron el diagnostico de LEC posterior. El paciente fue llevado a cirugía para reducción y cerclaje, sin complicaciones.

Perfil lipídico da carne de cordeiros da raça Morada Nova.

Objetivou-se nesse trabalho verificar se a idade ao abate e o uso de suplementação no período pré-desmame altera o perfil lipídico da carne de cordeiros da raça Morada Nova.

Experimental and numerical investigation on short and long term performance of macro-synthetic fibre reinforced concrete materials

Fibre Reinforced Concretes are innovative composite materials whose applications are growing considerably nowadays. Being composite materials, their performance depends on the mechanical properties of both components, fibre and matrix and, above all, on the interface. The variables to account for the mechanical characterization of the material, could be proper of the material itself, i.e. fibre and concrete type, or external factors, i.e. environmental conditions. The first part of the research presented is focused on the experimental and numerical characterization of the interface properties and short term response of fibre reinforced concretes with macro-synthetic fibers. The experimental database produced represents the starting point for numerical models calibration and validation with two principal purposes: the calibration of a local constitutive law and calibration and validation of a model predictive of the whole material response. In the perspective of the design of sustainable admixtures, the optimization of the matrix of cement-based fibre reinforced composites is realized with partial substitution of the cement amount. In the second part of the research, the effect of time dependent phenomena on MSFRCs response is studied. An extended experimental campaign of creep tests is performed analysing the effect of time and temperature variations in different loading conditions. On the results achieved, a numerical model able to account for the viscoelastic nature of both concrete and reinforcement, together with the environmental conditions, is calibrated with the LDPM theory. Different type of regression models are also elaborated correlating the mechanical properties investigated, bond strength and residual flexural behaviour, regarding the short term analysis and creep coefficient on time, for the time dependent behaviour, with the variable investigated. The experimental studies carried out emphasize the several aspects influencing the material mechanical performance allowing also the identification of those properties that the numerical approach should consider in order to be reliable.

Development, mechanical characterization and qualification in liquid lead of stainless steels for structural applications in the future fission and fusion nuclear reactors

The research activity carried out in the Brasimone Research Center of ENEA concerns the development and mechanical characterization of steels conceived as structural materials for future fission reactors (Heavy Liquid Metal IV Generation reactors: MYRRHA and ALFRED) and for the future fusion reactor DEMO. Within this framework, two parallel lines of research have been carried out: (i) characterization in liquid lead of steels and weldings for the components of the IV Generation fission reactors (GIV) by means of creep and SSRT (Slow Strain Rate Tensile) tests; (ii) development and screening on mechanical properties of RAFM (Reduced Activation Ferritic Martensitic) steels to be employed as structural materials of the future DEMO fusion reactor. The doctoral work represents therefore a comprehensive report of the research carried out on nuclear materials both from the point of view of the qualification of existing (commercial) materials for their application in the typical environmental conditions of 4th generation fission reactors operating with lead as coolant, and from the point of view of the metallurgical study (with annexed microstructural and mechanical characterization of the selected compositions / Thermo Mechanical Treatment (TMT) options) of new compositional variants to be proposed for the “Breeding Blanket” of the future DEMO Fusion Reactor.

Spazi postcoloniali: dislocazioni, diaspore, cartografie

La presente tesi di dottorato si propone di ricostruire criticamente la riflessione postcoloniale sullo spazio, riconoscendo nella critica postcoloniale l’introduzione di una fondamentale interrogazione degli spazi che sviluppa cartografie concettuali originali. Il lavoro si concentra sulla duplice operazione svolta dagli studi postcoloniali rispetto al tema degli spazi, riguardando, da una parte, le istanze critiche volte a condannare e contraddire le diverse spazialità del dominio coloniale; dall’altra, elaborando in risposta delle alternative concettuali forti, tali da offrire nuove immagini e strumenti per ripensare in modo abilitante gli spazi politici per il presente globale. Rispecchiando questo duplice indirizzo, la tesi si divide in due parti, precedute da un capitolo introduttivo, volto a presentare una strategia di fondo del pensiero postcoloniale sugli spazi, quella di un "entanglement" atto a ingarbugliare produttivamente fra loro le spazialità sottoposte a divisione e segregazione da parte del dominio coloniale (capitolo 1). A seguire, una pars destruens indaga la contestazione postcoloniale di specifiche spazialità coloniali, (capitolo 2); e discute la critica postcoloniale mossa alla geografia e alla cartografia moderne, in quanto strumenti di potere/sapere coloniale, atti alla costruzione di uno spazio globale strutturalmente asimmetrico, a cui consegue però, da parte postcoloniale, l’elaborazione di contro-cartografie critiche (capitolo 3). Segue una pars construens, dedicata a due concetti-chiave della riflessione postcoloniale sullo spazio, ovvero il pianeta, indagato come “sovrascrittura del globo”, la riflessione sul quale inoltre si fa occasione, da parte del pensiero postcoloniale, per intercettare istanze ecologiche urgenti e, insieme, riflettere sul problema del cosmopolitismo (capitolo 4); e il confine, la cui ricca e complessa ri-significazione in una prospettiva postcoloniale viene qui ricostruita nelle sue molte dimensioni (capitolo 5). Seguono delle conclusioni a fare un riassunto e un bilancio degli argomenti così ripercorsi, mettendo in luce in particolare i temi della dislocazione, della diaspora e della traduzione.

Bitumen aggregate adhesion and bitumen rheology of hard modified binders

The waterproofing of hydraulic structure is done traiditionally like laying road on dam surface but with specific modified binders. An italian firm recently patented a new method that is re-adaptation of typical surface treatment of roads. The purpose of this study is to find out best aggregate-bitumen mixture that can perform well under service conditions of a large hydraulic structure such as dams. So, 4 different hard modified bitumen were tested with 2 aggregate types i.e. limestone and basalt. The experimental program contained the testing of bitumen aggregate adhesion, using the rolling bottle test and rheology of hard modified binders using multiple stress creep and recovery test and dynamic viscosity test. The results and discussion are presented in detail in this work.

La Lussazione della Rotula - Confronto tra Trattamento Conservativo e Trattamento Chirurgico: una Revisione Sistematica della Letteratura.

Background: La lussazione traumatica della rotula rappresenta il 2-3% delle lesioni riguardanti il ginocchio. È una condizione comune negli adolescenti e colpisce maggiormente il sesso femminile. Si associa spesso ad instabilità rotulea, alti tassi di ridislocazione, dolore, difficoltà nel ritorno alle attività di vita quotidiana e allo sport e artrosi dell’articolazione femoro-rotulea. Obiettivo: Lo scopo di questa Revisione Sistematica è confrontare i risultati di studi randomizzati controllati che esaminano l’efficacia di due tipi di trattamento, chirurgico e conservativo, rispetto a: funzionalità del ginocchio, tasso di ridislocazione, qualità di vita e ritorno allo sport nei pazienti affetti da un primo episodio di lussazione rotulea. Metodi: La ricerca è stata condotta sulle banche dati PubMed, Cochrane Library e PEDro. Sono stati selezionati RCT in lingua inglese senza imporre limiti temporali, che presentavano entrambi i trattamenti, chirurgico e conservativo, e un follow up di almeno due anni. I partecipanti dovevano essere affetti unicamente da un primo episodio di lussazione. La qualità metodologica degli articoli è stata valutata tramite la PEDro scale. Risultati: Otto articoli hanno soddisfatto i criteri di eleggibilità e sono stati inclusi nella Revisione. Il punteggio medio alla PEDro scale di 3.6/10 ha rivelato una scarsa qualità metodologica degli articoli. La gran parte degli studi ha rilevato una riduzione del tasso di ridislocazione con il trattamento chirurgico, mentre non c’è concordanza nell’affermare la sua superiorità per migliorare la funzionalità del ginocchio. Conclusioni: Gli studi inclusi non hanno mostrato una chiara efficacia di un trattamento rispetto all’altro, se non riguardo al tasso di ridislocazione, ma la loro scarsa qualità metodologica rende tali risultati inaffidabili. Pertanto, sono necessari studi di qualità superiore per determinare con maggior precisione l’efficacia comparativa dei due interventi.