The rocks underlying Vulcan Ridge are mainly Proterozoic metasediments of the Lower and Middle Division of the Aldridge formation and Proterozoic (or later) Moyie intrusives. Most of the metasediments are fine-grained quartzites, phyllites, schists and hormfelses composed mainly of quartz, biotite, muscovite and little feldspar. Tourmaline is a minor constituent of most metasediments but in the upper part of the Lower Aldridge it commonly forms up to 30 percent of the rocks. It is believed to have formed metasomatically by solutions derived from the White Creek batholith. A lens-like deposit of breccia-conglomerates makes up the upper most part of the Lower Aldridge. Most of the deposit is composed of unsorted material - angular to subangular fragments of Aldridge type metasediments imbedded in abundant fine-grained matrix of similar composition. This deposit is believed to have formed by subaqueous slides or mudflows. The Moyie intrusives are sill-like bodies of dioritic and gabbroic rocks composed essentially of hornblende, plagioclase and variable amounts of quartz. Most of the variations in texture and composition apparent in some of the intrusives are probably due to alteration but some may also be due to magmatic differentiation and to assimilation of country-rocks. The metasediments in the southern part of the area have been subjected to regional metamorphism and are of low metamorphic grade. In the northern part of the area the rocks have been contact metamorphosed. Within approximately 1½ mile of the White Creek batholith they have been metamorphosed to phyllites, schists and hornfelses which attained or closely approached a medium grade of metamorphism characteristic of the hornblende hornfels facies. Retrogressive metamorphism is extensive in the rocks near the contact of the batholith and is attributed to hydro-thermal solutions derived from that intrusive. Structure of the rocks south of the White Creek batholith is dominated by northeasterly trending folds which have been refolded into a large anticline near the batholith, and by northeasterly striking, steep dipping faults. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Title page, table of contents and abstract only. The complete thesis in print form is available from the University of Adelaide Library. / The occurrence of palaeo-oil columns in Late Jurassic and Cretaceous reservoirs in the Vulcan sub-basin indicates that hydrocarbon accumulations have leaked. It is unclear whether accumulations have leaked through breach of top seal or fault seal. This study evaluates the top seal potential for hydrocarbon accumulations in the Vulcan Sub-basin. For this purpose a top seal potential assessment methodology was developed. Seal potential (SP) combines seal capacity (the hydrocarbon column height that can physically be held back by seal), seal geometry (the areal extent and thickness of the seal) and seal integrity (rock mechanical properties of the seal). Seal capacities are measured using mercury injection capillary pressure calculations. Areal extent is evaluated using sedimentological and sequence stratigraphic principles. Thickness is determined empirically from well logs and seismic data. Seal integrity is derived from a brittleness index. In addition, a component relating to data quality and quantity is included in seal potential evaluation. The main sample set for this study is composed of drill cuttings. For this reason a comparison of seal capacity results measured from cuttings and cores has verified that cuttings samples provide accurate seal capacity measurements. Lower Vulcan Formation SP ranges from low to high due to variations in seal capacity and thickness risks as well as data quality and quantity. High SP occurs in the main depocentres and low SP occurs on the palaeo-highs and basin margins. Upper Vulcan Formations SP ranges from low to moderate due to variations in seal capacity. Moderate SP occurs in the depocentres and low SP on the basin margins. In the Echuca Shoals Formations seal capacity. Formation seal extent and integrity as well as data quality and quantity are good. However seal thickness is inconsistent, resulting in SP variations from good to poor as a function of thickness. Jamieson Formation has high seal capacities, is thick and areally extensive, however the seal potential is locally moderate (for example on the Ashmore Platform) due to seal integrity risk. SP for the Jamieson is controlled by the thickness and the amount of calcite present in the rock, which affects the brittleness of the formation and hence the seal integrity. The Woolaston, Gibson and Fenelon (WGF) Formations are grouped together as a regional seal and in this group SP varies from low to high. The WGF rocks generally have high seal capacities, are areally extensive and thick with good data quality and quantity sample set wise. Where the WGF is predominantly marl and calcilutite some of the highest brittleness index values were recorded and hence the WGF has a low SP in these areas. Based on the overall seal potential analysis, almost all seals in the area are capable of holding back hydrocarbon columns greater then present or palaeocolums recorded. This suggests that hydrocarbon leakage in the Vulcan Sub-Basin did not occur as a result of top seal capillary failure. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1313021 / Thesis (Ph.D.) -- University of Adelaide, Australian School of Petroleum, 2008

A norma brasileira ABNT NBR 14323:2013 apresenta um método para o dimensionamento de lajes mistas de aço e concreto em situação de incêndio. No entanto, esse procedimento não inclui o efeito do comportamento de membrana da laje. Usando a teoria de placas para grandes deslocamentos, esta pesquisa estabelece que as altas temperaturas podem induzir uma considerável ação de membrana de tração, auxiliando na segurança da laje em situação de incêndio. No desenvolvimento de uma ferramenta para o dimensionamento a partir do método analítico de lajes mistas em situação de incêndio, uma série de estudos foi desenvolvida para a análise do comportamento de membrana de tração a altas temperaturas. O método analítico mais conhecido é o método de Bailey. Comparações entre os métodos de Bailey e da ABNT NBR 14323:2013, e análises empregando os programas Vulcan e MACS+ foram realizadas. Neste trabalho, compararam-se resultados empregando o método de Bailey e do programa de computador MACS+, que teve por base o próprio método de Bailey. Como esperado, os resultados foram similares. Ainda, neste trabalho, realizaram-se alguns estudos numéricos empregando o método dos elementos finitos, por meio do programa de computador Vulcan e compararam-se resultados entre o método de Bailey e Vulcan. Uma investigação sobre possíveis simplificações da formulação da ABNT NBR 14323:2013 também foi realizada. / The Brazilian standard ABNT NBR 14323:2013 presents a method for the composite slabs fire design. However, it doesnt include the effect of the slab behaving as a membrane. Using the theory of plates for large displacements, the research establishes that high temperatures can induce a considerable tensile membrane action, assisting in the safety of the slab in fire. In developing a tool for the analytical method composite slabs fire design, some studies were made to analyze the behavior of tensile membrane at high temperatures. The most popular analytical method is the Baileys method. In this study, analysis of the Baileys methods, the Brazilian standard and the Vulcan and MACS+ software were performed and the results were compared. As expected, the results were similar. Still, in this work, there have been some numerical studies employing the finite element method, using the computer program Vulcan, and results were compared between the Baileys method and Vulcan. An investigation about possible simplifications of the formulation presented by Brazilian standard were also developed.

A norma brasileira ABNT NBR 14323:2013 apresenta um método para o dimensionamento de lajes mistas de aço e concreto em situação de incêndio. No entanto, esse procedimento não inclui o efeito do comportamento de membrana da laje. Usando a teoria de placas para grandes deslocamentos, esta pesquisa estabelece que as altas temperaturas podem induzir uma considerável ação de membrana de tração, auxiliando na segurança da laje em situação de incêndio. No desenvolvimento de uma ferramenta para o dimensionamento a partir do método analítico de lajes mistas em situação de incêndio, uma série de estudos foi desenvolvida para a análise do comportamento de membrana de tração a altas temperaturas. O método analítico mais conhecido é o método de Bailey. Comparações entre os métodos de Bailey e da ABNT NBR 14323:2013, e análises empregando os programas Vulcan e MACS+ foram realizadas. Neste trabalho, compararam-se resultados empregando o método de Bailey e do programa de computador MACS+, que teve por base o próprio método de Bailey. Como esperado, os resultados foram similares. Ainda, neste trabalho, realizaram-se alguns estudos numéricos empregando o método dos elementos finitos, por meio do programa de computador Vulcan e compararam-se resultados entre o método de Bailey e Vulcan. Uma investigação sobre possíveis simplificações da formulação da ABNT NBR 14323:2013 também foi realizada. / The Brazilian standard ABNT NBR 14323:2013 presents a method for the composite slabs fire design. However, it doesnt include the effect of the slab behaving as a membrane. Using the theory of plates for large displacements, the research establishes that high temperatures can induce a considerable tensile membrane action, assisting in the safety of the slab in fire. In developing a tool for the analytical method composite slabs fire design, some studies were made to analyze the behavior of tensile membrane at high temperatures. The most popular analytical method is the Baileys method. In this study, analysis of the Baileys methods, the Brazilian standard and the Vulcan and MACS+ software were performed and the results were compared. As expected, the results were similar. Still, in this work, there have been some numerical studies employing the finite element method, using the computer program Vulcan, and results were compared between the Baileys method and Vulcan. An investigation about possible simplifications of the formulation presented by Brazilian standard were also developed.

Made available in DSpace on 2016-08-19T12:56:37Z (GMT). No. of bitstreams: 1 Dissertacao Andre.pdf: 2646720 bytes, checksum: 5239249ae6d8f92c287772beaafd5621 (MD5) Previous issue date: 2011-09-19 / This work presents a comparative study of Black Pearls 2000 (BP) and Vulcan XC-72R (obtained concerning the oxidation of ethanol, the nanomaterial Ni(II)(PAN)2/(VC) presented higher values of current than the Ni(II)(PAN)2/(BP). A heat treatment study was carried out for the nanocomposite Ni(II)(PAN)2/(VC) because this material has shown the highest current densities for ethanol oxidation. This material was heat treated (500, 600 and 700 °C), characterized and tested for electrochemical oxidation of ethanol, and compared with the nanocomposite prepared at 25 °C. The heat treatment showed significant influence on properties such as morphology, particle size of both the support and the metal structure, and electrocatalytic activity. The nanocomposite treated at 500 °C showed better performance for electrocatalytic oxidation of ethanol (VC) nanomateriais, used as support for the complex Ni(II)(PAN)2. The composites synthesized were characterized by the following techniques: Transmission Electron Microscopy (TEM), X-ray diffraction and Cyclic Voltammetry. The results showed that the carbon support Vulcan XC-72R, is more porous than the Black Pearls 2000 and both have approximately, the same average particle size. Voltammetric analysis showed that the nanocomposite Ni(II)(PAN)2 presented lower separation between the anodic and cathodic peak potential (ΔEp) , for the pair Ni2+ / Ni3+, than the Ni(II)(PAN)2, however Ni(II)(PAN)2 presented less current density, for this redox couple. The electrocatalytical activity of the two nanocomposites through ethanol oxidation was evaluated by the techniques cyclic voltammetry and chronoamperometry. For the cyclic voltammetric study, Ni(II)(PAN)2/(BP) presented a maximum oxidation for the ethanol at 0.5 V while Ni(II)(PAN)2/(VC) showed a maximum oxidation at 0.6 V, in sodium hydroxide solution 1 mol L-1 with a concentration of 0.137 mol L-1 ethanol. Considering the current densities. / O presente trabalho mostra o estudo comparativo entre nanomateriais de carbono Black Pearls 2000 (BP) e Vulcan XC-72R (VC), utilizados como suporte para o complexo Ni(II)(PAN)2. Os compósitos sintetizados foram caracterizados pelas seguintes técnicas: Microscopia Eletrônica de Transmissão (MET), Difração de Raios-X (DRX) e Voltametria Cíclica (VC). Os resultados obtidos por MET mostraram que o suporte de carbono Vulcan XC-72R possui mais espaços na superfície do que o Black Pearls 2000 e ambos, têm aproximadamente, o mesmo tamanho médio de partículas. A análise voltamétrica mostrou que o nanocompósito Ni(II)(PAN)2/BP apresentou menor separação entre os potenciais de pico (ΔEp) anódico e catódico, para o par Ni2+/Ni3+, em comparação com Ni(II)(PAN)2/VC, porém com menor densidade de corrente, referente a este par redox. A atividade eletrocatalítica dos nanocompósitos para oxidação de etanol foi avaliada pelas técnicas voltametria cíclica e cronoamperometria. Na voltametria cíclica, Ni(II)(PAN)2/BP apresentou pico de oxidação para etanol em 0,5 V e Ni(II)(PAN)2/VC apresentou pico de oxidação em 0,6 V, em solução de hidróxido de sódio 1 mol L-1 com concentração de 0,137 mol L-1 de etanol. Quanto as densidades de corrente obtidas na oxidação de etanol, Ni(II)(PAN)2/VC apresentou valores maiores do que Ni(II)(PAN)2/BP. Um estudo de tratamento térmico foi realizado para o nancompósito Ni(II)(PAN)2/VC em virtude deste ter apresentado maiores densidades de corrente para oxidação de etanol. Este material tratado termicamente (a 500, 600 e 700°C) foi caracterizado e testado eletroquimicamente para oxidação de etanol, e comparado com o nanocompósito preparado a 25°C. O tratamento térmico teve influência significativa em propriedades como: morfologia, tamanho da partícula tanto do suporte quanto do metal, estrutura e atividade eletrocatalítica. O nanocompósito tratado a 500°C apresentou melhor desempenho eletrocatalítico para oxidação de etanol.

Sigma IT Consulting in Växjö gave the authors of this paper a task to change the search engine in one of their projects. To get a scientific view of the project the authors specified two research questions that could be connected to Sigma's problem. This problem is interesting to investigate since search engines are frequently used all over the world and often more user-friendly than classic menu navigation. To find a solution to the problem two experiments were conducted. The result from the experiments showed that the search engine EPiServer Find were, ever so slightly, outperformed Elasticsearch in the terms of relevance. The response time, however, had no significant difference.

No description available.

<i>Bacchus, Vulcan and Metis walk into a bar . . .</i> The following dialogues took place beginning in January of this year. In a series of investigations through drawing, physical constucts and research, the project began to take shape. With the help of Bacchus, Vulcan and Metis, the building was given a body of its own. Ideas of the way a building ages, as well as the way the parts of the building relate to the whole, are the basis of the thesis. The building is a sort of beast with two heads: the foundry, and the speak-easy [with cunning navigating the straits]. / Master of Architecture

Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2016-11-11T09:51:24Z No. of bitstreams: 0 / Made available in DSpace on 2016-11-11T09:51:24Z (GMT). No. of bitstreams: 0 / PtBi/C e PdBi/C foram preparados em diferentes razões atômicas (100:0, 90:10, 80:20, 70:30, 60:40 e 50:50) pelo método de redução via borohidreto de sódio (com adição total da solução de borohidreto em uma única etapa) utilizando H2PtCl6.6H2O, Pd(NO3)2, (BiNO3)3.5H2O como fonte de metais, Vulcan® (XC72-Cabot) como suporte de carbono e com uma carga metálica correspondente a 20% em massa. Os eletrocatalisadores obtidos foram caracterizados por difração de raios-X (DRX), microscopia eletrônica de transmissão (MET) e voltametria cíclica (VC). A atividade dos diferentes materiais preparados para a oxidação eletroquímica do ácido fórmico foi realizada em eletrólito ácido e alcalino utilizando-se as técnicas de voltametria cíclica, e cronoamperometria. Para estes estudos foi utilizado a técnica do eletrodo de camada fina porosa. A caracterização eletroquímica permitiu comparar o desempenho eletroquímico da platina e paládio, além de avaliar o benefício da presença do bismuto nas razões atômicas propostas. Os difratogramas de raio-X (DRX) confirmaram para todos os compostos de PtBi/C e PdBi/C a formação da estrutura cúbica de face centrada (cfc) característicos da rede cristalina da platina e do Paládio respectivamente. Outros picos encontrados foram associados a presença de fases de óxido de bismuto em ambos os compostos, PtBi/C e PdBi/C. A microscopia eletrônica de transmissão (MET) indicou que a presença de maiores teores de bismuto não acarretaram em aumento do tamanho médio da partícula. Os resultados eletroquímicos em meio alcalino indicaram que ainda é necessário uma otimização da concentração de ácido fórmico para que possamos observar melhores resultados quanto à adição de bismuto na platina ou paládio, no entanto os estudos em meio ácido mostraram o efeito benéfico da adição de bismuto tanto para platina quanto para o paládio. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

The current dissertation, titled “Fire Response of Composite aerostructures” deals with a crucial subject of the aeronautics industry that is the fire response of composite aerostructures, more specifically the issue of interest in this work is the fuselage fire burnthrough from an external liquid jet-fuel pool fire. Other fire issues that “bother” the aeronautics industry are the fire spread inside the cabin, smoke generation and toxicity of the fumes, but these are not handled in the current dissertation. Aircraft structures are designed to withstand various loading scenarios during their operational life. These loading scenarios are associated to a great extent with normal aircraft operation (flight manoeuvres, take-off and landing). However there are situations where the aircraft structures are required to assure the safety of the passengers and crew. In the case of an emergency crash landing, the threat of an external jet-fuel fire always exists. Considering that the aircraft structure survives the impact, the survivability of the passengers and crew onboard the aircraft depends solely on the fire resistance of the aircraft structure. A measure of the fire resistance of an aircraft structure is the time needed for the flames to penetrate the fuselage and spread inside the cabin, the so-called, burn-through time. So far, the aircraft fire resistance has been extensively studied by conducting lab, medium and full scale tests. The early lab scale tests were performed by the Federal Aviation Administration (FAA) and involved the Bunsen-burner flammability test of coupons for developing fire safe interior materials. As the application of polymer materials on aircrafts kept increasing, the problem of fire burn-through due to external fire emerged. Marker was one of the first to perform full-scale fuselage burn-through tests to access the insulating performance of materials. Also a statistical analysis was performed by Cherry and Warren that accessed and analyzed data from past accidents and their work resulted in proving the importance of fuselage fire hardening and the passengers’ lives that could be saved using low-cost solutions. These works led the FAA to proposed new fire testing procedures for aircraft materials. The scope of this dissertation was to assess the performance of various structural materials in a pool-fire scenario. A simplified approach is made, approximating the pool-fire conditions with a flat panel burn-through test in accordance to the ISO2685:1998(E) Standard. The originality of the present work comes from the fact that it incorporates a multistage approach in order to investigate the behaviour and response of composite aircraft structures in the possibility of a fire event. The current approach goes down on material level in order to investigate and model the deterioration (decomposition) of the polymer composite. Thus, it investigates and proposes a methodology of how the thermophysical properties of the composite are deteriorated due to the fire event. It proceeds into developing a progressive-damage material model (material properties varying with the deterioration degree) and finally implementing this custom material model into a commercial FE package and solving the loading scenarios. Being more specific the current work begins with a quick review of the literature where incidents and work done on the burnthrough event for the past 20-30 years are summarized. It progresses then to presenting the various types of polymers used in the aircraft industry and their basic decomposition mechanisms, from the unsaturated polyesters to the epoxies and phenolics and in the end reference to the thermoplastics is made. Every organic material, hence, polymers used in aerospace applications, present a set of response characteristics when subjected to fire, specifically the heat release rate, thermal stability index, limiting oxygen index, flammability index, time-to-ignition, surface flame spread, mass loss, smoke density and smoke toxicity. Following is the backbone of this dissertation, the kinetics modelling. Two approaches are made, one simplified using single stage kinetics where the decomposition degree a is calculated based on the Arrhenius reaction theory and using the kinetic triplets (kinetic parameters) extracted from thermogravimetry, TGA, data using the Friedman multi-curve method. The second approach is more complicated and considers multi-stage decomposition of the polymer composite. Specifically a 3-stage reaction network is considered for every material, the LY-Ref, and the two modified batches, one with ammonium polyphosphate AP423 and the other both with AP423 and multi-wall carbon nanotubes MWCNT. Again the kinetic parameters, activation energy EA, frequency factor A, and reaction order n, are extracted for every step using the van Krevelen methodology. In the end using the reaction rates equations the reconstruction of the TGA curves is achieved with an error of less than 5% from the test data. Correlations that consider the material deterioration and affect the thermophysical properties of the materials are proposed. Those expressions are being developed for both of the two kinetic approaches, the single and multi stage. Another crucial part of this work is the measurement and calibration of the applied fire load. Again two fire load approaches are used, one according to the ISO2685 Standard where a propane burner was manufactured and calibrated according to the Standard for medium scale samples testing and a lab scale butane burner for small samples. The ISO2685 burner was also CFD simulated and the models calibrated against analytical expressions, ISO requirements and real measurements. The CFD simulations were performed so the heat flux or heat transfer coefficient to be extracted and used as input for the later thermal FE burnthrough models. The heat flux distribution of the lab-scale AML burner on the specimen surface was measured via a water cooled Schmit-Boelter SBG01 heat flux sensor manufactured by Hukseflux. Manufacturing and material details are presented concerning the samples used for every test campaign. Metallic (AL2024-T3) samples, CFRP neat and modified, and hybrid GLARE ones where manufactured. Also the experimental work performed is described. Cone calorimetry testing data are available, results from thermogravimetry tests, differential scanning calorimetry, and finally the burnthrough tests with both the testing apparatuses, the ISO2685 one and the AML lab-scale burner. The modelling work in this dissertation involved thermal models that were developed into a commercial FE package. It was not part of this work to develop a thermal solver so a commercial one was selected and all the developed methodology was adapted to its requirements and specifications. The boundary conditions on the models are presented both for the ‘hot’ front surface and the rear ‘cooling’ one. For the ‘hot’ one the heat flux distribution is used and for the ‘cooling’ one an equivalent convection is applied that accounts for both convective and radiative cooling. The decomposing material model is implemented into to FE solver via user defined subroutines for the single stage kinetics and the multi-stage approach. Finally the simulations were run and the results and models were compared against the available experimental results. Since so far the burnthrough response of aerostructures was limited to coupon, samples and medium size flat panels. A more realistic approach was performed by developing a mathematical model of a real size test. The certification tests conducted by the FAA are for full size fuselage sectors under the fire load of a burning jet-fuel pan pool-fire. A burning jet-fuel pool fire is a complex phenomenon on its own, combining it with a decomposing fuselage structure make the modeling approach even more difficult to simulate if not impossible. Required data for the pool-sizes under investigation were not available, so data for large external hydrocarbon pool fires from literature were used. Also, because the main characteristic of a jet-fuel (kerosene) pool fire is that the flames are not clear, on the contrary, great amount of shoot is produced making combustion modeling and radiative heat transfer to the fuselage even more of a challenge to model, it was decided to try and tackle this full-scale approach by a simplified the modeling approach. Instead of liquid fuel combustion, an equal hot air stream with mass flow, velocity and temperature properties extracted from literature correlation data was performed. Conclusively, in terms of completeness the benefit analysis performed by Cherry and Warren is presented in brief. The objective of their analysis was to assess the potential benefits, in terms of reduction of fatalities and injuries, resulting from improvements in fuselage burnthrough resistance to ground pool fires. Fire hardening of fuselages will provide benefits in terms of enhanced occupant survival and may be found to be cost beneficial if low-cost solutions can be found. The maximum number of lives saved per year in worldwide transport aircraft accidents, over the period covered by the data, if hardening measures were applied, was assessed to be 12.5 for the aircraft in its actual configuration (when the accidents occurred) and 10.5 for the aircraft configured to later airworthiness requirements. These figures are completely significant and give an extra confirmation that this work on investigating the fire response of composite aerostructures is on the right track. As the work of Cherry and Warren concluded, the fire hardening measures in order to be applicable need to be cost efficient. The concept under which this whole dissertation stepped on was to investigate the fire response of composite aerostructures and the possibility of hardening the structure itself without the use of extra protective layers that add cost and weight to the overall aircraft and its maintenance. In the end it was concluded that there is the possibility of hardening the fuselage structure by design and by material. Incorporating composites into the structure it is possible to prolong the burnthrough time at least for 4-5 minutes before auto ignition occurs on the inner side of the fuselage. Auto ignition of the inner side fuselage cabin materials is mentioned since in NONE of the burnthrough tests of the CFRP composites and the GLARE samples flame penetration was observed. / Στην παρούσα διατριβή με τίτλο «Ανάλυση της απόκρισης σύνθετων πολυμερών υλικών υπό συνθήκες φωτιάς. Εφαρμογή σε αεροπορικές κατασκευές» πραγματοποιείται εργασία στην αριθμητική προσομοίωση και πειραματική διερεύνηση της συμπεριφοράς αεροπορικών κατασκευών σε συνθήκες φωτιάς. Στην μέχρι τώρα βιβλιογραφία οι διάφοροι έλεγχοι για πιστοποίηση των αεροπορικών υλικών αλλά και των αεροσκαφών στο σύνολό τους αποτελούνταν από εκτενείς πειραματικές δοκιμές σε μεσαία κλίμακα καθώς και σε πλήρους κλίμακας κατασκευές. Οι προδιαγραφές των ελέγχων ορίζονται από την Ομοσπονδιακή Διεύθυνση Αεροπλοΐας των Ηνωμένων Πολιτειών της Αμερικής, Federal Aviation Administration FAA. Όπως γίνεται αντιληπτό πλήρους κλίμακας δοκιμές είναι χρονοβόρες αλλά και οικονομικά ασύμφορες, για τον λόγο αυτό τα τελευταία χρόνια πραγματοποιούνται προσπάθειες από την FAA για καθιέρωση Προτύπων ελέγχου μικρής κλίμακας τα οποία σε συνδυασμό με αριθμητικά μοντέλα θα είναι σε θέση να προβλέπουν την συμπεριφορά των αεροπορικών κατασκευών σε συνθήκες φωτιάς από την φάση του σχεδιασμού τους. Θα εξασφαλίζεται έτσι καλύτερη διαχείριση οικονομικών και υλικών πόρων. Στην βιβλιογραφία ο μεγαλύτερος όγκος αριθμητικής μοντελοποίησης έχει πραγματοποιηθεί στους τομείς της ναυπηγικής και των θαλάσσιων κατασκευών καθώς επίσης και τα τελευταία χρόνια στον τομέα της αστικής δόμησης. Αριθμητική δουλεία πάνω στην συμπεριφορά των αεροπορικών κατασκευών είναι υπερβολικά περιορισμένη και εκεί στοχεύει να συμβάλει η παρούσα διατριβή. Οι αεροπορικές κατασκευές εκτός των περιορισμών και προδιαγραφών που θέτουν οι άλλες εφαρμογές απαιτούν την ελαχιστοποίηση του προστιθέμενου βάρους στην κατασκευή. Διάφοροι τύποι πολυμερών συνθέτων υλικών χρησιμοποιούνται στην βιομηχανία, διακρινόμενα σε θερμοσκληρυνόμενα και θερμοπλαστικά. Αρχικά παρουσιάζονται τα θερμοσκληρυνόμενα ξεκινώντας από τους ευρέως χρησιμοποιούμενους πολυεστέρες και βινυλεστέρες, στις φαινολικές και εποξικές ρητίνες καταλήγοντας στους υψηλής θερμοκρασίας κυανεστέρες. Εν συνεχεία γίνεται αναφορά στα συνήθη χρησιμοποιούμενα θερμοπλαστικά, πολυπροπυλένιο PP, Poly-ether ether-ketone PEEK και polyphenylene Sulphide PPS. Φυσικά δεν παραλείπεται να γίνει σύντομη αναφορά και στις τυπικές διεργασίες θερμικής αποσύνθεσης των προαναφερθέντων πολυμερών. Η συμπεριφορά των σύνθετων πολυμερών υλικών σε συνθήκες φωτιάς περιγράφεται από κάποια χαρακτηριστικά μεγέθη τα οποία χρησιμοποιούνται για την ποιοτική και ποσοτική σύγκριση των διαφόρων υποψήφιων αεροπορικών υλικών. Συγκεκριμένα τα μεγέθη αυτά είναι: Heat Release Rate HRR, Thermal Stability Index TSI, Limited Oxygen Index LOI, Extinction Flammability Index ESI, Time-to-Ignition, Surface Flame Spread, Mass Loss, Smoke Density, Smoke Toxicity. Οι διαδικασίες ελέγχου και τα υπολογιζόμενα μεγέθη γίνονται βάσει διεθνών Προτύπων που κυρίως για τον τομέα της αεροναυπηγικής ορίζονται από την Ομοσπονδιακή Διεύθυνση Αεροπλοΐας FAA. Η αριθμητική προσομοίωση προυποθέτει γνώση της συμπεριφοράς των πολυμερών υλικών σε συνθήκες υψηλής θερμοκρασίας, για τον σκοπό αυτό πραγματοποιήθηκαν πειράματα απώλειας μάζας με χρήση θερμογραβιμετρίας TGA κατά την διάρκεια της οποίας η απώλεια μάζας καθώς και ο ρυθμός αυτής παρακολουθούνται και καταγράφονται σαν συνάρτηση του ρυθμού θέρμανσης. Μέσα από αυτά τα δεδομένα μπορεί να πραγματοποιηθεί εκτίμηση του τρόπου αποσύνθεσης του πολυμερούς. Αρχικά πραγματοποιήθηκε η θεώρηση της μονοβάθμιας αντίδρασης (single-stage reaction) που αποτελεί και την πλέον απλουστευμένη προσέγγιση. Στην θεώρηση αυτή θεωρείται πως η πολυμερής μήτρα περνάει από την «παρθένα» κατάσταση στην απανθρακομένη μέσα σε ένα βήμα. Η περιγραφή της αντίδρασης αυτής γίνεται με μια μονοβάθμια αντίδραση τύπου Arrhenius. Σε δεύτερο βήμα χρησιμοποιήθηκε κινητική θεωρία πολλαπλών σταδίων (multi-stage kinetics) σύμφωνα με την οποία πραγματοποιήθηκε ακριβέστερη προσέγγιση της απόσύνθεσης της πολυμερούς μήτρας των συνθέτων υλικών με απόκλιση μικρότερη του 5% από τα πειραματικά δεδομένα της θερμογραβιμετρείας (thermogravimetry). Και στις δύο προσεγγίσεις της αποσύνθεσης υπολογίσθηκαν οι κινηματικές παράμετροι: συντελεστής συχνότητας A (frequency factor), ενέργεια ενεργοποίησης ΕΑ (activation energy), τάξη αντίδρασης n (reaction order) για κάθε στάδιο. Με την ολοκλήρωση αυτού του σταδίου υπήρχε μια αξιόπιστη δυνατότητα αναπαράστασης της διαδικασίας αποσύνθεσης στο πείραμα της θερμογραβιμετρίας. Είναι γνωστό ότι οι διακυμάνσεις της θερμοκρασίας επηρεάζουν της τιμές των θερμοφυσικών ιδιοτήτων των υλικών. Αναλογιζόμενοι ότι στην διαρκεία της επιβολής της φλόγας στα σύνθετα υλικά όχι μόνο η θερμοκρασία αλλά και η σύσταση μεταβάλλεται συνεχώς λόγω της αποσύνθεσης κρίθηκε αναγκαία η ανάπτυξη μιας μεθοδολογίας που θα συμπεριλαμβάνει την επίδραση της αποσύνθεσης στην μεταβολή των θερμοφυσικικών ιδιοτήτων (θερμική αγωγιμότητα, ειδική θερμοχωρητικότητα και πυκνότητα) της πολυμερούς μήτρας και κατά συνέπεια του συνθέτου υλικού. Οι εξαγόμενες μαθηματικές σχέσεις χρησιμοποιήθηκαν στην αριθμητική προσομοίωση που ακολούθησε. Με σκοπό την ορθή αριθμητική μοντελοποίηση κρίνεται αναγκαία η μέτρηση και βαθμονόμηση του θερμικού φορτίου τον πειραματικών δοκιμών. Το μετρούμενο θερμικό φορτίου χρησιμοποιήθηκε εν συνεχεία ως φόρτιση στα αναπτυχθέντα μοντέλα. Χρησιμοποιήθηκαν δύο πειραματικές διατάξεις εφαρμογής φλόγας, μία μεσαίας κλίμακας σύμφωνα με τις διατάξεις του FAA Standard, που περιγράφεται στο ISO2685:1998(E) “Aircraft – Environmental test procedure for airborne equipment – Resistance to fire in designated fire zones” και μίας εργαστηριακής κλίμακος. Πραγματοποιήθηκε μέτρηση με θερμοζεύγη και καλορίμετρο νερού καθώς και αριθμητική μοντελοποίηση με χρήση CFD για την πρώτη διάταξη. Ενώ για την εργαστηριακής κλίμακας έγινε μέτρηση με θερμοζεύγη και ενός αισθητήρα θερμικού φορτίου «water-cooled Hukseflux Schmit-Boelter SBG01 sensor». Εν συνεχεία πραγματοποιήθηκε η κατασκευή των δοκιμίων των υποψήφιων υλικών καθώς και οι πειραματικές δοκιμές και έλεγχοι τους. Συγκεκριμένα πραγματοποιήθηκε: Θερμιδομετρία κώνου (cone calorimetry), Θερμογραβιμετρία (thermogravimetry), Θερμιδομετρία Διαφορικής Ανίχνευσης (Differencial Scanning Calorimetry, DSC), Μέτρηση Θερμικής αγωγιμώτητας, Δοκιμή διείσδυσης φλόγας (Fire burnthrough penetration). Καθώς ο χαρακτηρισμός της αποσύνθεσης των πολυμερών υλικών, η μεταβολή των θερμοφυσικών ιδιοτήτων, η μέτρηση και βαθμονόμηση του επιβαλλόμενου θερμικού φορτίου καθώς και οι πειραματικές δοκιμές έχουν ολοκληρωθεί ακολουθεί η αριθμητική προσομοίωση. Οι συνοριακές συνθήκες θερμικού φορτίου και ψύξης επιλέχθησαν ως εξής. Ως φόρτιση θεωρήθηκε η κατανομή του θερμικού φορτίου (σε kW/m2) στην εμπρός επιφάνεια του πάνελ. Στην ψύξη της πίσω επιφάνειας λήφθηκε υπόψη τόσο η ελεύθερη μεταφορά θερμότητας με επαφή όσο και η ακτινοβολία. Το μοντέλο της συμπεριφοράς του υλικού διαμορφώθηκε κατάλληλα ώστε να γίνει κατανοητό από τις απαιτήσεις ενός εμπορικού κώδικα Πεπερασμένων Στοιχείων επίλυσης θερμικών προβλημάτων και προσομοιώθηκαν οι πειραματικές δοκιμές διείσδυσης φλόγας των δύο πειραματικών διατάξεων, μεσαίας και εργαστηριακής κλίμακος. Πλέον της αριθμητικής προσομοίωσης της συμπεριφοράς σε φωτιά επίπεδων δοκιμίων αεροπορικών κατασκευών, πραγματοποιήθηκε προσπάθεια απλουστευμένης μοντελοποίησης των συνθηκών φλόγας ενός λιμνάζοντος όγκου καυσίμου αεροσκαφών στο εξωτερικό μιας ατράκτου. Δημιουργήθηκε ένα τρισδιάστατο ρευστομηχανικό μοντέλο πρόβλεψης του θερμικού φορτίου στην επιφάνεια μιας τυπικής ατράκτου σύμφωνα με τις προδιαγραφές γεωμετρίας του Προτύπου “Full-scale test evaluation of Aircraft fuel fire burnthrough resistance improvements” DOT/FAA/AR-98/52,1999. Τα ρευστομηχανικά αποτελέσματα συγκρίθηκαν με δεδομένα βιβλιογραφίας για μεγάλες φλεγόμενες δεξαμενές λιμνάζοντος καυσίμου. Εκτός από την μελέτη της απόκρισης των αεροπορικών κατασκευών σε συνθήκες φλόγας σκοπός της παρούσας εργασίας είναι και η παρουσίαση λύσεων οι οποίες θα έχουν την δυνατότητα της βελτίωσης της συμπεριφοράς των υπαρχουσών δομών καθώς και των μελλοντικών σύνθετων δομών. Ενδεικτικά αναφέρεται η δυνατότητα χρήσης νανοεγκλεισμάτων, και βελτιωμένων μονωτικών υλικών, π.χ. aerogels. Όπως έχει ήδη αναφερθεί οι αεροπορικές κατασκευές θέτουν τον περιορισμό της ελαχιστοποίησης του προστιθέμενου βάρους, για τον λόγο αυτό η ενίσχυση των συνθέτων υλικών θα πρέπει να πραγματοποιηθεί σε επίπεδο υλικού και σχεδιασμού. Πρέπει δηλαδή η ίδια η κατασκευή που είναι ικανή να φέρει τα μηχανικά φορτία να εξασφαλίζει και την πιστοποίηση της FAA για συνθήκες φωτιάς. Συνοψίζοντας, η παρούσα διατριβή πραγματοποιεί μια καινοτόμο, γρήγορη και αρκετά ακριβή προσέγγιση του σημαντικότατου ζητήματος της συμπεριφοράς των πολυμερικών σύνθετων αεροπορικών δομών σε συνθήκες φωτιάς Η πολυπλοκότητα του όλου φαινομένου επέβαλε την πραγματοποίηση παραδοχών και απλουστεύσεων. Καθώς όμως με την αυξανόμενη χρήση των συνθέτων υλικών στις αεροπορικές κατασκευές, ο τομέας της ασφάλειας σε συνθήκες φλόγας είναι συνεχώς αυξανόμενος και απαιτητικός. Για αυτό οι παραδοχές και θεωρήσεις της παρούσας διατριβής μπορούν να βελτιωθούν με χρήση νέων υπολογιστικών μεθόδων και πειραματικών δεδομένων με στόχο την ακόμα ακριβέστερη πρόβλεψη της συμπεριφοράς τον αεροπορικών δομών σε συνθήκες φλόγας.