A interação dinâmica resultante do impacto de esferas de aço contra chapas de alumínio é estudada através da representação numérica de testes experimentais, os quais imitam freqüentes colisões de pequenos fragmentos contra a fuselagem de aeronaves. Importância é dada à modelagem do comportamento visco-plástico do material da chapa, o que conduz à proposição de uma modificação no método de caracterização dinâmica mecânica de material, realizado através de um equipamento denominado Barra de Hopkinson. Adicionalmente, a influência de possíveis erros na seleção de parâmetros de simulação, relacionados ao contato, amortecimento estrutural e principalmente ao material, é discutida através de análises numéricas de sensibilidade. Testes de impacto foram conduzidos de forma a se obter a velocidade balística das chapas. O deslocamento máximo permanente das chapas a baixas velocidades também foi medido. O método de caracterização dinâmica de material proposto é então avaliado pela comparação dos resultados de simulações numéricas frente aos dados experimentais obtidos nos testes de impacto. As predições de deslocamento máximo permanente, para testes sem perfuração da chapa, e de velocidade balística, para testes de perfuração total, indicaram uma boa concordância numérico-experimental, respeitadas as observações realizadas acerca dos parâmetros envolvidos. / Dynamic interaction present on impact of steel spheres against aluminum panels is studied through a numerical model of experimental tests, which reproduce common collisions of small debris against airplane fuselages. This thesis emphasizes the panel-material visco-plastic behaviour modeling, which leads to a modification of the material dynamic characterization method, based on a Split Hopkinson Pressure Bar. Influence of possible errors in some numerical simulations parameters, related to contact, structural damping and material behaviour is also discussed by sensitivity numerical analyses. Impact tests were conducted to obtain the ballistic velocity of the panels. Also, the final maximum plate deformation at low velocities was measured. The proposed dynamic characterization method is explored by comparing the numerical simulation and the impact tests. The predicted maximum impact point displacement, for no perforation cases, and the ballistic velocity, for total perforation tests, present a good numerical-experimental agreement, bearing in mind the observations about the various used parameters.

Fundamental understanding of high strain rate deformation behavior of materials is critical in designing new alloys for wide-ranging applications including military, automobile, spacecraft, and industrial applications. High entropy alloys, consisting of multiple elements in (near) equimolar proportions, represent a new paradigm in structural alloy design providing ample opportunity for achieving excellent performance in high strain rate applications by proper selection of constituent elements and/or thermomechanical processing. This dissertation is focused on fundamental understanding of high strain-rate deformation behavior of several high entropy alloy systems with widely varying microstructures. Ballistic impact testing of face centered cubic Al0.1CoCrFeNi high entropy alloy showed failure by ductile hole growth. The deformed microstructure showed extensive micro-banding and micro-twinning at low velocities while adiabatic shear bands and dynamic recrystallization were seen at higher velocities. The Al0.7CoCrFeNi and AlCoCrFeNi2.1 eutectic high entropy alloys, with BCC and FCC phases in lamellar morphology, showed failure by discing. A network of cracks coupled with small and inhomogeneous plastic deformation led to the brittle mode of failure in these eutectic alloys. Phase-specific mechanical behavior using small-scale techniques revealed higher strength and strain rate sensitivity for the B2 phase compared to the L12 phase. The interphase boundary demonstrated good stability without any cracks at high compressive strain rates. The Al0.3CoCrFeNi high entropy alloy with bimodal microstructure demonstrated an excellent combination of strength and ductility. Ballistic impact testing of Al0.3CoCrFeNi alloy showed failure by ductile hole growth and demonstrated superior performance compared to all the other high entropy alloy systems studied. The failure mechanism was dominated by micro-banding, micro-twining, and adiabatic shear localization. Comparison of all the high entropy alloy systems with currently used state-of-the-art rolled homogenous armor (RHA) steel showed a strong dependence of failure modes on microstructural features.

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Le travail de thèse de doctorat porte sur une étude complète du comportement dynamique de trois aciers de blindage soumis à des impacts balistiques. Dans un premier temps, afin de comprendre les phénomènes mis en jeu pendant la perforation de cibles fines, des essais de caractérisation du comportement thermo-viscoplastique et de rupture ont été réalisés. Les paramètres des lois de comportement et des critères de rupture ont été identifiés pour alimenter un modèle numérique simulant l'essai de perforation. La réponse des cibles impactées par des projectiles coniques a ensuite été évaluée à l'aide d'essais de perforation. Grâce à cette étude, il est possible de valider l'implémentation des lois et des critères réalisée dans des codes de calcul. Un dispositif de mesure des efforts d'impact et de perforation a donc été développé au cours de la thèse. Il fût montré que la mesure des efforts ainsi obtenue n'est pas intrinsèque au matériau impacté mais qu'elle dépend de la réponse globale du dispositif support-cible. Les résultats numériques issus de l’analyse par la méthode des éléments finis (MEF) ont été comparés aux résultats expérimentaux. Il a été observé un bon accord en terme de courbes balistiques, de modes de rupture, d’efforts dynamiques et de bilan énergétique. La modélisation numérique montre que seule une description précise du comportement mécanique des matériaux et de la rupture permet d'avoir une bonne représentation des performances balistiques des aciers étudiés. Une attention toute particulière a été portée sur l’influence de la tri-axialité des contraintes locales initiée par la forme de l’impactant, de la vitesse de déformation et de la température sur le seuil de déformation à la rupture. En perspective, les résultats issus de cette étude pourront servir dans l'analyse de la réponse des aciers de blindage sous chargements par explosif / The main aim of this PhD thesis is to develop a comprehensive study of the dynamic behavior of three armor steels subjected to ballistic impact. In order to have better understanding of the phenomena which take place during the thin targets perforation process, characterization experiments allowing to describe of the thermo-viscoplastic behavior and fracture were carried out. The identification of the constitutive relations and the failure criteria parameters allow to establish a numerical model simulating the perforation test. The ballistic response of armor steels subjected to the impact of conical projectiles was then assessed using perforation testing. This experimental investigation aims at endorsing the implementation of the behavior and fracture models in the calculation software. An experimental set-up for perforation forces measurements was specially developed during the thesis. It has been found that this dynamic force measurement is not intrinsic to the target material. It is rather dependent on the structural response of the used set-up support-target during impact and perforation. The numerical results from the Finite Elements Analysis (FEA) were compared to the experimental data and good agreement was found in terms of ballistic curves, failure patterns, impact forces and energy balance. Numerical investigations show that only an accurate description of the mechanical behavior and the fracture allows a good prediction of the ballistic performances of armor steels. Close attention was paid to the influence of local stress triaxiality induced by the projectile nose shape, strain rate and temperature on the strain to fracture threshold. In the future, these investigations can be used in the behavior analysis of armor steels subjected to blast loading

Made available in DSpace on 2016-03-15T19:36:28Z (GMT). No. of bitstreams: 1 Christiano Gianesi Bastos Andrade.pdf: 4665123 bytes, checksum: 8d1e670ead9649307d1227e06331c6af (MD5) Previous issue date: 2011-05-05 / Fundo Mackenzie de Pesquisa / The ballistic-resistant glass is composed of layers of glass, polycarbonate or the like, or a polyurethane and poly(vinyl butyral) resin through an autoclaving process joins materials by obtaining the desired properties. The thickness and the quantity of blades vary with the level of ballistic resistance to be attained. Each manufacturer has its own composition and the Brazilian Army is responsible for certification of glasses. The delamination occurs with aging of the glass with ballistic resistance. Knowledge of the change in mechanical properties due to delamination of the glass is an important data due to use of they. Were compared the properties of glass samples irradiated by gama irradiation with glass samples not irradiated. The tests used were atomic absorption spectrometry, hardness, compression, flexure stress rupture testing, and testing ballistic tunnel test according to standard ballistic - NBR 15000. The data showed that samples irradiated are less resistant in tensile strength and ballistic test. / O vidro com resistência balística é composto por camadas de vidro, policarbonato ou similares, poliuretano e poli(vinil butiral) e uma resina que por meio de um processo de autoclavagem une os materiais obtendo as propriedades desejadas. As espessuras bem como, a quantidade de lâminas variam de acordo com o nível de resistência balística que se deseja alcançar. Cada fabricante possui sua própria composição sendo o Exército Brasileiro o responsável pela certificação dos vidros com resistência balística. A delaminação ocorre com o envelhecimento do vidro com resistência balística. O conhecimento da alteração das propriedades mecânicas relacionado a delaminação do vidro é um importante dado em razão da utilização dos mesmos. Compararam-se as propriedades das amostras de vidro exposto à radiação gama com amostras de vidro não irradiados. Os ensaios utilizados foram espectrometria de absorção atômica, dureza, compressão, tensão de ruptura à flexão em três pontos e o ensaio balístico em túnel de prova segundo a norma de balística - NBR 15000. Os dados mostraram que as amostras irradiadas possuíam menor resistência no ensaio de flexão em três pontos e também apresentaram menor resistência no ensaio balístico.

[pt] O objetivo deste trabalho foi avaliar as propriedades mecânicas, físicas e microestruturais de materiais compósitos cimentícios reforçados por fibras naturais e de laminados de bambu. O trabalho experimental foi direcionado para a determinação da tenacidade. Para se determinar a tenacidade foram utilizados três tipos de ensaios: impacto Charpy, impacto balístico e flexão em 3 pontos. Após os ensaios, a superfície de fratura dos corpos-de-prova foi analisada por microscopia eletrônica de varredura (MEV). Esta análise microestrutural serviu para determinar os modos de fratura e validar as hipóteses feitas nos modelos matemáticos utilizados. Foram usados modelos adaptados da literatura para a determinação da tenacidade e os valores teóricos obtidos foram confrontados com os experimentais. Determinou-se também através de modelos encontrados na literatura a tensão interfacial de todas as fibras utilizadas nesta pesquisa. Os modelos empregados para calcular a tenacidade e a tensão de adesão interfacial, se mostraram eficientes e válidos. Em segundo plano, porém não menos importante, ficou a determinação das propriedades térmicas dos materiais utilizados. Foram efetuados ensaios de condutividade térmica do compósito e ensaios termogravimétricos das fibras vegetais e do bambu. Os compósitos cimentícios foram reforçados por diferentes fibras naturais: polpa refinada de bambu (CPB), polpa de sisal (CPS), polpa de eucalipto (CPE), fibras curtas de sisal (CPFS) e wollastonita (CPW). As proporções das polpas de bambu, sisal e eucalipto utilizadas como reforço nas matrizes cimentícias foram de 8 por cento e 14 por cento em relação à massa do cimento, a da fibra curta de sisal (25 mm) foi de 3 por cento em relação ao volume e a da wollastonita foi de 11,5 por cento em relação à massa. Compóstios híbridos feitos com wollastonita e polpa de bambu (CPBW) foram também produzidos apenas variando a proporção da polpa de bambu em 8 por cento e 14 por cento e mantendo fixa a da wollastonita em 11,5 por cento. Como uma tentativa de se melhorar a resistência ao impacto, laminados CPB/AL foram também fabricados colando duas chapas de alumínio (liga 5052 H34) de espessura 0,8 mm em ambas às faces dos compósitos reforçados por fibra de bambu, formando assim compósitos sanduíche (CPBA). O bambu Moso (Phyllostachys heterocycla pubescens) com 5 anos de idade foi usado para fabricação dos laminados de bambu, sendo tratado com água fervida para a prevenção de ataques biológicos. Técnicas para a extração do laminado a partir de seu formato natural foram estudadas estabelecendo suas vantagens e desvantagens. Para o ensaio de impacto foram utilizados corpos-de-prova com dimensão nominal de 120 mm x 15 mm x 6 mm perfazendo um total de 18 corpos-de-prova. Para o de flexão foram realizados ensaios com uma lâmina simples de bambu (BL) e bambu laminado colado (BLC) com 3 camadas de lâminas dispostas ortogonalmente. Os resultados dos testes de impacto Charpy e flexão em 3 pontos comprovaram a boa tenacidade do bambu laminado quando submetido a cargas de impacto (42,54 kJ/m2) e a cargas estáticas (19,77 kJ/m2 para o laminado e 17,63 kJ/m2 para o laminado colado). Compósitos sanduíche constituídos de alumínio e laminados de bambu foram também fabricados. Estes foram analisados através de ensaios de impacto balísticos seguindo as recomendações da norma NIJ 0101.04. Observações no microscópico eletrônico de varredura foram realizadas para se analisar os mecanismos de falha dos laminados. / [en] The main objective of this work was to evaluate the mechanical, physical and microestructure properties of cementitious composite materials and bamboo laminates. The experimental program was focused on the determination of toughness. Three diferent types of tests were performed in order to establish it: Charpy impact, ballistic impact and three point bending test. After the tests, the fractured surface of the failed test specimens was observed using a Scanning Electron Microscope (SEM) to establish the failure mode. Mathematical models adapted from the available literature were used to determine the toughness from which the values were confronted to the ones obtained experimentally. It was also determined by mathematical models the interfacial bond stress of all fibers used in this research. The two models, used in the toughness and interfacial bond stress calculation, showed to be efficient, providing valid results. In second plan, but not less important, was the determination of the materials thermal properties. Thermal conductivity tests of the composites and thermogravimetry of the fibers and bamboo were performed. The cementitious composites were reinforced by different natural fibers: refined bamboo pulp (CPB), sisal pulp (CPS), eucalyptus pulp (CPE), short sisal fibers (CPFS) and wollastonite. The mass fraction of bamboo, sisal and eucalyptus pulp studied were 8 percent and 14 percent. For the wollastonite fiber the mass fraction studied was 11.5 percent and for the short sisal fiber a 3 percent volume fraction was studied. Hybrid composites made with wollastonite and bamboo pulp (CPBW) were also produced varying the bamboo fraction mass to 8 percent and 14 percent but keeping constant to 11.5 percent the wollastonite mass fraction. The slurry de-watering process was used in the production of all composites described before. To reduce the adverse effects of weathering on the cellulose fibers and to improve the impact load and flexural resistance of the composite, aluminum thin sheets were used to produce a sandwich composite lamina with the CPB, which was denominated as CPBA. Compound Adhesive gel from Otto Baumgart which is a type of epoxy was used to fix the aluminum sheets on the CPB. The use of aluminum has proved to give much higher impact resistance results when compared to the CPB ones. The 5 years old Moso bamboo (Phyllostachys heterocycla pubescens), which was previously treated in boiled water to eliminate biological agents, was used to produce the bamboo laminates. Techniques were developed to extract bamboo laminates from its natural form, establishing its advantages and disadvantages. For the Charpy impact test, a total of 18 specimens with nominal dimensions of 120 mm x 15 mm x 6 mm were tested. Laminated (BL) and 3 layer cross ply laminated bamboo (BLC) were tested in bending. A total of 9 specimens were tested per bamboo configuration. The BL specimens had nominal dimensions of 120 mm x 30 mm x 6 mm and the BLC were 120 mm x 30 mm x 17 mm. The results demonstrated the good toughness of bamboo laminates when subject to dynamic (42.54 kJ/m2) and to static load (19.77 kJ/m2 for the laminate and 17.63 kJ/m2 for the cross ply laminate). Aluminum thin sheets were again used to make sandwich composites, but now using the bamboo laminate (BLCA). The BLCA was tested using the ballistic impact test following the standard NIJ 0101.04. Analysis on the Scanning Eléctron Microscope (SEM) were performed in order to establish the laminate s failure mechanisms.

Depuis plusieurs décennies, l’évaluation des armes à létalité réduite (ALR) et des gilets pare-balles suscite l’intérêt majeur des forces de l’ordre autour du globe. En effet, ces armes présumées à létalité réduite ou non létales sont tenues d’occasionner uniquement une douleur suffisamment importante à un individu afin d’assurer sa neutralisation. Les gilets pare-balles, quant à eux, doivent garantir un certain niveau de protection pour réduire le risque de traumatismes lié à leur déformation dynamique. Le Centre de Recherche, d’Expertise et d’appui Logistique (CREL) du Ministère de l’Intérieur français a ainsi pour objectif le développement d’un outil de prédiction du risque lésionnel thoracique lors d’impacts balistiques non pénétrants. Cela permettrait alors d’évaluer les performances des ALR et des gilets pare-balles avant leur déploiement en théâtre d’opérations. Plus précisément, cette méthode doit uniquement être fondée sur la mesure directe du processus dynamique de déformation d’un bloc de gel synthétique soumis à un impact balistique. Pour répondre à ce besoin, l’approche numérique est considérée dans ces travaux de thèse par l’emploi du mannequin numérique du thorax humain HUByx comme un outil intermédiaire permettant la détermination de fonctions de transfert entre les mesures expérimentales sur un bloc de gel et le risque lésionnel. La reproduction de conditions d’impact réelles sur HUByx nécessite la caractérisation et la modélisation de projectiles ALR ainsi que de projectiles d’armes à feu et de gilets pare-balles. Elles reposent sur une procédure d’identification par méthode inverse appliquée à l’essai de Taylor pour la modélisation des ALR et à l’essai du cône dynamique d’enfoncement sur le bloc de gel pour celle du couple projectile/gilet pare-balles. Des travaux sont dédiés à la caractérisation mécanique et à la modélisation du gel synthétique sous sollicitations dynamiques. Enfin, une approche statistique basée sur des analyses de corrélation est introduite exploitant à la fois les mesures expérimentales, les données numériques ainsi que les rapports de cas de la littérature. Une cartographie du thorax associée au risque de fractures costales est établie et est uniquement fonction d’une mesure expérimentale. / For decades, the assessment of less-lethal weapons (LLW) and bulletproof vests has generated major interest from law enforcement agencies around the world. Indeed, these presumed less-lethal or non-lethal weapons are required to cause only significant pain to an individual to ensure their neutralization. Bulletproof vests, in turn, must provide a certain level of protection to reduce the risk of trauma related to their dynamic deformation. The Center for Research, Expertise and Logistics Support (CREL) of the French Ministry of the Interior aims to develop a tool to predict thoracic injury risk during non-penetrating ballistic impacts. It would therefore be possible to evaluate the performance of LLW and bulletproof vests before their deployment in operations. More precisely, this method must only be based on the direct measurement of the dynamic process of deformation of a synthetic gel block subjected to a ballistic impact. To address that issue, the numerical approach is considered in this thesis by the use of the human thorax dummy HUByx as an intermediate tool for the determination of transfer functions between experimental metrics on a gel block and the risk of injury. The reproduction of real impact conditions on HUByx thus requires the characterization and modeling of less-lethal projectiles as well as projectiles of firearms and bulletproof vests. They rely on an inverse method identification procedure applied to the Taylor test for modeling LLW and on the analysis of blunt impacts on the gel block for projectiles/bulletproof vests. Work is then dedicated to the mechanical characterization and modeling of the synthetic gel under dynamic loadings. Finally, a statistical approach based on correlation analyses is introduced using both experimental measurements, numerical data as well as case reports from the literature. A thorax mapping associated with the risk of rib fractures is established and only depends on an experimental metric.