When an aluminum alloy plate after rolling, non-uniform residual stress distributions existed inside the plate and defects, such as edge wave, middle wave, of the plate will be induced. Usually, a levelling process will be adopted to modify the plate flatness. By numerically simulating the tension levelling process, the purpose of this thesis is to understand the final dimensions and the residual stress distribution of the aluminum plate subjected to the tension levelling process. This study used the finite element method as the basic theory of the numerical simulation. A 3-D model of a cold-rolled plate with a side wave, subjected to tension levelling process was constructed. Then, the effects of the variations of the tensile ratio and residual stress distribution after rolled on the residual stress distribution after levelling and the improvement of flatness were studied. The simulation results showed that in the wave region, the tension levelling process could eliminate more than 90% of the residual stress, in the flat region was up to 80%.Also, after leveling, the residual stress distribution in the flat region was more uniform than the wave region. After-rolled residual stresses at the wave region affected the final peak position of the wave and the stress eliminated ratio of the wave region, but showed no significant effect on the final plate width and the residual strains. After-rolled residual stresses at the flat region affected the stress elimination ratio of the flat region only. The tensile ratio would affect the plate flatness, the plate width, stress elimination ratio, and the maximum residual stress. The higher of the tensile ratio, the more flatness of the plate would be obtained, but the higher residual strain would be induced and caused the lesser range of available plate.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第14163号 / 工博第2997号 / 新制||工||1445(附属図書館) / 26469 / UT51-2008-N480 / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 落合 庄治郎, 教授 河合 潤, 准教授 奥田 浩司 / 学位規則第4条第1項該当

No description available.

The mechanical behavior of the arterial wall is determined by the composition and structure of its internal constituents as well as the applied traction-forces, such as pressure and axial stretch. The purpose of this work is to develop new theoretical frameworks and experimental methodologies to further the understanding of arterial mechanics and role of the various intrinsic and extrinsic mechanically motivating factors. Specifically, residual deformation, matrix organization, and perivascular support are investigated in the context of their effects on the overall and local mechanical behavior of the artery. We propose new kinematic frameworks to determine the displacement field due to residual deformations previously unknown, which include longitudinal and shearing residual deformations. This allows for improved predictions of the local, intramural stresses of the artery. We found distinct microstructural differences between the femoral and carotid arteries from non-human primates. These arteries are functionally and mechanically different, but are geometrically and compositionally similar, thereby suggesting differences in their microstructural alignments, particularly of their collagen fibers. Finally, we quantified the mechanical constraint of perivascular support on the coronary artery by mechanically testing the artery in-situ before and after surgical exposure.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This study was developed with the objective to determinate the longitudinal deformations (DRL) resulting from growth stresses in standing and living trees in different clones of Eucalyptus spp. To do this, 12 clones of 9 years-old Eucalyptus spp., were selected, through annual increment means, which were planted at a spacing of 3.0 x 2.7 m. For measurements the variables of this research, 12 trees of each clone were selected, which the some variables were measured: basic density, bark thickness, diameter and total height. The measurements of longitudinal residual strain (DRL) were made in living trees with the extensometer (Growth Strain Gauge) using the CIRADForêt method. The readings were taken at four locations around the trunk of the tree following the guidance of planting (row, between rows). The measurements in the presence of winds were avoid, because with the movement of the tree, the support forces swing inside the trunk, changing the value recorded on the device. For levels of DRL, the results obtained in the study indicated that the clones had large variations between each other, and these had an average value considered high when compared with the literature. The clone 8 produced the lowest levels of deformation and it was considered an excellent genetic material. The clone 1 obtained the highest values of DRL. DRL variation occurred along the circumference of the tree trunk, and it was more pronounced on the east position. Analyzing the correlations among variables, it was found that the DRL was significantly correlated with the bark thickness, diameter and volume of standing tree. Basic density and height didn t have influence on the longitudinal residual strain. Some regression models were adjusted for DRL according to the bark thickness, diameter, height and volume to explain the behavior of this variable for each clone. Just for the basic density was not possible to set a significant model. / O presente estudo foi desenvolvido com o objetivo de determinar as deformações residuais longitudinais (DRL), decorrentes das tensões de crescimento em árvores em pé e vivas de diferentes clones de Eucalyptus spp. Para tanto, foram selecionados 12 clones do gênero Eucalyptus com 9 anos de idade, por meio da área basal (G), sendo, estes, plantados em um espaçamento 3,0 x 2,7 m . Para as medições das variáveis do estudo, foram selecionadas 12 árvores de cada clone, onde foram medidas as variáveis de densidade básica (DB), espessura de casca (EC), diâmetro a altura do peito (DAP) e altura total (H). As medições das deformações residuais longitudinais foram realizadas, em árvores vivas, com o auxílio do extensômetro (Growth Strain Gauge), pelo método CIRAD-Fôret. As leituras foram realizadas em quatro posições ao redor do tronco da árvore, seguindo a orientação do plantio (linha, entre linha). Evitou-se realizar as medições das DRL na presença de ventos, uma vez que, com o movimento da árvore, as forças de sustentação oscilam dentro do tronco, alterando o valor registrado no aparelho. Em relação aos níveis das DRL, os resultados obtidos no estudo indicaram que os clones apresentaram grande variações entre si, obtendo um valor médio considerado elevado quando comparado com a literatura. O clone 8 se destacou por apresentar os menores níveis de deformação, sendo considerado um ótimo material para programas de melhoramento genético. Já o clone 1, apresentou os maiores valores das DRL. Ocorreram variações das DRL, ao longo da circunferência do tronco das árvores, sendo mais acentuada na linha referente à posição Leste. Analisando as correlações entre as variáveis, verificou-se que as DRL apresentou correlações significativas com a EC, DAP e o volume da árvore em pé (VOL). A DB e H não se mostraram influentes sobre a deformação residual longitudinal. Para a DRL, foram ajustados modelos de regressão em função da EC, DAP, H e VOL para explicar o comportamento dessa variável para cada clone. Apenas para a DB não foi possível ajustar um modelo significativo.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / The study aimed to evaluate the silvicultural performance of Eucalyptus spp. clones and select superior clones with higher quality of the wood. The material used for the study was from a clonal test of interspecific hybrids of Eucalyptus spp., in the municipality of Tapes - state of Rio Grande do Sul, belonging to company CMPC Celulose Riograndense. The forest stand was established in August 2003, with initial spacing of 3.0 x 3.0 m, containing 138 clones. The clones were grouped by the diameter at breast height (DBH) and overall height (h), and 29 of them were selected for the study. For the sampling of trees DBH, h, bark thickness (EC), dynamic modulus of elasticity (Ed) using ultrasound and longitudinal residual strain (DRL) resulting from growth stresses. The DRL was measured in living trees with the extensometer method CIRAD-Fôret. Afterwards, 58 trees were felled and broken into logs to evaluate end splitting planks were taken to prepare speciments for wood physical and mechanical properties according to D 143-94 - ASTM (2000) standards. The end logs splitting (IRT) was evaluated in the field, covering the logs end during five days for subsequent measurement. The phenotypic variance components and indirect gain selection estimate for the clones in this study were determined by DRL, wood volume (Vsc), basic density (ρpond) and IRT. The clones showed enough genetic variability to be separated into groups according to DHB at three and seven years, and for h at seven years of age. The early selection at three years after planting can be used to identify Eucalyptus spp. clones with best growth. The DRL showed variability among clones, but no correlation with the dendrometric variables. The mean value for IRT was 0.46%. The DRL was highly correlated with TCL and IRT, however the ρpond and mechanical properties showed no correlations with the DRL. The clones belonging to group 1, which present the lowest levels for TCL and consequently lower IRT, can be considered potential for forest breeding programs. Clone selection performed by the variable DRL, Vsc, ρpond and IRT, provided satisfactory genetic gains, by improving the growth characteristics or improving quality of the wood. / DESEMPENHO SILVICULTURAL E SELEÇÃO DE CLONES DE Eucalyptus spp. PARA A QUALIDADE DA MADEIRA Autor: Rafael Beltrame Orientador: Dr. Clovis Roberto Haselein Data e Local da Defesa: Santa Maria, 14 de dezembro de 2012. O estudo teve como objetivos avaliar o desempenho silvicultural de clones de Eucalyptus spp. e selecionar clones superiores visando à qualidade da madeira. O material utilizado foi procedente de um teste clonal de híbridos interespecíficos de Eucalyptus spp., conduzido no município de Tapes-RS, pertencente à empresa CMPC Celulose Riograndense. O povoamento foi implantado em agosto de 2003, com espaçamento inicial de 3,0 x 3,0 m, contendo 138 clones. Os clones foram avaliados e agrupados quanto ao diâmetro à altura do peito (DAP) e altura total (h), selecionandose 29 deles para o estudo. Nas árvores, foram medidos o DAP, a h, a espessura de casca (EC), o módulo de elasticidade dinâmico (Ed) com auxílio do ultrassom e a deformação residual longitudinal (DRL) decorrente das tensões de crescimento. A DRL foi medida em árvores vivas, utilizando o extensômetro, pelo método CIRADFôret. Em seguida, 58 árvores foram abatidas e desdobradas em toras para avaliação das rachaduras de topo e confecção de amostras para a realização dos testes físicos e mecânicos, conforme a norma D 143-94 - ASTM (2000). O índice de rachaduras de topo das toras (IRT) foi avaliado a campo, ensacando as extremidades dessas por um período de cinco dias para posterior medição. A estimativa dos componentes da variância fenotípica e o ganho indireto de seleção para os clones do estudo foram determinadas por meio da DRL, volume sem casca (Vsc), massa específica básica ponderada (ρpond) e IRT. Os clones apresentaram variabilidade genética suficiente para serem separados em grupos quanto ao DAP, aos três e aos sete anos, e quanto à h das árvores, aos sete anos de idade. A seleção precoce aos três anos após o plantio pode ser empregada para identificar clones de Eucalyptus spp. com melhor vigor de crescimento. A DRL apresentou variabilidade entre os clones, porém não apresentou correlações com as variáveis dendrométricas. O valor médio do IRT foi de 0,46%. A DRL apresentou alta correlação com a TCL e o IRT, entretanto, a ρpond e as propriedades mecânicas não apresentaram correlações com a DRL. Os clones pertencentes ao grupo 1, por apresentarem os menores níveis para a TCL e, consequentemente, menores IRTs, podem ser considerados potenciais para programas de melhoramento genético florestal. A seleção de clones realizada por meio das variáveis DRL, Vsc, ρpond e IRT proporcionaram ganhos genéticos satisfatórios, tanto para o melhoramento das características de crescimento quanto para a qualidade da madeira.

This PhD thesis employed high energy synchrotron x-ray radiation to reveal atomic scale structural features occurring in plastically deformed Zr52.5Ti5Cu18Ni14.5Al10 (Vit105) bulk metallic glass (BMG). The study is divided into three parts: Strain evolution during in-situ compression, strain distribution maps in mechanically-imprinted BMG, and residual strain around a single shear band. 1. Strain evolution during in-situ compression The structural rearrangements occurring during compressive deformation of a plastically deformable BMG showed that the elastic and plastic deformation of the BMG is correlated to the structural changes at short- (SRO) and medium range order (MRO). In the elastic regime, the atomic distances at SRO vary linearly with macroscopic stress. Analysis of the area under radial distribution function indicates that a small fraction of bonds in the first shell is broken in the loading direction whereas some new bonds are formed in the transverse direction. Atomic bonds at SRO appeared significantly stiffer than the MRO shells. Compared to the macroscopic values of the elastic strain, Young’s modulus and Poisson's ratio, both SRO and MRO appeared significantly stiffer, implying that the elastic behavior of the BMG is not only ruled by simple compression of the atoms/clusters but also is aided by rearrangement of atoms/clusters. The deviation of MRO atomic strain-stress correlation from linearity at the onset of plastic deformation was attributed to the activation of irreversible shear transformation zones. It was demonstrated by a strong shear strain value at the onset of yielding. This value is in good agreement with the reported value of the critical shear strain needed for activation of an irreversible STZ. The length scale of 12.5 Å indicated the largest shear strain and is probably the most effective length scale in the formation of STZs. The atomic pairs at SRO with smallest shear strain have the least contribution to the STZs. It was also indicated that the typical fracture angle of this BMG can be explained by the orientation of maximum shear strain at the onset of catastrophic shear band formation. 2. Strain distribution map in mechanically-imprinted BMG In mechanical imprinting, the BMG plate is loaded between two tools with a regular array of linear teeth and, as a result, a regular pattern of linear imprints is created on the surface of the plate. Mechanically imprinting results in considerable tensile plasticity of brittle Vit105 BMG plate. The distribution of hardness and Young’s modulus values at the transverse cross section of imprinted plate probed via nanoindentation revealed oscillating soft and hard regions beneath the surface. Spatially-resolved strain maps obtained via high-energy nano-size beam X-ray diffraction exhibited that the plastic deformation during imprinting creates a spatially heterogeneous atomic arrangement, consisting of strong compressive and tensile strain fields as well as significant shear strain fields in the cross section. It was shown that the heat treatment diminishes the heterogeneous structure resulting in brittle behavior in tension. The analysis of strain tensor components based on changes in the first diffraction maximum of the structure function, q1, revealed that Ɛx, the strain perpendicular to the loading direction, changes from the compressive at near to the surface to the tensile mode at the center of the imprinted plate. In contrast, the strain component along the loading direction, Ɛy, changes from tensile near the surface to the compressive at the center. Beneath the surface, Ɛx reaches to values about 1.5% under the imprints where there is a negligible Ɛy. The distribution map of principal strains, Ɛ1 and Ɛ2, indicated that large regions with compressive Ɛ1 and Ɛ2 exist under the imprints which can result in blocking of the propagating shear bands in agreement with microstructural observations of shear banding after uniaxial tension. Moreover, the region beneath the border of the imprinted and un-imprinted parts has the highest residual shear strain. Microstructural observations indicated that such regions can nucleate new shear bands upon tensile loading of imprinted BMG plate. 3. Residual strain around a single shear band In order to probe structural changes in the shear-induced zone around a single shear band, the distribution of residual strains at short- and medium-range order around a single shear band was determined in cold-rolled BMG plate using the nano-focused high energy x-ray diffraction. Plastic deformation results in significant residual normal and shear strains at distances of more than 15 μm around the shear band. The residual normal strains exhibit an asymmetric distribution whereas the residual shear strain is distributed symmetrically around the shear band. The large amount of residual atomic shear strain magnitude at the vicinity of the shear band triggers the nucleation of the new shear bands. The coincidence of the direction of the nucleating secondary shear bands from the main shear band with the orientation of the residual shear strain at the vicinity of the mature shear band highlight the dominant role of the shear strain in determining further plastic deformation at regions near the shear band. / Im Rahmen dieser Arbeit wird hochenergetische Synchrotron Röntgenstrahlung zum Aufzeigen der strukturellen Veränderungen in plastisch verformtem Zr52.5Ti5Cu18Ni14.5Al10 metallischen Glas verwendet. Die Arbeit gliedert sich in drei Teile: Dehnungsentwicklung während in-situ Druckversuch, Dehnungsverteilung eines mechanisch geprägten massiven metallischen Glases, und Restdehnungen in der Umgebung eines einzenen Scherbandes. 1. Dehnungsentwicklung während in-situ Druckversuch Die während der Verformung auftretende strukturelle Neuordnung eines plastisch verformbaren metallischen Glases zeigt die Korrelation der elastischen und plastischen Verformung mit den strukturellen Änderungen in den Größenordnungen der Nah- (SRO) und mittelreichweitigen Ordnung (MRO). Im elastischen Bereich verändern sich die Atomabstände in der SRO linear mit der makroskopisch anliegenden Spannung. Die Untersuchung der Fläche unter der Radialen Verteilungsfunktion (RDF) deutet auf ein Aufbrechen eines geringen Anteils der Bindungen der ersten Schale in Druckspannungsrichtung und deren Neubildung quer dazu. Die atomaren Bindungen in der SRO erscheinen wesentlich steifer als in den MRO Schalen. Vergleicht man die Werte von elastischer Dehnung, E-Modul und Querkontraktionszahl mit ihren makroskopischen Gegenstücken erscheinen beide, SRO und MRO, wesentlich steifer. Dies zeigt, dass die elastische Verformung von metallischen Gläsern nicht nur von der einfachen Stauchung der Atome bzw. Atomgruppen bestimmt, sondern auch durch deren Neuanordnung unterstützt wird. Das Abweichen der Dehnungs-Spannungs-Korrelation vom linearen Verhalten in der MRO am Beginn der plastischen Verformung wird der irreversiblen Bildung von Schertransformations-zonen (STZ) zugeschrieben. Dies zeigt sich zudem in den erhöhten Scherdehnungswerten am Beginn der Dehngrenze, welche mit den in der Literatur berichteten Werten für die kritische Scherdehnung zum Bilden einer STZ übereinstimmen. Bei einem Atomabstand von 12,5 Å tritt der höchste Wert der Scherdehnung auf und markiert den effektivsten Längenbereich der STZ Bildung. Andererseits haben die atomaren Paare in der SRO mit der geringsten Scherdehnung den geringsten Beitrag an der STZ. Es zeigt sich außerdem, dass der typische Bruchwinkel dieses metallischen Glases über die Orientierung der maximalen Scherdehnung am Beginn der kritischen Scherbandbildung erklärt werden kann. 2. Dehnungsverteilung eines mechanisch geprägten massiven metallischen Glases Eine Prägung besteht darin, eine Platte metallischen Glases mit zwei Stempel, auf denen eine regelmäßige Anordnung von geradlinigen Kerben angebracht ist, zu belasten. Dadurch wird eine ebenso regelmäßige Anordnung von geradlinigen Kerben auf der Oberfläche des metallischen Glases erzeugt. Die plastische Verformbarkeit der Vit105 Platte im Zugversuch wird durch Prägung im Vergleich zur gegossenen Probe eindeutig verbessert. Die Untersuchung der Härte und des E-Moduls über den Querschnitt der geprägten Probe zeigt die Einbringung von Abwechselnd weichen und harten Regionen an der Oberfläche. Es wurden räumlich aufgelöste Dehnungskarten des geprägten metallischen Glases durch Beugung eines hochenergetischen nanometergroßen Röntgenstrahles erzeugt. Die Ergebnisse offenbaren, dass die durch Prägung eingebrachte plastische Verformung eine räumlich heterogene Atomanordnung erzeugt, welche aus starken Druck- und Zugdehnungsfeldern besteht. Zusätzlich wird eine signifikante Scherdehnung in die Probe eingebracht. Die Wärmebehandlung beseitigt diese heterogene Struktur und führt sie fast auf den Ausgangszustand zurück. Die Analyse der Dehnungstensorkomponenten basierend auf Änderungen im erstem Maximum des Strukturfaktors, q1, zeigt, dass sich Ɛx von der Oberfläche zur Mitte der Platte hin von einer Stauchung in eine Dehnung umwandelt. Im Gegensatz dazu wandelt sich die Komponente Ɛy von der Oberfläche zur Mitte der Platte hin von einer Dehnung in eine Stauchung um. An der Oberfläche unter den Eindrücken, wo Ɛy vernachlässigbar ist, erreicht Ɛx Werte von ca. 1.5 %. Die Verteilungskarten der Hauptdehnungen zeigt, dass beide e1 und e2 unterhalb der Kerben als Stauchungen vorhanden sind. Daraus resultiert das Blockieren und Ablenken der sich ausbreitenden Scherbänder, was an Zugproben im REM beobachtet werden kann. Weiterhin hat der Bereich an der Grenze der geprägten und nicht geprägten Regionen die höchste Restscherdehnung. Mikrostrukturelle Beobachtungen deuten darauf hin, dass solche Bereiche unter Zuglast Keimstellen für neue Scherbänder sind. 3. Restdehnungen in der Umgebung eines einzenen Scherbandes Es wurde ein einzelnes Scherband einer kaltgewalzte Platte mittels Beugung eines hochenergetischen nanometergroßen Röntgenstrahles untersucht. Die strukturellen Unterschiede in der scherinduzierten Zone um ein einzelnes Scherband werden durch die Verteilung der Restdehnungen in SRO und MRO bestimmt. Plastische Verformung führt zu signifikanten Restnormal- und Restscherdehnungen in Entfernungen von mehr als 15 µm um das Scherband. Die Restnormaldehnungen zeigen eine asymmetrische Verteilung, wohingegen die Restscherdehnungen auf beiden Seiten des Scherbandes symmetrisch verteilt sind. Der große Betrag der atomaren Restscherdehnung in der Nähe des Scherbandes führt zur Bildung von neuen Scherbändern. Das Zusammenfallen der Richtung des sich bildenden sekundären Scherbandes und der Orientierung der Restscherdehnung, in der Nähe des primären Scherbandes, demonstriert die dominierende Rolle der Scherdehnung bei weiterer plastischer Verformung in der Nähe des Scherbandes.

Submitted by Celso Magalhaes (celsomagalhaes@ufrrj.br) on 2017-06-20T15:28:09Z No. of bitstreams: 1 2016 - Pablo Vieira dos Santos.pdf: 2713237 bytes, checksum: 034b9528933152d64f409aa5701ceba6 (MD5) / Made available in DSpace on 2017-06-20T15:28:09Z (GMT). No. of bitstreams: 1 2016 - Pablo Vieira dos Santos.pdf: 2713237 bytes, checksum: 034b9528933152d64f409aa5701ceba6 (MD5) Previous issue date: 2016-02-26 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / Forest restoration is an important mechanism which can recover anthropized environments. In this context, the use of native species in order to wood production has become a very positive alternative in the economic viability of this activity, so that, know information about native species with potential for production of high quality wood, used in forest restoration, is an important task. Concerning this, the objective of this study was to evaluate the quality of the wood Cariniana legalis (Mart.) Kuntze from forest restoration plantings, through non-destructive methods. Were selected 20 individuals in the field through a silvicultural assessment and then were determined dendrometric characteristics: diameter at breast height (DBH), total height, tree standing volume and bark thickness. Four different non-destructive methods of assessing wood quality based on the DBH (1.30 m from the base of the tree): extensometry, resistograph, impulse tomograph and x-ray densitometry (pulling out wood samples by Pressler probe). The longitudinal residual strain (LRS) average of wood was 0.054 mm, a value lower than that found in the literature for many species, as for the Eucalyptus genus. The amplitudes generated by resistograph allowed the estimation the basic density values of wood Cariniana legalis, presenting a positive and significant correlation (r = 0.68) at 1% significance level. The average apparent density average, obtained by X-ray densitometry, was 0.528 g / cm3. In general, Cariniana legalis threes were homogeneous, with good sanity wood (without internal rot or hollow) and moderately dense density being easy workability and suitable for the furniture industry. / A restaura??o florestal ? um importante mecanismo, no qual se consegue recuperar ambientes antropizados. Neste contexto, o uso de esp?cies nativas visando a produ??o madeireira tem se tornado uma alternativa bastante positiva na viabiliza??o econ?mica desta atividade, de modo que, conhecer informa??es a respeito de esp?cies nativas com potencial na produ??o de madeira de alta qualidade, utilizadas na restaura??o florestal, ? uma tarefa de grande import?ncia. Nesse sentido, o objetivo deste trabalho foi avaliar a qualidade da madeira de Cariniana legalis (Mart.) Kuntze proveniente de plantios de restaura??o florestal, atrav?s de m?todos n?o destrutivos. Foram selecionados 20 indiv?duos no campo por meio de uma avalia??o silvicultural e em seguida determinou-se as caracter?sticas dendrom?tricas (di?metro ? altura do peito (DAP), altura total, volume da ?rvore em p? e a espessura da casca). Quatro diferentes m?todos n?o destrutivos de avalia??o da qualidade da madeira foram utilizados, sendo eles a extensometria, resistograf?a, tomografia de impulso e densitometria de raios X (retirando-se amostras do lenho por meio da sonda de Pressler), todos os ensaios tiveram como refer?ncia a altura do DAP (1,30m a partir da base da ?rvore). A deforma??o residual longitudinal (DRL) m?dia da madeira foi de 0,054 mm, valor este inferior ao encontrado na literatura para muitas esp?cies, como para o g?nero Eucalyptus. As amplitudes geradas pelo resist?grafo permitiram estimar os valores de densidade b?sica da madeira de Cariniana legalis, apresentando uma correla??o positiva e significativa (r = 0,68) ao n?vel de 1% de signific?ncia. A densidade aparente m?dia, obtida por meio da densitometria de raios X, foi de 0,528 g/cm3. De maneira geral os indiv?duos de Cariniana legalis se mostraram homog?neos, apresentando boa sanidade do lenho (sem ocos internos ou podrid?es) e densidade moderadamente densa, sendo de f?cil trabalhabilidade e indicada para a ind?stria moveleira

This PhD thesis employed high energy synchrotron x-ray radiation to reveal atomic scale structural features occurring in plastically deformed Zr52.5Ti5Cu18Ni14.5Al10 (Vit105) bulk metallic glass (BMG). The study is divided into three parts: Strain evolution during in-situ compression, strain distribution maps in mechanically-imprinted BMG, and residual strain around a single shear band. 1. Strain evolution during in-situ compression The structural rearrangements occurring during compressive deformation of a plastically deformable BMG showed that the elastic and plastic deformation of the BMG is correlated to the structural changes at short- (SRO) and medium range order (MRO). In the elastic regime, the atomic distances at SRO vary linearly with macroscopic stress. Analysis of the area under radial distribution function indicates that a small fraction of bonds in the first shell is broken in the loading direction whereas some new bonds are formed in the transverse direction. Atomic bonds at SRO appeared significantly stiffer than the MRO shells. Compared to the macroscopic values of the elastic strain, Young’s modulus and Poisson's ratio, both SRO and MRO appeared significantly stiffer, implying that the elastic behavior of the BMG is not only ruled by simple compression of the atoms/clusters but also is aided by rearrangement of atoms/clusters. The deviation of MRO atomic strain-stress correlation from linearity at the onset of plastic deformation was attributed to the activation of irreversible shear transformation zones. It was demonstrated by a strong shear strain value at the onset of yielding. This value is in good agreement with the reported value of the critical shear strain needed for activation of an irreversible STZ. The length scale of 12.5 Å indicated the largest shear strain and is probably the most effective length scale in the formation of STZs. The atomic pairs at SRO with smallest shear strain have the least contribution to the STZs. It was also indicated that the typical fracture angle of this BMG can be explained by the orientation of maximum shear strain at the onset of catastrophic shear band formation. 2. Strain distribution map in mechanically-imprinted BMG In mechanical imprinting, the BMG plate is loaded between two tools with a regular array of linear teeth and, as a result, a regular pattern of linear imprints is created on the surface of the plate. Mechanically imprinting results in considerable tensile plasticity of brittle Vit105 BMG plate. The distribution of hardness and Young’s modulus values at the transverse cross section of imprinted plate probed via nanoindentation revealed oscillating soft and hard regions beneath the surface. Spatially-resolved strain maps obtained via high-energy nano-size beam X-ray diffraction exhibited that the plastic deformation during imprinting creates a spatially heterogeneous atomic arrangement, consisting of strong compressive and tensile strain fields as well as significant shear strain fields in the cross section. It was shown that the heat treatment diminishes the heterogeneous structure resulting in brittle behavior in tension. The analysis of strain tensor components based on changes in the first diffraction maximum of the structure function, q1, revealed that Ɛx, the strain perpendicular to the loading direction, changes from the compressive at near to the surface to the tensile mode at the center of the imprinted plate. In contrast, the strain component along the loading direction, Ɛy, changes from tensile near the surface to the compressive at the center. Beneath the surface, Ɛx reaches to values about 1.5% under the imprints where there is a negligible Ɛy. The distribution map of principal strains, Ɛ1 and Ɛ2, indicated that large regions with compressive Ɛ1 and Ɛ2 exist under the imprints which can result in blocking of the propagating shear bands in agreement with microstructural observations of shear banding after uniaxial tension. Moreover, the region beneath the border of the imprinted and un-imprinted parts has the highest residual shear strain. Microstructural observations indicated that such regions can nucleate new shear bands upon tensile loading of imprinted BMG plate. 3. Residual strain around a single shear band In order to probe structural changes in the shear-induced zone around a single shear band, the distribution of residual strains at short- and medium-range order around a single shear band was determined in cold-rolled BMG plate using the nano-focused high energy x-ray diffraction. Plastic deformation results in significant residual normal and shear strains at distances of more than 15 μm around the shear band. The residual normal strains exhibit an asymmetric distribution whereas the residual shear strain is distributed symmetrically around the shear band. The large amount of residual atomic shear strain magnitude at the vicinity of the shear band triggers the nucleation of the new shear bands. The coincidence of the direction of the nucleating secondary shear bands from the main shear band with the orientation of the residual shear strain at the vicinity of the mature shear band highlight the dominant role of the shear strain in determining further plastic deformation at regions near the shear band. / Im Rahmen dieser Arbeit wird hochenergetische Synchrotron Röntgenstrahlung zum Aufzeigen der strukturellen Veränderungen in plastisch verformtem Zr52.5Ti5Cu18Ni14.5Al10 metallischen Glas verwendet. Die Arbeit gliedert sich in drei Teile: Dehnungsentwicklung während in-situ Druckversuch, Dehnungsverteilung eines mechanisch geprägten massiven metallischen Glases, und Restdehnungen in der Umgebung eines einzenen Scherbandes. 1. Dehnungsentwicklung während in-situ Druckversuch Die während der Verformung auftretende strukturelle Neuordnung eines plastisch verformbaren metallischen Glases zeigt die Korrelation der elastischen und plastischen Verformung mit den strukturellen Änderungen in den Größenordnungen der Nah- (SRO) und mittelreichweitigen Ordnung (MRO). Im elastischen Bereich verändern sich die Atomabstände in der SRO linear mit der makroskopisch anliegenden Spannung. Die Untersuchung der Fläche unter der Radialen Verteilungsfunktion (RDF) deutet auf ein Aufbrechen eines geringen Anteils der Bindungen der ersten Schale in Druckspannungsrichtung und deren Neubildung quer dazu. Die atomaren Bindungen in der SRO erscheinen wesentlich steifer als in den MRO Schalen. Vergleicht man die Werte von elastischer Dehnung, E-Modul und Querkontraktionszahl mit ihren makroskopischen Gegenstücken erscheinen beide, SRO und MRO, wesentlich steifer. Dies zeigt, dass die elastische Verformung von metallischen Gläsern nicht nur von der einfachen Stauchung der Atome bzw. Atomgruppen bestimmt, sondern auch durch deren Neuanordnung unterstützt wird. Das Abweichen der Dehnungs-Spannungs-Korrelation vom linearen Verhalten in der MRO am Beginn der plastischen Verformung wird der irreversiblen Bildung von Schertransformations-zonen (STZ) zugeschrieben. Dies zeigt sich zudem in den erhöhten Scherdehnungswerten am Beginn der Dehngrenze, welche mit den in der Literatur berichteten Werten für die kritische Scherdehnung zum Bilden einer STZ übereinstimmen. Bei einem Atomabstand von 12,5 Å tritt der höchste Wert der Scherdehnung auf und markiert den effektivsten Längenbereich der STZ Bildung. Andererseits haben die atomaren Paare in der SRO mit der geringsten Scherdehnung den geringsten Beitrag an der STZ. Es zeigt sich außerdem, dass der typische Bruchwinkel dieses metallischen Glases über die Orientierung der maximalen Scherdehnung am Beginn der kritischen Scherbandbildung erklärt werden kann. 2. Dehnungsverteilung eines mechanisch geprägten massiven metallischen Glases Eine Prägung besteht darin, eine Platte metallischen Glases mit zwei Stempel, auf denen eine regelmäßige Anordnung von geradlinigen Kerben angebracht ist, zu belasten. Dadurch wird eine ebenso regelmäßige Anordnung von geradlinigen Kerben auf der Oberfläche des metallischen Glases erzeugt. Die plastische Verformbarkeit der Vit105 Platte im Zugversuch wird durch Prägung im Vergleich zur gegossenen Probe eindeutig verbessert. Die Untersuchung der Härte und des E-Moduls über den Querschnitt der geprägten Probe zeigt die Einbringung von Abwechselnd weichen und harten Regionen an der Oberfläche. Es wurden räumlich aufgelöste Dehnungskarten des geprägten metallischen Glases durch Beugung eines hochenergetischen nanometergroßen Röntgenstrahles erzeugt. Die Ergebnisse offenbaren, dass die durch Prägung eingebrachte plastische Verformung eine räumlich heterogene Atomanordnung erzeugt, welche aus starken Druck- und Zugdehnungsfeldern besteht. Zusätzlich wird eine signifikante Scherdehnung in die Probe eingebracht. Die Wärmebehandlung beseitigt diese heterogene Struktur und führt sie fast auf den Ausgangszustand zurück. Die Analyse der Dehnungstensorkomponenten basierend auf Änderungen im erstem Maximum des Strukturfaktors, q1, zeigt, dass sich Ɛx von der Oberfläche zur Mitte der Platte hin von einer Stauchung in eine Dehnung umwandelt. Im Gegensatz dazu wandelt sich die Komponente Ɛy von der Oberfläche zur Mitte der Platte hin von einer Dehnung in eine Stauchung um. An der Oberfläche unter den Eindrücken, wo Ɛy vernachlässigbar ist, erreicht Ɛx Werte von ca. 1.5 %. Die Verteilungskarten der Hauptdehnungen zeigt, dass beide e1 und e2 unterhalb der Kerben als Stauchungen vorhanden sind. Daraus resultiert das Blockieren und Ablenken der sich ausbreitenden Scherbänder, was an Zugproben im REM beobachtet werden kann. Weiterhin hat der Bereich an der Grenze der geprägten und nicht geprägten Regionen die höchste Restscherdehnung. Mikrostrukturelle Beobachtungen deuten darauf hin, dass solche Bereiche unter Zuglast Keimstellen für neue Scherbänder sind. 3. Restdehnungen in der Umgebung eines einzenen Scherbandes Es wurde ein einzelnes Scherband einer kaltgewalzte Platte mittels Beugung eines hochenergetischen nanometergroßen Röntgenstrahles untersucht. Die strukturellen Unterschiede in der scherinduzierten Zone um ein einzelnes Scherband werden durch die Verteilung der Restdehnungen in SRO und MRO bestimmt. Plastische Verformung führt zu signifikanten Restnormal- und Restscherdehnungen in Entfernungen von mehr als 15 µm um das Scherband. Die Restnormaldehnungen zeigen eine asymmetrische Verteilung, wohingegen die Restscherdehnungen auf beiden Seiten des Scherbandes symmetrisch verteilt sind. Der große Betrag der atomaren Restscherdehnung in der Nähe des Scherbandes führt zur Bildung von neuen Scherbändern. Das Zusammenfallen der Richtung des sich bildenden sekundären Scherbandes und der Orientierung der Restscherdehnung, in der Nähe des primären Scherbandes, demonstriert die dominierende Rolle der Scherdehnung bei weiterer plastischer Verformung in der Nähe des Scherbandes.

<div>In this thesis, the role of location-specific microstructural features in the fatigue performance of the safety-critical aerospace components made of Nickel (Ni)-base superalloys and linear friction welded (LFW) Titanium (Ti) alloys has been studied using crystal plasticity finite element (CPFE) simulations, energy dispersive X-ray diffraction (EDD), backscatter electron (BSE) images and digital image correlation (DIC).</div><div><br></div><div>In order to develop a microstructure-sensitive fatigue life prediction framework, first, it is essential to build trust in the quantitative prediction from CPFE analysis by quantifying uncertainties in the mechanical response from CPFE simulations. Second, it is necessary to construct a unified fatigue life prediction metric, applicable to multiple material systems; and a calibration strategy of the unified fatigue life model parameter accounting for uncertainties originating from CPFE simulations and inherent in the experimental calibration dataset. To achieve the first task, a genetic algorithm framework is used to obtain the statistical distributions of the crystal plasticity (CP) parameters. Subsequently, these distributions are used in a first-order, second-moment method to compute the mean and the standard deviation for the stress along the loading direction (σ_load), plastic strain accumulation (PSA), and stored plastic strain energy density (SPSED). The results suggest that an ~10% variability in σ_load and 20%-25% variability in the PSA and SPSED values may exist due to the uncertainty in the CP parameter estimation. Further, the contribution of a specific CP parameter to the overall uncertainty is path-dependent and varies based on the load step under consideration. To accomplish the second goal, in this thesis, it is postulated that a critical value of the SPSED is associated with fatigue failure in metals and independent of the applied load. Unlike the classical approach of estimating the (homogenized) SPSED as the cumulative area enclosed within the macroscopic stress-strain hysteresis loops, CPFE simulations are used to compute the (local) SPSED at each material point within polycrystalline aggregates of 718Plus, an additively manufactured Ni-base superalloy. A Bayesian inference method is utilized to calibrate the critical SPSED, which is subsequently used to predict fatigue lives at nine different strain ranges, including strain ratios of 0.05 and -1, using nine statistically equivalent microstructures. For each strain range, the predicted lives from all simulated microstructures follow a log-normal distribution; for a given strain ratio, the predicted scatter is seen to be increasing with decreasing strain amplitude and are indicative of the scatter observed in the fatigue experiments. Further, the log-normal mean lives at each strain range are in good agreement with the experimental evidence. Since the critical SPSED captures the experimental data with reasonable accuracy across various loading regimes, it is hypothesized to be a material property and sufficient to predict the fatigue life.</div><div><br></div><div>Inclusions are unavoidable in Ni-base superalloys, which lead to two competing failure modes, namely inclusion- and matrix-driven failures. Each factor related to the inclusion, which may contribute to crack initiation, is isolated and systematically investigated within RR1000, a powder metallurgy produced Ni-base superalloy, using CPFE simulations. Specifically, the role of the inclusion stiffness, loading regime, loading direction, a debonded region in the inclusion-matrix interface, microstructural variability around the inclusion, inclusion size, dissimilar coefficient of thermal expansion (CTE), temperature, residual stress, and distance of the inclusion from the free surface are studied in the emergence of two failure modes. The CPFE analysis indicates that the emergence of a failure mode is an outcome of the complex interaction between the aforementioned factors. However, the possibility of a higher probability of failure due to inclusions is observed with increasing temperature, if the CTE of the inclusion is higher than the matrix, and vice versa. Any overall correlation between the inclusion size and its propensity for damage is not found, based on inclusion that is of the order of the mean grain size. Further, the CPFE simulations indicate that the surface inclusions are more damaging than the interior inclusions for similar surrounding microstructures. These observations are utilized to instantiate twenty realistic statistically equivalent microstructures of RR1000 – ten containing inclusions and remaining ten without inclusions. Using CPFE simulations with these microstructures at four different temperatures and three strain ranges for each temperature, the critical SPSED is calibrated as a function of temperature for RR1000. The results suggest that critical SPSED decreases almost linearly with increasing temperature and is appropriate to predict the realistic emergence of the competing failure modes as a function of applied strain range and temperature.</div><div><br></div><div>LFW process leads to the development of significant residual stress in the components, and the role of residual stress in the fatigue performance of materials cannot be overstated. Hence, to ensure fatigue performance of the LFW Ti alloys, residual strains in LFW of similar (Ti-6Al-4V welded to Ti-6Al-4V or Ti64-Ti64) and dissimilar (Ti-6Al-4V welded to Ti-5Al-5V-5Mo-3Cr or Ti64-Ti5553) Ti alloys have been characterized using EDD. For each type of LFW, one sample is chosen in the as-welded (AW) condition and another sample is selected after a post-weld heat treatment (HT). Residual strains have been separately studied in the alpha and beta phases of the material, and five components (three axial and two shear) have been reported in each case. In-plane axial components of the residual strains show a smooth and symmetric behavior about the weld center for the Ti64-Ti64 LFW samples in the AW condition, whereas these components in the Ti64-Ti5553 LFW sample show a symmetric trend with jump discontinuities. Such jump discontinuities, observed in both the AW and HT conditions of the Ti64-Ti5553 samples, suggest different strain-free lattice parameters in the weld region and the parent material. In contrast, the results from the Ti64-Ti64 LFW samples in both AW and HT conditions suggest nearly uniform strain-free lattice parameters throughout the weld region. The observed trends in the in-plane axial residual strain components have been rationalized by the corresponding microstructural changes and variations across the weld region via BSE images. </div><div><br></div><div>In the literature, fatigue crack initiation in the LFW Ti-6Al-4V specimens does not usually take place in the seemingly weakest location, i.e., the weld region. From the BSE images, Ti-6Al-4V microstructure, at a distance from the weld-center, which is typically associated with crack initiation in the literature, are identified in both AW and HT samples and found to be identical, specifically, equiaxed alpha grains with beta phases present at the alpha grain boundaries and triple points. Hence, subsequent fatigue performance in LFW Ti-6Al-4V is analyzed considering the equiaxed alpha microstructure.</div><div><br></div><div>The LFW components made of Ti-6Al-4V are often designed for high cycle fatigue performance under high mean stress or high R ratios. In engineering practice, mean stress corrections are employed to assess the fatigue performance of a material or structure; albeit this is problematic for Ti-6Al-4V, which experiences anomalous behavior at high R ratios. To address this problem, high cycle fatigue analyses are performed on two Ti-6Al-4V specimens with equiaxed alpha microstructures at a high R ratio. In one specimen, two micro-textured regions (MTRs) having their c-axes near-parallel and perpendicular to the loading direction are identified. High-resolution DIC is performed in the MTRs to study grain-level strain localization. In the other specimen, DIC is performed on a larger area, and crack initiation is observed in a random-textured region. To accompany the experiments, CPFE simulations are performed to investigate the mechanistic aspects of crack initiation, and the relative activity of different families of slip systems as a function of R ratio. A critical soft-hard-soft grain combination is associated with crack initiation indicating possible dwell effect at high R ratios, which could be attributed to the high-applied mean stress and high creep sensitivity of Ti-6Al-4V at room temperature. Further, simulations indicated more heterogeneous deformation, specifically the activation of multiple families of slip systems with fewer grains being plasticized, at higher R ratios. Such behavior is exacerbated within MTRs, especially the MTR composed of grains with their c-axes near parallel to the loading direction. These features of micro-plasticity make the high R ratio regime more vulnerable to fatigue damage accumulation and justify the anomalous mean stress behavior experienced by Ti-6Al-4V at high R ratios.</div><div><br></div>