Rozprawy doktorskie na temat „Planar Faults”

Phase interface and stacking fault are two common planar defects in metallic materials. In the present thesis, the interfacial energy and the generalized stacking fault energy of random alloys are investigated using density functional theory formulated within the exact muffin-tin orbitals (EMTO) method in combination with the coherent-potential approximation (CPA).The interfacial energy is one of the key physical parameters controlling the formation of the Cr-richα’ phases during the phase decomposition in Fe-Cr ferrite stainless steels. This decomposition is believed to cause the so-called“475°C embrittlement”. Aluminum addition to ferritic stainless steels was found to effectively suppress the deleterious 475oC embrittlement. The effect of Al on the interfacial energy and the formation energy of Fe-Cr solid solutions are studied in this thesis. The interface between the decomposed Fe-rich α and Cr-rich α phases carries a positive excess energy, which represents a barrier for the process of phase separation. Our results show that for the α-Fe70Cr20Al10/α0-Fe100−x−yCryAlx(0≤x≤10, 55≤y≤80) interface, the Al content(x) barely changes the interfacial energy. However, when Al is partitioned only in the alpha phase, i.e. for the α-Fe100−x−yCryAlx/α0-Fe10Cr90(0≤x≤10,0≤y≤25) interface, the interfacial energy increases with Al concentration due to the variation of the formation energies of the Fe-Cr alloys upon Al alloying. The intrinsic energy barriers (IEBs) of the γ surface (also called generalized stacking fault energy, GSFE) provide fundamental physics for understanding the plastic deformation mechanisms in face-centred cubic metals and alloys. In this thesis, the GSFEs of the disordered Cu-X (X=Al, Zn, Ga, Ni) and Pd-X (X=Ag,Au) alloys are calculated. Studying the effect of segregation of the solutes to the stacking fault planes shows that only the local chemical composition affects the GSFEs. Based on the calculated GSFEs values, the previously revealed “universal scaling law” between these IEBs is demonstrated to be well obeyed in random solid solutions. This greatly simplifies the calculations of the twinning parameters or the critical twinning stress. Adopting two twinnability measure parameters derived from the IEBs, we find that in binary Cu alloys, Al, Zn and Ga increase the twinnability, while Ni decreases it. Aluminum and gallium yield similar effects on the twinnability. Our theoretical predictions are in line with the available experimental data. These achievements open new possibilities in understanding and describing the plasticity of complex alloys.

QC 20141104

The lack of ductility of the B2 NiAl alloy stands in the way of promising applications. In an effort to understand the dislocation behavior, computer simulation of the planar faults involved in the core spreadings of <100> and <111> dislocations was carried out. Seven γ-surfaces were computed for different crystallographic planes ({110}, {112}, {123}, {210}, {100}, {111} and {122}). Stable APB's are observed in the {110} and {112} planes but they are deviated from the exact 1/2a<111> position. No other stable planar fault was observed. The dislocation core spreadings are explained by the energy balance among the directions of lowest restoring forces observed in the γ-surfaces. The complete <111> screw dislocation was stable in the simulation. According to the stable APB's, two dissociation reactions of the <111> screw dislocation in the {110} and {112} planes are proposed. The simulation of metastable superpartials shows that the dissociation in the {112} planes is very close to a stable dissociation.
Master of Science

Orientador: Gilberto Pechoto de Melo
Banca: Vicente Lopes Júnior
Banca: Raquel Santini Leandro Rade
Resumo: Hoje em dia um dos fatores de interesse das indústrias no desenvolvimento de novas técnicas de detecção e localização de falhas é a preocupação com a segurança de seus sistemas, tendo-se a necessidade de supervisão e monitoramento de modo que as falhas sejam detectadas e corrigidas o mais rápido possível. Verifica-se na prática que determinados parâmetros dos sistemas podem variar durante o processo, devido a características específicas ou o desgaste natural de seus componentes. Sabe-se também que, mesmo nos sistemas bem projetados, a ocorrência de trincas em alguns componentes pode provocar perdas econômicas ou conduzir a situações perigosas. Os observadores de estado podem reconstruir os estados não medidos do sistema, desde que os mesmos sejam observáveis, tornando possível, desta forma, estimar as medidas nos pontos de difícil acesso. A técnica dos observadores de estado consiste em desenvolver um modelo para o sistema em análise e comparar a estimativa da saída com a saída medida, a diferença entre os dois sinais presentes resulta em um resíduo que é utilizado para análise. Neste trabalho foi montado um banco de observadores associado a um modelo de trinca de modo a acompanhar o progresso da mesma. Os resultados obtidos através de simulações computacionais em uma placa engastada discretizada pela técnica dos elementos finitos e as análises experimentais realizadas foram bastante satisfatórios, validando a metodologia desenvolvida.
Abstract: Nowadays a main factor of interest in industries in the development of new techniques for detection and localization of faults is the concern with the security of its systems. There is the need of supervising and monitoring the machines to detect and correct the fault as soon as possible. In practice it is verified that some determined parameters of the systems can vary during the process, due to the specific characteristics or the natural wearing of its components. It is known that even in well-designed systems the occurrence of cracks in some components can induce economic losses or lead to dangerous situations. The state observers methodology can reconstruct the unmeasured states of the system, since they are observable, becoming possible in this way to estimate the measures at points of difficult access. The technique of state observers consists of developing a model for the system under analysis and to compare the estimated with the measured exit, and the difference between these two signals results in a residue that is used for analysis. In this work was set up a bank of observers associated to a model of crack in order to follow its progress. The results obtained through computational simulations in a cantilever plate discretized by using the finite elements technique and the accomplished experimental analysis were sufficiently satisfactory, validating the developed methodology.
Mestre

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Hoje em dia um dos fatores de interesse das indústrias no desenvolvimento de novas técnicas de detecção e localização de falhas é a preocupação com a segurança de seus sistemas, tendo-se a necessidade de supervisão e monitoramento de modo que as falhas sejam detectadas e corrigidas o mais rápido possível. Verifica-se na prática que determinados parâmetros dos sistemas podem variar durante o processo, devido a características específicas ou o desgaste natural de seus componentes. Sabe-se também que, mesmo nos sistemas bem projetados, a ocorrência de trincas em alguns componentes pode provocar perdas econômicas ou conduzir a situações perigosas. Os observadores de estado podem reconstruir os estados não medidos do sistema, desde que os mesmos sejam observáveis, tornando possível, desta forma, estimar as medidas nos pontos de difícil acesso. A técnica dos observadores de estado consiste em desenvolver um modelo para o sistema em análise e comparar a estimativa da saída com a saída medida, a diferença entre os dois sinais presentes resulta em um resíduo que é utilizado para análise. Neste trabalho foi montado um banco de observadores associado a um modelo de trinca de modo a acompanhar o progresso da mesma. Os resultados obtidos através de simulações computacionais em uma placa engastada discretizada pela técnica dos elementos finitos e as análises experimentais realizadas foram bastante satisfatórios, validando a metodologia desenvolvida.
Nowadays a main factor of interest in industries in the development of new techniques for detection and localization of faults is the concern with the security of its systems. There is the need of supervising and monitoring the machines to detect and correct the fault as soon as possible. In practice it is verified that some determined parameters of the systems can vary during the process, due to the specific characteristics or the natural wearing of its components. It is known that even in well-designed systems the occurrence of cracks in some components can induce economic losses or lead to dangerous situations. The state observers methodology can reconstruct the unmeasured states of the system, since they are observable, becoming possible in this way to estimate the measures at points of difficult access. The technique of state observers consists of developing a model for the system under analysis and to compare the estimated with the measured exit, and the difference between these two signals results in a residue that is used for analysis. In this work was set up a bank of observers associated to a model of crack in order to follow its progress. The results obtained through computational simulations in a cantilever plate discretized by using the finite elements technique and the accomplished experimental analysis were sufficiently satisfactory, validating the developed methodology.

Orientador: Carlos Alberto Cimini Junior
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: O principal objetivo deste trabalho, foi desenvolver uma metodologia para identificar impacto em placas laminadas de materiais compósitos, a fim de reduzir o tempo de inspeção e assim otimizar o intervalo de inspeção para uma determinada estrutura, já que muitas vezes é necessário interromper a sua operação. Uma compreensão abrangente dos efeitos de interação estrutura, sensores piezelétricos e objetos utilizados para aplicar cargas de impacto foi essencial. Este trabalho efetua uma análise numérica a partir dos tempos que conduziram ondas de deformação para alcançar os sensores e os seus efeitos sobre a exatidão dos resultados, obtidos pelo algoritmo desenvolvido, bem como a exatidão da metodologia aplicada. Sensores piezelétricos fabricados pela International APC e um sistema de aquisição de dados da National Instruments foram utilizados para obter respostas de ondas de tensão geradas por cargas de impacto. Uma identificação simples e robusta do impacto em tempo real com base na triangulação foi implementada. O uso de recursos computacionais através da plataforma Labview, juntamente com um algoritmo implementado no código computacional, forneceu resultados promissores, após testes realizados em configurações de placas experimentais monitoradas com redes de sensores piezelétricos. A metodologia proposta foi validada para placas de material isotrópico (aço) e anisotrópico (carbono/epóxi) apresentando bons resultados. A interface foi desenvolvida para ser aplicada a materiais com diferentes índices de anisotropia, onde se pode ajustar os valores de velocidade das ondas em diferentes direções. Observou-se que o erro máximo medido foi de 0,028 m. O código computacional apresentou-se robusto para identificar o local do impacto em qualquer ponto da placa em tempo real. Foi possível também comprovar para as diferentes massas de impacto que um procedimento simples de triangulação combinado com as características de velocidade de propagação das ondas proporciona um meio de localizar impactos
Abstract: The main objective of this work was to develop a methodology for identifying impact in laminated plates of composite materials in order to reduce inspection time and thus reduce the inspection interval for a given structure, since it is often necessary to stop its operation. A comprehensive understanding of the interaction effects of structure, piezoelectric sensors and objects used to apply impact loads was essential. This work demonstrates the numerical analysis of time leading waves of deformation to reach the sensors and their effect on not only the accuracy of the results obtained by the algorithm but also the accuracy of the methodology applied. In this work, piezoelectric sensors manufactured by International APC and data acquisition system of National Instruments were used. A simple and robust real-time impact identification based on triangulation was implemented. The use of computational resources within Labview platform along with a computer code implemented algorithm provided promising results after testing experimental settings for plates monitored with of piezoelectric sensors. The proposed methodology was validated for isotropic (steel) and anisotropic (carbon/epoxy) plate materials with fairly good results. The interface was designed to be applied to materials with different degrees of anisotropy, adjusting the values of wave velocity in different directions for composite materials. It was observed that the maximum error was 0.028 m. The computer code was robust enough to identify the impact location at any point of the plate in real time. It was also possible to demonstrate for different impact masses that a simple triangulation procedure combined with the characteristics of wave propagation provides a methodology for locating impacts
Mestrado
Mecanica dos Sólidos e Projeto Mecanico
Mestre em Engenharia Mecânica

Orientador: Jose Maria Campos dos Santos
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: Neste trabalho, estudam-se os fenômenos de propagação de ondas elásticas em placas simples e acopladas e se propõe unia metodologia para análise do comportamento vibracional médio cm frequência-espaço com o objetivo de identificar como as vibrações se propagam através dessas estruturas em médias e altas freqüências. Para isso utilizou-se de métodos de energia originados da Análise de Fluxo de Energia (EFA) e que têm como variáveis primárias a densidade de energia e fluxo de energia. Duas formulações foram usadas para resolver as equações diferenciais de energia aproximada derivada du EFA: o Método dos Elementos Finitos de Energia (EFEM) e o Método do Elemento Espectral de Energia (ESEM). O Método do Elemento Espectral (SEM) foi uma outra formulação estudada para resolver as equações diferenciais de propagação de onda em placa fina, bem como para validar a metodologia proposta. Diferentes tipos de acoplamentos foram investigados e implementados tais como: placa-placa, placa com reforço e placa com dano. Para isso, desenvolveram-se relações de acoplamentos que descrevem essas descontinuidades estruturais. Uma investigação experimental do comportamento vibracional de uma placa simples e com reforço foi realizada para verificar os resultados do ESEM. De forma geral, observa-se que os resultados obtidos pelos modelos simulados apresentaram um comportamento semelhante aos resultados encontrados experimentalmente
Abstract: In this research, propagation phenomena of elastic waves to simple and coupled plates are investigated and a methodology, based on energy methods, is proposed to predict the space- and frequency-averaged vibrational response of these structures, at mid and high frequencies. These methods, originated from Energy Flow Analysis, use as primary variables the energy density and the energy flow, which are parameters to vibrational analysis. Two methodologies are used to solve approximated energy differential equations derived from EFA: Energy Finite Element Method (EFEM) and Energy Spectral Element Method (ESEM). Another formulation the Spectral Element Method (SEM), is used to solve differential wave equation of thin plates in terms of displacement, based on classical mechanics; moreover this method is applied to validate the proposed methodology. Different discontinued structures were investigated, such as plate-plate, reinforced plate and damaged plate. To this purpose, coupled relationships that represent these discontinuities are developed. An experimental investigation of vibrational response of a simple and reinforced plate was performed to verify the results of ESEM. The experimental results, calculated in terms of energy variables, to both analyzed structures, showed a good agreement with the simulated models
Doutorado
Mecanica dos Sólidos e Projeto Mecanico
Mestre em Engenharia Mecânica

This thesis aims to use vibration and acoustic noise analysis to help a production line of a certain motor type to ensure good quality. Noise from the gearbox is sometimes present and the way it is detected is with a human listening to it. This type of error detection is subjective, and it is possible for human error to be present. Therefore, an automatic test that pass or fail the produced Brush Less Direct Current (BLDC)-motors is wanted. Two measurement setups were used. One was based on an accelerometer which was used for vibration measurements, and the other based on a microphone for acoustic sound measurements. The acquisition and analysis of the measurements were implemented using the data acquisition device, compactDAQ NI 9171, and the graphical programming software, NI LabVIEW. Two methods, i.e., power spectrum analysis and machine learning, were used for the analyzing of vibration and acoustic signals, and identifying faults in the gearbox. The first method based on the Fast Fourier transform (FFT) was used to the recorded sound from the BLDC-motor with the integrated planetary gearbox to identify the peaks of the sound signals. The source of the acoustic sound is from a faulty planet gear, in which a flank of a tooth had an indentation. Which could be measured and analyzed. It sounded like noise, which can be used as the indications of faults in gears. The second method was based on the BLDC-motors vibration characteristics and uses supervised machine learning to separate healthy motors from the faulty ones. Support Vector Machine (SVM) is the suggested machine learning algorithm and 23 different features are used. The best performing model was a Coarse Gaussian SVM, with an overall accuracy of 92.25 % on the validation data.

This Master‘s thesis is focused on theoretical study of twinning in magnetic shape memory alloys based on Ni2MnGa using ab initio calculations of electronic structure within the projector augmented wave method. In particular, the effect of increasing concentration of manganese at the expense of gallium was studied on total energy and stress profiles along different deformation paths in the (10-1)[101] shear system of non-modulated martensite. Further, this work deals with the effect of the concentration of manganese on the energy of planar fault caused by presence of partial dislocation due to motion of twin boundary. The results show that the shear modulus in studied shear system increases with the increasing concentration of manganese as well as energy barrier and deformation characteristics along shear deformation paths increases, which makes the shear more difficult in Mn-rich alloys. Increasing concentration of manganese also leads to rising the planar fault energy. All these effects can be responsible for lower mobility of twin boundaries in alloys with higher concentration of manganese.

L'objectif de ce travail est de proposer des methodes simples d'estimation du mouvement sismique, applicables facilement, particulierement dans le cas de milieux urbains. Ce sont, en effet, les grandes agglomerations qui sont souvent le siege de degats catastrophiques, et il est donc necessaire de pouvoir fournir des techniques faciles a mettre en uvre pour l'etude du mouvement sismique auquel les structures construites doivent resister. Dans la premiere partie, nous etudierons une methode d'estimation des effets de site lies a la geologie locale, basee sur le calcul du rapport spectral entre composantes horizontales et verticale (rapport h/v), sur des enregistrements de bruit de fond. Nous avons, dans un premier temps, realise une etude par simulation numerique permettant de mettre en evidence certains des parametres qui controlent l'utilisation de cette methode, ainsi que ses limites de validite. Une comparaison avec d'autres techniques classiques d'estimation des effets de site met en evidence les possibilites et les inconvenients de chacune d'elles, dans le cadre d'une grande ville. La deuxieme partie de ce travail concerne la simulation de mouvements forts, avec pour objectifs les points suivants: fournir une methode egalement applicable en milieux urbains, etre en mesure de produire des simulations en champ proche, reduire la complexite et le temps de calcul necessaires a la simulation, pouvoir effectuer des simulations a priori en des sites ou aucun mouvement fort n'a encore ete enregistre. Pour essayer de satisfaire ces objectifs nous proposons l'utilisation d'une technique basee sur le principe de la methode des fonctions de green empiriques. Nous utilisons ici des fonctions de green theoriques, l'enregistrement de petits seismes etant tres difficile en zone urbaine. Le seisme cible est defini par un nombre de parametres relativement reduit: son moment sismique ainsi que la taille et l'orientation du plan de faille

High temperature metallic structural materials, such as Ni-base superalloys owe their strength to a two-phase microstructure consisting of an fcc matrix strengthened by intermetallic A3B type precipitates. The performance of these alloys derives from the exceptional high temperature strength of the L12-ordered A3B precipitate, which in turn is strongly influenced by planar faults created when the precipitate is sheared. In this context, the broad goal of this work is to understand the role of composition on planar fault energies in A3B compounds with L12 structure. Towards this aim, electronic structure calculations using density functional theory (DFT) was used to evaluate fault energies through direct simulations of faults and though indirect means involving analytical models. In the first part of the thesis, the effect of composition on the planar fault energies, elastic anisotropy, deformation modes and yield strength anomaly were explored in five pseudo-binaries (Ni, Co)3(Al,X) compositions of γ' (L12), where X = Ti, Ta, W, Ni. It was observed fault energies and deformation modes are sensitive to composition. The results are in good agreement with literature and can provide explanations for the deformation behaviour of both (Ni)3(Al, X) and Co3(Al,W). Though the results are encouraging, the above DFT calculations of fault energies are time-consuming, highlighting the need for high throughput models. In the second part of the thesis, such a model was developed to estimate these energies in well-known and novel A3B compositions. The new model treats the planar fault as a diffuse interface and allows estimation of fault energy in terms of energy of geometrically close packed structures with the same A3B composition and a bonding environment akin to that of the fault. The proposed model was used to predict energies of different superlattice faults in over 40 A3B compounds. The model was found to be highly accurate even without use of fitting parameters and has a fifteen-fold computational advantage over direct simulation. The model was extended to novel A3B compounds based on Pt3X, Rh3X and Ir3X where data is presently lacking. Despite the efficiency of the model, it had limitations in predicting fault energies in non-binary compositions. To account for this, in the last section of this thesis, a novel quasi-chemical model incorporating the far-field composition effects, was developed. The model was validated for several pseudo-binary systems and it was found that be more accurate than the diffuse interface model. The two models were then extended to predict fault energies in binary L12-ordered A3B compounds at high temperatures, complex multicomponent L12-ordered A3B compounds, and binary D019-ordered A3B compounds.

碩士
國立臺灣科技大學
資訊管理系
91
Layered cubic planar graph consists of a sequence of cycles C0, C1,…, Cn such that each pair of successive cycles, Ci, Ci+1, is joined by radial line segments. ki is the fixed number of edges in layer i that is incident to each face in layer i-1, and join Ci-1 and Ci. In this thesis, we focus on two-layered cubic planar graphs that consist of three concentric circles. The layered cubic planar graphs have Hamiltonian cycle. The theorem of the edge-coloring can be used to prove the Hamiltonian of the graph. In this thesis, we survey that whether two-layered cubic planar graph is still Hamiltonian when it has one faulty node. As the result of verifying, it is not. We provide different methods according to the location of the faulty node and that k2 is even or odd. Then it has different result.

碩士
國立臺灣海洋大學
資訊工程學系
102
Switching networks is widely used in the fields of computer communication, parallel processing, distributed processing, switch hierarchy and IC Routing. For improving the system performance, increasing the ability and reducing the time of switching, we generally use non-blocking switching networks. However, using a lot of switching elements and brings complicated connection will increase the cost. The switching elements of every kinds of switching networks, have certain lifespan. If the switching elements damage, it will cause the switching networks lose its ability of switching. However, most previous studies on switching networks have focused on the design of the framework, development of connection algorithms recently. Few researchers have addressed fault-tolerant design. In this article, we recommend a new type of non-blocking switching network, called Unrestrained Planar Switching Networks (UPSN). We present an important rule which guide to how to generate an unrestrained non-blocking planar switching networks for an UPSN with n inputs. An n input UPSN is, the types of (n-1)! Non-blocking planar switching network can be formed. If we let the switching elements of UPSN as comparator, every UPSN could considered planar sorting networks. In this article, we will design Self-routing algorithm of the planar switching network we composed and the connection algorithm of every UPSN. The last, we will design fault-tolerant for every UPSN. This fault-tolerant design can allow any one switch damage in UPSN. We placed backup switches in the switching network. For an n input UPSN, we just only need n-1 backup switches in best and 2n-4 in worst. When any one switch damage, after we use select algorithm to choose backup switches, it will return to non-blocking switching network and according UPSN’s characteristic.

碩士
元智大學
資訊工程研究所
88
In this thesis, we propose a fault-containing self-stabilizing algorithm for coloring planar graphs. We call a system self-stabilizing if, regardless of the initial state, the system will return to legitimate state after finite steps. For the proposed algorithm: (1) only one node will correct data after single fault occurs, the system will reach legitimate state, (2) the time complexity from any single fault is O(△), where△is maximum node degree. In fact, single transient fault in expect to occur more frequently in practice, so it is more valuable from practical point of view.