No description available.

This thesis presents a study of the dependency of loosening parameters on secondary locking features of threaded inserts subjected to dynamic shear loads. Secondary locking is used to assist and/or provide redundancy to the primary locking feature (threads) in preventing preload loss in almost any mechanical applications. Two different secondary locking features are studied: the Locking Heli-Coil insert and the Loctite Threadlocker (R) applied before assembly to a Standard Heli-Coil insert. Five parameters are studied in this thesis: percentage loss of initial preload, initial rate of preload loss, secondary rate of preload loss, steady-state value, and the final preload value. Statistical analysis was used to quantify the dependencies between locking levels. Results show that the loss of initial preload is dependent on secondary locking features, the initial and secondary rate of preload loss are dependent on secondary locking features, the steady-state value and the final preload value are dependent on secondary locking features. Also, due to secondary locking features, 83% of the "Locking Heli-Coil with Braycote" tests reached steady-state while only 16% of the "Standard Heli-Coil with Loctite" tests reached steady-state even though the final preload value were higher for "Standard Heli-Coil with Loctite."

Submitted by Maria Suzana Diniz (msuzanad@hotmail.com) on 2015-11-11T12:54:10Z No. of bitstreams: 1 arquivototal.pdf: 3130568 bytes, checksum: 6027ca9752d1e2aa1c67e8101efa2e8f (MD5) / Made available in DSpace on 2015-11-11T12:54:10Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 3130568 bytes, checksum: 6027ca9752d1e2aa1c67e8101efa2e8f (MD5) Previous issue date: 2014-10-31 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Studies have shown that the presence of people generates changes in the dynamic behavior of structures due to the increase of mass and the ability of the human body to absorb energy, justifying the representation of the human body by mass-spring-damper models. In situations where the mass of people are significant in relation to the mass of the structure, as in the case of temporary stands, the effect becomes more pronounced. These structures have less stiffness in the lateral direction, justifying the purpose of the present study to investigate the effect in this direction that causes the presence of people in a temporary grandstand. For the development, a prototype grandstand with a capacity of approximately 100 people was assembled in the laboratory and modal tests were performed with the empty structure and also partially occupied by people. Models in finite element (FE) were developed using the software Ansys. Experimental data and FE model results with 5, 8 and 12 people seated were correlated to adjust a biodynamic model representing seated and standing spectators. The biodynamic model, conceived as a single degree of freedom (SDOF), was proposed in a survey undertaken, being adapted to the conditions of the people in the stands. Transient analysis using ANSYS were also performed to adjust the damping coefficient of biodynamic models. Once the biodynamic models were defined, investigations on the vibration properties of the structure when it was gradually occupied by these models were performed. The results show significant changes in natural frequencies of stucture when occupied by seated and standing people when compared with the natural frequencies of the empty stand. These situations demonstrate the importance of considering the effect of people in temporary grandstand and its representation through biodynamic models. / Estudos têm demonstrado que a presença de pessoas gera modificações no comportamento dinâmico das estruturas em virtude do acréscimo de massa e da capacidade que o corpo humano possui de absorver energia, justificando a representação do corpo humano por modelos tipo massa-mola-amortecedor. Nas situações em que a massa das pessoas é significativa em relação à massa da estrutura, como é o caso das arquibancadas temporárias, o efeito torna-se mais acentuado. Essas estruturas têm menor rigidez na direção lateral, justificando o objetivo da presente pesquisa de investigar para esta direção o efeito que a presença de pessoas provoca em uma arquibancada temporária. Para o desenvolvimento da pesquisa, um protótipo de arquibancada com capacidade aproximada para 100 pessoas foi montada em laboratório e testes modais foram realizados com a estrutura vazia e parcialmente ocupada por pessoas. Modelos em elementos finitos (EF) foram desenvolvidos no software Ansys. Dados experimentais e resultados do modelo em EF da arquibancada com 5, 8 e 12 pessoas sentadas e em pé foram correlacionados para ajustar um modelo biodinâmico representando espectadores sentados e m pé. Um modelo biodinâmico de um grau de liberdade (1GDL) foi proposto em pesquisa já realizada, sendo adaptado para as condições das pessoas na arquibancada. Análises transientes utilizando o Ansys também foram realizadas para ajustar o coeficiente de amortecimento dos modelos biodinâmicos. Definidos os modelos biodinâmicos, investigações sobre as propriedades de vibração da estrutura quando foi gradualmente ocupada por estes modelos, foram realizadas. Os resultados demonstram mudanças significativas nas frequências naturais da estrutura quando ocupada por pessoas sentadas e em pé, quando comparadas com as frequências naturais da arquibancada vazia. Estas situações demonstram a importância de se considerar o efeito da presença de pessoas sentadas e em pé em arquibancadas temporárias e sua representação através de modelos biodinâmicos.

In this thesis, transverse vibration of a cracked beam on an elastic foundation and the effect of crack and foundation parameters on transverse vibration natural frequencies are studied. Analytical formulations are derived for a beam with rectangular cross section. The crack is an open type edge crack placed in the medium of the beam and it is uniform along the width of the beam. The cracked beam rests on an elastic foundation. The beam is modeled by two different beam theories, which are Euler-Bernoulli beam theory and Timoshenko beam theory. The effect of the crack is considered by representing the crack by rotational springs. The compliance of the spring that represents the crack is obtained by using fracture mechanics theories. Different foundation models are discussed / these models are Winkler Foundation, Pasternak Foundation, and generalized foundation. The equations of motion are derived by applying Newton&#039 / s 2nd law on an infinitesimal beam element. Non-dimensional parameters are introduced into equations of motion. The beam is separated into pieces at the crack location. By applying the compatibility conditions at the crack location and boundary conditions, characteristic equation whose roots give the non-dimensional natural frequencies is obtained. Numerical solutions are done for a beam with square cross sectional area. The effects of crack ratio, crack location and foundation parameters on transverse vibration natural frequencies are presented. It is observed that existence of crack reduces the natural frequencies. Also the elastic foundation increases the stiffness of the system thus the natural frequencies. The natural frequencies are also affected by the location of the crack.

Made available in DSpace on 2014-06-11T19:31:36Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-05-25Bitstream added on 2014-06-13T20:02:27Z : No. of bitstreams: 1 nogueira_m_dr_botfca.pdf: 1692230 bytes, checksum: 9f3d4ea1e577719bc503399ced136ac4 (MD5) / A classificação e padronização da madeira serrada é uma atividade de rotina, desenvolvida por países que se apresentam como grandes consumidores deste material. O Brasil não pratica a classificação dos materiais à base de madeira, em geral. Essa afirmação é particularmente verdadeira para o caso da madeira serrada. Em outros segmentos de mercado, em que o país ocupa posição de destaque como fornecedor internacional, tem-se visto forçado a estabelecer padrões mínimos de qualidade e a atingir marcas de conformidade, para continuidade dos fornecimentos. O Centro Virtual de Pesquisas em Madeiras - CEVEMAD, através do Laboratório de Ensaios de Materiais - FCA/UNESP tem desenvolvido pesquisas com o intuito principal de avaliar a sensibilidade dos ensaios não-destrutivos na avaliação de alguns defeitos potenciais presentes correntemente nas madeiras de rápido crescimento (notadamente pinus e eucalipto). No enfoque dado pelo CEVEMAD - Centro Virtual de Pesquisas em Madeiras, os ensaios não-destrutivos são encarados como ferramenta alternativa e/ou complementar no processo de classificação das madeiras (classificações quanto às classes de resistência e categorias de qualidade). Este trabalho teve como objetivo principal avaliar a sensibilidade dos principais métodos não-destrutivos como ferramentas alternativas e/ou complementares no processo classificatório de vigas (6cm x 12cm x 280 cm) de Eucalyptus sp. As madeiras empregadas no programa experimental foram obtidas a partir de material genético disponibilizado por empresas de reflorestamento da região do cerrado do Estado de Minas Gerais - MG. Foram amostradas 296 vigas de dimensões estruturais (6cm x 12cm x 280cm) de 10 clones distintos de Eucalyptus, que foram ensaiadas não-destrutivamente... / The classification and standardization of the sawn wood is an usual activity, developed by countries that come as great consumers of this material. Brazil does not practice the classification of wood base materials, in general. This is particularly true for the case of the sawn wood. In other segments, in which Brazil occupies prominente position as international supplier, it has been forced to establish minimum patterns of quality and to reach conformity marks. The Virtual Center of Researches on Wood - CEVEMAD, through the Laboratory of Testing Materials - FCA/UNESP - Sao Paulo State University - Brazil has carried out researches with the main objective of evaluating the sensibility of non-destructive tests in the evaluation of potential defects in wood from fast grown plantation (especially Pinus and Eucalyptus). In its peculiar focus, non-destructive tests are considered as alternative and/or complementary tool in the sawn wood classification process (either mechanical and visual classification). This work had the main objective of evaluating the sensibility of most common non-destructive tests in the classification of dimension lumber of from fast grown Eucalyptus plantation. Wood was obtained from genetic material supplied cultivated at Curvelo region, Minas Gerais State, Brazil. 296 beams of structural dimensions (6 cm x 12 cm x 280 cm) from 10 different clones of Eucalyptus were sampled. Beams were non-destructively (stress wave, ultrasound and resonance methods) and destructively (static bending and compression parallel to grain) tested. The results of tests were correlated, being considered the present defects in each one of the studied pieces and the non-destructive tests showed sensibility in the classification of pieces of structural dimensions of the sawn wood of Eucalyptus when framed in strips of velocity, both in the green condition and in the equilibrium moisture... (Complete abstract click electronic access below)

Made available in DSpace on 2016-06-02T20:09:05Z (GMT). No. of bitstreams: 1 DissMC.pdf: 5176018 bytes, checksum: f426ba516c8cecc516100eda5321f84b (MD5) Previous issue date: 2007-02-02 / Universidade Federal de Minas Gerais / This research had for purpose comparatively to verify the accuracy of the techniques of transverse vibration and ultrasound to the values gotten in static testings, for sawed wood used in structures. With the results gotten in the development of the present research it was possible to calibrate the coefficient of modification (kmod, 3) of NBR 7190:1997, besides increasing the relative knowledge to the nondestructive tests in wood. In the experimental methodology studies with parts of structural members of Eucalyptus grandis, Eucalyptus citriodora, Pinus sp and Goupia glabra had been carried through, which had been classified using the techniques of ultrasound and transverse vibration, for the determination of the dynamic modulus of elasticity (Ed). Simultaneously to the tests with ultrasound they had been carried through the visual grading and tests of static bending (MOE). The values of coefficient of determination for the technique of transverse vibration (R² = 0,75, R² = 0,80, R² = 0,93 and R² = 0,89) and for the technique of ultrasound (R2 = 0,65, R2 = 0,76, R2 = 0,66 and R2 = 0,88), gotten respectively for the Eucalyptus grandis, Eucalyptus citriodora, Pinus sp and Goupia glabra are significant, demonstrating that the techniques of ultrasound and transverse vibration are important tools for nondestructive inference of the modulus of elasticity of wood. The technique of transverse vibration presented better resulted in relation to the ultrasound, therefore it presents one better tack enters the physical model of the phenomenon and the corresponding associated mathematical model. In the determination of the values of coefficient of modification kmod, 3, was verified that the technique of transverse vibration presented superior values of coefficient in relation the ultrasound technique, therefore allows a classification next to the values gotten in the static bending. / Este trabalho teve por finalidade verificar a acuracidade das técnicas de ultra-som e vibração transversal comparativamente aos valores obtidos em ensaios estáticos, para madeira serrada empregada em estruturas. Com os resultados obtidos no desenvolvimento deste trabalho foi possível calibrar o coeficiente de modificação (kmod,3) da NBR 7190:1997 - Projeto de Estruturas de Madeira, além de ampliar o conhecimento relativo aos ensaios não-destrutivos em madeira. Na metodologia experimental foram realizados estudos com peças de dimensão estrutural das espécies Eucalyptus grandis, Eucalyptus citriodora, Pinus sp e Goupia glabra, as quais foram classificadas mecanicamente utilizando as técnicas de ultra-som e vibração transversal, para a determinação do módulo de elasticidade dinâmico (Ed). Simultaneamente aos ensaios com ultra-som realizou-se a classificação visual das peças e ensaios de flexão estática (MOE). Os valores de coeficiente de determinação para a técnica de vibração transversal (R²= 0,75, R²= 0,80, R²= 0,93 e R²= 0,89) e para a técnica de ultra-som (R2 = 0,65, R2 = 0,76, R2 = 0,66 e R2 = 0,88), obtidos respectivamente para as espécies Eucalyptus grandis, Eucalyptus citriodora, Pinus sp e Goupia glabra, são significativos, demonstrando que as técnicas de ultra-som e vibração transversal são importantes ferramentas para inferência não-destrutiva do módulo de elasticidade da madeira. A técnica de vibração transversal apresentou melhores resultados em relação ao ultra-som, pois apresenta uma melhor aderência entre o modelo físico do fenômeno e o correspondente modelo matemático associado. Na determinação dos valores de coeficiente de modificação kmod,3, verificou-se que a técnica de vibração transversal apresentou valores superiores de coeficiente em relação a técnica de ultra-som, pois esta permite uma classificação mais próxima dos valores obtidos na flexão estática.

A series of experimental results about unusual heating of carbon nanotubes by microwaves is analyzed in this dissertation. Two of vibration types, cantilever type (one end is fixed and the other one end is free), the second type is both ends are fixed, have been studied by other people. A third type of forced vibration of carbon nanotubes under an alternating electromagnetic field is examined in this paper. Heating of carbon nanotubes (CNTs) by microwaves is described in terms of nonlinear dynamics of a vibrating nanotube. Results from the model provide a way to understand several observations that have been made. It is shown that transverse vibrations of CNTs during microwave irradiation can be attributed to transverse parametric resonance, as occurs in the analysis of Melde's experiment on forced longitudinal vibrations of a stretched elastic string. For many kinds of carbon nanotubes (SWNT, DWNT, MWNT, ropes and strands) the resonant parameters are found to be located in an unstable region of the parameter space of Mathieu's equation. Third order wave equations are used to qualitatively describe the effects of phonon-phonon interactions and energy transfer from microwaves to CNTs. This result provides another way to input energy from microwaves to carbon nanotubes besides the usual Joule heating via electron-phonon interaction. This model appears to be the first to point out the role of nonlinear dynamics in the heating of CNTs by microwaves.

No description available.

Antes de utilizar as toras de madeira como elemento estrutural é necessário avaliar as propriedades mecânicas desse material tanto por inspeção visual quanto por ensaio mecânico. A técnica de vibração transversal tem se destacado entre os demais métodos de Avaliação Não-Destrutiva para madeira serrada por obter estimativas acuradas do módulo de elasticidade à flexão. Contudo, testes prévios com essa técnica evidenciaram dificuldades de empregá-la na avaliação a rigidez à flexão de toras. O objetivo deste trabalho foi propor um método de ensaio para estimar o módulo de elasticidade na flexão de toras de madeira por meio de vibração transversal. O método proposto foi testado e validado em uma amostra de 40 toras de Eucalyptus sp. Foram obtidas boas correlações entre o módulo de elasticidade estático e o módulo de elasticidade dinâmico obtido pelo ensaio de vibração transversal. / Before using the wood logs as a structural element is necessary to evaluate the mechanical properties of this material by visual inspection and mechanical testing. The transverse vibration technique has stood out among the other methods of Non-Destructive Evaluation for lumber to obtain accurate estimates of the bending modulus of elasticity. However, previous tests showed difficulties with this technique to use it to evaluate the bending stiffness of logs. The aim of this work is to propose a test method to estimate the bending modulus of elasticity of wood logs by means of transverse vibration. The proposed method was tested and validated on a sample of 40 logs of Eucalyptus sp. It was obtained good correlation between the static bending and dynamic modulus of elasticity obtained by transverse vibration test.

The level of axial compressive load on an existing column is one of the most important parameters to be known. This thesis aims to investigate current state of the art of NDT techniques, their application, and investigate alternative ways of using current technology to estimate the axial compressive load on columns. For this purpose, transverse vibration technique, ultrasonic pulse velocity method, and waveform and frequency content evaluation of ultrasound are investigated and implemented. Analytical and experimental studies on column transverse vibration frequency and axial load relationship are conducted and presented. The measured experimental lateral vibration frequency of the first bending mode decreased under increased axial compressive load as expected from analytical studies. Relationships between axial load and vibration frequency are derived and defined for different boundary conditions. Relationship charts are prepared for complicated solution sets. Numerical calculations, laboratory and field tests revealed that natural frequencies of slender columns are more sensitive to axial load changes. The available ultrasonic methods are investigated and described. Stress wave propagation in anisotropic solids is studied. Previous works have shown that the propogation velocity of stress waves depends on the density, Poisson&rsquo / s ratio, modulus of elasticity of the medium, and the state of stress. The orientation of the loading direction to the wave propogation direction, the couplant (ultrasonic transmission gel) uniformity, variability in the pressure applied to hold the transducers, alignment of the transmitting and recieving transducers, accuracy and modelling of Poisson&rsquo / s ratio make the ultrasonic testing more complicated.