Dissertations / Theses on the topic 'Dynamic elastic modulus'

The movement and control of the vocal folds within the laryngeal cavity enables three crucial physiological functions: 1) allowing respiration by opening, 2) aiding in airway protection by closing, and 3) regulating sound production during phonation. Although treatment options have improved, many of the estimated 7.5 million individuals in the United States who are annually affected by voice-related disorders still face serious challenges related to dysphonia and dysphagia. The need for improved voice-disorder treatments has motivated the work presented in this dissertation which focuses on modeling and manufacturing the vocal folds and aims to answer three main questions: 1) what are the mechanical properties of the vocal folds and how do they change across the full vocal range? 2) how do those properties influence the dynamic behavior of the tissue? and 3) can we manufacture a synthetic vocal fold model that exhibits a desired and controllable dynamic behavior? First, the elastic properties of sixteen porcine vocal folds were evaluated through uniaxial tensile tests on a custom built experimental setup. Stress-strain data was analyzed using an optimization method to yield continuous model parameters which described the linear and nonlinear elastic regions as well as transition points between those regions. Next, the impact of the vocal fold elastic properties on the frequencies of vibration was evaluated through dynamic tests on excised porcine larynges. Sound data was analyzed via a spectrogram and through the use of fast Fourier transforms to study changes in the frequency of vibration while the vocal folds were stretched. Additionally, a mathematical aeroelastic model of phonation was implemented to further evaluate the changing elastic properties on vocal fold dynamics. Next, eight synthetic vocal fold models were created, each with varying mechanical properties and a geometry based on reported anatomical measurements of porcine vocal folds. The synthetic models were then dynamically tested to further study the impact of changes in mechanical properties on the dynamic behavior of the synthetic vocal folds.
Doctor of Philosophy
The movement and control of the vocal folds within the voice-box enables three crucial physiological functions: 1) allowing respiration by opening, 2) aiding in airway protection and swallowing by closing, and 3) regulating sound production during vocalization. Although treatment options have improved, many of the estimated 7.5 million individuals in the United States who are annually affected by voice-related disorders still face serious challenges related to speech production and swallowing which often results in significant detrimental impacts to quality of life. The need for improved treatments is most easily observed in the evaluation of treatment options following a total laryngectomy, which is a procedure where the entire voice-box is removed often due to cancer. Following a laryngectomy, all three of the vital functions of the vocal folds are immediately impacted as patients adjust to breathing through and protecting a redirected airway and are forced to use alternative methods of speech production which often result in monotone or robotic-sounding speech. The need for improved voice-disorder treatments has motivated the work presented in this dissertation which focuses on modeling and manufacturing the vocal folds and aims to answer three main questions: 1) what are the mechanical properties of the vocal folds? 2) how do those properties influence the dynamic behavior of the tissue during sound production? and 3) can we manufacture synthetic vocal folds that produce a desired and controllable dynamic behavior? Sixteen porcine vocal fold samples were mechanical tested to evaluate the elastic properties of the tissue. Next, porcine voice-box samples were experimentally tested in a way that simulated sound production by subjecting the samples to a heated and humidified air flow, similar to the air flow conditions coming out of the lungs. In this way, the relationship between the tissue properties and the frequencies of sound was investigated. Lastly, the synthetic vocal fold samples were evaluated using a similar experimental protocol to further investigate the impact of changing structural properties on the dynamics of the vocal folds during sound production.

Environment conditions and moisture presence in masonry structures may affect durability or even mechanical properties of architectural heritage. Among all the deterioration causes, the degradation of historic masonry by freeze-thaw cycles and different moisture amount are considered to evaluate their influence on elastic properties. Therefore, two experimental campaigns were carried out in the present study. The first one was performed at the Dept. of Geotechincal Engineering at Tongji University, to assess the influence of freeze-thaw cycles on elastic modulus of historic Chinese brick. The static elastic modulus was evaluated from the compressive strength test on masonry specimens subjected to different numbers of freeze-thaw cycles. Moreover, strength decay of the masonry was investigated, also analysing data obtained during ultrasonic test (UPV, non-destructive test). The aim of this step was to obtain the dynamic elastic modulus. Thanks to interpolation of the obtained data it was possible to improve the knowledge of the Elasticity modulus’ reduction of historic masonry subjected to freeze-thaw cycles. The second experimental campaign was performed at DICAM, University of Bologna, on ancient Chinese and Italian bricks, to assess the sensitivity of dynamic elastic modulus to moisture amount. In particular the influence of water presence in the material pores on the UPV measurements. The close relationship between the ultrasonic pulse velocity and the moisture content was investigated on brick cores in dry, 50% saturated and saturated conditions. Practical value and one of the main contribution of the experiments was the investigation of external factor and intrinsic properties of porous materials which directly influence the ultrasonic pulse velocity test.

Free-layer hard or soft coating material can be used for enhancing the inherent damping capacity (energy dissipation ability) of a structure under cyclic bending deformation. This may help to attenuate the vibration amplitude at the resonance frequency. In this study, dynamic mechanical and damping properties of a carbon based (CNx) coating material have been investigated. For determining the material properties of this coating, two samples (600 μm and 800 μm thick carbon nitride (CNx) film layers) were produced and deposited onto two internal turning tools by using the plasma enhanced chemical vapor deposition (PECVD) process. The deposition process was conducted at the room temperature with the magnetron sputtering of a copper and a subsequent graphite target plate in a highly ionized plasma and reactive environment of Ar, N2 and C2H2 gases. Eigen frequencies and system loss factors of the uncoated and coated tools were extracted, for the first two fundamental bending modes (mode X and mode Y), from the ‘drive point’ measurements of free hanging impact tests at the free-free boundary condition. Modulus of elasticity and loss factor of the coating material has been deduced through the comparison between the eigen frequencies and resonance amplitudes of the identical bending modes extracted from the experimental and analytical frequency response functions. The results obtained from the experimental modal analyses and the iterative finite element analyses show that, compared to the substrate, the flexural stiffness and the damping capacity of the coated tools have increased notably. The resonant frequencies of the coated samples have been shifted to the higher frequency levels, and the frequency response acceleration amplitudes have been attenuated dramatically. Elastic modulus and loss factor range of the coating material have been found to be in the range of 32.5 GPa to 49.1 GPa and 0.004 to 0.0245 respectively. Comparison between the analytical frequency response functions of the CNx coating material and 3M-112 viscoelastic material coated samples (for 800 μm film thickness) has anticipated that the coating material has higher loss modulus (energy dissipation ability) as opposed to the viscoelastic material. Scanning electron microscope images of the cross-section of a coated sample have revealed that the frictional energy losses between the interfaces of the carbon-nitride columnar micro-structures dominate the inherent damping mechanism of the coating material. Voids and porosities, present between the columnar clusters, further increase the energy dissipation ability of the coating material by enhancing the interface slippage mechanism during the cyclic bending deformation.

Moisture-induced damage is one the major causes of deterioration of asphalt pavements and extensive research has been conducted on this topic. Theoretical and experimental results have led the researchers to believe that moisture-induced damages are caused mainly by the generation of pore water pressure in asphalt mixtures when traffic passes over a pavement. The Moisture Induced Sensitivity Tester (MIST) has been recently developed to simulate the phenomenon of repeated pore pressure generation and deterioration in the laboratory. The objective of this study was to evaluate moisture-induced damage in typical Maine Department of Transportation (DOT) asphalt mixes, with the use of MIST, pre and post testing, and analysis of data. The MIST was used to condition Hot Mix Asphalt (HMA) samples that were compacted from eight typical Maine DOT mixes, with different types of aggregates and asphalt binder. A modified Dynamic modulus test in Indirect Tensile Mode was used for the determination of damage. A layered elastic model, along with a fatigue-cracking criterion, was utilized to assess the total impact on the pavement lives. Monte Carlo analysis was conducted to determine the distribution of number of repetitions to failure of pavements that are subjected to moisture damage. The major conclusions are that most of the mixes are likely to experience a reduction in their life due to the effect of moisture and that the Micro-Deval and the fine aggregate absorption test results can be related to such damage. A composite factor, consisting of both of these test results, is recommended for regular use by the DOT to screen mixes with high moisture damage potential.

Ultrasonic Pulse Velocity (UPV) and Rebound test as non-destructive techniques may effectively contribute to in situ analysis of bricks and masonries elements for the restoration, rehabilitation and strengthening of historic buildings. Fired-clay bricks were commonly used in buildings in ancient China, but there is few knowledge on their behaviour in environmental conditions. Moisture is one of the main factors that cause deterioration in historic building, in particular in areas with natural freeze-thaw cycles. In this work, two laboratory experiments were carried out, at Tongji University, China, and DICAM Department of Bologna University, Italy, respectively. Fired-clay bricks about 200 years old were collected from demolished buildings in Changzhi City in Shanxi Province, belonging to the Yellow River Region, where the climate involves natural freeze-thaw cycles. The aim was to evaluate how the frost damage changes the physical and mechanical properties of Chinese historical bricks and masonries. Several non-destructive methods were used, focusing on the effectiveness of Ultrasonic Pulse Velocity (UPV) for evaluating physical and mechanical properties of Chinese historic grey bricks and masonries. Destructive tests were also used to evaluate compressive strength and static elastic modulus. The samples showed a reduction of their properties due to freeze-thaw cycles. The presence of water affected the values of the analysed parameters, leading to a decrease of UPV. The trend determined by these methods can be used to assess the uniformity of bricks and to detect areas of poor quality or deteriorated masonry structures.

This work solves creation of calibration relations to determine cube compressive strength, dynamic and static elastic modulus of alkali-activated concrete by non-destructive methods. Alkali-activated concrete is spoken of as a new material used in civil engineering. It shows different properties than normal concrete based on Portland cement. That's why the modification of common calibration relation seems necessary. Fresh concrete was made in the concrete plan ŽPSV a.s., Uherský Ostroh in three mixtures and always in the number of 18 cubes and 3 prisms. The samples were tested by impact hammer Schmidt type L, type N, SilverSchmidt PC-N and by ultrasound in 6 time periods of three specimens. After that, the cube compressive strength was determined. Status of static elastic modulus was determined in a time period of 28 days. The results are calibration relations to determine the progress of compressive strength and modulus of elasticity for each method and their combination.

Este trabalho apresenta dois tipos de ensaios não destrutivos para a correlação do módulo dinâmico com a resistência à compressão para elementos de concreto. Os métodos de ensaio são a ultrassonografia e o método de excitação por impulso utilizando o equipamento Sonelastic®. Neste trabalho estão descritos seus funcionamentos, aplicações e limitações. A ultrassonografia, através da propagação de ondas sonoras, fornece, indiretamente, o módulo de elasticidade dinâmico. Com o método de excitação por impulso obtêm-se as frequências naturais e os modos de vibração do elemento estudado, o que permite determinar seu módulo dinâmico. Primeiramente, estes ensaios foram utilizados em corpos-de-prova cilíndricos e lajes alveolares produzidas em laboratório para a obtenção das curvas de correlação e, em seguida, estes mesmos ensaios foram realizados na fábrica de concreto pré-moldado. Para elementos de geometria complexa, como é o caso das lajes alveolares, apresenta-se uma metodologia para a obtenção de uma equação analítica para o cálculo do módulo dinâmico no ensaio de excitação por impulso. Estes métodos tiveram o objetivo final de avaliar a resistência à compressão do concreto na pista de protensão da fábrica, e então determinar o melhor momento para a desforma e corte do cabo de protensão. Com ambos os métodos, obteve-se ótimas correlações do módulo dinâmico com a resistência à compressão dos elementos em laboratório. Na fábrica de concreto pré-moldado não foi possível obter uma curva de correlação representativa de toda a laje na pista de protensão, porém foi possível registrar um bom indicativo de que é possível obter boas correlações para futuras pesquisas no assunto
This work presents two types of non-destructive testing for the correlation of the dynamic elastic modulus with the compressive strength. The test methods are the ultrasonography and the impulse excitation using the Sonelastic® equipment. In this work the equipaments operations, applications and limitations are also described. The ultrasound test indirectly supplies the dynamic elastic modulus through the propagation of sound waves. The natural frequencies and the vibration modes of the studied elements are obtained through impulse excitation method allowing to determine its dynamic modulus. To start, these tests were used in cylindrical specimens and hollow core slabs produced in the laboratory to obtain the correlation curves, and then these same methods were performed in the pre-cast concrete plant. As for complex geometric elements, as in the case of hollow core slabs, a methodology is applied in order to obtain an analytic equation to calculate the dynamic modulus in the impulse excitation test. These methods had the final goal the evaluation of the strength of prestressed concrete lying on track of the plant, so as to determine the best moment to demold and cut the prestressed cable. Excellent correlations of the dynamic modulus with compressive strength of the elements made in laboratory were obtained using both methods. It was not possible to obtain in the precast concrete plant a representative correlation curve of the whole slab on the track, nevertheless, it was possible to record a good indication that it is possible to obtain good correlations for future research.

Předložená magisterská práce se zabývá možným použitím vitrifikovaného lignitového lóžového popele jako náhrada slinku v kompozitních cementech. Byly zkoumány vlivy přidaného vitrifikovaného lóžového popele, jeho jemnosti, alkalických roztoků a jejich koncentrací. Byly připraveny kompozitní cementy v souladu s normou DIN EN 197 – 1. V těchto cementech bylo nahrazeno 30 % slinku vitrifikovaným lóžovým popelem. Konkrétně byly připraveny kompozitní cementy s vitrifikovaným lóžovým popelem o jemnosti 5549 cm2/g a 8397 cm2/g. Dále byly přidány alkalické roztoky hydroxidů a síranů vždy o dvou různých koncentracích, za účelem stimulace pucolánové a/nebo geopolymerní reakce. Mechanické vlastnosti připravených vzorků byly charakterizovány mechanickým testováním na prizmách s rozměry 40×40×160 mm, jak je specifikováno v normě DIN EN 196 – 1. Byla provedena nedestruktivní měření dynamického elastického modulu a destruktivní testovaní na pevnosti v tlaku a v ohybu. Distribuce velikosti částic a chemická analýza vstupních materiálů byla vykonána pomocí laserové granulometrie a rentgenové fluorescence. U zatvrdlých kompozitů bylo dále zkoumáno po 2 a 28 dnech hydratace fázové složení s využitím metody rentgenové difrakce a mikrostruktura s využitím skenovací elektronové mikroskopie. Výsledky ukázaly, že mechanické vlastnosti jsou nezávislé na množství přidaných alkálií stejně jako na jemnosti přidaného vitrifikovaného lóžového popele. Nicméně, znatelně nižší mechanické pevnosti byly pozorovány pro vzorky, které byly aktivovány hydroxidy, pravděpodobně kvůli brzké tvorbě silikátového hydrogelu. Vzorky aktivované sírany nedosáhly pevností jako referenční malta.

Collagen type I is an extracellular matrix (ECM) protein that affords tensile strength and biological scaffolding to numerous vertebrate and invertebrate tissues. This strength has been attributed to the triple-helical structure of the collagen type I molecules, their organization into fibrils, and the presence of inter-molecular, covalent, enzymatic crosslinks. There are several different types of these crosslinks; their composition is tissue-specific and dependent upon factors such as age and health. Furthermore, these enzymatic crosslinks tend to form specifically at amino/N- and carboxy/C-terminal crosslinking sites. The mechanical behavior of collagen type I has been investigated, via experiment and theory, at the level of the molecule, microfibril, fibril, and fiber. However, the influence of different enzymatic crosslinks and their location (e.g., N- vs. C-site) on the mechanics of collagen type I has not been investigated in the literature.

We employed molecular dynamics to model the mechanical behavior of uncrosslinked and crosslinked ~23-nm-long molecular segments and ~65-nm-long microfibril units of collagen type I. We then used these molecular simulations to construct a model of a single collagen type I fibril by considering the ~65-nm-long microfibril units arranged in series and then in parallel.

When a uniaxial deformation was applied along the long axis of the molecular models, N-crosslinks aligned rapidly at lower strains followed by C-crosslinks more gradually at higher strains, leading to a two-stage crosslink recruitment. Then when comparing the influence of different enzymatic crosslinks, significant differences were observed for the high-strain elastic moduli of our microfibril unit models, namely and in increasing order, uncrosslinked, immature crosslinked (HLKNL and deH-HLNL), mature HHL-crosslinked, and mature PYD-crosslinked. At the fibril level, our low- and high-strain elastic moduli were in good agreement with some literature data, but in over-estimation of several other literature reports. Future work will seek to address simplifications and limitations in our modeling approach. A model such as this, accounting for different enzymatic crosslink types, may allow for the prediction of the mechanics of collagen fibrils and collagenous tissues, in representation of healthy and diseased states.
Ph. D.

[EN] The test for determining the resonance frequencies has traditionally been used to investigate the mechanical integrity of concrete cores, to assess the conformity of concrete constituents in different accelerated durability tests, and to ascertain constitutive properties such as the elastic modulus and the damping factor. This nondestructive technique has been quite appealed for evaluation of mechanical properties in all kinds of durability tests. The damage evolution is commonly assessed from the reduction of dynamic modulus which is produced as a result of any cracking process. However, the mechanical behavior of concrete is intrinsically nonlinear and hysteretic. As a result of a hysteretic stress-strain behavior, the elastic modulus is a function of the strain. In dynamic tests, the nonlinearity of the material is manifested by a decrease of the resonance frequencies, which is inversely proportional to the excitation amplitude. This phenomenon is commonly referred as fast dynamic effect. Once the dynamic excitation ceases, the material undergoes a relaxation process whereby the elastic modulus is restored to that at rest. This phenomenon is termed as slow dynamics. These phenomena (fast and slow dynamics) find their origin in the internal friction of the material. Therefore, in cement-based materials, the presence of microcracks and interfaces between its constituents plays an important role in the material nonlinearity. In the context of the assessment of concrete durability, the damage evolution is based on the increase of hysteresis, as a result of any cracking process. In this thesis three different nondestructive techniques are investigated, which use impacts for exciting the resonant frequencies. The first technique consists in determining the resonance frequencies over a range of impact forces. The technique is termed Nonlinear Impact Resonant Acoustic Spectroscopy (NIRAS). It consists in ascertaining the downward resonant frequency shift that the material undergoes upon increasing excitation amplitude. The second technique consists in investigating the nonlinear behavior by analyzing the signal corresponding to a single impact. This is, to determine the instantaneous frequency, amplitude and attenuation variations corresponding to a single impact event. This technique is termed as Nonlinear Resonant Acoustic Single Impact Spectroscopy (NSIRAS). Two techniques are proposed to extract the nonlinear behavior by analyzing the instantaneous frequency variations and attenuation over the signal ring down. The first technique consists in discretizing the frequency variation with time through a Short-Time Fourier Transform (STFT) based analysis. The second technique consists of a least-squares fit of the vibration signals to a model that considers the frequency and attenuation variations over time. The third technique used in this thesis can be used for on-site evaluation of structures. The technique is based on the Dynamic Acousto- Elastic Test (DAET). The variations of elastic modulus as derived through NIRAS and NSIRAS techniques provide an average behavior and do not allow derivation of the elastic modulus variations over one vibration cycle. Currently, DAET technique is the only one capable to investigate the entire range of nonlinear phenomena in the material. Moreover, unlike other DAET approaches, this study uses a continuous wave source as probe. The use of a continuous wave allows investigation of the relative variations of the elastic modulus, as produced by an impact. Moreover, the experimental configuration allows one-sided inspection.
[ES] El ensayo de determinación de las frecuencias de resonancia ha sido tradicionalmente empleado para determinar la integridad mecánica de testigos de hormigón, en la evaluación de la conformidad de mezclas de hormigón en diversos ensayos de durabilidad, y en la terminación de propiedades constitutivas como son el módulo elástico y el factor de amortiguamiento. Esta técnica no destructiva ha sido ampliamente apelada para la evaluación de las propiedades mecánicas en todo tipo de ensayos de durabilidad. La evolución del daño es comúnmente evaluada a partir de la reducción del módulo dinámico, producido como resultado de cualquier proceso de fisuración. Sin embargo, el comportamiento mecánico del hormigón es intrínsecamente no lineal y presenta histéresis. Como resultado de un comportamiento tensión-deformación con histéresis, el módulo elástico depende de la deformación. En ensayos dinámicos, la no linealidad del material se manifiesta por una disminución de las frecuencias de resonancia, la cual es inversamente proporcional a la amplitud de excitación. Este fenómeno es normalmente denominado como dinámica rápida. Una vez la excitación cesa, el material experimenta un proceso de relajación por el cual, el módulo elástico es restaurado a aquel en situación de reposo. Este fenómeno es denominado como dinámica lenta. Estos fenómenos ¿dinámicas rápida y lenta¿ encuentran su origen en la fricción interna del material. Por tanto, en materiales basados en cemento, la presencia de microfisuras y las interfaces entre sus constituyentes juegan un rol importante en la no linealidad mecánica del material. En el contexto de evaluación de la durabilidad del hormigón, la evolución del daño está basada en el incremento de histéresis, como resultado de cualquier proceso de fisuración. En esta tesis se investigan tres técnicas diferentes las cuales utilizan el impacto como medio de excitación de las frecuencias de resonancia. La primera técnica consiste en determinar las frecuencias de resonancia a diferentes energías de impacto. La técnica es denominada en inglés: Nonlinear Impact Resonant Acoustic Spectroscopy (NIRAS). Ésta consiste en relacionar el detrimento que el material experimenta en sus frecuencias de resonancia, con el aumento de la amplitud de la excitación. La segunda técnica consiste en investigar el comportamiento no lineal mediante el análisis de la señal correspondiente a un solo impacto. Ésta consiste en determinar las propiedades instantáneas de frecuencia, atenuación y amplitud. Esta técnica se denomina, en inglés, Nonlinear Single Impact Resonant Acoustic Spectroscopy (NSIRAS). Se proponen dos técnicas de extracción del comportamiento no lineal mediante el análisis de las variaciones instantáneas de frecuencia y atenuación. La primera técnica consiste en la discretización de la variación de la frecuencia con el tiempo, mediante un análisis basado en Short-Time Fourier Transform (STFT). La segunda técnica consiste en un ajuste por mínimos cuadrados de las señales de vibración a un modelo que considera las variaciones de frecuencia y atenuación con el tiempo. La tercera técnica empleada en esta tesis puede ser empleada para la evaluación de estructuras in situ. La técnica se trata de un ensayo acusto-elástico en régimen dinámico. En inglés Dynamic Acousto-Elastic Test (DAET). Las variaciones del módulo elástico obtenidas mediante los métodos NIRAS y NSIRAS proporcionan un comportamiento promedio y no permiten derivar las variaciones del módulo elástico en un solo ciclo de vibración. Actualmente, la técnica DAET es la única que permite investigar todo el rango de fenómenos no lineales en el material. Por otra parte, a diferencia de otras técnicas DAET, en este estudio se emplea como contraste una onda continua. El uso de una onda continua permite investigar las variaciones relativas del módulo elástico, para una señal transito
[CAT] L'assaig de determinació de les freqüències de ressonància ha sigut tradicionalment empleat per a determinar la integritat mecànica de testimonis de formigó, en l'avaluació de la conformitat de mescles de formigó en diversos assajos de durabilitat, i en la terminació de propietats constitutives com són el mòdul elàstic i el factor d'amortiment. Esta tècnica no destructiva ha sigut àmpliament apel·lada per a l'avaluació de les propietats mecàniques en tot tipus d'assajos de durabilitat. L'evolució del dany és comunament avaluada a partir de la reducció del mòdul dinàmic, produït com resultat de qualsevol procés de fisuración. No obstant això, el comportament mecànic del formigó és intrínsecament no lineal i presenta histèresi. Com resultat d'un comportament tensió-deformació amb histèresi, el mòdul elàstic depén de la deformació. En assajos dinàmics, la no linealitat del material es manifesta per una disminució de les freqüències de ressonància, la qual és inversament proporcional a l'amplitud d'excitació. Este fenomen és normalment denominat com a dinàmica ràpida. Una vegada l'excitació cessa, el material experimenta un procés de relaxació pel qual, el mòdul elàstic és restaurat a aquell en situació de repòs. Este fenomen és denominat com a dinàmica lenta. Estos fenòmens --dinámicas ràpida i lenta troben el seu origen en la fricció interna del material. Per tant, en materials basats en ciment, la presència de microfissures i les interfícies entre els seus constituents juguen un rol important en la no linealitat mecànica del material. En el context d'avaluació de la durabilitat del formigó, l'evolució del dany està basada en l'increment d'histèresi, com resultat de qualsevol procés de fisuración. En esta tesi s'investiguen tres tècniques diferents les quals utilitzen l'impacte com a mitjà d'excitació de les freqüències de ressonància. La primera tècnica consistix a determinar les freqüències de ressonància a diferents energies d'impacte. La tècnica és denominada en anglés: Nonlinear Impact Resonant Acoustic Spectroscopy (NIRAS). Esta consistix a relacionar el detriment que el material experimenta en les seues freqüències de ressonància, amb l'augment de l'amplitud de l'excitació. La segona tècnica consistix a investigar el comportament no lineal per mitjà de l'anàlisi del senyal corresponent a un sol impacte. Esta consistix a determinar les propietats instantànies de freqüència, atenuació i amplitud. Esta tècnica es denomina, en anglés, Nonlinear Single Impact Resonant Acoustic Spectroscopy (NSIRAS). Es proposen dos tècniques d'extracció del comportament no lineal per mitjà de l'anàlisi de les variacions instantànies de freqüència i atenuació. La primera tècnica consistix en la discretización de la variació de la freqüència amb el temps, per mitjà d'una anàlisi basat en Short-Time Fourier Transform (STFT). La segona tècnica consistix en un ajust per mínims quadrats dels senyals de vibració a un model que considera les variacions de freqüència i atenuació amb el temps. La tercera tècnica empleada en esta tesi pot ser empleada per a l'avaluació d'estructures in situ. La tècnica es tracta d'un assaig acusto-elástico en règim dinàmic. En anglés Dynamic Acousto-Elastic Test (DAET). Les variacions del mòdul elàstic obtingudes per mitjà dels mètodes NIRAS i NSIRAS proporcionen un comportament mitjà i no permeten derivar les variacions del mòdul elàstic en un sol cicle de vibració. Actualment, la tècnica DAET és l'única que permet investigar tot el rang de fenòmens no lineals en el material. D'altra banda, a diferència d'altres tècniques DAET, en este estudi s'empra com contrast una ona contínua. L'ús d'una ona contínua permet investigar les variacions relatives del mòdul elàstic, per a un senyal transitori. A més, permet la inspecció d'elements per mitjà de l'accés per una sola cara.
Eiras Fernández, JN. (2016). Studies on nonlinear mechanical wave behavior to characterize cement based materials and its durability [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/71439
TESIS
Premiado

Il est bien établi que les propriétés mécaniques et rhéologiques d'une large classe de matériaux vitreux amorphes met en jeu - contrairement aux dislocations dans les cristaux - des rearrangements structuraux localisés formant par un processus de cascade des bandes de cisaillements. Cette localisation de la déformation est observée dans divers systèmes vitreux ainsi que dans des simulations numériques. Cette réponse mécanique complexe reste mal comprise à une échelle microscopique et il n'est pas clair si l'écoulement plastique peut être associé à une origine structurale locale ou à des processus purement dynamiques.Dans cette thèse nous envisageons ces problématiques à l'aide de simulations atomiques athermales sur un système Lennard-Jones modèle. Nous calculons le tenseur élastique moyenné localement sur une échelle nanométrique. A cette échelle, le verre est assimilable à un matériau composite comprenant un échafaudage rigide et des zones fragiles. L'étude détaillée de la déformation plastique à différents taux de cisaillement met en évidence divers régimes d'écoulement. En dessous d'un taux de cisaillement critique dépendant de la taille du système, la réponse mécanique atteind une limite quasistatique (effets de taille fini, cascades d'événements plastiques, contrainte seuil) alors que pour des taux de cisaillement plus importants les propriétés rhéologiques sont fixées par le taux de cisaillement imposé. Dans ce régime nous mettons en évidence la croissance d'une longueur de coopérativité dynamique et discutons de sa dépendance avec le taux de cisaillements.

O módulo de elasticidade do concreto é uma propriedade muito importante para o projeto estrutural. Apesar do comportamento tensão-deformação não linear do concreto, uma estimativa adequada desta propriedade é fundamental para a análise estrutural, avaliação de efeitos de segunda ordem e verificações de deslocamentos. Em especial, o módulo de elasticidade dinâmico é uma propriedade muito importante na análise de vibrações excessivas. Todavia, sua determinação é tipicamente feita a partir do módulo de elasticidade estático. Os códigos normativos usualmente apresentam equações para estimativas do módulo de elasticidade estático a partir da resistência do concreto à compressão, densidade e tipo de agregado utilizado. Logo, outra limitação de tais estimativas é a não consideração de características da zona de transição além do tipo, fração volumétrica e dimensão dos agregados empregados na mistura. Por outro lado, a teoria dos materiais compósitos multifásicos permitiu, nos últimos tempos, o avanço dos modelos de previsão das propriedades do material. Portanto, o entendimento isolado do comportamento da pasta, areia, brita, argamassa e zona de transição é importante para a previsão do comportamento do compósito concreto. Desta forma, utilizou-se do ensaio acústico para a caracterização de variadas dosagens de pasta, argamassa, rocha e concreto. Assim, foi possível investigar a correlação entre as propriedades dinâmicas do compósito concreto e sua microestrutura. Variações de parâmetros como o fator água-cimento, maturidade, presença de superplastificante e tipo de agregado graúdo utilizado na mistura impuseram variados padrões microestruturais, e estes foram avaliados frente às propriedades dinâmicas do material, em especial, ao módulo de elasticidade dinâmico. Também foi possível a constatação da interdependência microestrutural entre o módulo de elasticidade dinâmico, módulo de cisalhamento e coeficiente de amortecimento. Já o coeficiente de Poisson apresentou pouca correlação com as outras propriedades supracitadas. Finalmente fez-se a inferência sobre a precisão das estimativas para módulo de elasticidade dinâmico através das equações empíricas contidas em normas e dos modelos teóricos obtidos via formulação para materiais bifásicos. Uma curva que correlaciona o módulo de elasticidade dinâmico e estático foi proposta para a maturidade referente aos 28 dias.
The modulus of elasticity of concrete is a very important property for structural design. Despite the nonlinear stress-strain behavior of concrete, an appropriate estimate of this property is essential for structural analysis, evaluation of second-order effects and excessive deflexions. In particular, the dynamic modulus of elasticity is an important property in analysis of excessive vibration. However, this value is often estimated from the static modulus. Design codes usually contain equations estimating the static modulus based on compressive strength of concrete, density and type of aggregate used. Another limitation of such estimates is neglecting the characteristics of the transition zone, and the type, size and volume fraction of the aggregates used in the mixture. On the other hand, the theory of multiphase composites materials has allowed in recent times, advances of predictive models of material properties. Therefore, the isolated understanding of paste behavior, sand, gravel, mortar and transition zone is important for predicting concrete composite behavior. In this way, the acoustic test it was utilized for characterization of the various mixes of the paste, mortar, rock and concrete. Thus, it was possible to investigate the correlation between the dynamic properties of the composite concrete and its microstructure. Variations in parameters such as the water-cement ratio, maturity, presence of superplasticizer and type of coarse aggregate used in the mix, imposed various microstructural patterns, and these were evaluated face to the material dynamic properties, in particular to the dynamic modulus of elasticity. Detected a microstructural interdependence between the dynamic modulus of elasticity, shear modulus and damping coefficient It was also. On the other hand, the Poisson ratio, presented low correlation with the other properties mentioned. Finally an inference about the accuracy of estimates for dynamic modulus of elasticity through empirical equations contained in standards and theoretical models obtained by the formulation for biphasic materials was made. A curve that correlates the dynamic and static modulus of elasticity was proposed for the age of 28 days.

A radiação ionizante de fontes de radiação gama ou geradores de raios-x é frequentemente utilizada na ciência médica, como em exames de radiodiagnóstico, radioterapia e esterilização de aloenxertos. A radiação ionizante é capaz de quebrar cadeias polipeptidicas e provocar a libertação de radicais livres, pela radiólise de moléculas de água. A radiação ionizante interage também com o material orgânico a nível molecular, podendo alterar as suas propriedades mecânicas. No caso específico do tecido ósseo, estudos reportam que a radiação ionizante induz alterações nas moléculas de colágeno e reduzem a densidade de ligações cruzadas intermoleculares. O objetivo deste estudo foi verificar as alterações promovidas por diferentes doses de radiação ionizante no tecido ósseo utilizando a técnica de Espectroscopia Transformada de Fourier com Reflexão Total Atenuada (ATR-FTIR), e também a análise dinâmico-mecânica. Amostras de osso bovino foram irradiadas usando irradiador de Cobalto-60, com cinco doses diferentes: 0,01 kGy, 0,1 kGy, 1 kGy, 15 kGy e 75 kGy. Para estudar os efeitos da radiação ionizante sobre a estrutura química do osso foram avaliadas a relação material orgânico por material inorgânico, a relação de sub-bandas de amida I e o índice de cristalinidade. As alterações mecânicas foram determinadas por meio do módulo de elasticidade e do valor do amortecimento. Para verificar se as mudanças químicas e as características mecânicas de osso possuem alguma relação, realizou-se um estudo sobre a correlação entre as análises feitas com os dados espectroscópicos e as análises mecânicas. Foi possível avaliar os efeitos de diferentes doses de radiação ionizante no tecido ósseo. Com a análise por espectroscopia ATR-FTIR, foi possível observar as modificações dos componentes orgânicos e na organização cristais de hidroxiapatita. Também foram observadas alterações no módulo elástico e na tangente de delta (dissipação de energia mecânica). Foram encontradas altas correlações com significância estatística entre a relação das bandas (amida III + colágeno)/v1,v3, PO43- com a tangente de delta, e entre a relação 1/FHMW e o módulo elástico.
Ionizing radiation from gamma radiation sources or X-ray generators is frequently used in Medical Science, such as radiodiagnostic exams, radiotherapy, and sterilization of haloenxerts. Ionizing radiation is capable of breaking polypeptidic chains and causing the release of free radicals by radiolisys.of water. It interacts also with organic material at the molecular level, and it may change its mechanical properties. In the specific case of bone tissue, studies report that ionizing radiation induces changes in collagen molecules and reduces the density of intermolecular crosslinks. The aim of this study was to verify the changes promoted by different doses of ionizing radiation in bone tissue using Fourier Transform Infrared Spectroscopy (FTIR) and dynamic mechanical analysis (DMA). Samples of bovine bone were irradiated using Cobalt-60 with five different doses: 0.01 kGy, 0.1 kGy, 1 kGy, 15 kGy and 75 kGy. To study the effects of ionizing irradiation on the chemical structure of the bone, the sub-bands of amide I, the crystallinity index and relation of organic and inorganic materials, were studied. The mechanical changes were evaluated using the elastic modulus and the damping value. To verify whether the chemical changes and the mechanical characteristics of the bone were correlated, the relation between the analysis made with spectroscopic data and the mechanical analysis data was studied. It was possible to evaluate the effects of different doses of ionizing radiation in bone tissue. With ATR-FTIR spectroscopy, it was possible to observe changes in the organic components and in the hidroxyapatite crystals organization. Changes were also observed in the elastic modulus and in the damping value. High correlation with statistical significance was observed among (amide III + collagen)/v1,v3, PO43- and the delta tangent, and among 1/FHWM and the elastic modulus.

Pour les roches saturées, la comparaison entre les mesures ultrasoniques (1 MHz) au laboratoire et les mesures sismiques (100 Hz) ou de diagraphie (10 kHz) sur le terrain n’est pas directe à cause de la dispersion des vitesses des ondes. Les mécanismes impliqués dans la dépendance en fréquence sont les écoulements de fluides à différentes échelles provoqués par le passage de l’onde. La dispersion et l’atténuation des modules élastiques de roches carbonatées ont été étudiées expérimentalement. Les calcaires étudiés sont : un Lavoux, un Indiana intact et craqué thermiquement, un calcaire Urgonien de Provence (Rustrel), et un coquina pré-sel du Congo. Les mesures ont été faites sur une large gamme de fréquence, en combinant les techniques d’oscillations forcées (10-3 to 102 Hz) et ultrasoniques (1 MHz) dans une presse triaxiale, pour différentes pressions effectives. Le forçage peut être hydrostatique pour mesurer un module d’incompressibilité, ou axial pour mesurer le module de Young et le coefficient de Poisson. Pour étudier l’effet de la viscosité, les mesures ont été faites en condition sèche, puis saturée en glycérine et en eau. Le drainage global et le mécanisme d’écoulement crack-pore ont été caractérisés, en termes d’amplitude de dispersion, d’atténuation viscoélastique, et de fréquence de coupure. Pour nos échantillons, la théorie de Biot-Gassmann s’est montrée valide pour les fréquences sismiques (10-100 Hz) sauf pour l’Indiana craqué thermiquement. La dispersion liée à des écoulements crackspores a été observée pour tous les échantillons sauf le Lavoux. Les fréquences de coupures de ceux-ci sont toutes dans la gamme des fréquences des diagraphies (10 kHz) pour des conditions de saturation en eau. Un modèle simple, combinant poroélasticité et milieux effectifs, a été développé pour prédire la dispersion des modules sur toute la gamme de fréquence, et s’est montré généralement en accord avec les résultats expérimentaux
For fluid-saturated rocks, comparing ultrasonic measurements (1 MHz) in the laboratory and seismic (100 Hz) or logging (10 kHz) measurements in the field is not straightforward due to dispersion of the bodywave velocities. The frequency-dependent mechanisms involved are wave-induced fluid flows that occur at different scales. The dispersion and the attenuation of the elastic moduli of four fluid-saturated carbonate rocks have been studied experimentally. The selected limestones were a Lavoux, an intact and thermally cracked Indiana, a Urgonian limestone from Provence (Rustrel), and a presalt coquina from offshore Congo. Measurements were done over a large frequency range, by the combination of forced oscillations (10-3 to 102 Hz) and ultrasonic measurements (1 MHz) in a triaxial cell, at various effective pressures. The forced oscillations were either hydrostatic to deduce the bulk modulus, or axial to deduce Young’s modulus and Poisson’s ratio. The measurements were done in dry-, glycerinand water-saturated conditions to investigate the effect of viscosity. For all our samples, the global drainage and the squirt-flow mechanisms were characterized experimentally, in terms of amplitude of dispersion, amount of viscoelastic attenuation, and cut-off frequencies. Biot- Gassmann’s theory was found to be valid at seismic frequencies (10-100 Hz) for all the samples except the thermally cracked Indiana. Squirt-flow transitions were observed for all the samples, except the Lavoux. The cut-off frequencies were all in the range of logging frequencies (10 kHz), for watersaturated conditions. A simple model, combining poroelasticity and the noninteraction approximation effective medium, was developed to predict the dispersion of the moduli over the whole frequency range, and was generally in agreement with the experimental results

Thesis (Ph. D.)--University of Alberta, 2010.
Title from pdf file main screen (viewed on Mar. 18, 2010). A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Geophysics, Department of Physics, University of Alberta. Includes bibliographical references.

碩士
國立高雄第一科技大學
營建工程研究所
101
The study conducts static and dynamic tests on soil-cement samples mixed by three levels of cement contents: 10%, 20% and 30%. Test results are used to identify the relevancy of mechanical properties. Dynamic testing follows a CNS 1239-A3052 method for determining longitudinal natural frequencies of ordinary concrete samples; excitation of soil-cement samples are introduced by small steel balls and waveforms recorded by accelerometer in time are analyzed by Fourier analysis to generate the dynamic modulus of elasticity. Static testing is based on ASTM D4832-02 method for determining the compressive strength of controlled low strength materials; extensometers are used to measure deformations, and the slope of load-deformation curves by linear regression produces the static modulus of elasticity. Test equipment need be examined in advance with standard samples. Dynamic test procedure is validated by examining the natural frequency of various steel bars having given modulus of elasticity and density. Static test procedure is validated by standard load cells and Vernier scale. The test results for all soil-cement samples indicate that dynamic test is more consistent and dynamic modulus of elasticity is higher than static modulus, with their difference reducing when cement ratios increase.

no
Low frequency (0.1¿2 Hz) dynamic mechanical analysis on individual type I collagen fibrils has been carried out using atomic force microscopy (AFM). Both the elastic (static) and viscous (dynamic) responses are correlated to the characteristic axial banding, gap and overlap regions. The elastic modulus (¿5 GPa) on the overlap region, where the density of tropocollagen is highest, is 160% that of the gap region. The amount of dissipation on each region is frequency dependent, with the gap region dissipating most energy at the lowest frequencies (0.1 Hz) and crossing over with the overlap region at ¿0.75 Hz. This may reflect an ability of collagen fibrils to absorb energy over a range of frequencies using more than one mechanism, which is suggested as an evolutionary driver for the mechanical role of type I collagen in connective tissues and organs.
BBSRC

For evaluation and quality control of concrete structures, the impact resonant frequency method is widely accepted for monitoring structure in-service properties and detecting structural damage. Common defects in concrete include consolidation problems during casting and development of micro-cracks during stages of hydration. Monitoring the dynamic characteristics of concrete plays an essential role in detecting real-time and early stages of deterioration. Ample research is focused on detecting large defects, however not much information is available on detection of minor defects of composites like fiber reinforced concrete. Change of elastic behavior when Polypropylene fibers are added as reinforcement is investigated. Destructive tests on structures in-service are not always feasible thus leaving non-destructive condition assessment as the only option. Amongst the various non-destructive tests available, vibrational tests provide a practical method to predict the dynamic moduli of structures (dynamic modulus of elasticity, dynamic modulus of rigidity and dynamic Poisson’s ratio). The objective of this research is to assess the dynamic elastic properties of Polypropylene Fiber Reinforced Concrete (PFRC) in correlation with induced cracks and common consolidation defects using a lab developed non-destructive testing method that relies on impulse excitation and stress wave propagation to measure changes in the resonant frequency when polypropylene fibers are added to concrete. In the experimental program, two fiber sizes, macro and micro, with various volume contents have been used for casting PFRC cylinders and prisms. Fundamental resonant frequencies were measured for all cylinders and prisms in the transverse and longitudinal directions. All measured frequencies are directly related to the low-strain dynamic modulus of elasticity. In addition, PFRC prisms were used to investigate the relationship between the dynamic modulus of elasticity and modulus of rigidity. Several batches of similar mixtures are used to investigate different parameters that affect the resonant frequency of concrete such as the water to cement ratio, curing condition and age. Results indicated a decrease in the resonant frequency and elastic properties with an increase of the fiber content or length. Micro fibers showed higher dynamic elastic moduli when compared to macro fibers of the same mixture under saturated curing conditions. Post-cracked PFRC cylinders and flexural fractured prisms retained some of the resonant frequency with macro fibers exhibiting better elastic recovery when cracked.
Graduate

No
Tunica adventitia, the outer layer of blood vessels, is an important structural feature, predominantly consisting of collagen fibrils. This study uses pseudostatic atomic force microscopy (AFM) nanoindentation at physiological conditions to show that the distribution of indentation modulus and viscous creep for the tunica adventitia of porcine aorta and pulmonary artery are distinct. Dynamic nanoindentation demonstrates that the viscous dissipation of the tunica adventitia of the aorta is greater than the pulmonary artery. We suggest that this mechanical property of the aortic adventitia is functionally advantageous due to the higher blood pressure within this vessel during the cardiac cycle. The effects on pulsatile deformation and dissipative energy losses are discussed.

碩士
國立東華大學
資訊工程學系
102
In recent years, mobile computing, mobile device applications, and cloud computing have drawn more and more attention. Offering quality mobile cloud services has become an important research topic. There are two common ways to provide mobile cloud services. One is to execute the services on a cloud center, and the other is to download APP programs from clouds to mobile devices and update data before executing services. Both methods face the problem of instability of wireless networks and topographical constraints. It causes intermittent services or even worse the need to wait and restart when a service is completely interrupted. Hardware limitations of mobile devices also impose problems. Therefore, how to integrate all available platforms and resources to provide seamless services is a major problem for mobile cloud computing. Early research of our lab have developed a highly elastic mobile cloud service framework which can dynamically determine the most efficient service configuration for allocating service components on cloud centers, base stations, client devices and peer devices. However, the best way to migrate service components and data between consecutive configurations is still left unexplored. In this thesis, we design a service migration architecture and migration algorithm to identify the migration targets and to find the best migration path. We compare the proposed method with traditional cloud migration under three simulated environments on migration time and download completion rate. Experimental results show that our method is much faster than traditional cloud migration. Cross parameters interaction analysis reveals that the performance is much more sensitive to user speed than data size and the number of service components.