Recent development of additive manufacturing technologies has led to lack of information on the base materials being used. A need arises to know the mechanical behaviors of these base materials so that it can be linked with macroscopic mechanical behaviors of 3D network structures manufactured from the 3D printer. The main objectives of my research are to characterize properties of a material for an additive manufacturing method (commonly referred to as 3D printing). Also, to model viscoelastic properties of Procast material that is obtained from 3D printer. For this purpose, a 3D CAD model is made using ProE and 3D printed using Projet HD3500. Series of uniaxial tensile tests, creep tests, and dynamic mechanical analysis are carried out to obtained viscoelastic behavior of Procast. Test data is fitted using various linear and nonlinear viscoelastic models. Validation of model is also carried out using tensile test data and frequency sweep data. Various other mechanical characterization have also been carried out in order to find density, melting temperature, glass transition temperature, and strain rate dependent elastic modulus of Procast material. It can be concluded that melting temperature of Procast material is around 337°C, the elastic modulus is around 0.7-0.8 GPa, and yield stress is around 16-19 MPa.

A public domain code "Object Oriented Finite element analysis for materials science" (OOF) has been extended to include tools for analysis of viscoelastic materials. Utility of these tools has been discussed along with possible applications in this publication. Added features in OOF include means to quantitatively analyze the spatiotemporal response of a composite polymeric material in dynamic as well as in static deformation conditions. These coupled with the existing features of OOF, in particular, the complete analysis of mechanical characteristics of materials provide a comprehensive tool for the studies of time dependent behavior of variety of materials including polymeric solid composites, polymer nanocomposites, polymer blends, block copolymers, and so on. The viscoelastic module draws its strength from the underlying OOF architecture to provide a macroscopic evaluation of mechanical properties using microstructural details. An application of this module for deformation analysis is the characterization of mechanical behavior a polymer nanocomposites. The deformation behaviour of polymer composite depends on the combined characteristic relaxation times of its constituents as well as its microstructural details. Results of analysis are expected to provide better insight into the role of microstructure as well as the role of interphase on the average mechanical / Singapore-MIT Alliance (SMA)

Adhesively bonded joints have been investigated for several decades. In most analytical studies, the Bernoulli-Euler beam theory is employed to describe the behaviour of adherends. In the current work, three analytical models are developed for adhesively bonded joints using the Timoshenko beam theory for elastic material and a Bernoulli-Euler beam model for viscoelastic materials. One model is for the peeling test of an adhesively bonded joint, which is described using a Timoshenko beam on an elastic foundation. The adherend is considered as a Timoshenko beam, while the adhesive is taken to be a linearly elastic foundation. Three cases are considered: (1) only the normal stress is acting (mode I); (2) only the transverse shear stress is present (mode II); and (3) the normal and shear stresses co-exist (mode III) in the adhesive. The governing equations are derived in terms of the displacement and rotational angle of the adherend in each case. Analytical solutions are obtained for the displacements, rotational angle, and stresses. Numerical results are presented to show the trends of the displacements and rotational angle changing with geometrical and loading conditions. In the second model, the peeling test of an adhesively bonded joint is represented using a viscoelastic Bernoulli-Euler beam on an elastic foundation. The adherend is considered as a viscoelastic Bernoulli-Euler beam, while the adhesive is taken to be a linearly elastic foundation. Two cases under different stress history are considered: (1) only the normal stress is acting (mode I); and (2) only the transverse shear stress is present (mode II). The governing equations are derived in terms of the displacements. Analytical solutions are obtained for the displacements. The numerical results show that the deflection increases as time and temperature increase. The third model is developed using a symmetric composite adhesively bonded joint. The constitutive and kinematic relations of the adherends are derived based on the Timoshenko beam theory, and the governing equations are obtained for the normal and shear stresses in the adhesive layer. The numerical results are presented to reveal the normal and shear stresses in the adhesive.

Made available in DSpace on 2014-06-11T19:23:28Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-08-21Bitstream added on 2014-06-13T18:50:36Z : No. of bitstreams: 1 arandaselverio_g_me_sjrp.pdf: 1103053 bytes, checksum: 82b446306de04f7e3cee32bff6293b57 (MD5) / Exopolissacarídeos (EPS) são polímeros produzidos por uma grande variedade de microrganismos e possuem diferentes propriedades estruturais, físicas e químicas. A investigação das propriedades reológicas de suas soluções é importante devido ao crescente interesse na aplicação comercial de polissacarídeos, principalmente na indústria de alimentos. Assim, o objetivo deste trabalho foi investigar as características reológicas dos exopolissacarídeos R1, R2, R3 e R4 produzidos por diferentes linhagens de Rhizobium e Mesorhizobium. Análises quantitativas mostraram que o teor de ácido urônico encontrado em R3 (8,4 %) foi maior que em R1 (2,4 %), R2 (1,7 %) e R4 (0,8 %). A cromatografia de filtração em gel mostrou que R2 e R3 são mais homogêneos e menos polidispersos. Hidrólise ácida total e análise por HPAEC/PAD mostrou glucose como constituinte básico majoritário dos EPS, além de galactose e manose. Todos os polissacarídeos apresentaram comportamento não-Newtoniano, com características de soluções pseudoplásticas nas concentrações de 2, 5 e 10 g/L. O modelo reológico de Ostwald-de-Waele (Lei da Potência) foi utilizado para representar os dados experimentais de tensão de cisalhamento versus taxa de deformação. Os EPS R1, R2 e R4 demonstraram pequeno aumento na viscosidade em presença de NaCl, e apresentaram comportamento viscoelástico de gel, sendo R1 o que apresenta características de gel mais forte. O EPS R3 manteve-se como o menos viscoso, tanto em meio aquoso quanto em solução salina, provavelmente devido ao maior percentual de ácidos urônicos em sua estrutura. Além disso, R3 exibiu comportamento de solução diluída a baixas concentrações, e viscoelástico de gel fraco em concentrações mais elevadas. A análise da influência da temperatura sobre o comportamento viscoelástico das soluções polissacarídicas mostrou... / Exopolysaccharides (EPS) are polymers produced by a great variety of microorganisms and possess different structural, physical and chemical properties. Investigation of rheological properties of these solutions is important due to an increasing interest in polysaccharides commercial applications, mainly in food sectors. The objective of this work was investigate rheological characteristics of exopolysaccharides R1, R2, R3 and R4 produced by different Rhizobium and Mesorhizobium strains. Quantitative analysis showed that uronic acid component found in R3 (8,4 %) was higher than R1 (2,4 %), R2 (1,7 %) and R4 (0,8 %). Gel filtration chromatography indicated that EPS R2 and R3 are more homogeneous and less polidisperse. Acid hydrolysis and HPAEC/PAD analysis revealed that glucose was the main monosaccharide, beyond galactose and mannose. All exopolysaccharides had non-Newtonian behavior, with pseudoplastic characteristics at concentrations of 2, 5 and 10 g/L. The Ostwald-de-Waele (Power Law) was the rheological model used to represent the experimental data of the shear stress versus shear rate. EPS R1, R2 and R4 demonstrated a slight increase in viscosity in presence of NaCl, and viscoelastic behavior, R1 had strong gelling characteristics. The EPS R3 was less viscous, in water solutions and presence of salt, probably due to a high percentual of uronic acids on its structure. Moreover, R3 exhibited diluted solution behavior at low concentration, and viscoelastic weak gelling at high concentrations. Analysis of temperature influence over polysaccharide solutions viscoelastic behavior showed that EPS R1, R2 e R4 had strong gelling characteristics, at concentrations of 5 g/L.

No description available.

No description available.

Resumo: Exopolissacarídeos (EPS) são polímeros produzidos por uma grande variedade de microrganismos e possuem diferentes propriedades estruturais, físicas e químicas. A investigação das propriedades reológicas de suas soluções é importante devido ao crescente interesse na aplicação comercial de polissacarídeos, principalmente na indústria de alimentos. Assim, o objetivo deste trabalho foi investigar as características reológicas dos exopolissacarídeos R1, R2, R3 e R4 produzidos por diferentes linhagens de Rhizobium e Mesorhizobium. Análises quantitativas mostraram que o teor de ácido urônico encontrado em R3 (8,4 %) foi maior que em R1 (2,4 %), R2 (1,7 %) e R4 (0,8 %). A cromatografia de filtração em gel mostrou que R2 e R3 são mais homogêneos e menos polidispersos. Hidrólise ácida total e análise por HPAEC/PAD mostrou glucose como constituinte básico majoritário dos EPS, além de galactose e manose. Todos os polissacarídeos apresentaram comportamento não-Newtoniano, com características de soluções pseudoplásticas nas concentrações de 2, 5 e 10 g/L. O modelo reológico de Ostwald-de-Waele (Lei da Potência) foi utilizado para representar os dados experimentais de tensão de cisalhamento versus taxa de deformação. Os EPS R1, R2 e R4 demonstraram pequeno aumento na viscosidade em presença de NaCl, e apresentaram comportamento viscoelástico de gel, sendo R1 o que apresenta características de gel mais forte. O EPS R3 manteve-se como o menos viscoso, tanto em meio aquoso quanto em solução salina, provavelmente devido ao maior percentual de ácidos urônicos em sua estrutura. Além disso, R3 exibiu comportamento de solução diluída a baixas concentrações, e viscoelástico de gel fraco em concentrações mais elevadas. A análise da influência da temperatura sobre o comportamento viscoelástico das soluções polissacarídicas mostrou... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Exopolysaccharides (EPS) are polymers produced by a great variety of microorganisms and possess different structural, physical and chemical properties. Investigation of rheological properties of these solutions is important due to an increasing interest in polysaccharides commercial applications, mainly in food sectors. The objective of this work was investigate rheological characteristics of exopolysaccharides R1, R2, R3 and R4 produced by different Rhizobium and Mesorhizobium strains. Quantitative analysis showed that uronic acid component found in R3 (8,4 %) was higher than R1 (2,4 %), R2 (1,7 %) and R4 (0,8 %). Gel filtration chromatography indicated that EPS R2 and R3 are more homogeneous and less polidisperse. Acid hydrolysis and HPAEC/PAD analysis revealed that glucose was the main monosaccharide, beyond galactose and mannose. All exopolysaccharides had non-Newtonian behavior, with pseudoplastic characteristics at concentrations of 2, 5 and 10 g/L. The Ostwald-de-Waele (Power Law) was the rheological model used to represent the experimental data of the shear stress versus shear rate. EPS R1, R2 and R4 demonstrated a slight increase in viscosity in presence of NaCl, and viscoelastic behavior, R1 had strong gelling characteristics. The EPS R3 was less viscous, in water solutions and presence of salt, probably due to a high percentual of uronic acids on its structure. Moreover, R3 exhibited diluted solution behavior at low concentration, and viscoelastic weak gelling at high concentrations. Analysis of temperature influence over polysaccharide solutions viscoelastic behavior showed that EPS R1, R2 e R4 had strong gelling characteristics, at concentrations of 5 g/L. / Orientador: Maria de Lourdes Corradi Custódio da Silva / Coorientador: Ana Lúcia Barretto Penna / Banca: Eliana Gertrudes de Macedo Lemos / Banca: Javier Telis Romero / Mestre

[pt] O Acrilonitrila-Butadieno-Estireno (ABS) é um polímero de grande uso industrial, sendo empregado em inúmeros produtos. Muitas de suas aplicações necessitam de uma elevada resistência a combustão seja pela presença de cargas elétricas (Efeito Joule) ou a exposição a ambientes de altas temperaturas. No entanto, o ABS, de modo semelhante a maioria dos polímeros, não é tão resistente a combustão, sendo necessário o emprego de aditivos Retardantes de Chamas (RC). A introdução desses aditivos pode, entretanto, acarretar alteração nas propriedades mecânicas, de forma que é necessário se comparar o comportamento do material com e sem aditivos. Particularmente importante é o comportamento a longo prazo, como a fluência. Assim, nesse trabalho foi avaliado o comportamento a fluência do ABS sem aditivo e de três sistemas ABS/RC. Foi usado um sistema empregando um aditivo comercial à base de bromo (ABS − Br), que serviu como base de comparação e dois sistemas recentemente desenvolvidos, empregando bio-retardantes, a saber: ácido tânico (TA) e polifosfato de amônio (APP). Os resultados dos ensaios mostraram que o aditivo comercial não acarretou variação da vida em fluência em relação ao ABS sem aditivo. Por outro lado, os resultados indicaram que a vida em fluência foi reduzida quando o aditivo APP foi incorporado e que aumentou quando o TA foi adicionado. Os dados experimentais dos ensaios de fluência foram usados para avaliar o comportamento viscoelástico dos quatro grupos de materiais. O ABS teve seu comportamento adequadamente representado pelo modelo de Burgers, assim como a ABS com aditivo à base de bromo. O modelo que melhor descreveu o comportamento do ABS com APP foi o modelo modificado de Burgers (Streched Burgers). Nem todas as amostras do ABS com TA apresentaram fluência no intervalo de tempo usado e o modelo que melhor descreveu o comportamento foi o do sólido linear padrão. / [en] Acrylonitrile-Butadiene-Styrene (ABS) is a polymer of great industrial use, being used in numerous products. Many of its applications require a high resistance to combustion, either due to the presence of electrical charges (Joule Effect) or exposure to high temperature environments. However, ABS, like most polymers, is not as resistant to combustion, requiring the use of Flame Retardant (RC) additives. The introduction of these additives can, however, lead to changes in the mechanical properties, so it is necessary to compare the behavior of the material with and without additives. Particularly important is long-term behavior such as fluency. Thus, in this work, the creep behavior of ABS without additive and of three ABS/RC systems was evaluated. A system employing a commercial bromine-based additive (ABS − Br) was used, which served as a basis for comparison and two recently developed systems employing bio-retardants, namely: tannic acid (TA) and ammonium polyphosphate (APP) . The test results showed that the commercial additive did not cause a change in creep life compared to ABS without additive. On the other hand, the results indicated that the creep life was reduced when the APP additive was incorporated and that it increased when the TA was added. Experimental data from creep tests were used to evaluate the viscoelastic behavior of the four groups of materials. ABS had its behavior adequately represented by the Burgers model, as well as ABS with bromine-based additive. The model that best described the behavior of ABS with APP was the modified Burgers model (Streched Burgers). Not all ABS samples with TA showed fluence in the time interval used and the model that best described the behavior was the standard linear solid.

Cette thèse fait l’objet du développement d’un modèle numérique de la phase d’imprégnation d’une préforme lors du procédé de fabrication d’un matériau composite par infusion sous vide de type VARI (Vacuum Assisted Resin Infusion). La caractérisation in situ du comportement mécanique dans l’épaisseur d’une préforme (essais d’infusion réels) est confrontée à sa caractérisation ex situ par une machine de traction/compression. L’effet de différents paramètres est mis en valeur sur le comportement de la préforme (type de chargement appliqué, état de saturation, influence de la viscosité du fluide et de la vitesse de déformation). Les essais ont révélé le caractère viscoélastique d’un renfort de type tissé lors de sa décompression à l’état imprégné et ont permis la définition d’une loi de comportement viscoélastique non-linéaire du renfort lors de cette phase. En vue d’étendre l’usage de cette loi de comportement mécanique à une large gamme de renforts, la même démarche expérimentale est appliquée au cas d’un renfort de type mat, au comportement élastique non-linéaire. La forme générale de la loi de comportement proposée se veut être adaptée à la description des deux types de renforts testés, où les éventuels effets viscoélastiques sont pris en compte selon le renfort étudié. Suite à l’implantation de la nouvelle loi de comportement dans un code numérique dédié à la simulation de la phase de remplissage d’un moule, la comparaison entre les résultats numériques et ceux des essais d’infusion sous vide prouve la fiabilité de ce nouveau modèle pour ces deux renforts à l’architecture bien distincte. / This thesis focuses on the development of a numerical model for the preform impregnation during the VARI (Vacuum Assisted Resin Infusion) process for the manufacturing of a composite material. The in situ characterization of the mechanical behavior in the thickness direction of a preform (real infusion tests) was compared with an ex situ characterization by a universal testing machine. The preform behavior was characterized for different parameters such as loading type, saturation state, influence of fluid viscosity and strain rate. All the tests revealed the viscoelastic behavior of a woven fabric during its decompression in the impregnated state, leading to the definition of a non-linear viscoelastic constitutive law of the woven fabric during this phase. To extend the use of this mechanical constitutive law to a wide range of fabrics, the same experimental approach was applied to the case of a random mat fabric with non-linear elastic behavior. The generalized form of the constitutive law is adapted to the description of the two types of fabrics while the potential viscoelastic effects are taken into account according to the fabric type. After the implementation of the new constitutive law in a numerical code for the simulation of a mold filling process, the comparison between numerical and experimental results has proved the reliability of the new numerical model for these two reinforcements with distinct architectures.

Η κατανόηση των φαινομένων που λαμβάνουν χώρα κατά την αλληλεπίδραση κυττάρου βιοϋλικού και η συσχέτιση μηχανικών παραμέτρων του κυττάρου με πολύπλοκες διεργασίες στο εξωκυττάριο (ECM) περιβάλλον οδηγεί το μέλλον στο σχεδιασμό των βιοϋλικών. Σκοπός της διατριβής ήταν η διερεύνηση της προσκόλλησης και των μεταβολών των μηχανικών ιδιοτήτων οστεοβλαστών στους αρχικούς χρόνους προσκόλλησης σε υπόστρωμα του βιοπολυμερούς χιτοζάνης. Η προετοιμασία υποστρωμάτων χιτοζάνης έγινε με ομοιοπολική πρόσδεση του βιοπολυμερούς σε επιφάνεια γυαλιού (επιφάνεια ελέγχου). Με φασματοσκοπία φωτοηλεκτρονίων από ακτίνες Χ επιβεβαιώθηκε η μεταβολή της επιφανειακής χημικής σύστασης. Η μέση επιφανειακή τραχύτητα, με χρήση Μικροσκοπίας Ατομικής Δύναμης, βρέθηκε 4 φορές μεγαλύτερη στη χιτοζάνη σε σύγκριση με το γυαλί, ενώ η μέση γωνία διαβροχής ήταν περίπου 3 φορές μεγαλύτερη στη χιτοζάνη. Ο αριθμός και η μέση επιφάνεια εξάπλωσης των προσκολλημένων κυττάρων, προσδιορίστηκαν από φωτογραφίες ηλεκτρονιακού μικροσκοπίου σάρωσης και χρήση λογισμικού ανάλυσης εικόνας. Μέχρι τα 30 λεπτά, ο αριθμός ήταν μεγαλύτερος στη χιτοζάνη, ενώ μετά τα 45 λεπτά, στο γυαλί. Σε όλους τους χρόνους, η μέση επιφάνεια εξάπλωσης ήταν μεγαλύτερη στη χιτοζάνη. Για την ποσοτικοποίηση της προσκόλλησης, χρησιμοποιήθηκε η τεχνική της μικροπιπέττας σε πειράματα αποκόλλησης μεμονωμένων οστεοβλαστών. Υπολογίστηκε η “ώθηση αποκόλλησης”, I, ως το ολοκλήρωμα της εφαρμοζόμενης δύναμης στο χρόνο (I=SFdt) για την πλήρη αποκόλληση ενός κυττάρου και βρέθηκε στατιστικά μεγαλύτερη στη χιτοζάνη σε όλους τους χρόνους. Με την τεχνική Ποσοτικής Αλυσιδωτής Αντίδρασης Πολυμεράσης, η έκφραση των γονιδίων ιντεγκρινών αν, α4, β1 και β3 βρέθηκε σημαντικά αυξημένη στη χιτοζάνη από τα 30 στα 120 λεπτά. Με συνεστιακό μικροσκόπιο σάρωσης, παρατηρήθηκε αυξημένη έκφραση της κινάσης εστιακής προσκόλλησης στη χιτοζάνη στα 30 και στα 120 λεπτά. Τέλος, χρησιμοποιήθηκε η τεχνική της μικροπιπέττας σε πειράματα εφελκυσμού και ερπυσμού των οστεοβλαστών και υπολογίστηκαν οι μεταβολές του μέτρου Young, Ε, και του φαινόμενου ιξώδους, η. Οι μέσες τιμές βρέθηκαν αυξημένες στην πορεία της προσκόλλησης στις δύο επιφάνειες, παρουσιάζοντας υψηλότερες τιμές στη χιτοζάνη. Η παρούσα διατριβή είναι μια ολοκληρωμένη φαινομενολογική προσέγγιση της μηχανικής συμπεριφοράς της οστεοβλάστης κατά την προσκόλληση. Η προσκόλληση στη χιτοζάνη συνοδεύεται από μεταβολές στη μηχανική συμπεριφορά και συνδέεται με κρίσιμες βιοχημικές διεργασίες. / The understanding of the phenomena that take place during cell-biomaterial interaction and the correlation of cell mechanical parameters with complicated processes at the extracellular environment (ECM) is driving the future of biomaterial design. The aim of the present study was the investigation of attachment and of alterations of mechanical properties of osteoblasts during the initial phase of attachment on chitosan biopolymer substrate. The preparation of the chitosan substrates was done with covalent immobilization of the biopolymer on glass surface (control substrate). X-Ray photolelectron spectroscopy confirmed the alteration of the surface chemical composition. Mean surface roughness, as measured by Atomic Force Microscopy, was increased 4-fold compared to glass, while the mean contact angle was found 3 times higher on chitosan substrate. The mean number and spreading area of the attached cells, were determined by Scanning Electron Microscopy images and the use of image processing program. Up to 30 minutes, the number of attached cells was higher on chitosan, while after 45 minutes, it was on glass. At all time points, the mean spreading area was greater on chitosan. To quantify attachment, the micropipette aspiration technique was used at experiments of detachment of individual osteoblasts. The ‘’detachment impulse’’, I, was calculated, as the integral of the applied force at time required (I=SFdt) for complete detachment of one cell, and it was found statistically higher on chitosan at all attachment times. With the quantified Polymerase Chain Reaction, the αν, α4, β1 and β3 gene integrin expression was found significantly increased from 30 to 120 minutes of attachment on chitosan. Using confocal scanning microscopy, higher expression of focal adhesion kinase was observed on chitosan at 30 and 120 minutes of attachment. Additionally, the micropipette aspiration technique was used at stretching and creep experiments so as to calculate the alterations of cell’s Young modulus, E, and apparent viscosity, η. Mean values were increased at the course of spreading for both surfaces, demonstrating greater values on chitosan. The present study is a complete phenomenological approach of the mechanical behavior of osteoblasts during attachment. Attachment on chitosan is accompanied by alterations of the mechanical behavior and is associated with critical biochemical processes.