A research project at Linnaeus University focuses on optimizing theadhesives joints between wood and glass, with the aim of obtain stiffcomponents that can act as a load and stabilizing elements and still betransparent. But there is, however, still a lack of knowledge regarding theadhesive materials which need to be further investigated. This thesis focused on testing six different adhesives in relaxation and todetermine the viscosity (η) and modulus of elastic (MOE, E). Viscosity andMOE are then used in combination in a standard linear solid model (SLS)describing the viscoelasticity mathematically. Figures and tables are used topresent the results and the evaluation. The so determined parameters can beused in e.g. finite element models for the design of load bearing timber glasscomposites.

Real-time, bedside observation of patient clotting is essential in various surgeries in the operating room (OR), but specifically during cardiac surgeries. The objective of this thesis is to design and test a new piezoelectric device that can be used for viscoelasticity measurement with time as a Point of Care (POC) test. Slow turnaround times (TAT) of current methods to monitor blood viscoelastic changes in patients have led to excessive bleeding and the need for blood transfusions in many situations (Despotis et al, 1997). This study shows that the phase shift produced by a resonator sensor can be related to the viscosity of a liquid. By monitoring a phase shift between an actuator and sensor pair, a numeric relationship can be generated and suffice as a calibration curve for each probe. At a calculated error averaging a maximum of 2%, and coefficient of determination and correlation coefficient exceeding 0.95, two probes have been tested in various glycerin solutions and prepared for whole blood experimentation. They have also been tested in varying temperatures to simulate effectiveness in a dynamic environment, similar to that of clotting whole blood.

O espalhamento de ondas de som tem por objetivo compreender a natureza de propagacao de ondas sonoras incidentes e espalhadas, para diferentes estruturas e geometrias dos centros espalha- dores que formam um meio desordenado. Na literatura, em geral, obtemos informacoes relativas ao espalhamento acustico em regioes distantes dos centros espalhadores (aproximacao de campo distante), para algumas formas de onda incidentes e de particulas espalhadoras. Buscando compre- ender o comportamento ondulatorio em regioes proximas ao centro espalhador e em seu interior, nosso estudo fornece uma descricao analitica dos campos de radiacao acustica nessas regioes. Ini- cialmente, considera-se o problema do espalhamento de uma onda plana acustica plana (viajando num fluido ideal newtoniano) por uma particula esferica fluida, com caracteristicas distintas das do fluido inicial. Ainda, calculamos a energia interna armazenada nesse centro espalhador como funcao do volume da esfera espalhadora, bem como do comprimento da onda em seu interior, de sua amplitude e da densidade do centro espalhador. Posteriormente, os materiais espalhadores sao considerados de natureza viscoelastica (que apresentam comportamentos viscosos e elasticos sob a acao de forcas externas), por serem viaveis na modelagem de celulas biologicas e polimeros, em geral. Para isso, tratamos formalmente da fisica de materiais elasticos, como deformacoes e tensoes, a fim de respaldar o tratamento do modelo viscoelastico de Kelvin-Voigt fracionario usado em nosso estudo. Obtivemos formulas fechadas para os coeficientes de espalhamento (bem como os coeficientes das ondas internas ao centro espalhador) desse problema em questao, a partir da solucao de um sistema linear de equacoes. Os resultados permitem a construcao de uma teoria de base para um estudo generalizado do espalhamento de ondas acusticas por materiais viscoelasticos, perspectiva a ser conduzida num futuro proximo. / The sound wave scattering aims to understand the propagation nature of scattered and incident sound waves, for different structures and geometries of the scattering centers that form a disordered environment. In the literature, in general, we obtain information regarding the acoustic scattering in regions distant from the scattering centers (far-field approximation), for some incident wave- forms and scattering particles. In order to understand the undulatory behavior in regions close to and within the scattering center, our study provides an analytical description of the acoustic radiation fields in these regions. First, the problem considered is the scattering of an acoustic plane wave (previously traveling through an ideal newtonian fluid) by a spherical fluid particle, with distinct acoustic characteristics from the initial fluid. Still, it is determined the internal acoustic energy stored in this scattering center, as a function of the scattering spheres volume, as well as the wavelength in its interior, its amplitude and the density of the scattering center. Later, the scattering materials are considered to be viscoelastic (which exhibit viscous and elas- tic behavior when subjected to external forces), as they are feasible in the modeling of biological cells and polymers in general. For such, we deal formally with elastic materials physics, such as deformations and tensions, in order to deal with the Kelvin-Voigt viscoelastic model used in this problem. Were determined closed formulas for the scattering coefficients for this problem (as well as the internal wave coefficients), from the solution of a linear system of equations. The results allow the construction of a fundamental theory for a generalized study of sound wave scattering by viscoelastic materials, which is a goal to be achieved in a near future.

Este trabalho descreve a preparação, caracterização e mecanismos de interação de compósitos de colágeno aniônico:ramsana, com o propósito de desenvolver géis injetáveis para correções plásticas com concentrações similares aquelas encontradas comercialmente, e sem o uso do glutaraldeído. Os materiais foram caracterizados por eletroforese, espectroscopia no infravermelho, estabilidade térmica, propriedades reológicas e ensaios de fluidez. Os materiais obtidos independentemente do processamento, são formados por colágeno não desnaturado, com preservação da estrutura secundária da proteína. Os estudos reológicos mostraram um comportamento viscoelástico para todas as preparações independentemente do pH, e com módulo de armazenamento sempre maior que o módulo de perda (G\'>G\" e d<45o), bem como uma maior resistência à deformação de géis de colágeno aniônico:ramsana equilibrados a pH 7,4 com relação aos géis equilibrados a pH 3,5. Medidas de viscosidade mostraram que além de um comportamento não newtoniano, a adição do polissacarídeo mesmo em baixas concentrações promove efeitos significativos sobre a viscosidade dos géis, indicando que a interação colágeno ramsana além de não comprometer a estrutura secundária do colágeno, sugere que esta interação ocorre provavelmente por ordenação da água ao redor do complexo formado. Já viscosidade dinâmica encontradas para as diferentes preparações, indicam que os compósitos obtidos são candidatos potenciais para serem utilizados em laringologia. Ensaios de fluidez mostraram que a força necessária para o escoamento de géis contendo ramsana foi sempre significativamente menor e com um perfil mais homogêneo do que aquela determinada para o colágeno aniônico, sugerindo que a associação colágeno aniônico:ramsana pode substituir com vantagens o glutaraldeído na estabilização das preparações comerciais do gel. / This work describes the preparation, characterization and mechanisms of interaction anionic collagen:rhamsam composites, with the purpose of developing injectable gels for plastic corrections with similar concentrations to the commercially founded without the use of glutaraldehyde. The materials were characterized by electrophoresis, infrared spectroscopy, thermal stability, rheological properties and fluidity tests. The materials obtained independently from processing are formed by no desnaturated collagen with the preservation of secondary structure protein. The rheological studies showed a viscoelastic behavior for all the preparations independently of pH, and with storage modulus always greater than the loss modulus (G’>G’’ and d<45o), as well a higher resistence to the deformation of anionic collagen:rahamsan gels equilibrated at pH 7.4 in relation to the gels equilibrated at pH 3.5. Measure of viscosity showed that besides a non Newtonian behavior of the polysaccharide addition even at low concentrations causes significant effects on the viscosity of the gels, indicating that collagen:rhamsan interaction probably occurs due to the water disposition around the complex already formed and it does not damage the secondary structure of the collagen. On the other hand, dynamic viscosity found for different preparations indicate that the composites obtained are potential candidates to be utilized in laringology. Flow experiments indicated that the force needed for the extrusion for anionic collagen:rhamsan composites, in comparison to anionic collagen, was significantly smaller and associated with a smooth flow, suggesting that the collagen anionic:rhamsan association can substitute glutaraldehyde with advantage in the stabilization for the gels commercial preparations.

The Hydro Muscle is a soft linear actuator which utilizes hydraulic pressure and elastic properties of its core for actuation. The Hydro Muscle has been recruited to actuate bio-inspired robot systems using a classic set point tracking feedback control system. A more efficient method is to develop a model-based control system which uses a dynamic model of the Hydro Muscle. The dynamic behavior of the Hydro Muscle which describes the relation between the forces exerted to the resultant motion can be studied with the help of a dynamic viscoelastic model. A dynamic viscoelastic model defines the force exerted by the Hydro Muscle as a function of the hydraulic pressure, the tensile expansion of the Hydro Muscle and the rate of its tensile expansion. Multivariable linear regression is employed to generate a model to relate fluid pressure, tensile expansion, and the rate of tensile expansion to the force exerted by the Hydro Muscle. The developed model can be utilized to implement a model-based control algorithm for the force control of individual joints. This model-based control design could be extended to systems involving multiple Hydro Muscles to allow for a modular control system. The design and test of multi-fiber Hydro Muscle actuated biologically inspired ankle is considered to study control strategies for multi-fiber system. A set-point tracking control algorithm with a proportional differential controller is used to minimize the tracking error. Modular force variation with sequential recruitment of Hydro Muscle is studied.

This thesis contributes to recent interest within medical imaging regarding the development and clinical application of magnetic resonance elastography (MRE) to the human brain. MRE is a non-invasive phase-contrast MRI technique for measurement of brain mechanical properties in vivo, shown to reflect the composition and organisation of the complex tissue microstructure. MRE is a promising imaging biomarker for the early characterisation of neurodegeneration due to its exquisite sensitivity to variation among healthy and pathological tissue. Neurodegenerative diseases are debilitating conditions of the human nervous system for which there is currently no cure. Novel biomarkers are required to improve early detection, differential diagnosis and monitoring of disease progression, and could also ultimately improve our understanding of the pathophysiological mechanisms underlying degenerative processes. This thesis begins with a theoretical background of brain MRE and a description of the experimental considerations. A systematic review of the literature is then performed to summarise brain MRE quantitative measurements in healthy participants and to determine the success of MRE to characterise neurological disorders. This review further identified the most promising acquisition and analysis methods within the field. As such, subsequent visits to three brain MRE research centres, within the USA and Germany, enabled the acquisition of exemplar phantom and brain data to assist in discussions to refine an experimental protocol for installation at the Edinburgh Imaging Facility, QMRI (EIF-QMRI). Through collaborations with world-leading brain MRE centres, two high-resolution - yet fundamentally different - MRE pipelines were installed at the EIF-QMRI. Several optimisations were implemented to improve MRE image quality, while the clinical utility of MRE was enhanced by the novel development of a Graphical User Interface (GUI) for the optimised and automatic MRE-toanatomical coregistration and generation of MRE derived output measures. The first experimental study was performed in 6 young and 6 older healthy adults to compare the results from the two MRE pipelines to investigate test-retest agreement of the whole brain and a brain structure of interest: the hippocampal formation. The MRE protocol shown to possess superior reproducibility was subsequently applied in a second experimental study of 12 young and 12 older cognitively healthy adults. Results include finding that the MRE imaging procedure is very well tolerated across the recruited population. Novel findings include significantly softer brains in older adults both across the global cerebrum and in the majority of subcortical grey matter structures including the pallidum, putamen, caudate, and thalamus. Changes in tissue stiffness likely reflect an alteration to the strength in the composition of the tissue network. All MRE effects persist after correcting for brain structure volume suggesting changes in volume alone were not reflective of the detected MRE age differences. Interestingly, no age-related differences to tissue stiffness were found for the amygdala or hippocampus. As for brain viscosity, no group differences were detected for either the brain globally or subcortical structures, suggesting a preservation of the organisation of the tissue network in older age. The third experiment performed in this thesis finds a direct structure-function relationship in older adults between hippocampal viscosity and episodic memory as measured with verbal-paired recall. The source of this association was located to the left hippocampus, thus complementing previous literature suggesting unilateral hippocampal specialisation. Additionally, a more significant relationship was found between left hippocampal viscosity and memory after a new procedure was developed to remove voxels containing cerebrospinal fluid from the MRE analysis. Collectively, these results support the transition of brain MRE into a clinically useful neuroimaging modality that could, in particular, be used in the early characterisation of memory specific disorders such as amnestic Mild Cognitive Impairment and Alzheimer's disease.

The ability to understand and predict the flow behaviour of non-Newtonian fluids in swirling flow is industrially important for the efficient design and performance of processes which utilise fluids with complex rheological properties. In particular, fluids with elastic properties are not well described by non-Newtonian constitutive models, such that predictions using such models must be carefully validated. A benchmark problem is proposed here which provides a well defined geometry to study the swirling flow of non-Newtonian fluids as a test case for the validation of constitutive models. The confined swirling flow utilised is a torsionally driven cavity where the test fluid is confined in a cylinder with a rotating bottom lid, and stationary side walls and top lid. The flow field is three-dimensional and consists of both a primary motion, which is directed azimuthally, and a secondary motion, which is located in the radial and axial plane of the cylinder and driven by inertial and/or elastic forces.

The ability to understand and predict the flow behaviour of non-Newtonian fluids in swirling flow is industrially important for the efficient design and performance of processes which utilise fluids with complex rheological properties. In particular, fluids with elastic properties are not well described by non-Newtonian constitutive models, such that predictions using such models must be carefully validated. A benchmark problem is proposed here which provides a well defined geometry to study the swirling flow of non-Newtonian fluids as a test case for the validation of constitutive models. The confined swirling flow utilised is a torsionally driven cavity where the test fluid is confined in a cylinder with a rotating bottom lid, and stationary side walls and top lid. The flow field is three-dimensional and consists of both a primary motion, which is directed azimuthally, and a secondary motion, which is located in the radial and axial plane of the cylinder and driven by inertial and/or elastic forces.

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)

The purpose of this work was to develop a practical method for constitutive modelling of polyethylene, based on a phenomenological approach, which can be applied for structural analysis. Polyethylene (PE) is increasingly used as a structural material, for example in pipes installed by trenchless methods where relatively low stiffness of PE reduces the required installation forces, chemical inertness makes it applicable for corrosive environments, and adequate strength allows to use it for sewer, gas and water lines. Polyethylene exhibits time-dependent constitutive behaviour, which is also dependent on the applied stress level resulting in nonlinear stress-strain relationships. Nonlinear viscoelastic theory has been well established and a variety of modelling approaches have been derived from it. In order to be able to realistically utilize the nonlinear modelling approaches in design, a simple method is needed for finding the constitutive formulation for a specific polyethylene type. In this study, time-dependent constitutive relationships for polymers are investigated for polyethylene materials. Creep tests on seven polyethylene materials were conducted and the experimental results indicate strong nonlinear viscoelasticity in the material responses. Creep tests on seven materials were conducted for 24 hours for modelling purposes. However, creep tests up to fourteen days were performed on one material to study long-term creep behaviour. Multiple-stepped creep tests were also investigated. Constant rate (load and strain rate) tensile tests were conducted on two of the seven polyethylene materials. A practical approach to nonlinear viscoelastic modelling utilizing both multi-Kelvin element theory and power law functions to model creep compliance is presented. Creep tests are used to determine material parameters and models are generated for four different polyethylene materials. The corroboration of the models is achieved by comparisons with the results of different tensile creep tests, with one dimensional step loading test results and with test results from load and displacement rate loading.