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This thesis presents the results for the temperature variation of the Differential Group Delay (DGD) measurements of a Dispersion Compensation Module (DCM) and interprets the results with a theoretical DGD model based on glass viscoelastic properties and estimated values of some of glass parameters. The results of our analysis demonstrate the existence of long birefringence relaxation times on the order of many hours in response to temperature changes. These results could be of significance in interpreting the behavior of optical fiber systems.

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The object of this research was to determine if an acceptable angel food cake alternative could be produced that had reduced calories and sucrose content. This was accomplished through replacing sucrose in meringue, angel food cake batter, and baked angel food cakes with polydextrose and either sucralose, acesulfame-K, or Rebaudioside A at different replacement levels (25, 50, 75, 100%). Meringue and cake batter properties were measured using rheological techniques. Baked angel food cakes were analyzed based on height, weight loss, moisture content, color, and TPA analysis. With meringue batter, 100% sucrose replacement was unacceptable since undissolved polydextrose made analyzing and end products impractical. While 75% sucralose and acesulfame-K sucrose replacement exhibited comparable air incorporation to the sucrose control in cake batter, baked angel food cakes showed a decrease in functional properties. Polydextrose was likely the cause. 25% sucralose and acesulfame-K sucrose replacement were no different from sucrose cakes in regards to height, overall textural appearance, crumb pore size, and hardness. These cakes resulted in an overall calorie reduction of 18.7%. In every experiment, Rebaudioside A replacement treatments exhibited trends opposite of sucralose and acesulfame-K treatments. Rebaudioside A treatments performed the worst for rheological properties and TPA analysis.

Thermally bonded nonwovens are low-price substitutes for traditional textiles. They are used in many areas including filtration, automotive and aerospace industries. Hence, understanding deformation behaviours of these materials is required to design new products tailored for specific applications in different areas. Because of their complex and random structure, numerical simulations of nonwoven materials have been a challenging task for many years. The main aim of the thesis is to develop a computational modelling tool to simulate the effect of design parameters on structural behaviour of low-density nonwoven materials by using a finite element method. The modelling procedure is carried out with a parametric modelling technique, which allows a designer to run a series of analyses with different design parameters and observe the effects of these parameters on the mechanical behaviour of nonwoven materials. The thesis also presents the study of rate dependent behaviour of nonwoven fibres. Novel test and data-interpretation procedures are proposed to determine the creep behaviour of fibres in the nonwoven structure. Some case studies are presented to demonstrate the effectiveness of the model. The developed computational tool allows macro and micro-scale structural investigation of nonwoven materials. Two additional studies are presented, performed with the developed tool. In the first study, the effect of design parameters on tensile stiffness of nonwovens was determined by performing numerical analyses with various nonwoven models. In the second one, strain distribution in fibres is studied thoroughly together with factors affecting the distribution. The models, developed in the thesis can also be employed in further studies of nonwovens, such as investigation of their damage and fracture behaviour.

Several aspects of vehicle-pavement interaction have been studied and discussed in this thesis. Initially the pavement response is studied through a quasi-static and a dynamic computationally efficient framework under moving traffic loads. Subsequently, a non-stationary stochastic solution has been developed in order to account for the effect of pavement surface deterioration on pavement service life.The quasi-static procedure is based on a superposition principle and is computationally favourable, as it requires only a reduced incremental problem to be solved numerically. Using the developed framework, the effect of vehicle configuration and traffic characteristics on the damage induced in pavements is investigated numerically. It is shown that the developed numerical model provides a more accurate explanation of different distress modes.In the dynamic approach the pavement roughness and vehicle suspension system are linked to a dynamic pavement model in order to account for the dynamic effects of vehicle-pavement interaction on pavement response. A finite element method is employed in order to establish the response function for a linear viscoelastic pavement structure with dynamic effects taken into account. The developed computational procedure is applied to evaluate the effect of the pavement surface roughness on the pavement structure response to truck traffic loadings.Furthermore, the deterioration trends for the flexible pavement surface have been investigated based on field measurements of longitudinal profiles in Sweden. A predictive function is proposed for surface deterioration that is based on the average gradient of yearly measurements of the road surface profiles in Swedish road network. The developed dynamic framework is further elaborated to a non-stationary stochastic approach. The response of the flexible pavement is given for a non-stationary random case as the pavement surface deteriorates in pavement service life, thus influencing the magnitude of the dynamic loads induced by the vehicles. The effect of pavement surface evolution on the stress state induced in the pavement by moving traffic is examined numerically. Finally the effect of surface deterioration on pavement service life has been investigated and discussed in the thesis by incorporating the proposed prognostic surface deterioration model into a ME design framework. The results are discussed for different case studies with different traffic regimes. It was indicated that the predicted pavement service life decreases considerably when the extra dynamic loads, as a result of pavement surface deterioration, has been taken into account. Furthermore, the effect of performing a predictive rehabilitation process (i.e. resurfacing) has been studied by employing a LCC framework. The application of preventive maintenance was shown to be effective, especially when the deterioration rate is high. / <p>QC 20141119</p>

This doctoral thesis is focused on composites based on polypropylene and wood flour. Firstly, the experimental work deals with preparation of composites based on wood flour with various concentrations and isotactic polypropylene with various melt flow indexes. In terms of this study, one polypropylene, which can have also practical use, was chosen. Further, this polypropylene is investigated with various types and concentrations of wood flour. Also, the attention is devoted to the modification of polypropylene by a specific β-nucleating agent. The differences are compared and described between the composites with neat and nucleated polypropylene. Further, the work is focused on solvent extraction of wood flour. The effect of extraction and solvent of wood flour is also examined in composites with neat and nucleated polypropylene. On prepared composites, the rheological, structural and thermal properties are studied. These properties differ depending on specific type of wood flour, its concentration and specific type of polypropylene.

<p>The main objectives of this research are: (i) to elaborate a unified nonlinear viscoelastic model for rubber-like materials, in finite strain, accounting for material softening under deformation, and for damage induced anisotropy, (ii) to conceive, implement and test, simple, robust and efficient frictional rolling and sliding contact algorithms, in steady-state, as alternatives to existing, general purpose, contact solving strategies, (iii) to develop and verify high fidelity and computationally efficient modeling tools for isotropic and anisotropic viscoelastic objects in steady-state motion, (iv) to investigate, numerically and through experimentation, the influence of various material parameters, including material nonlinearities such at the Payne effect and the Mullins effect, as well as geometric parameters and contact surface conditions, on viscoelastic rolling resistance, and (iv) to explore, analytically and through experimentation, the conditions under which favorable mechanical synergies occur between material components and develop novel composites with improved structural performances.</p><p>A new constitutive model that unifies the behavioral characterizations of rubber-like materials in a broad range of loading regimes is proposed. The model reflects two fundamental aspects of rubber behavior in finite strain: (i) the Mullins effect, and (ii) hyper-viscoelasticity with multiple time scales, including at high strain rates. Suitable means of identifying the system's parameters from simple uniaxial extension tests are explored. A directional approach extending the model to handle softening induced anisotropy is also discussed.</p><p>Novel, simple, and yet robust and efficient algorithms for solving steady-state, frictional, rolling/sliding contact problems, in two and three dimensions are presented. These are alternatives to powerful, well established, but in particular instances, possibly `cumbersome' general-purpose numerical techniques, such as finite-element approaches based on constrained optimization. The proposed algorithms are applied to the rolling resistance of cylinders and spheres.</p><p>Two and three-dimensional boundary element formulations of isotropic, transversely isotropic, and fully orthotropic, compressible and incompressible, viscoelastic layers of finite thickness are presented, in a moving frame of reference. The proposed formulations are based on two-dimensional Fourier series expansions of relevant mechanical fields in the continuum of the layers and support any linear viscoelastic material model characterized by general frequency-domain master-curves. These modeling techniques result in a compliance matrix for the upper boundary of the layers, including the effects of steady-state motion. Such characterizations may be used as components in various problem settings to generate sequences of high fidelity solutions for varying parameters. These are applied, in combination with appropriate contact solvers, to the rolling resistance of rigid cylinders and spheres.</p><p>The problem of a viscoelastic sphere moving across a rigid surface is significantly more complicated than that of a rigid indenter on a viscoelastic plane. The additional difficulties raised by the former may explain why previous work on this topic is so sparse. A new boundary element formulation for the multi-layered viscoelastic coating of a rigid sphere is developed. The model relies on the assumption of a relatively small contact surface in order to decouple equilibrium equations in the frequency domain. It is applied in combination with an adapted rolling contact solving strategy to the rolling resistance of a coated sphere.</p><p>New modeling approaches yielding rolling resistance estimates for rigid spheres (and cylinders) on viscoelastic layers of finite thicknesses are also introduced, as lower-cost alternatives to more comprehensive solution-finding strategies, including those proposed in this work. Application examples illustrate the capabilities of the different approaches over their respective ranges of validity.</p><p>The computational tools proposed in this dissertation are verified by comparison to dynamic finite element simulations and to existing solutions in limiting cases. The dependencies of rolling resistance on problem parameters are explored. It is for instance shown that, on orthotropic layers, the dissipated power varies with the direction of motion, which suggests new ways of optimizing the level of damping in various engineering applications of very high impact. Interesting lateral viscoelastic effects resulting from material asymmetry are unveiled. These phenomena could be harnessed to achieve smooth and `invisible' guides across three-dimensional viscoelastic surfaces, and hence suggest new ways of controlling trajectories, with a broad range of potential applications.</p><p>A new experimental apparatus is designed and assembled to measure viscoelastic rolling resistance. Experiments are conducted by rolling steel balls between sheets of rubber. Principal sources of measurement error, specific to the device, are discussed. Rolling resistance predictions are obtained using the computational tools presented in this dissertation, and compared to the measurements. Interesting conclusions are drawn regarding the fundamental influence of the Payne effect on viscoelastic rolling friction.</p><p>The work presented in this dissertations finally touches on the mechanical behavior of casing-infill composite tubes, as potential new lightweight structural elements. The axial behavior of composite circular tubes is addressed analytically. The influence of material parameters and geometry on structural performances are revealed and presented in original graphical forms. It is for instance shown that significantly improved overall stiffness and capacity at yield can be obtained using a moderately soft and highly auxetic infill, which further highlights the need to develop new lightweight auxetic materials, without compromising their stiffness. It is furthermore concluded that limited mechanical synergies can be expected in metal-polymer composite tubes, within the linear range of the materials involved. This prediction is confirmed by a bending experiment conducted on an Aluminum-Urethane composite tube. The experiment however reveals unexpected and quite promising mechanical synergies under large deformations. This novel composite has a potential influence on the design and performance of lightweight protecting structures against shocks and accelerations due to impacts, which justifies that it be characterized further.</p> / Dissertation

The objective of this study is to characterize the long-term behavior of an austenitic-ferritic stainless steel-based pretensioned system for strengthening reinforced concrete bridge pier caps in shear. Stress relaxation experiments were conducted on UNS S32101 stainless steel bars subjected to various initial stresses and temperatures within the low homologous temperature (LHT) regime. Data from these experiments were used to develop a viscoplastic constitutive model to describe the long-term time- and temperature-dependent behavior of the stainless steel bars. This mechanics-based approach is integrated with an analytical method based on strut-and-tie analysis to compute the shear strength of reinforced concrete pier caps strengthened with this external pretensioned system.