The purpose of this study was learn how the diffusion, swelling, and crystallization processes are coupled during solvent-induced crystallization of poly(ether ether ketone) (PEEK). Unoriented amorphous PEEK films were immersed in aprotic organic liquids at ambient temperature and bulk properties or characteristics were monitored as a function of immersion time. The sorption behavior, Tg and Tm° suppression, crystallinity, and dynamic mechanical response were correlated as a function of solvent chemistry and immersion time. The saturation time of methylene chloride, 1,3-dichloropropane, tetrahydrofuran, cyclopentanone, chlorobenzene, toluene, diethyl ketone, and ethylbenzene in amorphous PEEK films were found to range from hours to days depending on the level of polymer-solvent interactions. In-situ isochronal DMA spectra show that the Tg of PEEK was suppressed from 150 ° C to below ambient temperature such that crystallization was kinetically feasible during ambient immersion. In addition, an increase in viscoelastic dispersion was attributed to the presence of crystallinity. From dynamic mass uptake and wide-angle x-ray diffraction (WAXD) results, it was found that the bulk sorption rate was equal to the bulk crystallization rate for all solvent systems that promoted SINC and PEEK exhibited diffusion-limited crystallization, irrespective of the nature of the transport mechanism. In addition, the solvent-induced crystals exhibit preferred orientation as supported by photographic WAXD. A distinct sorption front, observed with scanning electron microscopy, further supports the scenario of diffusion-controlled crystallization and one-dimensional diffusion. Isothermal DMA spectra for THF, cyclopentanone, and chlorobenzene, indicate that, as the solvent diffuses into the films, the stiffness of the polymer decreases at short times, begins to increase, and then reaches a relatively time-independent value. It was determined that the initial decrease in the storage modulus was due to the incredible plasticization of the amorphous phase. When the films contained greater than 60 % of the ultimate crystallinity, the storage modulus was observed to increase as a result of the reinforcing effect of the solvent-induced crystals. WAXD and mass uptake results confirm that the plateau in the storage modulus coincides with the completion of bulk crystallization and saturation of the amorphous phase. / Ph. D.

Expansive soils, which are widely referred to as problematic soils are extensively found in many countries of the world, especially in semi-arid and arid regions. Several billions of dollars are spent annually for maintenance or for repairs to the structures constructed with and within expansive soils. The major problems of expansive soils can be attributed to the volume changes associated with the alternate wetting and drying conditions due to the influence of environmental factors. Pile foundations have been widely accepted by practicing engineers as a reasonably good solution to reduce the damages to the structures constructed on expansive soils. Typically, piles foundations are extended through the active layer of expansive soil to reach the bedrock or placed on a soil-bearing stratum of good quality. Such a design and construction approach typically facilitates pile foundations to safely carry the loads from the superstructures and reduce the settlement. However, in many scenarios, damages associated with the pile foundations are due to the expansion of the soil that is predominantly in the active zone that contributes to the pile uplift. Such a behavior can be attributed to the water infiltration into the expansive soil, which is a key factor that is associated with the soil swelling. Due to this phenomenon, expansive soil typically moves upward with respect to the pile. This generates extra positive friction on the pile because of the relative deformation. If the superstructure is light or the applied normal stress on the head of the piles is not significant, it is likely that there will be an uplift of the pile contributing to the damage of the superstructure. In conventional engineering practice, the traditional design methods that include the rigid pile method and the elastic pile method are the most acceptable in pile foundation design. These methods are typically based on a computational technique that uses simplified assumptions with respect to soil and water content profile and the stiffness and shear strength properties. In other words, the traditional design method has limitations, as they do not take account of the complex hydromechanical behavior of the in-situ expansive soils. With the recent developments, it is possible to alleviate these limitations by using numerical modeling techniques such as finite element methods. In this thesis, a three-dimensional finite element method was used to study the hydro-mechanical behavior of a single pile in expansive soils during the infiltration process. In this thesis, a coupled hydro-mechanical model for the unsaturated expansive soil is implemented into Abaqus software for analysis of the behavior of single piles in expansive soils during water infiltration. A rigorous continuum mechanics based approach in terms of two independent stress state variables; namely, net normal stress and suction are used to form two three-dimensional constitutive surfaces for describing the changes in the void ratio and water content of unsaturated expansive soils. The elasticity parameters for soil structure and water content in unsaturated soil were obtained by differentiating the mathematical equations of constitutive surfaces. The seepage and stress-deformation of expansive soil are described by the coupled hydro-mechanical model and the Darcy’s law. To develop the subroutines, the coupled hydro-mechanical model is transferred into the coupled thermal-mechanical model. Five user-material subroutines are used in this program. The user-defined field subroutine (USDFILD) in Abaqus is used to change and transfer parameters. Three subroutines including user-defined material subroutine (UMAT), user-defined thermal material subroutine (UMATHT), and user-defined thermal expansion subroutine (UEXPAN) are developed and used to calculate the stress-deformation, the hydraulic behavior, and the expansion strain, respectively. Except for the coupled hydro-mechanical model of unsaturated expansive soils, a soil-structure interface model is implemented into the user-defined friction behavior subroutine (FRIC) to calculate the friction between soil and pile. The program is verified by using an experimental study on a single pile in Regina clay. The results show that for the single pile in expansive soil under a vertical load, water infiltration can cause a reduction in the pile shaft friction. More pile head load is transferred to the pile at greater depth, which increases the pile head settlement and pile base resistance. In future, the proposed method can also be extended for verification of other case studies from the literature. In addition, complex scenarios can be investigated to understand the behavior of piles in expansive soils.

Natural fibers show potential to replace glass fibers in thermoset and thermoplastic composites. Kenaf is a bast-type fiber with high specific strength and great potential to compete with glass fibers. In this research kenaf/epoxy composites were analyzed using Dynamic Mechanical Analysis (DMA). A three-point bend apparatus was used in the DMA testing. The samples were tested at 1 hertz, at a displacement of 10 μm, and at room temperature. The fiber volume content of the kenaf was varied from 20%-40% in 5% increments. Ten samples of each fiber volume fraction were manufactured and tested. The flexural storage modulus, the flexural loss modulus, and the loss factor were reported. Generally as the fiber volume fraction of kenaf increased, the flexural storage and flexural loss modulus increased. The loss factor remained relatively constant with increasing fiber volume fraction. Woven and chopped fiberglass/epoxy composites were manufactured and tested to be compared with the kanaf/epoxy composites were manufactured and tested to be compared with the kenaf/epoxy composites. Both of the fiberglass/epoxy composites reported higher flexural storage and flexural loss modulus values. The kenaf/epoxy composites reported higher loss factor values. The specific flexural storage and specific flexural loss modulus were calculated for both the fiberglass and kenaf fiber composites. Even though the kenaf composites reported a lower density, the fiberglass composites reported higher specific mechanical properties.

This thesis is concerned with the design, analysis and optimisation of semi-solid or non- pneumatic tyres. More specifically, the thesis is intended to show how the FEA software package Abaqus can be used to determine whether or not an AirBoss tyre meets performance criteria in regards load/deformation criteria and if there is a likelihood of failure through overheating of the tyre during service.The work is intended to clearly explain the nature of natural rubber from a molecular description through to phenomenological descriptions used to solve for stresses, strains, creep and relaxation phenomena and temperature generation through hysteresis losses within the structure of the rubber compound.The thesis examines practical ways to obtain data for use in the analysis and describes test equipment (both "off-the-shelf" and purpose built) to obtain the required information.The objective is to progress, step by step, through the stages of analysis beginning with information to predict static loading conditions for the tyre. Viscoelastic behaviour, such as creep and relaxation are predicted and then tested to determine the correlation and refine test data before proceeding to the next stage of analysis.Ultimately, a prediction is made as to the temperature distribution throughout a section of the non-pneumatic tyre. A testing rig is described which has been built to test the analysis and enable a comparison to be made between FEA prediction and "real life".

This work focuses on polymer glasses relaxation behavior. Polymethylmethacrylate was chosen as a typical representative of polymer glasses. Relaxation processes were studied by dynamical mechanical spectroscopy and differential scanning calorimetry was used as a supplemental analysis. Relaxation process above Tg and high values of rubberlike plateau modulus were observed in thermomechanical spectra. High temperature relaxation transition was studied from the perspective of thermal history, frequency and axial stress dependence and influence of molecular structure was also investigated. Apparent activation energies of studied processes and their axial stress dependence for polymethylmethacrylate were determined. On the basis of obtained data, a hypothesis was developed which connects high temperature relaxation process with molecular process responsible for strain hardening.

No description available.

No description available.

The frequent use of high-density polyethylene pipes over the last decades has been possible because these pipes are lightweight, corrosion resistant, unlikely to have leaks, and are low cost. The chain structure of the polymer, the extrusion and cooling conditions, the resulting morphology and the ambient conditions all play an important role in the pipe's performance. A new generation of high density polyethylene resins has improved the performance of pipes, but brought new challenges to their testing and characterization. There is a need to understand the rheological behavior of the resins, their processing, and their associated properties in a finished pipe. The rheological behavior of the resins was studied to characterize the effect of high molecular weight tails in a bimodal molecular weight distribution. The use of cone-and-plate and parallel-plate geometries in a rheometer provided simple flow that characterized the steady and dynamical response of the polymer melts. The rheological measurements detected differences in the resins: the resin with higher molecular weight tail showed increased zero shear-rate viscosity, a much slower relaxation of stresses and a resin that more readily deviates from linear viscoelastic behavior. The rheology of the resins allowed modeling their flow through different extrusion dies. The flow channels for pipe dies are thick, so velocities and shear rates are low. Using a different die had a larger impact in shear rates and stresses compared to using different resins. The resin with higher molecular weight shows much higher shear stresses for the same die and temperature, which makes processing harder. The flow of a fluid through a pipe causes constant stress, which at long enough times is one the reasons for pipe failure. Tests that characterize the service lifetime of pipes take long times and are expensive. Dynamical mechanical analysis allows characterizing the viscoelastic properties of the pipe and creep testing confirms that shift factors work for viscoelastic properties measured inde-pendently. For the characterized pipes, one hour of testing at 80 °C is equivalent to a month of test-ing at 25 °C. This works characterizes pipes made from two resins and two different dies. The meas-urements showed that the pipes were statistically the same. / Doctor of Philosophy / The use of high-density polyethylene pipes has thrived over the last decades. This has been possible because these pipes are lightweight, corrosion resistant, unlikely to have leaks, and are low cost. The structure of the polymer and the manufacturing process both affect the pipe's performance. A new generation of high density polyethylene resins has improved the performance of the pipes, but brought new challenges to their testing and characterization. There is a need to understand the flow characteristics of the resins and their properties as a finished pipe. The flow behavior of the polymers in simple geometries gave insights into the polymer's structure. A higher molecular weight resin showed increased resistance to flow and deviated from ideal behavior more readily. These flow characteristics let one model certain aspects of the manufacturing process. Pipe manufacturing is a slow process because of the high resistance to flow of the polymer. Changing the processing equipment, and to a minor degree changing the resins, had an important impact in the manufacturing process. The tests that characterize the service lifetime of pipes take long times and are expensive. When pipes have fluids flowing at high pressures, it takes decades for them to fail. There are viscoelastic tests that allow much quicker characterization of pipes and help predict their long term behavior. This works characterizes pipes made from two resins and two different dies. This works characterizes pipes made from two resins and two different dies. The measurements showed that the pipes were statistically the same.

Polymers containing less than 10 mol % of ions (ionomers) have been studied in depth for their potential in producing polymers with tailored properties for specific applications. A small molar percentage of ions can be incorporated into a polymer to drastically enhance the properties of the polymer. An ionomer that has been studied is that of isoprene copolymerized with sodium styrene sulfonate (poly(I-co-NaSS)). Research has been performed relating to the synthesis and chemical characterization of the copolymers. However, an in depth study of the way the physical properties are affected by a change in ion concentration has not been presented. Thus, it is the goal of this thesis to synthesize a series of poly(I-co-NaSS) copolymers with varying levels of sulfonated styrene and characterize their physical properties. The poly(I-co-NaSS) polymers, containing a range of 1.15 to 4.74 mol % NaSS, were polymerized using free radical emulsion polymerization. The copolymer compositions were confirmed using combustion sulfur analysis. Dynamic light scattering indicated that large aggregates were present in solution. These aggregates were large enough that capillary intrinsic viscosities could not be measured. Small angle x-ray scattering (SAXS) and thermal analysis showed little change as the ion concentration was increased, while tensile, stress relaxation and adhesion properties were improved. The absence of changes in the SAXS patterns indicated that there was an absence of a well-defined ionic aggregate, while the mechanical properties showed evidence of electrostatic interactions. This can be at least partially attributed to ionic interactions on a smaller scale (doublets, triplets). / Master of Science

The increase and change in traffic loading in recent years has resulted in the introduction of a new range of high performance asphalt binders. These new binders known as modified asphalt binders, have a more complex behavior than traditional binders. A review of the current mathematical models shows that most of them suffer from different drawbacks that make them inadequate for their intended application. To describe the behavior of straight and modified binders in the thermorheologically simple linear viscoelastic region, two models are proposed. Models to characterize the absolute value of the complex shear modulus (|G*|) and the phase angle (d) were developed using the matching function approach and validated by an experimental program. The dynamic mechanical properties of two typical paving grade binders and three modified binders were tested at intermediate and high service temperatures. Short-term and long-term aging were simulated by the rolling thin film oven test and the pressure aging vessel test, respectively. A dynamic shear rheometer with parallel plate configuration was used to conduct the dynamic mechanical tests at frequencies between 0.06 to 188.5 rad/sec and temperatures ranging from 5 to 75°C. Prior to the frequency sweeps, strain sweeps were performed to establish the linear viscoelastic region. Results indicated a strong susceptibility to the defined strain at intermediate temperatures; however, strain susceptibility was less pronounced at high temperatures. Frequency sweeps were then conducted at a constant strain corresponding to greater than 95% of the initial complex shear modulus as established by AASHTO TP5 for straight asphalts. The Time-Temperature Superposition Principle was used to construct the master curves. The shift factors were determined based on the complex shear modulus master curves and verified for the phase angle, storage shear modulus and loss shear modulus. After construction of the master curves, non-linear regression was used to fit the proposed models to the experimental data. Comparison between the measured and predicted values indicated a good agreement for frequencies higher than 10⁵ rad/sec. The phase angle model was found to adequately describe unmodified binder with a small percentage of errors (less than 6%). On the other hand, the phase angle model was found unable to simulate the plateau region observed for polymer-modified binders. However, the error in this case was found to be relatively small (from zero to 10%). The ability of the models to estimate other viscoelastic functions, e.g. storage shear modulus (G'), loss shear modulus (G"), and relaxation spectrum (H(t)), was found to be adequate. / Master of Science