The main objective of this study is to develop and validate a framework for microstructural modeling of asphalt composite materials using a coupled thermo-viscoelastic, thermo-viscoplastic, and thermo-viscodamage constitutive model. In addition, the dissertation presents methods that can be used to capture and represent the two-dimensional (2D) and three-dimensional (3D) microstructure of asphalt concrete. The 2D representative volume elements (RVEs) of asphalt concrete were generated based on planar X-ray Computed Tomography (CT) images. The 2D RVE consists of three phases: aggregate, matrix, and interfacial transmission zone (ITZ). The 3D microstructures of stone matrix asphalt (SMA) and dense-graded asphalt (DGA) concrete were reconstructed from slices of 2D X-ray CT images; each image consists of the matrix and aggregate phases. The matrix and ITZ were considered thermo-viscoelastic, thermo-viscoplastic, and thermo-viscodamaged materials, while the aggregate is considered to be a linear, isotropic elastic material. The 2D RVEs were used to study the effects of variation in aggregate shape, distribution, volume fraction, ITZ strength, strain rate, and temperature on the degradation and micro-damage patterns in asphalt concrete. Moreover, the effects of loading rate, temperature, and loading type on the thermo-mechanical response of the 2D and 3D microstructures of asphalt concrete were investigated. Finally, the model parameters for Fine Aggregate Mixture (FAM) and full asphalt mixture were determined based on the analysis of repeated creep recovery tests and constant strain rate tests. These material parameters in the model were used to simulate the response of FAM and full asphalt mixture, and the results were compared with the responses of the corresponding experimental tests. The microstructural modeling presented in this dissertation provides the ability to link the microstructure properties with the macroscopic response. This modeling combines nonlinear constitutive model, finite element analysis, and the unique capabilities of X-ray CT in capturing the material microstructure. The modeling results can be used to provide guidelines for designing microstructures of asphalt concrete that can achieve the desired macroscopic behavior. Additionally, it can be helpful to perform 'virtual testing' of asphalt concrete, saving numerous resources used in conducting real experimental tests.

Total knee joint replacements (TKRs) are a commonly used treatment when joint pain becomes a major issue and the function of activities of daily living is impaired. TKRs may last for up to 20 years; however, younger and physically more active patients are receiving TKRs, necessitating increased prosthesis life-time. There has been considerable interest in more cartilage-like materials for the tibial inlay of a TKR. Compliant, rubbery polymers may be a first step towards such a material. In this thesis, finite element analysis (FEA) was utilized to assess the feasibility of polycarbonate urethane (PCU) in a TKR application. Mechanical characterisation of PCU55D and PCU80A was performed in order to better understand the deformation behaviour of these materials. Mechanical test data was then used to tune and validate a hyperelastic material model. In a last step, the material model was applied to a static FE knee model which was used to simulate five discrete loading cases: three gait cycle events, stair climbing and squatting. Contact pressure, contact area and von Mises stress of the PCU inlay were compared to literature and to a standard ultra-high molecular weight polyethylene (UHMWPE) inlay. The contact area of the articulating implant surfaces was on average 345% greater in PCU than in UHMWPE and contact pressure was on average 77% lower in PCU than in UHMWPE. The difference between TKRs simulated with a PCU tibial inlay and those simulated with a UHMWPE inlay increased with increasing flexion angle. The contact pressures measured in TKRs simulated with a PCU tibial inlay were well below values that are expected to cause damage to the polymer, possibly reducing the risk of wear. The contact areas found in TKRs simulated with a PCU tibial inlay were close to what has been reported for the natural knee. Considering the low contact pressures even at high flexion angles, where initial congruency is limited, it may be feasible to design less conforming knee prostheses that still exhibit low contact pressures, allowing for a greater range of motion. The reported results strongly indicate that compliant polymers may offer an opportunity to improve current TKRs. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2009-08-11 14:59:50.801

A verified elasto-viscoplastic finite element model is used to develop a better understanding of the performance of embankments with geosynthetic reinforcement constructed over rate-sensitive soil. The interaction between reinforcement and prefabricated vertical drains (PVDs) and their effects on time-dependent behaviour of embankments are examined. For rate-sensitive soils, the generation of creep-induced pore pressures following the end of construction is evident along the potential slip surface. As a result, the minimum factor of safety with respect to embankment stability occurs after the end of construction. The combined use of reinforcement and PVDs are shown to provide an effective means of minimizing creep-induced excess pore pressure, increasing overall stability, and decreasing deformation of the embankments. The combined effects of the viscoelastic properties of geosynthetic reinforcement (polyester, polypropylene and polyethylene) and the rate-sensitive nature of foundation soils on the performance of embankments are examined. The effect of various factors, including reinforcement type (i.e., stiffness and viscosity), soil viscosity, construction rate and allowable long-term reinforcement strain, on the time-dependent behaviour of embankments are considered. The long-term performance of reinforced embankments is investigated for different maximum allowable long-term reinforcement strains. From a series of finite element analyses, the ideal allowable reinforcement strains to minimize embankment deformation while providing optimum long-term service height of the embankment, considering the effect of soil and reinforcement viscosity, are proposed for soils similar to those examined in this study. The currently proposed design methods for embankments with creep-susceptible reinforcement over rate-sensitive soils appear to be overly conservative. This study proposes a refined approach for establishing the allowable long-term reinforcement strains that are expected to provide adequate performance while reducing the level of conservativeness of reinforced embankment design. Finally, a previously developed elasto-viscoplastic constitutive model is modified to incorporate the effect of soil structure using a state-dependent fluidity parameter and damage law. The model was evaluated against data from a well-documented case study of a reinforced test embankment constructed on a sensitive Champlain clay deposit in Saint Alban, Quebec. The benefit of basal reinforcement and the effect of reinforcement viscosity are then discussed for these types of soil deposits. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2011-01-21 22:26:40.133

Deep-corrugated steel culverts (with a corrugation wavelength of 400mm and amplitude of 150mm) can be used as an effective alternative for short-span bridges. Current design methods are typically based on two-dimensional finite element analysis. This thesis reports results from three-dimensional finite element analysis, with explicit modelling of the geometry of the corrugated plates (called corrugated analyses) and employing the orthotropic shell theory (called orthotropic analyses), for a specific box culvert having a 10 m span and 2.4 m rise. The results were compared to previously reported experimental data where a specific large span box culvert was tested under controlled laboratory conditions. The behaviour of the box culvert under small vertical displacement without any soil support was modelled to isolate the structure response. The box culvert was also modelled when subject to fully loaded dump truck, and when loaded using a tandem axle frame to service and ultimate loads. Both corrugated and orthotropic analyses successfully captured the response of the box culvert when backfilled and loaded using dump truck and axle frame loading. It was found that the orthotropic model overestimated the culvert stiffness at the ultimate limit state, but provided effective estimates of response up to the factored design loads. The corrugated model with geometric nonlinearity was required to capture the real behaviour of the corrugated plates up to the ultimate limit state. New insight into the failure mechanisms of the box culvert were provided by the corrugated model analysis. A parametric study was then performed for 86 different long-span box and arch culverts, examining live load spreading in the axial direction, number of loaded lanes, design truck position, culvert geometry, plate thickness, and the existence of pavement. The results were then compared to the moment and thrust equations in the 2006 Canadian Highway Bridge Design Code (CHBDC) to check the performance of the current design equations. CHBDC equations overestimated the earth and live load bending moments, and did not give the correct trend for different spans. CHBDC thrust equations were found to underestimate the earth and live load thrust values for arch culverts. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2011-04-26 15:33:45.103

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To evaluate the impact of reduced truck tire pressure on strain response of low volume spring-restricted roads, research was conducted on two instrumented pavement sections in Manitoba, Canada. Tire pressure control systems tests were carried out at the sections in spring and fall 2009. Measured maximum tensile strain at the bottom of asphalt layer decreased by 15-20% when tire pressure was reduced by 50%. Measured strain at the bottom of asphalt layer in fall is about 50% less than in spring. The effects of gauge orientation, truck speed, and tire offset from the strain gauge were also analyzed. A finite element model with static load was developed and verified. The bearing capacity is lower in spring than in normal condition for flexible pavements subject to deep frost action. Reduced tire pressure is effective to reduce bottom up failure of the pavement, and is less effective to prevent rutting.

In this thesis, a two-dimensional (2D) finite element (FE) model was developed from the patient’s hip DXA image to evaluate osteoporotic fracture risk. The loading configuration was designed to simulate a lateral fall onto the greater trochanter. Bone inhomogeneous mechanical properties (e.g. Young’s modulus) assigned to the FE model were correlated to bone mineral density captured in DXA image using empirical functions. In-house MATLAB codes were developed to investigate the effects of different factors such as bone mineral density, femoral neck length, neck diameter, neck angle and patient’s body weight on fracture risk. The 2D FE model constructed from DXA image was able to de-termine the factors which affect fracture risk to a greater extent based on the location of femur. The model developed here can be considered as a first attempt for investigating the effects of different parameters on fracture risk using patient specific 2D FE method.

Laser forming is an innovative technique that uses a defocused laser beam to form sheet metal by thermal stresses rather than external forces. Promising potential applications of laser forming include rapid prototyping, straightening, aligning and adjusting of macro/micro-metallic components. Research to-date on laser forming has been largely focused, theoretically and experimentally, on the problem of characterization of process parameters on the forming results, and computational simulations of laser forming remain limited only providing the insight into the process. This study investigates the laser forming processes using the finite element analysis with respect to material responses during the processes, including complex processes, process optimization, process reliability and the effects of thermal and mechanical material properties. The first part of this thesis describes a nonlinear transient three-dimensional heat transfer finite element model and a rate dependent three-dimensional deformation model, which are developed for the laser forming simulations. Simulations are performed using an indirect coupled thermal-structural method for the processes of a straight-line heating, a circle-line heating, and a laser micro-adjustment. The thermo-mechanical behaviours during the straight-line heating process are presented in terms of temperature, stress and strain, and displacement distributions. The emphasis in the circle-line heating simulations is placed on the characterization of the quality of the deformed geometry by obtaining the radial and circumferential waviness. The micron size movements induced by laser point heating are focused the simulations of the micro-adjustment process. Simulation results are validated by comparison with published data or correlation to engineering point of view. The second part of this thesis presents the development of an effective method to determine optimum process parameters in laser forming. For the process optimization, design optimisation techniques are introduced into the finite element analysis of the laser forming process. The optimum parameter values to produce a predefined bend angle of 3° in the straight-line heating process are sought by two optimization procedures - one is the procedure involving the non-gradient method and the other is the gradient-based method. Optimum values of laser power, feed rate, beam diameter and number of passes are determined to produce a predefined bend angle in a multiple straight-line heating process using the two optimization procedures. A more suitable optimisation method for laser forming is chosen, which is used for a new optimisation problem to generate a maximum bend angle in a single pass of laser forming. In the third part of this thesis, a strategy to assess the reliability of the laser forming process is established by employing a well-known reliability analysis method, the Monte Carlo simulation. Robustness of the straight-line heating process of producing 3° with the optimum parameters determined by process optimization is evaluated with regard to the uncertain input variables of laser power, feed rate, plate thickness and coefficient of thermal expansion via the Monte Carlo simulations based on the finite element simulations of the process. The final part of this thesis identifies the effects of material properties on the bend angle resulting from laser forming. Process sensitivity to the properties of coefficient of thermal expansion, thermal conductivity, specific heat capacity and elastic modulus is investigated by measuring the Pearson product-moment correlation coefficient between the properties and the bend angle, which are based on the Monte Carlo simulations of laser forming. The conclusion is that the developed finite element models contribute to a better understanding of the laser forming process, and the optimization procedure is able to be used for straightening, aligning and adjusting of components.

This thesis first describes the reverse method of transformer design. An existing magnetic model for full-core shell-type transformers, based on circuit theory, is summarised. A magneto-static finite element model is introduced and two sample transformers are analysed. The magnetic model based on finite element analysis is shown to be more accurate than the model based on circuit theory. Partial-core resonant transformers are then introduced and their characteristics are explained using an equivalent circuit model. A method of measuring the winding inductances under resonant operation is developed and used to investigate the characteristics of two different tuning methods. A finite element model of the partial-core resonant transformer is developed by adopting the model for full-core shell-type transformers. The model results accurately match the measured inductance variation characteristics of three sample transformers and predict the onset of core saturation in both axial-offset and centre-gap arrangements. A new design of partial-core resonant transformer is arrived at, having an alternative core and winding layout, as well as multiple winding taps. The finite element model is extended to accommodate the new design and a framework of analysis tools is developed. A general design methodology for partial-core resonant transformers with fixed inductance is developed. A multiple design method is applied to obtain an optimal design for a given set of specifications and restrictions. The design methodology is then extended to devices with variable inductance. Three design examples of partial-core resonant transformers with variable inductance are presented. In the first two design examples, existing devices are replaced. The new transformer designs are significantly lighter and the saturation effects are removed. The third design example is a kitset for high-voltage testing, with the capability to test any hydro-generator stator in New Zealand. The kitset is built and tested in the laboratory, demonstrating design capability. Other significant test results, for which no models have yet been developed, are also presented. Heating effects in the core are reduced by adopting an alternative core construction method, where the laminations are stacked radially, rather than in the usual parallel direction. The new kitset is yet to be used in the field.