No description available.

<p> The effect of strain hardening rate and material strength on the development of surface roughness in AA6111 was investigated. No measurable change in the rate of roughening, or in the surface morphology was observed due to altering the strain hardening rate by using different test temperatures. Changing the material strength and strain hardening rate by altering the precipitation state also gave no significant change in either roughening rate or morphology with respect to strain. The development of surface roughness is also independent of strain history. Samples subjected to an intermediate polish after 20% true strain resumed roughening at the same rate regardless of amount of previous tensile strain. The development of surface roughness is dependent on only the strain level to which the sheet is deformed. The surface morphology seems to be controlled by the combination and distribution of texture components on the surface. The rate of roughening is grain size dependent and the surface grain size may provide a key to controlling roughening. </p> / Thesis / Master of Applied Science (MASc)

The concept of the Forming Limit Diagram (FLD) has proved to be useful for representing conditions for the onset of sheet necking, and is now a standard tool for characterizing materials in terms of their overall forming behavior. In this study, the M-K approach, in conjunction with Gurson model, is used to calculate FLDs. The influences of mechanical properties, including strain hardening, strain rate sensitivity, as well as the void nucleation, growth and coalescence, on the FLDs are examined. Most sheet metals undergo multiple deformation modes (strain paths) when being formed into complex manufacturing parts. When the strain path is changed in the deformation processing of metal, it's work-hardening and flow strength differs from the monotonic deformation characteristics. As a consequence, sheet metal formability is very sensitive to strain path changes. In this study, the hardening behavior and damage evolution under non-proportional loading paths are investigated. The effect of strain path change on FLDs is studied in detail. FLDs are conventionally constructed in strain space and are very sensitive to strain path changes. Alternatively, many researchers represented formability based on the state of stress rather than the state of strain. They constructed a Forming Limit Stress Diagram (FLSD) by plotting the calculated principal stresses at necking. It was concluded that FLSDs were almost path-independent. In this work, the FLSD has been constructed under non-proportional loading conditions to assess its path dependency when damage effect is included. / Thesis / Master of Applied Science (MASc)

The use of polymeric materials in the manufacturing industry has vastly increased since the 1950’s. Because of the large amounts of material involved in modern processing operations, attempts have been made over the years to numerically simulate the processes, in the hope of optimizing operating parameters. However, in contrast to other, more traditional materials such as steel or glass, there is not a well understood connection between the microscopic structure and the (highly non-linear) macroscopic physical response of polymers. Because of this lack of microscopic cause - macroscopic effect knowledge, many descriptions of the physical response of polymers are largely phenomenological ones; that is, the equations used to model the stress/strain response make no attempt to convey information about the microscopic structure of the material.</p> <p> In the present work, five constitutive equations - Mooney-Rivlin, Ogden, G’Sell Two-term Polynomial and K-BKZ - are used to model the stress/strain response of two different polymers commonly used in thermoforming and blowmolding operations, ABS and HDPE, to uniaxial elongation and equibiaxial extension. The models are compared to experimental stress/strain data obtained from an industrial source, and the applicability of their predictions are investigated with regards to variations in strain, strain rate and temperature. Lastly, since the vast majority of real processes involve biaxial, not uniaxial, deformations, the ability of the models to predict equibiaxial response using parameters fit solely to uniaxial data is considered, in order to investigate the possibility of being able to forego the need for expensive, difficult biaxial tests. / Thesis / Master of Engineering (MEngr)

No description available.

The human gut is colonized by a vast bacterial community that is currently rather well characterized at the species level. Yet, each of these species harbor a tremendous amount of individual genetic variations. Our understanding of the human gut microbiome, its dynamics, composition and impact on host health requires a deeper characterization of its bacteria. The amount of publicly available shotgun sequencing data as well as development of computational tools allowed to reach strain-level resolution in metagenomic analysis. In this thesis, I present systematic approaches to study the strain-level variation using complementary phylogenetic and pangenomic methods aiming to address fundamental questions about microbiome transmission in early life as well as impact of functions encoded by microbiome strains on host health. Across two different cohorts, I used a recently-developed strain-tracking method to assess the impact of delivery conditions on the initial seeding of the infant gut microbiome. While mode of delivery (vaginal or C-section) had a great impact on the amount of mother strains transmitted to the infant, place of delivery (home or hospital) and breastfeeding duration also had an impact on the ongoing development, strain replacement or persistence over the first year of life. In comparison, the father appeared as a stable source of strains independent of the delivery mode. This initial mother seeding, despite being reduced in C-section delivery, can be compensated by Fecal Microbiota Transfer, demonstrating the need of fecal microbiota exposure in seeding during vaginal delivery. In addition, strain dynamics was shown partially explained by differences in the carbohydrates degrading capacities, especially the ability to feed on Human Milk Oligosaccharides. These differences in metabolism between strains were also observed by their respective empirical growth rate that was seen associated with transmission and persistence in the infant gut. To further systematically assess the differences of metabolic capacities between strains and the impact on hosts, I developed a new method to identify gene groups (PanPhlAn Genomic Islands, PGIs) co-present across conspecific strains in metagenomic samples. By applying this method on a large collection of over 10,000 samples, I was able to build a set of 5,315 PGIs. Deeper characterization of these PGIs revealed horizontal gene transfer across species, high variation in carbohydrate metabolism capacities and association with the host lifestyle and health status. Together, these analyses demonstrated the complementary aspects of strain variation andstressed out the need to encompass both strain phylogeny and gene content to fully understand the microbiome at the strain-level.

Examination of deformation temperature, flow vorticity, and strain symmetry in the Loch Eriboll, Loch More, and Assynt regions of the Moine thrust zone (MTZ) in northwest Scotland allows quantitative kinematic and thermal characterization of a crustal-scale shear zone at the base of the Scandian (435-425 Ma) orogenic wedge. Quartz crystal fabrics, kinematic vorticity (Wm), and strain estimates from the ductile thrust sheets in this region are used to determine how pure and simple shear components of deformation are partitioned, and indicate that these processes may be thermally, structurally, and lithologically dependent. Vorticity analysis of samples collected along strike in the MTZ and overlying Moine nappe indicate that Scandian thrusting and deformation involved a considerable pure shear component. Integrated strain and vorticity estimates indicate that significant sub-vertical foliation normal shortening has occurred as nappe stacking progressed. Along strike Wm variation could not be directly correlated with changes in footwall structural architecture, lithology, deformation temperatures, or structural depth and are thus interpreted to reflect local variability driven by a complex interplay of these and possibly other factors. Quartz c- and a-axis fabrics indicate that deformation in the footwall of the Moine thrust involved plane strain to general flattening strain with only a minor rotational (non-coaxial) component. In contrast, deformation in the Moine nappe was strongly non-coaxial, as indicated by asymmetric single girdle c-axis fabrics. Quartz c-axis opening angles and microstructures suggest that deformation temperatures increase from north to south and from structurally lower to structurally higher levels in the footwall to the Moine thrust. Vertical ductile thinning must be accommodated by either volume loss or extrusion of material towards the synorogenic topographic surface. Extrusion towards the synorogenic topographic surface implies a causal link between upper and lower crustal processes, with significant implications for the kinematic, geometric, and kinetic (deformation rates) evolution of the Scandian orogenic wedge. New thermobarometric and deformation temperature estimates are combined with structural and kinematic investigations to characterize the thermal structure of the Moine, Ben Hope, and related nappes. At the leading edge of the Moine thrust, subhedral garnets with prograde compositional growth zoning yield peak temperatures (grt-bio) of 440-492 °C at 4.5-6.0 kbars from Creagan Meall Horn to northern Assynt. Three samples collected at similar structural positions along the leading edge of the Moine nappe yield deformation temperatures of 420-460 °C, as determined from quartz c-axis opening angles. At the structurally highest position in the Moine nappe, garnet prograde compositional zoning profiles are preserved and samples yields P-T estimates of 565-571 °C (grt-bio) and 4.5-5.1 kbar (GRAIL barometer, minimum pressure due to absence of Al2SiO5 phase). Quartz c-axis fabrics of samples collected at similar structural positions yield deformation temperature estimates of 490-565 °C. In the structurally higher Ben Hope nappe, two phases of prograde compositional growth zoning are preserved in garnet bearing amphibolite near Portvasgo. The later outer garnet rim records P-T conditions of 655-672 °C at 3.9-5.1 kbars. The inverted metamorphic sequence from the Moine to the Naver thrust is mostly intact and is interpreted to be Scandian (435-420 Ma) in age. It is likely that the formation of this inverted sequence is due to a combination of progressive accretion of successively lower grade thrust sheets onto the base of the Scandian wedge and heating of the Moine and Ben Hope nappes from above by the relatively higher temperature migmatites of the Naver thrust. Vertical ductile thinning, in conjunction with erosion and normal faulting, likely led to rapid exhumation of the Scandian nappe pile and in turn preserved the inverted metamorphic sequence. / Ph. D.

The Occupational Stress Inventory Revised Edition (OSI-R) and an Individual Data Form were used to determine the turnover intentions of rehabilitation counselors based on an interactive model of stress, strain, and coping. Occupational stress, strain, coping resources, and turnover intentions were examined in relationship with various demographic variables collected from a national sample of 982 members of the American Rehabilitation Counselors Association (ARCA). Demographic variables included age, gender, ethnicity, certification status as a Certified Rehabilitation Counselor (CRC), years of experience, practice setting, the number of clients on a counselor's caseload, and the amount of hours worked per week. Data were collected through a mail survey, with a response rate of 67% (N = 657). However, of those respondents only 22% (N=145) had complete data and met the inclusion criteria. Inclusion criterion consisted of considering oneself to be employed full-time as a practicing rehabilitation counselor. Based on the usable data (N=145), respondents were on average 44 years old and Caucasian, with 63% being female. Over half of the respondents were certified as rehabilitation counselors, with an average number of nine years of certification. The average number of years of experience as a rehabilitation counselor was approximately ten and respondents worked an average of 45 hours per week with an average caseload size of 88 clients. Path analysis was used to analyze causal relationships among turnover related variables. The hypothesized model included age, experience, number of clients on a caseload, occupational stress, strain, coping resources, and turnover intention. The tested model explained 37.5% of the variance in turnover intentions. The results suggest that the turnover intentions of rehabilitation counselors is meaningfully accounted for by variables contained in the model. Occupational stress produced the largest significant effect (B=.404) and had the most influence on turnover intentions. This indicates that it is occupational stress inherent in the job functions of rehabilitation counselors, and not individual coping resources or demographic variables that account for turnover in the field of rehabilitation. Therefore rehabilitation agencies should examine the roles that they place rehabilitation counselors in versus the individual characteristics of rehabilitation counselors in order to reduce turnover in the field. / Ph. D.

Sensor-embedded tires, known as intelligent tires, have been widely studied because they are believed to provide reliable and crucial information on tire-road contact characteristics e.g., slip, forces and deformation of tires. Vehicle control systems such as ABS and VSP (Vehicle Stability Program) can be enhanced by leveraging this information since control algorithms can be updated based on directly measured parameters from intelligent tire rather than estimated parameters based on complex vehicle dynamics and on-board sensor measurements. Moreover, it is also expected that intelligent tires can be utilized for the purpose of the analysis of tire characteristics, taking into consideration that the measurements from the sensors inside the tire would contain considerable information on tire behavior in the real driving scenarios. In this study, estimation methods for the tire-road contact features by utilizing intelligent tires are investigated. Also, it was discussed how to identify key tire parameters based on the fusion technology of intelligent tire and tire modeling. To achieve goals, extensive literature reviews on the estimation methods using the intelligent tire system was conducted at first. Strain-based intelligent tires were introduced and tested in the laboratory for this research. Based on the literature review and test results, estimation methods for diverse tire-road contact characteristics such as slippages and contact forces have been proposed. These estimation methods can be grouped into two categories: statistical regressions and model based methods. For statistical regressions, synthetic regressors were proposed for the estimation of contact parameters such as contact lengths, rough contact shapes, test loads and slip angles. In the model-based method, the brush type tire model was incorporated into the estimation process to predict lateral forces. Estimated parameters using suggested methods agreed well with measured values in the laboratory environment. By utilizing sensor measurements from intelligent tires, the tire physical characteristics related to in-plane dynamics of the tire, such as stiffness of the belt and sidewall, contact pressure distribution and internal damping, were identified based on the combination of strain measurements and a flexible ring tire model. The radial deformation of the tread band was directly obtained from strain measurements based on the strain-deformation relationship. Tire parameters were identified by fitting the radial deformations from the flexible ring model to those derived from strain measurements. This approach removed the complex and repeated procedure to satisfy the contact3 constraints between the tread and the road surface in the traditional ring model. For tires with different specifications, identification using the suggested method was conducted and their results are compared with results from conventional methods and tests, which shows good agreements. This approach is available for the tire standing still or rolling at low speeds. For tires rolling at high speeds, advanced tire model was implemented and associated with strain measurements to estimate dynamic stiffness, internal damping effects as well as dynamic pressure distributions. Strains were measured for a specific tire under various test conditions to be used in suggested identification methods. After estimating key tire parameters step by step, dynamic pressure distributions was finally estimated and used to update the estimation algorithm for lateral forces. This updated estimation method predicted lateral forces more accurately than the conventional method. Overall, this research will serve as a stepping stone for developing a new generation of intelligent tire capable of monitoring physical tire characteristics as well as providing parameters for enhanced vehicle controls. / PHD

The liver is one of the most frequently injured abdominal organs in motor vehicle collisions. Although previous studies have quantified the tensile failure properties of human liver parenchyma at 48hrs postmortem, it is currently unknown how the material properties change between time of death and 48hrs postmortem. Therefore, the purpose of this study was to quantify the effects of postmortem degradation on the tensile material properties of bovine liver parenchyma when stored in DMEM or saline. Fourteen fresh bovine livers were obtained from a local slaughter house and stored in either DMEM or saline as large blocks, small blocks, or slices of tissue. Multiple parenchyma dog-bone samples from each liver were tested once to failure at three time points: ~6hrs, ~24hrs, and ~48hrs postmortem. The data were then analyzed to determine if there were significant changes in the material properties with respect to postmortem time. The results showed that the failure strain decreased significantly between 6hrs and 48hrs after death when stored as large blocks in saline. Conversely, neither the failure stress nor failure strain changed significantly with respect to postmortem time when stored as large blocks in DMEM. The modulus did not significantly change for tissue stored as large blocks in either fluid. Preliminary results indicated that reducing the tissue storage size had a negative effect on the material properties and cellular architecture. Overall, this study illustrated that the effects of postmortem liver degradation varied with respect to the preservation fluid, storage time, and storage block size. / MS