An ever increasing demand to exploit oil and natural gas reserves has significantly increased extraction activities even in the remotest regions of the Arctic and sub-Arctic regions of the Canadian North. Steel pipelines are the most efficient mode for transporting and distributing these resources. These pipelines, particularly buried in cold region, often subjected to extreme geo-environmental conditions, where significant inelastic deformation may occur resulting in localized wrinkles. Under continued deformation, there is a possibility of excessive cross-sectional deformation at wrinkle locations, eventually leading to fracture or damage in the pipe wall jeopardizing pipeline safety and integrity . Prior research indicated that occurrence of fracture in pipe wrinkle is rare under monotonic load-deformation process. However, a recent field fracture was observed within the wrinkle location of an energy pipeline. Similar failure mode was observed in a laboratory specimen at the University of Alberta. Both field and laboratory observations had indicated that the final failure was a “tearing” failure at the fold of the telescopic wrinkles resulting from monotonic application of axial load not aligned with pipe axis. This research program was designed to study this specific failure mode and to develop design tool for pipeline engineers. This research started with examining the failed field and test specimens. A preliminary investigation was carried out using nonlinear finite element (FE) model to simulate test and field behaviour. Numerical results have indicated that even under monotonic loading, significant strain reversals could occur at the wrinkle fold . Presence of these strain reversals was proposed as the preliminary failure criterion responsible for this unique failure mechanism. In next phase, a full-scale ‘pipe-wrinkling’ test program was carried out concurrent to this research to better understand the loading condition responsible for this type of failure. Results of this test program have shown the presence of tearing fracture or rupture in the pipe walls of several of test specimens. A series of FE analyses was then carried out to predict and verify the behaviour of these test specimens. After successful simulation of the test behaviour, further numerical analyses were carried out using tension coupon model developed herein to simulate the material behaviour using the material test data and hence to formulate the limiting conditions in terms of critical strain responsible for the tearing failure. Based on these numerical results, a double criterion  ‘Strain Reversal’ and ‘Critical Equivalent Plastic Strain Limit’, were proposed to predict tearing fracture of wrinkled pipe under monotonic loading. Results of these numerical analyses have demonstrated that the proposed criteria predict this failure mode with reasonable accuracy. In the final phase of this research, a parametric study was carried out to consider the effect of different parameters on failure modes of wrinkled pipe. Results of this parametric study describe the range of parameters under which the tearing mechanism can/may exhibit. / Structural Engineering

Complex wrinkle patterns have been observed in various thin film systems, typically with integrated hard and soft materials for various technological applications as well as in nature. The underlying mechanism of wrinkling has been generally understood as a stress-driven instability. On an elastic substrate, equilibrium and energetics set the critical condition and select the wrinkle wavelength and amplitude. On a viscous substrate, wrinkles grow over time and kinetics select the dominant wavelength. More generally, on a viscoelastic substrate, both energetics and kinetics play important roles in determining the critical condition, the growth rate, and wrinkle patterns. The dynamics of wrinkling, while analogous to other phase ordering phenomena, is rich and distinct under the effects of a variety of stress conditions and nonlocal film-substrate interactions. In this study, a new mathematical model is developed for wrinkling of isotropic and anisotropic elastic films on viscoelastic substrates. Analytic solutions are obtained by a linear perturbation analysis and a nonlinear energy minimization method, which predict the kinetics of wrinkle growth at the initial stage and the equilibrium states at the long-time limit, respectively. In between, a power-law coarsening of the wrinkle wavelength is predicted by a scaling analysis. Numerical simulations confirm the analytical predictions and show diverse wrinkle patterns under various stress conditions. For isotropic elastic films, a transition from parallel wrinkles to zigzag patterns is predicted under anisotropic biaxial stresses. For cubic crystal films, the anisotropic elastic property leads to formation of orthogonal wrinkle patterns under equi-biaxial stresses. In general, the competition between the stress anisotropy and the material anisotropy controls the evolution of wrinkle patterns. Based on the mathematical model, two potential applications of the wrinkling phenomenon are explored, one for surface patterning and the other for estimating viscoelastic properties of thin polymer films. The theoretical and numerical results from this study are compared with experimental observations that are available in literature and through collaborations with experimental groups. The last chapter of this dissertation considers ratcheting-induced wrinkling for an elastic film on an elastoplastic substrate under cyclic temperatures, demonstrating an analogy between plastic ratcheting and viscous creep. / text

No description available.

L’usage de matériaux composites est en plein essor dans le monde de l’industrie, particulièrement dans des domaines comme l’aéronautique, les transports ou la production d’énergie et ce développement amène une forte production de structures composites, notamment des pièces de grandes dimensions. La conception de ces structures en composite nécessite une connaissance approfondie du comportement mécanique du composite afin de garantir l’intégrité de la structure. Or le comportement mécanique des matériaux composites est de nature hétérogène avec une certaine variabilité sur les différents paramètres mécaniques. Cette variabilité est causée par deux principales sources : la variabilité intrinsèque au matériau due à des variations physiques au sein du composite, et la variabilité due aux défauts de mise en œuvre. La thèse, qui est présentée, s’intéresse à cette deuxième source de variabilité, à savoir la présence de défauts de mise en œuvre et son influence sur le comportement mécanique du composite. Deux défauts de mise en œuvre sont étudiés dans cette thèse, la porosité et le plissement, en suivant une analyse probabiliste. La première partie de l’étude rassemble l’ensemble de l’état de l’art sur les défauts de porosité et de plissement, ainsi que sur les analyses probabilistes dans le domaine des composites. Une deuxième partie de l’étude se consacre à la caractérisation probabiliste des défauts de porosité et de plissement en analysant la variabilité de chaque paramètre caractéristique du défaut et en la modélisant à l’aide de loi de distribution qui sont implémentées dans un code de calcul afin de modéliser numériquement la porosité observée expérimentalement. Une troisième partie de l’étude s’intéresse à l’influence des défauts de porosité et de plissement sur le comportement mécanique en quasi-statique et en fatigue. Cette étude mécanique compare les résultats d’essais expérimentaux sur un matériau sain, deux matériaux avec deux taux de porosité différents et sur deux matériaux avec un plissement de dimensions différentes, afin de pouvoir quantifier l’influence des défauts et déterminer un modèle de dégradation des propriétés mécaniques en fonction du défaut. L’étude mécanique en quasi-statique est complétée par une analyse de la variance afin de bien séparer la variabilité des propriétés mécaniques due aux défauts et celle due directement à l’essai lui-même. L’ensemble des résultats de cette étude permet donc d’identifier les deux types de défauts avec un ensemble de paramètres caractéristiques, ainsi que leur influence sur le comportement mécanique, tout en prenant en compte la variabilité observée sur les défauts et leur influence mécanique, et de modéliser numériquement l’ensemble de ces observations. / The use of composite materials increases in the world of industry, particularly in sectors such as aeronautics, transport or energy production and this development leads to a strong production of composite structures, including large dimensions. The design of these composite structures requires a thorough knowledge of the mechanical behavior of the composite to ensure the integrity of the structure. However, the mechanical behavior of composite materials is heterogeneous in nature with a certain variability on the different mechanical parameters. This variability is caused by two main sources: the intrinsic variability of the material due to physical variations within the composite, and the variability due to defects in implementation. The thesis, which is presented, focuses on this second source of variability, namely the presence of implementation defects and its influence on the mechanical behavior of the composite. Two defects of implementation are studied in this thesis, porosity and wrinkle, following a probabilistic analysis. The first part of the study brings together all the state of the art on porosity and wrinkle defects, as well as on probabilistic analyzes in the field of composites. A second part of the study is devoted to the probabilistic characterization of porosity and wrinkle defects by analyzing the variability of each characteristic parameter of the defect and modeling it using a distribution law that are implemented in a calculation code to numerically model the experimentally observed porosity. A third part of the study focuses on the influence of porosity and wrinkle defects on quasi-static and fatigue mechanical behavior. This mechanical study compares the results of experimental tests on a healthy material, two materials with two different porosity states and two materials with a wrinkle of different dimensions, in order to be able to quantify the influence of the defect and to determine a model of degradation of mechanical properties according to the defect. The quasi-static mechanical study is supplemented by an analysis of the variance in order to separate the variability of the mechanical properties due to the defect and that due directly to the test itself. All the results of this study thus make it possible to identify the two types of defects with a set of characteristic parameters, as well as their influence on the mechanical behavior, while taking into account the variability observed on the defects and their mechanical influence, and to model numerically all these observations.

Context. Real time rendering has many challenges to overcome, one of them being character realism. One way to move towards realism is to use wrinkle maps. Although already used in several games, there might be room for improvement, common practice suggests using two wrinkle maps, however, if this number can be reduced both texture usage and workload might be reduced as well. Objectives. To determine whether or not it is possible to reduce the number of wrinkle maps from two to one without having any significant impact on the perceived realism of a character. Methods. After a base character model was created, a setup in Maya were made so that dynamic wrinkles could be displayed on the character using both one and two wrinkle maps. The face were animated and rendered, displaying emotions using both techniques. A two-alternative forced choice experiment was then conducted where the participants selected which implementation displaying the same facial expression and having the same lighting condition they perceived as most realistic. Results. Results showed that some facial expressions had more of an impact of the perceived realism than others, favoring two wrinkle maps in every case where there was a significant difference. The expressions with the most impact were the ones that required different kinds of wrinkles at the same area of the face, such as the forehead, where one variant of wrinkles run at a more vertical manner and the other variant runs horizontally along the forehead. Conclusions. Using one wrinkle map can not fully replicate the effect of using two when it comes to realism. The difference on the implementations are dependant on the expression being displayed.

Controlling the specific adhesive properties of surfaces is a technologically complex challenge that has piqued the interest of many research groups around the world. While many scientists have used complex topographic and chemically altered surfaces to tune adhesion, others have shown that naturally occurring phenomena, such as elastic instabilities, can impact adhesion. We provide a thorough investigation into the effects of periodic surface buckling instabilities, or wrinkles, on adhesion. Wrinkles are an attractive surface patterning alternative as they form spontaneously over large areas and their dimensions, namely wavelength and amplitude, can be controlled on length scales relevant for adhesion control. We focus on the development of fundamental relationships that relate wrinkle adhesion to materials properties and topographic feature geometry. To accomplish this goal, we first investigate the separation of a flat rigid punch from a single elastic cylinder, which models the separation of a single wrinkle. The knowledge gained from this study is then utilized to develop a scaling expression relating adherence force to wrinkle geometry, materials properties, and testing geometry. This scaling theory is validated by varying these parameters systematically in a series of model wrinkle adhesion experiments. Added complexity in the form of varied crosslinker density, which alters the ratio of storage to loss moduli, and geometric confinement effects on wrinkle adhesion are then studied. Finally, a novel technique for fabricating biaxial wrinkles with two independently-adjusted wavelengths is developed, adding an additional parameter which can be tuned to further control adhesion. A single elastic cylinder was probed with a finite rigid flat probe, allowing the separation mechanism of a single "macro" scale wrinkle to be determined. Rather than a long cylinder contact mechanism, which has been utilized in describing wrinkle adhesion mechanisms in the past, an elliptical contact area approximation was found to more appropriately describe the single cylinder adhesion data. To consider the impact of an array of cylinders on adhesion, a model wrinkle system comprised of an elastomeric foundation and chemically-simple polymer film was developed. The wrinkle wavelength, amplitude, substrate modulus, and probe radius were varied, and the normal adhesive response of each aligned wrinkled surface was determined. Overall, wrinkles were found to decrease the separation force relative to a smooth surface and the separation force varied inversely with the square root of a wrinkle dimension, either wavelength or amplitude. The effects of viscoelasticity on the adhesion of a wrinkled substrate that is geometrically confined was studied. Wrinkled surface features were molded onto the surface of a rigid cylindrical probe, and the normal adhesion of these probes contacting thin elastomeric films fabricated with varying crosslinker concentrations was measured. The materials-defined length scale relating adhesion energy and modulus controlled the wrinkle feature sizes that impacted the adhesive response of each smooth film. In the most highly crosslinked films, small wrinkles increased both the separation force and adhesion energy of the interface two-fold, while large wrinkles reduced adhesion to almost nothing. Capitalizing on knowledge gained in the fabrication of many wrinkled surfaces, a novel technique for fabricating biaxial wrinkles was developed. Aligned wrinkles were formed on a partially crosslinked substrate, the modulus of the substrate was increased by allowing the material to crosslink completely, and a mechanical compressive strain was then imposed orthogonal to the primary wrinkle direction. This process resulted in the formation of biaxial wrinkled surfaces with two distinct, independently controlled lateral dimensions or wavelengths.

The application of the wrinkle measuring method described in Müller et al. (2017) and the subsequent evaluation algorithm of a range of deep-drawn samples were used to determine the influences and interdependencies of blankholder force, tool temperatures, and drawing height on the formation of wrinkles in paperboard. The main influences were identified and quantitatively evaluated. For the given experimental space, a regression function was derived and validated in further experiments. It was shown that a quadratic regression was superior to the previously used linear regression. The findings were discussed and compared with the results of similar experiments from past publications. Special attention was given to the wrinkles formed and the resulting quality of the formed paperboard cups. The restrictions of the data acquisition from the measuring method that was used and limitations of the model were presented to demonstrate the reliability of the results.

No description available.

Young adult dystopian fictions follow the patterns established by the classic adult dystopias such as George Orwell's 1984 and Aldous Huxley's Brave New World, but not completely. Young adult dystopias tend to end happily, a departure from the nightmarish ends of Winston Smith and John Savage. Young adult authors resist hopelessness, even if the fictional world demands it. Using a rhetorical approach established by Wayne Booth in The Rhetoric of Fiction and The Company We Keep, this thesis traces the reasons for the inclusion of hope and the strategies by which hope is created and maintained. Booth's rhetorical approach recognizes that a narrative is a relational act. At issue in this study is the consideration of what follows from viewing a narrative as a dynamic exchange between text, author and reader. Through a focus on rhetoric as identification, the responsibilities of both the author and the reader to a text are identified and discussed. Three young adult novels, A Wrinkle in Time by Madeleine L'Engle, The Giver by Lois Lowry and Feed by M.T. Anderson will be analyzed as case studies. Together the analysis of these novels reveals that storytelling is an act of forging identifications and forming alliances. The reader becomes more than just a spectator of the author's rhetoric; the reader is a fully involved member of the interpretive and evaluative process.

The application of the wrinkle measuring method described in Müller et al. (2017) and the subsequent evaluation algorithm of a range of deep-drawn samples were used to determine the influences and interdependencies of blankholder force, tool temperatures, and drawing height on the formation of wrinkles in paperboard. The main influences were identified and quantitatively evaluated. For the given experimental space, a regression function was derived and validated in further experiments. It was shown that a quadratic regression was superior to the previously used linear regression. The findings were discussed and compared with the results of similar experiments from past publications. Special attention was given to the wrinkles formed and the resulting quality of the formed paperboard cups. The restrictions of the data acquisition from the measuring method that was used and limitations of the model were presented to demonstrate the reliability of the results.