Flotation process is mineral processing technique used for separating valuable minerals from the gangue. The research presented in this thesis deals with assessing features that can help in measuring the performance (observing) bitumen flotation process and modeling damage in flotation units. A timely measure of oilsands and process stream contents can be used to observe and control the separation performance. To this end, flotation experiments were conducted and hyperspectral images of the ore and the process stream were taken to determine whether spectral information can predict the bitumen and fines content of ore samples and establish relationship a between these variables and the froth colour. Several features that appear to correspond to clay and quartz were present. Flotation cells are prone to wear damage by particles entrained in the slurry. A wear damage model was developed to predict the damage accumulated over a period of time. Particle image velocimetry experiments were conducted on physical flotation model to understand the flow behavior of the solid particles near the wall of the flotation unit. A preliminary wear test was conducted for qualitative assessment of wear. Recommendations were made for validating the damage model. / Engineering Management

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This dissertation proposes a modi ed internal state variable (ISV) inelastic damage model that was motivated by experimental structure{property relations of thermoplastics. In particular, a new damage model was developed for glassy, amorphous thermoplastics. ISV evolution equations are de ned through thermodynamics, kinematics, and kinetics for isotropic damage arising from two di erent inclusion types: pores and particles. The damage arising from the particles and crazes is accounted for by three processes: damage nucleation, growth, and coalescence. Damage nucleation is de ned as the number density of voids/crazes. The associated ISV rate equation is a function of stress state, molecular weight, fracture toughness, particle size, particle volume fraction, temperature, and strain rate. The damage growth is based upon a single void growing and its growth is de ned by an ISV rate equation that is a function of stress state, strain rate sensitivity, and strain rate. The coalescence ISV equation enables interaction between voids and crazes and is a function of the nearest neighbor distance between voids/crazes, size of voids/crazes, temperature, and strain rate. The damage arising from pre-existing voids employs the Cocks{Ashby void growth rule. The total void volume fraction is a summation of the damage arising from particles, pores, and crazes. Micromechanical modeling results for a single void compare well to experimental ndings garnered from the literature. This formulation is then implemented into a nite element analysis. For damage evolution, comparisons are made between a one-dimensional material point simulator and a three-dimensional nite element (FE) simulation. Finally, good agreement is found between impact experiments and FE impact simulations using the implemented model.

This thesis presents investigations on the potential negative effects of wind turbine noise on the human ear from a sound point source (i.e. wind farm). In Chapter 2, the tectorial membrane, which is a crucial gelatinous structural matrix located within the cochlea of the inner ear, is considered to have a similar constitutive stress-strain relationship to that of an elastomer (rubber) in tension. The tectorial membrane appears to stretch when subjected to constant heavy sound stimulation. The tectorial membrane is modeled as a simply-supported beam with an external load Pext applied at midspan. A virtual work approach is used to balance the external work at midspan Pextδz of the tectorial membrane with the internal strain energy from its hysteresis loops. These hysteresis loops quantify the amount of damage that the tectorial membrane undergoes due to an applied external loading. Normalized damage tables are presented at the end of the chapter to suggest safe distances away from the wind turbines to limit damage to the tectorial membrane. Chapter 3 considers a hypothetical autonomous village constructed in South Pretoria, South Africa. This village accommodates approximately 2000 people (~500 families) and receives electricity for hot water from a nearby 2.5 MW wind farm. The design process for the village is discussed from an architectural and design standpoint. The wind farm specifications, specifically the number of 2.5 MW wind turbines needed to provide electricity for hot water, are established. Results from Chapter 2 are used to suggest minimum safe distances between the wind farm and the autonomous village in the context of limiting damage to the tectorial membrane.

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Ce travail de thèse s’inscrit dans le cadre de la modélisation multi-échelle des matériaux composites à renfort tissé dans le but de prévoir leur comportement mécanique et leur tenue. Les objectifs de cette étude sont de caractériser et de modéliser de manière discrète les mécanismes d’endommagement à l’échelle mésoscopique (échelle du renfort de fibres) afin d’évaluer leur influence sur le comportement mécanique macroscopique des matériaux composites tissés. La démarche adoptée consiste tout d’abord à caractériser expérimentalement les mécanismes d’endommagement d’un matériau composite tissé à renfort de fibres de verre et matrice époxy. Les mécanismes observés sont des fissures intra-toron et des décohésions inter-torons en pointe de fissure. Afin de modéliser ces mécanismes d’endommagement, une géométrie représentative du composite, obtenue par simulation du procédé de compaction du renfort, et un maillage conforme de cette géométrie sont choisis. Les fissures et les décohésions sont modélisées de manière discrète dans le maillage à éléments finis de la cellule élémentaire représentative du composite. L’amorçage des endommagements dans le composite est déterminé en utilisant un critère couplant une condition en contrainte et une condition en énergie. La propagation de ces endommagements dans le matériau est évaluée à l’aide d’une approche basée sur la mécanique de la rupture incrémentale. L’approche proposée permet de prévoir l’amorçage et la propagation des endommagements en prenant en compte les possibles couplages entre les endommagements, et de faire le lien entre les endommagements observés à l’échelle mésoscopique et le comportement mécanique macroscopique du matériau. / The topic of this PhD thesis is multi-scale modeling of woven composites with the aim of predicting their mechanical behavior and strength. The objectives of the presented work are the experimental characterization and numerical modeling of damage at the mesoscopic scale (scale of the reinforcing fabric) in order to evaluate its influence on the macroscopic mechanical behavior of woven composites. First, the characteristic damage mechanisms of a woven composite made of glass fibers and epoxy matrix are determined experimentally. Intra-yarn cracks and decohesions between yarns at the crack tips are observed. In order to model these damage mechanisms at the mesoscopic scale, a geometry representative of the composite, obtained from numerical simulation of the dry fabric compaction, and a conformal mesh of this geometry have been selected. Discrete cracks and decohesions are inserted into the finite element mesh of the composite unit cell. Crack initiation is studied using a coupled criterion based on both a stress and an energy condition. The propagation of cracks and decohesions is modeled using a method based on Finite Fracture Mechanics. The proposed approach allows evaluating of the influence of the damage mechanisms observed at the mesoscopic scale on the macroscopic mechanical behavior of the studied material.

The paper presents the study of spalling effect occurring under tensile loading in thin-walled TRC specimens. The experimentally observed failure patterns are first classified and the performed experiment design is explained and discussed. A parameter study of spalling effect with varied thickness of concrete cover and reinforcement configurations including both the textile fabrics and the yarns provided the basis for numerical analysis of the effect. The applied numerical model was designed in order to capture the initiation and propagation of longitudinal cracks leading to the separation of concrete blocks from the textile fabrics. A meso-scopic material resolution in a single crack bridge is used for the simulation exploiting the periodic structure of the crack bridges both in the lateral and in the longitudinal direction of the TRC specimens. The matrix was modeled using an anisotropic damage model falling in the microplane-category of material models. The bond between yarn and matrix follows a non-linear bond-law calibrated using pull-out tests. The epoxy-impregnated reinforcement is considered as a homogeneous bar.

The paper presents the study of spalling effect occurring under tensile loading in thin-walled TRC specimens. The experimentally observed failure patterns are first classified and the performed experiment design is explained and discussed. A parameter study of spalling effect with varied thickness of concrete cover and reinforcement configurations including both the textile fabrics and the yarns provided the basis for numerical analysis of the effect. The applied numerical model was designed in order to capture the initiation and propagation of longitudinal cracks leading to the separation of concrete blocks from the textile fabrics. A meso-scopic material resolution in a single crack bridge is used for the simulation exploiting the periodic structure of the crack bridges both in the lateral and in the longitudinal direction of the TRC specimens. The matrix was modeled using an anisotropic damage model falling in the microplane-category of material models. The bond between yarn and matrix follows a non-linear bond-law calibrated using pull-out tests. The epoxy-impregnated reinforcement is considered as a homogeneous bar.

This thesis has two parts. In the first part, we use the results of new fatigue experiments conducted with variable load levels as well as variable stress ratios to critically assess three (two old and one relatively new) cumulative fatigue damage models. These models are deterministic. Such models are usually tested using multiple blocks of periodic loading with differing amplitudes. However, available data pertains to zero-mean loading, and does not investigate the role of variable stress ratio (Smin/Smax). Here, we present experimental results for variable stress ratios. Two specimen geometries and two materials (Al 2014and Al 2024)are tested. Manson’s double linear damage rule (DLDR)gives the highest accuracy in predicting the experimental outcome, even in the presence of variable stress ratios, whereas predictions of the newer model (“A constructive empirical theory for metal fatigue under block cyclic loading,” Proceedings of the Royal Society A, 464 (2008), 1161-1179) are slightly inferior. The widely used Miner’s rule is least accurate in terms of prediction. The merits and drawbacks of these models, in light of the experimental results, are as follows. The DLDR, though accurate, has minor scientific inconsistencies and no clear generalization. The constructive model has possible generalizability and more appealing scientific consistency, but presently has poorer accuracy. Miner’s rule, least accurate, lies within the constructive approach for special parameter values. The DLDR can guide the new (constructive)approach through new parameter fitting criteria. In the second part of this thesis, we consider the scatter in fatigue life and use the Weibull distribution to describe ‘S-N-P’ curves. We first assume homoscedasticity (load-independent or constant variance) and present a way to draw a p-percentile line on a log-log load-life plot. Then heteroscedasticity (load-dependent variance) in fatigue life is incorporated and a simple statistical model is proposed, to obtain a straight line percentile plot at a pre-specified probability of survival ps. The proposed method is illustrated for Al 2014-T6 and Al 2024-T4 data sets (extracted manually) from MMPDS-01 (a data handbook).

The reliability of modern gas turbine engines is largely due to careful damage tolerant design a method of structural design based on the assumption that flaws (cracks) exist in any structure and will continue to grow with usage. With proper monitoring, largely in the form of periodic inspections at conservative intervals reliability and safety is maintained. These methods while reliable can lead to the early retirement of some components and unforeseen failure if design assumptions fail to reflect reality. With improvements to sensor and computing technology there is a growing interest in a system that could continuously monitor the health of structural aircraft as well as forecast future damage accumulation in real-time. Through the use of two-dimensional and three-dimensional numerical modeling the initial goals and findings for this continued work include: (a) establishing measurable parameters directly linked to the health of the blade and (b) the feasibility of detecting accumulated damage to the structural material and thermal barrier coating as well as the onset of damage causing structural failure.