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Ortho-Planar Mechanisms for Microelectromechanical SystemsLusk, Craig P. 07 July 2005 (has links) (PDF)
A method for representing the design space of ortho-planar mechanisms has been developed. The method is based on the Theorem of Equality of Orientation Set Measures (TEOSM) which allows mechanisms to be represented by points in an abstract space. The method is first developed for single loop planar folded mechanisms with revolute joints, and later extended to mechanisms with prismatic joints and to spherical folded mechanisms. Functions which assign a value to each point in design space can be used to describe classes of mechanisms and evaluate their utility for MEMS design. Additionally, this work introduces the use of spherical mechanisms in MEMS design. Spherical mechanisms have characteristics that may be useful in MEMS, including the capability of spatial positioning of a link and the ability to convert rotation about an axis perpendicular to the substrate to rotation about an axis parallel to the substrate. Spherical kinematics has been used to develop three novel mechanisms, the Micro Helico-Kinematic Platform (MHKP), the Spherical Bistable Mechanism (SBM), and the Three-degree-of-freedom Platform (3DOFP). Mathematical models of these devices have been developed and MEMS prototypes have been designed and fabricated.
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Preparation and Characterization of Tb-Co Magnetic FilmsBeignon, Roméo January 2022 (has links)
Thin films of terbium-cobalt alloy have been deposited by magnetron sputtering. They exhibit an out-of-plane magnetic anisotropy that may result in elongated domains. The effect of thicknesses and compositions on the domain structure has been studied systematically. The composition and thickness of the films have been verified by Rutherford backscattering spectrometry and x-ray reflectivity. The domain structure was imaged by magnetic force microscopy and hysteresis loops were measured by MOKE (Magneto-optical Kerr effect). Very long and contrasted domains are obtained on the as-grown film with a thickness of 290 Å containing 8.1\% of terbium. Similar very elongated domains are obtained for other thicknesses and compositions if the films are demagnetized.
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Improvement Of Rotation Capacity Of Composite Beam-To-HSS Column Connections Using External Horizontal StiffenersAfshar Arjmand, Mahdi 01 December 2023 (has links) (PDF)
Improvement of Rotation Capacity of Composite Beam-to-HSS Column Connections Using External Horizontal Stiffeners
Mahdi Afshar Arjmand
This thesis focuses on the analysis of out-of-plane deformation (OOP) in column flange located in the panel zone of composite beam-to-column steel connection, as a critical aspect of steel structural engineering. This type of connection is an integral component of steel structures, and understanding their behavior is essential for ensuring safety and performance. The investigation involves examining the causes, factors influencing, and potential mitigation strategies for out-of-plane deformation of HSS flange column in these connections. Beam-to-column connections play a vital role in transferring loads and maintaining structural stability. Out-of-plane deformation, where the flange displaces from its primary plane, can compromise the connection's performance. This study aims to shed light on the mechanisms causing out-of-plane deformation and explore techniques to minimize its effects. Out-of-plane deformation of column flange connections can result from various factors, including eccentric loading, bending moments, torsion, and material properties. Understanding these causes is crucial for accurate analysis and design. Analytical methods and numerical simulations, such as finite element analysis (FEA), are employed to predict and quantify out-of-plane deformation. Models are created to represent real-world connections, enabling the exploration of their behavior under different loads and conditions. The study investigates strategies to mitigate out-of-plane deformation, such as adding horizontal stiffeners, or vertical stiffeners. These approaches aim to enhance the column flange’s resistance to out-of-plane displacements and improve overall structural performance. Real-world case studies of steel beam to-column connections are analyzed to demonstrate the effects of out-of-plane deformation and the efficacy of mitigation strategies. The results highlight the importance of accurate analysis and design to ensure connection integrity. Based on the findings, the study proposes design guidelines for flange-column connections to minimize out-of-plane deformation. These guidelines provide engineers with insights into optimizing connection design and ensuring stability under varying loads.
The unique characteristic of beam-to-HSS column connections is the out-of-plane deformation of the HSS column flange at the beam web-to-column flange interface which can reduce contribution of the connection web to the overall resistance of the connection. To explore effect of the column flange OOP deformation, performance of three connection types, namely composite beam-to-HSS column connection, composite beam-to-HSS column connection with slab-column gap, and bare beam-to-HSS column connections are evaluated using pre-validated 3D finite element (FE) simulations. FE models can simulate low-cycle fatigue and post-rupture behavior of the connection. Comprehensive global and local responses are presented and discussed. It is found that column compactness, i.e., column’s width-to-thickness ratio, has considerable effect on maximum moment capacity, rotation capacity, post rupture residual capacity and energy dissipation capability of the connection. On the other hand, external horizontal stiffeners can significantly increase the rotation capacity of the connection. External horizontal stiffeners in steel beam-to-column connections are crucial for boosting structural efficiency and load-bearing capacity. Carefully designed, accurately placed, and securely attached, they ensure a reliable and safe system capable of withstanding diverse loads and environmental conditions, contributing to the long-term safety and stability of the entire steel structure.
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Analysis of a Thin-Walled Curved Rectangular Beam with Five Degrees of FreedomMoghal, Khurram Zeshan 13 December 2003 (has links)
A study of a thin-walled curved rectangular box beam under torsion and out-of-plane bending is documented in this thesis. A new one-dimensional theory that takes into account warping and distortion in the beam cross-sections is the main focus. Existing available theories for thin-walled curved beams lack rigorous theoretical development, and most have ignored the effects of warping and distortion. A higher order theory including two additional degrees of freedom corresponding to warping and distortion was derived. The conventional three degrees of freedom model was compared with the new five degrees of freedom model. The variation of beam thickness to control and decrease the high distortion variable is investigated.
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Development of a Rigid Polyurethane Foam-Reinforced Resilient Masonry Wall SystemForsythe, Carly M. 04 1900 (has links)
<p>Unreinforced masonry (URM) constitutes a large part of current building inventory worldwide, and this type of construction also represents a major seismic risk, especially in developing countries where URM is widely used. During an earthquake, URM walls are unable to dissipate seismic forces without experiencing considerable damage or collapse. Due to their lack of ductility, URM walls fail in a brittle manner, which can leads to damaged face shells becoming falling debris and a major source of hazard. The aim of this study is to investigate the applicability of using polyurethane foams as an inexpensive reinforcement technique for both retrofitting existing and new URM construction.</p> <p>Experimental testing of the reinforced masonry walls showed a large increase in the resiliency of the wall, with an increase in the out-of-plane capacity of up to 34 times over the URM specimen, and with the addition of rope reinforcement an increase in the out-of-plane capacity of up to 90 times the URM specimen was achieved. This system allows walls to experience a considerable amount of deflection before ultimate failure is reached. Within certain limits, the polyurethane foam is able to demonstrate elastic characteristics. By developing foam with higher densities, higher compressive, tensile, flexural and shear strengths can be reached. This type of reinforcement allows for less damage during low seismic events, and through the greater resiliency of the system, walls are able to remain stable and exhibit post-peak strength during a stronger seismic event. In its ultimate limit state, the wall will fail, however collapse is typically prevented – reducing the amount of hazardous debris and saving the lives of the buildings occupants.</p> / Master of Applied Science (MASc)
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Response of Two-Way Reinforced Masonry Infill Walls under Blast LoadingSmith, Nicholas L. 04 1900 (has links)
<p>The increased public safety concerns to the consequences of deliberate and accidental explosions have led to the development of the Canadian (CSA S850- 12) and American (ASCE 59-11) blast standards. There is an urgent need to investigate and quantify the response of structural components under such extreme loading conditions. This is especially important for masonry components, where research has been limited due to the misconception that masonry (both reinforced and unreinforced) is an inadequate material for blast hardening applications. The standards allow the use of experimental testing or dynamic analysis in order to determine peak responses and evaluate them in terms of the code prescribed performance limits and accompanying levels of damage. The current study investigates the response of non-integral and non-participating infill walls designed to undergo two-way out-of-plane response and detailed to fail in flexure under static loading conditions. Through experimental blast testing and dynamic model validation of reduced-scale walls under a range of design-basis threat (DBT) levels, this study shows that reinforced masonry is a viable alternative for blast protection. However, the current flexural-based code requirements, thought to be conservative, may be inadequate at loads of higher impulse where shear damage is prevalent. This study also shows the influence that changing the boundary configuration and level of reinforcement has on the peak response, where the performance limits of the current codes makes no provisions for these parameters.</p> / Master of Applied Science (MASc)
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Finite Element Analysis of Unreinforced Concrete Block Walls Subject to Out-of-Plane LoadingHe, Zhong 12 1900 (has links)
<p>Finite element modeling of the structural response of hollow concrete block walls subject to out-of-plane loading has become more common given the availability of computers and general-purpose finite element software packages. In order to develop appropriate models of full-scale walls with and without openings, a parametric study was conducted on simple wall elements to assess different modeling techniques. Two approaches were employed in the study, homogeneous models and heterogeneous models. The linear elastic analysis was carried out to quantify the effects of the modeling techniques for hollow blocks on the structural response of the assembly, specifically for out-of-plane bending. Three structural elements with varying span/thickness ratios were considered, a horizontal spanning strip, a vertical spanning strip and a rectangular wall panel supported on four edges. The values computed using homogeneous and heterogeneous finite element models were found to differ significantly depending on the configuration and span/thickness ratio of the wall.</p><p>Further study was carried out through discrete modeling approach to generate a three-dimensional heterogeneous model to investigate nonlinear behaviour of full-scale walls under out-of-plane loading. The Composite Interface Model, established based on multi-surface plasticity, which is capable of describing both tension and shear failure mechanisms, has been incorporated into the analysis to capture adequately the inelastic behaviour of unit-mortar interface.An effective solution procedure was achieved by implementing the Newton-Raphson method, constrained with the arc-length control method and enhanced by line search algorithm. The proposed model was evaluated using experimental results for ten full-size walls reported in the literature. The comparative analysis has indicated very good agreement between the numerical and experimental results in predicting the cracking and ultimate load values as well as the corresponding crack pattern. / Thesis / Master of Applied Science (MASc)
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<b>NUMERICAL ANALYSIS OF IN-PLANE SHEAR BEHAVIOR OF SC WALLS UNDER COMBINED LOADINGS</b>Nikhil Mittal (19164610) 22 July 2024 (has links)
<p dir="ltr">Steel-concrete composite (SC) walls are increasingly gaining interest as an alternative to reinforced concrete (RC) walls for safety-related nuclear facilities. The major loading for the SC design is seismic loading. Seismic loading results in combined in-plane shear with axial or out-of-plane moment loading on SC structures. The primary resistance against the lateral loading in these structures is provided by in-plane shear resistance. While the AISC N690 design code includes equations for determining in-plane shear capacity and combined loading, its guidance is limited to pure in-plane shear capacity, in-plane shear combined with out-of-plane moments and combined out-of-plane shear forces. It lacks comprehensive design equations for combined loadings, such as in-plane shear with axial or out-of-plane moment loading. Additionally, the N690 design equation for in-plane shear capacity is somewhat conservative. Understanding the behavior of SC walls under these combined loadings is crucial for their optimal design.</p><p dir="ltr">This research addresses this gap by performing numerical investigation based on the finite element modelling (FEM) and mechanics-based approaches to analyze the behavior of SC walls under these loadings. The models were verified and validated using data from previous experimental studies. A parametric study was conducted to evaluate the impact of various design and material parameters on the in-plane shear capacity under combined loadings. Based on the parametric data and linear regression analysis, design equations were formulated to predict the in-plane shear capacity. Interaction envelopes were developed to compare the results from these models with those from previous numerical studies. Finally, practical design guidance and design equations were provided to design these structures.</p>
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Failure and damage progression of 3D woven composite structures subjected to out-of-plane loadingPanchal, Dhaval January 2017 (has links)
Three-dimensionally woven composites are a relatively new class of material that offer improved out-of-plane performance by including through-the-thickness mechanical reinforcement compared to traditional laminated composite structures. The mechanical properties are highly dependent upon the weave architecture as this dictates the nature of the through the thickness reinforcement and its effect in improving out-of-plane shear strength. A comparison of two testing methods, Short Beam Strength, and Five Point Bending was conducted over a range of span to thickness ratios with the latter found to be more consistent at producing shear failure over a greater range of span to thickness ratios, although evidence of matrix crushing was present in both, and flexural failure in the Short Beam Strength test. Two weave architectures, the orthogonal and angle weave were subjected to the Five Point Bending test and the failure and damage progression behaviour of both weave architectures were characterised using Digital Image Correlation analysis to measure the edge strain through the thickness of the specimens. This testing showed the angle weave architecture had in general a higher failure strength, and more gradual failure due to longer debonding cracks. The orthogonal weave architecture showed a characteristic post-failure response indicative of crack bridging with discrete load recovery and load drop phases. A numerical model developed from previous work builds on the mosaic modelling method and was modified to include cohesive elements in order to simulate interface debonding via the maximum stress criterion. The simulations are consistently 15 20% greater in failure loads, and 8 - 12% greater in failure shear stresses than those found from the averaged experimental results over the range of tested span to thickness ratios. Post failure response was not modelled. The work presented in this thesis is another step towards gaining a thorough understanding of the mechanical properties of 3D woven composite structures, focussing in particular on out of plane shear strength. The modified mosaic modelling method used showed it is effective at modelling the out of plane testing of orthogonal 3D woven composite structures, and offer the potential to predict the failure of larger composite structures of the same construction and 3D woven architecture although developments are still needed in modelling the post failure response.
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Mastering the influence of thermal fluctuations on the magnetization switching dynamics of spintronic devices / Maitrise de l'influence des fluctuations thermiques sur la dynamique de commutation des dispositifs spintroniquesLacoste, Bertrand 13 November 2013 (has links)
Les mémoires magnétiques à couple de transfert de spin (STTRAM) sont des mémoires vives non-volatiles et endurantes très prometteuses pour remplacer les mémoires à base de condensateurs. Cependant, pour les technologies actuelles de STTRAM à aimantation planaire ou hors-du-plan, le temps de commutation est limité à 10~ns car le processus de renversement de l'aimantation est stochastique, déclenché par les fluctuations thermiques. Dans l'optique de rendre la commutation déterministe et plus rapide, une approche consiste à ajouter à la jonction tunnel magnétique une autre couche polarisante en spin, avec une aimantation orthogonale à celle de la couche de référence. Nous nous sommes intéressé plus particulièrement aux jonctions tunnels magnétiques planaires avec un polariseur perpendiculaire (à aimantation hors du plan). Le STT du polariseur perpendiculaire amorce le retournement d'aimantation, mais il provoque aussi des oscillations de la résistance de la jonction entre ses valeurs extrêmes. Cette particularité est mise à profit pour la réalisation de nano-oscillateurs (STO). Dans cette thèse, la dynamique d'aimantation du système comprenant une couche libre planaire, une couche de référence planaire et un polariseur perpendiculaire est étudiée, aussi bien expérimentalement que théoriquement (analytiquement et en simulations), dans l'approximation de macrospin. Dans le cas d'une couche libre oscillante sous l'action du STT du polariseur perpendiculaire, une description précise de ces oscillations est présentée, dans laquelle le champ d'anisotropie, le champ appliqué et le STT de la couche de référence planaire sont traités en perturbations. Dans le cas d'une couche libre ferrimagnétique synthétique (SyF), les expressions analytiques des courants critiques et des équations du mouvement sont calculées et comparées aux simulations. Ces résultats sont ensuite utilisés pour réaliser le diagramme de phase du système complet. L'anisotropie uniaxiale joue un role important, ce qui est confirmé par des mesures de retournement en temps réel réalisées sur des échantillons de nano-piliers à base de MgO. L'influence relative des STT provenant de la couche de référence et du polariseur perpendiculaire peut être ajsutée en jouant sur le rapport d'aspect des cellules, ce qui permet d'obtenir un retournement controlé en moins d'une nanoseconde avec une STTRAM. / Spin-transfer torque magnetic random-access memory (STTRAM) are very promising non-volatile and enduring memories to replace charged-based RAM. However, in conventional in-plane or out-of-plane STTRAM technologies, the switching time is limited to about 10~ns because the reversal process is stochastic i.e. it is triggered by thermal fluctuations. In order to render the reversal deterministic and faster, an approach consists in adding to the magnetic tunnel junction (MTJ) stack another spin-polarizing layer whose magnetization is orthogonal to that of the MTJ reference layer. We particularly investigated the case where a perpendicular polarizer is added to an in-plane magnetized tunnel junction. The STT from the perpendicular polarizer initiates the reversal, but it also creates oscillations of the resistance between its two extremal values. This behavior is usually interesting to realize STT nano-oscillators (STO). In this thesis, the dynamics of the system comprising an in-plane free layer, an in-plane reference layer and a perpendicular polarizer is studied both experimentally and theoretically (analytically and by simulations) in the framework of the macrospin approximation. For a single layer free layer oscillating due to the STT of the perpendicular polarizer, an accurate description of the oscillations is presented, in which the anisotropy field, the applied field and the in-plane STT are treated as perturbations. In the particular case of a synthetic ferrimagnetic (SyF) free layer, analytical expressions of the critical currents and of the oscillations equation of motion are computed and compared to simulations. These results are used to determine the phase diagram of the complete system. The in-plane anisotropy field is found to play a dramatic role, which is confirmed by experimental data from real-time measurements on MgO-based nano-pillars. It is shown that the cell aspect ratio can be used to tune the relative influence of the STT from the in-plane reference layer and from the out-of-plane polarizer. This allows achieving well controlled sub-nanosecond switching in STTRAM.
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