Les propriétés mécaniques d’un ski alpin, dont sa longueur, le profil des carres (aussi nommé le profil de largeur), le profil de cambrure et les distributions de rigidités en flexion et en torsion, sont des facteurs déterminants de sa performance. Un des aspects essentiels de cette performance est la stabilité directionnelle du ski en virage; il est généralement accepté qu’un ski pour experts nécessitera une plus grande stabilité qu’un ski pour skieurs débutants ou intermédiaires. Cependant, il n’existe aucune étude sur l’étendue du niveau de stabilité que présentent les différents skis alpins modernes. Ce projet a pour but d’identifier cette étendue du niveau de stabilité par le biais de simulations numériques, ainsi que d’explorer l’effet des différentes propriétés mécaniques sur la stabilité d’un ski. Afin d’y parvenir, une nouvelle méthode a été développée afin de mesurer les distributions de rigidités en flexion et en torsion et les profils de cambrure et des carres d’un ski en moins de 5 minutes avec une précision d’environ 5%. Cette méthode a été utilisée pour mesurer les propriétés mécaniques de 179 skis de différents types (skis de courses, skis récréatifs, skis de haute randonnée, skis de neige poudreuse, etc.), soit un échantillon varié de la gamme entière des skis alpins commercialement disponibles. Un outil de simulation numérique a été développé et utilisé afin d’évaluer la stabilité de ces skis. Un modèle simple pour rapidement estimer la stabilité a été développé et est fortement corrélé avec les niveaux de stabilité évalués par le biais des simulations. Ce modèle simple permet d’estimer la stabilité d’un ski sans avoir recours à des simulations ou des essais expérimentaux. Ce modèle simple permet aussi de comprendre l’effet des différentes propriétés mécaniques d’un ski sur son niveau de stabilité.

Le bruit émis par une motoneige est une composante importante de sa conception, car elle doit satisfaire les normes en vigueur. Les différentes parties de la machine, du moteur jusqu'à l'habillage, en passant par la transmission, sont toutes autant de sources potentielles de vibration et de bruit. Si le bruit d'une transmission continuellement variable (CVT) de motoneige semble dû aux vibrations qui l'excitent, on peut légitimement penser intégrer des solutions classiques de l'industrie, comme les volants d'inertie ou encore les pendules centrifuges. Néanmoins, les contraintes de couple et d'encombrement rendent une telle intégration plus diffcile. La vitesse de rotation variable est aussi une composante à prendre en compte. Ainsi, après avoir développé une méthodologie permettant de comparer avec fiabilité différents modèles de CVT pour ainsi mieux cerner les paramètres importants des mécanismes de génération de bruit et vibration, nous expliciterons la démarche de conception d'une solution innovante de réduction des vibrations, appelée amortisseur dynamique en torsion auto-accordé (ADT2A), que l'on veut être une solution adaptée aux différents enjeux énoncés (fortes amplitudes de couple, adaptation de l'amortissement à la vitesse de rotation). Les essais qui seront menés sur la preuve de concept devront permettre de mieux maîtriser les paramètres de sa modélisation. Ce concept tentera de répondre aux besoins de machines dont les vibrations en torsion peuvent être sources de niveaux de bruit élevés ou dont les vibrations s'avèreraient gê- nantes voire critiques. Il présente aussi des paramètres, dont les connaissances devront être accrues par le biais de tests sur bancs d'essais et de modèles, comme l'effet des conditions de guidage/accordage sur la fréquence de résonance et ce, afin de le modéliser plus fidèlement pour l'optimiser et l'intégrer sur véhicule.

Background: Accurate assessment of left ventricular (LV) systolic function in chronic severe primary mitral regurgitation (MR) is important as the aim is to consider surgical repair prior to the onset of irreversible LV dysfunction. However this can be difficult to judge as conventional measures of LV function (such as ejection fraction, EF) may remain normal despite impaired LV contractility due to the increased preload of the condition. Advanced echocardiographic techniques, including deformation imaging, appear promising as they are less load dependent. As the earliest symptoms in severe MR are usually exertional, this study aimed to assess markers of LV deformation on exercise in patients with normal resting EF in order to try and identify the earliest signs of LV decompensation.Methods: Transthoracic echocardiography was carried out at rest and on submaximal supine exercise in asymptomatic patients with moderate to severe chronic primary MR and matched controls. Conventional contractile reserve (CR) as measured by EF change on exercise was used to subdivide patients into those with preserved (CR+) and abnormal (CR-) LV function. Myocardial strain and twist were assessed using the speckle tracking technique.Results: MR patients failed to show the normal enhancement in systolic twist on exercise. The onset and peak of untwisting were delayed in MR at rest and normalised on exercise in CR+ but not in CR-. Abnormalities in twist on exercise worsened with increasing resting preload. Longitudinal strain tended to increase normally on exercise in CR+ but not in CR-. Systolic longitudinal strain rate correlated with twist at rest and on exercise, whereas diastolic strain rate correlated with the timing of untwisting on exercise.Conclusion: Abnormalities in myocardial deformation are seen at rest and on exercise in patients with severe MR, particularly in those with decompensated LV function. This may contribute to the development of functional impairment with progressive disease.

A viabilidade da utilização de próteses modulares cimentadas em diáfises de fêmur em cães foi demonstrada, porém diversos autores relatam a falha de aderência entre as próteses e os ossos como uma das principais complicações. O presente trabalho teve como objetivo investigar biomecanicamente a interface implante metálico, osso e capa de cimento ósseo de com diferentes espessuras de cimento ósseo utilizadas para a estabilização da prótese. Para tanto foram utilizados fêmures bilaterais de 24 cadáveres de cães com peso acima de 15 quilos que foram divididos em quatro grupos, o primeiro grupo composto por oito fêmures utilizou uma espessura de capa de cimento de 1,0 a 1,5 mm, o segundo grupo, composto por oito fêmures, utilizou uma capa de cimento de 2,0 a 2,5 mm e o terceiro grupo, composto por oito fêmures, utilizou uma capa de cimento compreendida entre o intervalo de 3,0 a 3,5 mm de espessura. Os fêmures foram submetidos a ensaios destrutivos de torção onde foram avaliados a rigidez à torção e torque máximo suportado pela interface implante metálico, osso e capa de cimento ósseo. O quarto grupo, denominado de controle, composto pelos fêmures contralaterais íntegros, foram submetidos ao mesmo ensaio de torção que as peças onde foram utilizadas as próteses. Os resultados encontrados foram que nas condições apresentadas neste estudo não foi encontrada diferença biomecânica estatisticamente significante, em relação à rigidez à torção e torque máximo, na utilização de capas de cimento na faixa de 1 mm e 2,5 mm e entre 2 mm e 3,5 mm. Porém houve diferença quando comparado as faixas de espessura de cimento entre os grupos de 1 mm a 1,5mm e de 3 mm a 3,5 mm. / The feasibility of modular cemented prosthesis in the femoral diaphysis was demonstrated in dogs, but several authors report loosening of bone, cement and implant interface as a major complication. The objective of this study was to evaluate the stabilization of the prosthesis using different thicknesses of cement layer. For this study 48 femurs from 24 dogs weighing over 15 kilograms were used. They were separated in four groups, the first group with eight femurs used a cement mantle from 1.0 to 1.5 mm, the second group, with eight femurs, used a cement mantle from 2.0 to 2.5 mm and the third group, with eight femurs, used a cement layer from 3.0 to 3.5 mm. The femurs were submitted to destructive torsion tests where they were evaluated due to the values of torsional rigidity and maximum torque shown by the implant, bone and bone cement interface. In the fourth group were the remaining intact femurs, they were evaluated using the same torsion test used on the other groups. The results were that under the present conditions we found no biomechanical differences relative to torsional rigidity and maximum torque, using cement layers between 1 mm and 2.5 mm and between 2 mm and 3.5 mm. But we found biomechanical differences between groups of 1 mm to 1.5 mm and 3 mm to 3.5 mm.

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No / The torsional response of rotor systems comprising bearings, inertia discs, and relatively long, slim shafts is considered. Lumped, finite element and hybrid, distributed-lumped parameter procedures are employed to represent the rotor systems of concern in efforts aimed at increasing accuracy, integrity, and computational efficiency. Rotor, shaft, and bearing elements of arbitrary dimensions, constructed from materials with differing mechanical properties, can be accommodated within the system models formulated. General results for multiple rotor assemblies are derived. Simple computational techniques are employed to obtain the frequency response and time domain characteristics for the models proposed. Analytical validation of the resonance conditions identified is provided. Application studies are presented for purposes of comparison.

<p> A general, consistent, nonlinear theory for open thin-walled elastic beams is presented. The theory takes into account geometric nonlinearities caused by large rotation of the cross section of the beam. The nonlinear differential equations of deformation and response are derived by means of application of Hamilton's principle. It is found that the set of equations reduces to the results obtained by Cullimore and Gregory in the special cases of large uniform torsion of thin-walled members. A solution of a thin-walled beam, subjected to large non-uniform torsional deformation due to application of torques at the ends, is obtained. Comparison is made on the torque - rotation characteristics of a thin-walled beam subjected to large uniform torsion and large non-uniform torsion to show the effect of end constraint from warping.</p> <p> A set of nonlinear equations to study the stability of a thin-walled beam of open cross section, under axial loading (spatial stability) and lateral loading (lateral stability), is presented. Using the derived equations, the dynamic stability of thin-walled beams of symmetrical and monosymmetrical cross sections subjected to axial loads, is investigated. The regions of parametric instability, the steady state amplitudes of oscillations, once parametric instability takes place, and the non-steady state solutions, to show the growth of the parametric oscillations, are carried out.</p> <p> The effect of viscous damping on the steady state amplitude and the growth behaviour of the parametrically excited oscillations is shown. The dynamic stability of a thin-walled beam of symmetrical I section and a monosymmetrical split ring section are worked out in detail as examples.</p> / Thesis / Doctor of Philosophy (PhD)

Mechanical strength of polylactic acid (PLA) is increasingly relevant with time because of its attractive mechanical properties and 3D printability. Additive manufacturing (AM) methods, such as fused deposition modeling (FDM), stereolithography (SLA), and selective laser sintering (SLS), serve a vital role in assisting designers with cheap and efficient generation of the desired components. This document presents research to investigate the anisotropic response of multi-oriented PLA subjected to multiple monotonic loading conditions. Although empirical data has previously been captured for multi-oriented PLA under tensile and compressive loading conditions, the data has yet to be applied with regard to a representative component geometry. The tensile and compressive empirical data were ultimately used to develop elastic and yield constitutive models which aided in the characterization of PLA under torsion and bending. This representative component geometry is expected to experience a combined torsion and bending load condition in an effort to address this integral gap in the mechanical properties of multi-oriented PLA. In addition to the acquired empirical data, finite element analysis (FEA) and analytical modeling are employed to supplement the accurate modeling of future component analysis. As a result of the proposed array of experiments, the torsional and bending capabilities of PLA are forecasted to vary based on the print orientation. Lastly, the broader impact of this work is dedicated to addressing the material's capability to operate in environments which possess significant torsion and bending such as model aircraft wings and shafts for remote controlled cars.

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