Rotator cuff (RC) muscle insertion was previously thought to consist of singular, individual tendons inserting onto predefined areas on the greater and lesser tuberosities. However, more recent publications describe the RC muscle tendons as forming a singular insertion across the tuberosities, consisting of both tendinous and capsular portions. Orthopaedic surgeons are now considering these two layers in their surgical approach and treatment plans; therefore this study aimed to test and compare the elastic modulus and maximum load to failure for both tendinous and capsular layers taken from supraspinatus (SS), infraspinatus (IS) and subscapularis (SC). Fourteen (n = 14) fresh/frozen arms were used in this study. Each RC muscle was reverse dissected and trimmed to a 2 x 2cm strip, which was separated into its two layers, still attached to the humerus. An Instron 1342 with a 1kN load cell was used to place the samples under tensile testing till failure (Newtons/N). Accompanying Integrated Design Tools (IDT) NX8-S2 cameras captured images for full-field strain measurements with the Image Systems TEMA software package through digital image correlation (DIC). SS, IS, and SC tendinous layers yielded higher average elastic moduli readings (72.34 MPa, 67.04 MPa, and 59.61 MPa respectively) compared to their capsular components (27.38 MPa, 32.45 MPa, and 41.49 MPa respectively). Likewise, the tendinous layers for SS, IS and SC all showed higher average loads to failure (252.74 N, 356.27 N and 385.94 N, respectively) when compared to the capsular layers (211.21 N, 168.54 N and 281.74 N, respectively). These biomechanical differences need to be taken into account during surgical repair owing to the fact that, should these layers be repaired as one singular structure, it may place the weaker less elastic, capsular layer under more strain, possibly leading to either re-tear complications or reduced postoperative healing and functionality. Thus, based on the results, it is recommended that surgeons consider and repair each layer independently for better postoperative biomechanical integrity. / Dissertation (MSc)--University of Pretoria, 2019. / Anatomy / MSc / Unrestricted

New materials, optimized for increased strength, ductility, and other desirable properties, have the potential to improve every aspect of modern living. To achieve these optimums, the necessary technological advancements are impeded mainly by the limits of available material models. Innovations in this field rely on research into the nature of material behavior. While a typical model of material behavior in the region near yield involves the initial linear elastic response, followed by yield and isotropic hardening, this fails to explain various important phenomena that manifest in a range of materials, such as pre-yield nonlinearity, anelasticity, yield point phenomena, hardening stagnation, and the Bauschinger effect. These effects have been explained over the past century with the theories of Cottrell atmospheres, the Orowan by-pass mechanism, and back stress. This manuscript compares data from experimental observation in tantalum to these theories to better understand the micromechanisms occurring near yield. Understanding deformation in this region has significant implications in structural and mechanical engineering, as well has having direct applications in the forming of metals. Forty-four dogbone-shaped samples were cut from 99.99% pure tantalum and pulled in load-unload-load and multi-cycle loop tensile tests at room temperature. The specimens were either single crystal, whose orientations were chosen based on desired active slip mode determined by Schmid factors, or bicrystal, based on the orientation of the single grain boundary. Sample behavior was simulated in both crystal plasticity and General Mesoscale finite element models to assist in interpreting results and in suggesting plausible micromechanisms. The experimental results and crystal plasticity simulations suggest alternate explanations to some of the discussed mechanical theories of near-yield deformation. The combined experimental / modeling approach indicates that other slip systems, besides the conventionally assumed {110}, are activated upon yield; particularly the {112} system. The breakaway model traditionally associated with the yield point phenomenon may also be better explained through a different mechanism; back stress development during deformation is shown to result in the observed behavior. Lastly, as is well-known, the Taylor formulation, upon which most crystal plasticity models are based, does not adequately predict yield stress behavior in the presence of grain boundaries; once again, an internal stress mechanism matches much better with the experimental results on single and bicrystals. While not all observations could be fully explained by simply adding internal stress generation to a standard crystal plasticity model, this work anticipates further studies to enable more accurate predictive modeling capabilities and increase understanding of the mechanisms driving the fundamental material properties necessary for future progress.

Slender structures like plates and shells -- for which at least one dimension is much smaller than the others -- are lightweight, flexible, and offer considerable strength with little material. As such, these structures are abundant in nature (e.g. flower petals, eggshells, and blood vessels) and design (e.g. bridge decks, fuel tanks, and soda cans). However, with slenderness comes suceptibility to large and often sudden deformations, which can be wildly nonlinear, as bending is energetically preferable to stretching. Though once considered categorically undesirable, these instabilities are often coveted nowadays in the engineering community. They provide mechanical explanations for observations in nature like the wrinkled structure of the brain or the snapping mechanism of the Venus fly trap, and when precisely controlled, enable the design of functional devices like artificial muscles or self-propelling microswimmers. As a prerequisite, these achievements require a thorough understanding of how thin structures "shape-shift" in response to stimuli and confinement. Advancing this fundamental knowledge is the goal of this thesis. In the first two chapters, we consider the shape-selection of shells and plates that are confined by their environment. The shells are made by residual swelling of silicone elastomers, a process that mimics differential growth, and causes initially flat structures to irreversibly morph into curved shapes. Flattening the central region forces further reconfiguration, and the confined shells display multi-lobed buckling patterns. These experiments, finite element (FE) simulations, and a scaling argument reveal that a single geometric confinement parameter predicts the general features of this shape-selection. Next, in experiments and molecular dynamics (MD) simulations, we constrain intrinsically flat sheets in the same manner, so that their center remains flat when we quasi-statically force them through a ring. In the absence of planar confinement, these sheets form a well-studied conical shape (the developable cone or d-cone). Our annular d-cone buckles circumferentially into patterns that are qualitatively similar to the confined shells, despite the distinct curvatures and loading methods. This is explained by the dominant role of confinement geometry in directing deformation, which we uncover via a scaling argument based on the elastic energy. There are also marked differences between the way plates and shells change shape, which we highlight when we investigate the rich dynamics of reconfiguration. In the final two chapters, we demonstrate how mechanics, geometry, and materials can inform the design of structures that use instabilities to function. We observe in experiments that dynamic loading causes a spherical elastomer shell to buckle at ostensibly subcritical pressures, following a substantial time delay. To explain this, we show that viscoelastic creep deformation lowers the critical load in the same predictable, quantifiable way that a growing defect would in an elastic shell. This work offers a pathway to introduce tunable, time-controlled actuation to existing mechanical actuators, e.g. pneumatic grippers. The final chapter aims at reducing the energy input required for bistable actuators, wherein snap-through instability is typically induced by a stimulus applied to the entire shell. To do so, we combine theory with 1D finite element simulations of spherical caps with a non-homogeneous distribution of stimuli--responsive material. We demonstrate that restricting the active area to the shell boundary allows for a large reduction in its size, while preserving snap-through behavior. These results are stimulus-agnostic, which we demonstrate with two sets of experiments, using residual swelling of bilayer silicone elastomers as well as a magneto-active elastomer. Our findings elucidate the underlying mechanics, offering an intuitive route to optimal design for efficient snap-through. / 2022-05-06T00:00:00Z

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18657号 / 工博第3966号 / 新制||工||1610(附属図書館) / 31571 / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 岩田 博夫, 教授 木村 俊作, 教授 秋吉 一成 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19743号 / 工博第4198号 / 新制||工||1647(附属図書館) / 32779 / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 田畑 泰彦, 教授 秋吉 一成, 教授 木村 俊作 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Student Number : 9202983Y - PhD thesis - School of Computational and Applied Mathematics - Faculty of Science / A derivation is given of the constitutive equation for an incompressible transversely isotropic hyperelastic material in which the direction of the anisotropic director is unspecified. The field equations for a transversely isotropic incompressible hyperelastic material are obtained. Nonlinear radial oscillations in transversely isotropic incompressible cylindrical tubes are investigated. A second order nonlinear ordinary differential equation, expressed in terms of the strain-energy function, is derived. It has the same form as for radial oscillations in an isotropic tube. A generalised Mooney-Rivlin strainenergy function is used. Radial oscillations with a time dependent net applied surface pressure are first considered. For a radial transversely isotropic thin-walled tube the differential equation has a Lie point symmetry for a special form of the strain-energy function and a special time dependent applied surface pressure. The Lie point symmetry is used to transform the equation to an autonomous differential equation which is reduced to an Abel equation of the second kind. A similar analysis is done for radial oscillations in a tangential transversely isotropic tube but computer graphs show that the solution is unstable. Radial oscillations in a longitudinal transversely isotropic tube and an isotropic tube are the same. The Ermakov-Pinney equation is derived. Radial oscillations in thick-walled and thin-walled cylindrical tubes with the Heaviside step loading boundary condition are next investigated. For radial, tangential and longitudinal transversely isotropic tubes a first integral is derived and effective potentials are defined. Using the effective potentials, conditions for bounded oscillations and the end points of the oscillations are obtained. Upper and lower bounds on the period are derived. Anisotropy reduces the amplitude of the oscillation making the tube stiffer and reduces the period. Thirdly, free radial oscillations in a thin-walled cylindrical tube are investigated. Knowles(1960) has shown that for free radial oscillations in an isotropic tube, ab = 1 where a and b are the minimum and maximum values of the radial coordinate. It is shown that if the initial velocity v0 vanishes or if v0 6= 1 but second order terms in the anisotropy are neglected then for free radial oscillations, ab > 1 in a radial transversely isotropic tube and ab < 1 in a tangential transversely isotropic tube. Radial oscillations in transversely isotropic incompressible spherical shells are investigated. Only radial transversely isotropic shells are considered because it is found that the Cauchy stress tensor is not bounded everywhere in tangential and longitudinal transversely isotropic shells. For a thin-walled radial transversely isotropic spherical shell with generalised Mooney-Rivlin strain-energy function the differential equation for radial oscillations has no Lie point symmetries if the net applied surface pressure is time dependent. The inflation of a thin-walled radial transversely isotropic spherical shell of generalised Mooney-Rivlin material is considered. It is assumed that the inflation proceeds sufficiently slowly that the inertia term in the equation for radial oscillations can be neglected. The conditions for snap buckling to occur, in which the pressure decreases before steadily increasing again, are investigated. The maximum value of the parameter for snap buckling to occur is increased by the anisotropy.

No description available.

This thesis explores the cross-price elasticity of rail and bus usage with gasoline prices. This is done to see how the short-run cross price elasticity has changed and to see if the same long-run relationship can be seen in the long run as previous pooled models. It is done in order to investigate whether policies such as higher gasoline taxes may make consumers move from car usage towards public transportation. Historically the cross-price elasticity has been around 0.2 with a higher elasticity for rail than for buses. The relationship also seemed to be greater in the long run than short run. Investigating this long run cross price elasticity for modes of public transportation separately would give greater insight into how consumers behave when gasoline prices shift. An ARDL model was therefore used to investigate the long run coefficients of gasoline prices with rail usage and bus usage separately as well as the short run coefficients. No cointegration could be found in this model for the two different modes. The results of the short-run cross-price elasticity seemed to be greater for buses as a direct effect, while it was greater at first lag for rail usage. The cross-price elasticity was lower for the period than previous studies, indicating that the cross-price elasticity may have decreased. The reasons for this cannot be concluded, but theory may explain these differences by the availability in substitutes for the periods, or lower levels of gasoline prices in recent years. This thesis therefore suggests further studies that investigate how usage of rail affects the usage of buses in metropolitan areas, and how the attributes of a modes of public transportation may change the usage of another form of public transportation.

We introduce to computer graphics the Pseudo-Rigid-Body Mechanism (PRBM) and the chain algorithm from mechanical engineering, with a unified tutorial from disparate source materials. The PRBM has been used successfully to simplify the simulation of non-linearly elastic beams, using deflections of an analogous spring and rigid-body linkage. It offers computational efficiency as well as an automatic parameterization in terms of physically measurable, intuitive inputs which fit naturally into existing animation work flows for character articulation. The chain algorithm is a technique for simulating the deflection of complicated elastic bodies in terms of straight elastic elements, which has recently been extended to incorporate PRBM beam-elements in three dimensions. We present a new, mathematically equivalent optimization of the 3D PRBM chain algorithm, from its former asymptotic complexity of O(n^2) in the number of elements n, to O(n). We also extend an existing PRBM for combined moment-force loads to 3D, where the existing 3D PRBM chain algorithm was limited to 3D PRBM elements for a moment-only load. This optimization and extension are validated by duplicating prior experimental results, but substituting the new optimization and combined-load elements. Finally, a loose road-map is provided with several key considerations for future extension of the techniques to dynamic simulations.

[pt] A mecânica dos meios contínuos tem atraído um grande interesse nos últimos tempos, o que é demonstrado pela numerosa publicação a respeito, em que autores como A.C Eringen C. Truesdell, L.I Sedov, Green- Zerna tratam da teoria em geral e desenvolvem tópicos particulares. A complexidade do campo de estudo cria uma grande dificuldade de formulação. O presente trabalho desenvolve uma notação intrínseca consiste, em que as relações das variáveis descrevendo o espaço e o tempo são de caracterização clara, permitindo produzir uma formulação clara, permitindo produzir uma formulação geral da teoria da Mecânica do Contínuo. O estudo é feito de maneira geral, admitindo deformações finitas, e os resultados obtidos são simplificados por aproximações. No primeiro capítulo estudamos a geometria da deformação, que recebe uma interpretação geométrica, e obtemos os invariantes que necessitaremos no desenvolvimento das relações constitutivas. Estudamos, relacionamentos deformações e deslocamento, taxa de deformação e velocidades, e terminaremos com as equações da compatibilidade. O capitulo dois estuda os princípios físicos obedecidos por um conjunto em movimento, permitindo obter de equações para formulação dos problemas. No capitulo três desenvolvemos um modelo geral de meio elástico e particularizamos os resultados até chegarmos à elasticidade clássica, enquanto que, no capitulo quatro as equações são aplicadas para descrição do movimento dos fluidos e idéias e viscosas. Finalizamos nosso trabalho com duas aplicações, uma no campo da elasticidade e outra no da mecânica dos fluidos. / [en] Mechanics of continua has atracted a gat interest in our time, which is proved by numerous publications on the matter, on whitch autors like A more than C. Eurigen, C. Trueesdell, L. I. Sedov, Green –Zenna treat the theory in general and develop particular topics. The complexity of this fiels of study creates a great difficulty of formulation. The present work develops a consistent intrinsic notation, on which the relations of variables describing space and time are of clear characterization allowing to produc a general formulation of the theory of continuum Mechanics. This study is done a general manner, admitting finite deformations beig the results obtained simplified by approximations. In the first chapter we study the geometry of deformation, whitch receiveis a geometrical interpratation, and we obtain the invariants wich be needed for developing the constittutive relations. We study kinematics of the motion, relate deformations and velocities and finish with the compatibility equations. Chapter two studies physical principles followed by a continum inmotion, allowing us to obtain a system of equations that is enough to problems formulation. In chapter three we develop a general model of elastic media and particularize the results as far as to reach the classical elasticity, where as, in chapter four, general equations are applied to describe the motion of ideak and viscous fluids. We finish our work with two applications, one in the field of Elasticity and the other in Fluid Mechanics.