Although the relationship between increased anteversion and abnormal motor control in children with cerebral palsy is well documented there are no published studies that look at the possible links between motor control and femoral anteversion in children without neurological deficits. Children with intoeing gait are reported to be clumsy; but this clumsiness is usually ascribed to the gait angle. The aim of this study, therefore, is to explore the possible relationship between detorsion of the femur during growth and the development of hip posture and movement. Hip internal and external rotation are commonly used as a clinical measure of anteversion of the femur. In this study the range of hip internal and external rotation (as a clinical measure of anteversion) was related to performance of motor tasks requiring control of the posture and movement of the hip. If the degree of femoral anteversion is linked to the development of motor control, the next step would be to investigate the effectiveness of exercise programmes on the process of detorsion of the femur in children with excessive medial femoral torsion.

The natural variation of strength properties within brittle materials leads to size effect, a well-known phenomenon whereby the mean strength of a material is observed to decrease as the stressed volume increases. An important implication of size effect is that size adjustment parameters must be incorporated into multi-axial constitutive and failure models used in numerical simulations to predict material response to loading. This experimental study seeks to verify and quantify the presence of depth effect under shear failure in the orthotropic principal material directions of parallel strand lumber (PSL) and laminated veneer lumber (LVL). Torsion tests have been performed on specimens of fixed length and differing cross section to get a pure shear failure, by using a Universal Test Machine. The experimental results indicate that there is no depth effect for LVL from torsional shear stresses. PSL testing was limited to one size, and depth effect was not evaluated. A finite element model was built to simulate the torsional test for the 44x140mm LVL specimen. Comparing the experimental test results and the simulation results, the model provided an accurate prediction of the torsional test for Structural Composite Lumber.

Paper is used in a wide range of applications, each of which has specific requirements on mechanical and surface properties. The role of paper strength on paper performance is still not well understood. This work addresses the mechanical properties of paper by utilizing fiber network simulation and consists of two parts.In the first part, we use a three-dimensional model of a network of fibers to describe the fracture process of paper accounting for nonlinearities at the fiber level (material model and geometry) and bond failures. A stress-strain curve of paper in tensile loading is described with the help of the network of dry fibers; the parameters that dominate the shape of this curve are discussed. The evolution of network damage is simulated, the results of which are compared with digital speckle photography experiments on laboratory sheets. It is concluded that the original strain inhomogeneities due to the structure are transferred to the local bond failure dynamics. The effects of different conventional and unconventional bond parameters are analyzed. It has been shown that the number of bonds in paper is important and that the changes in bond strength influence paper mechanical properties significantly.In the second part, we proposed a constitutive model for a fiber suitable for cyclic loading applications. We based the development of the available literature data and on the detailed finite-element model of pulp fibers. The model provided insights into the effects of various parameters on the mechanical response of the pulp fibers. The study showed that the change in the microfibril orientation upon axial straining is mainly a geometrical effect and is independent of material properties of the fiber as long as the deformations are elastic. Plastic strains accelerate the change in microfibril orientation. The results also showed that the elastic modulus of the fiber has a non-linear dependency on a microfibril angle,with elastic modulus being more sensitive to the change of microfibril angle around small initial values of microfibril angles. These effects were incorporated into a non-linear isotropic hardening plasticity model for beams and tested in a fiber network in cycling loading application model, using the model we estimated the level of strains that fiber segments accumulate at the failure point in a fiber network.The main goal of this work is to create a tool that would act as a bridge between microscopic characterization of fiber and fiber bonds and the mechanical properties that are important in the papermaking industry. The results of this work provide a fundamental insight on mechanics of paper constituents in tensile as well as cyclic loading. This would eventually lead to a rational choice of raw materials in paper manufacturing and thus utilizing the environment in a balanced way. / <p>QC 20130605</p>

The goal of this paper is to extend Sanders Mac Lane's formulation of the torsion product as equivalence classes of projective chain complexes in the setting of modules over a ring to the setting of modules over small categories. The motivation to extend the definition was with a specific view to the orbit category. The main difficulty was in defining an appropriate dual for modules over small categories. During the course of our investigation it was discovered that modules over small categories can be formulated as modules over a matrix ring without losing any of the key features. / Thesis / Master of Science (MSc)

No description available.

No description available.

No description available.

An analytical model of cracked composite beams vibrating in coupled bending-torsion is developed. The beam is made of fiber-reinforced composite with fiber angles in each ply aligned in the same direction. The crack is assumed open. The local flexibility concept is implemented to model the open crack and the associated compliance matrix is derived. The crack introduces additional boundary conditions at the crack location and these effects in conjunction with those of material properties are investigated. Free vibration analysis of the cracked composite beam is presented. The results indicate that variation of natural frequencies in the presence of a crack is affected by the crack ratio and location, as well as the fiber orientation. In particular, the variation pattern is different as the magnitude of bending-torsion coupling changes due to different fiber angles. When bending and torsional modes are essentially decoupled at a certain fiber angle if there is no crack, the crack introduces coupling to the initially uncoupled bending and torsion. Based on the crack model, aeroelastic characteristics of an unswept composite wing with an edge crack are investigated. The cracked composite wing is modeled by a cracked composite cantilever and the inertia coupling terms are included in the model. An approximate solution on critical flutter and divergence speeds is obtained by Galerkin's method in which the fundamental mode shapes of the cracked wing model in free vibration are used. It is shown that the critical divergence/flutter speed is affected by the elastic axis location, the inertia axis location, fiber angles, and the crack ratio and location. Moreover, model-based crack detection (size and location) by changes in natural frequencies is addressed. The Cawley-Adams criterion is implemented and a new strategy in grouping frequencies is proposed to reduce the probability of measurement errors. Finally, sensitivity of natural frequencies to model parameter uncertainties is investigated. Uncertainties are modeled by information-gap theory and represented with a collection of nested sets. Five model parameters that may have larger uncertainties are selected in the analysis, and the frequency sensitivities to uncertainties in the five model parameters are compared in terms of two immunity functions. / Ph. D.

<p dir="ltr">Post-tensioned concrete is a popular structural system in modern bridge design, allowing for longer bridge spans and the construction of curved, spliced, and segmental girders. When designed and constructed properly, post-tensioned concrete can offer improved durability over reinforced concrete as it is more resistant to cracking. However, corrosion of prestressing strands can compromise the integrity of post-tensioned construction. Grouting has been the primary method of providing corrosion protection to the prestressing strands. However, grouting of tendons presents numerous limitations and results in multiple problems in practice. As a result, there has been increased interest in the use of unbonded tendons. Corrosion protection can still be achieved in unbonded tendons through the use of flexible fillers such as grease and microcrystalline wax. Limited research has been conducted on unbonded tendons, and no known research exists regarding the behavior of unbonded tendons subject to torsion. The objective of this research was to investigate the torsional behavior and strength of unbonded post-tensioned bridge girders. The scope of work included testing six specimens to investigate the difference in behavior between bonded and unbonded tendons as well as the influence of internal versus external ducts. The influence of transverse reinforcement was also considered.</p>

Passfederverbindungen (PFV) können infolge tribologischer und spanungsmechanischer Schädigungsmechanismen versagen, welche wiederum an unterschiedlichen Orten im Nutbereich entweder Risse initiieren (Gestaltfestigkeit) oder unzulässig große plastischen Deformation verursachen. Die aktuell gängigen Auslegungsrichtlinien erfassen die Zusammenhänge nur unzureichend. Mit dieser Arbeit wird ein tieferes Verständnis aufgebaut, um dadurch die Festigkeit der PFV präziser abzuschätzen. Die Untersuchungen zur Gestaltfestigkeit der PFV bestätigen die deutliche Unterschät-zung der Kerbwirkung, die mit steigender Werkstofffestigkeit weiter zunimmt. Auf Basis der experimentellen Untersuchungen konnten neue Kerbwirkungszahlen ermittelt werden, welche diese Diskrepanz beseitigen. PFV versagen als Folge der Reibdauerermüdung, was von numerischen und fraktografischen Analysen untermauert wurde. Diesbezüglich wurde die Anwendbarkeit der tribologischen Festigkeitsbeurteilung auf Basis von s.g. Reibdauerkorrosionsfaktoren bestätigt. Wenn die Rissinitiierung der PFV an der freien Oberfläche erfolgt, kann die Kerbwirkung mittels örtlicher Methoden abgeschätzt werden. Für die hier durchgeführten Untersuchungen zur plastischen Aufweitung der Wellennut wurde das neue Versagenskriterium der plastischen Nutaufweitung formuliert. Auf Grundlage der Basisversuche wurde ein Messverfahren entwickelt und ein Grenzwert festgelegt, ab welchem die Verbindung als ausgefallen gewertet werden kann.:Inhaltsverzeichnis VII Kurzzeichenverzeichnis X Abkürzungen XIII 1 Einleitung und Motivation 1 2 Stand der Technik / Grundlagen zur PFV 4 2.1 Grundlegender Aufbau einer PFV 4 2.2 Dimensionierung von PFV 5 2.2.1 Berechnung der Übertragungsfähigkeit auf Basis von Flächenpressung 6 2.2.2 Berechnung der Gestaltfestigkeit auf Basis von Nennspannungen 7 2.2.3 Berechnung der Gestaltfestigkeit auf Basis örtlich ermittelter Spannungen 7 3 Stand der Forschung 9 3.1 Festigkeit von PFV 9 3.2 Deformation der Nut bei PFV 20 4 Zielstellung und Aufbau der Arbeit 22 5 Untersuchungsmethoden 26 5.1 Experimentell 26 5.1.1 Versuchsperipherie 26 5.1.2 Versuchsprogramm und -durchführung 28 5.1.3 Grundlagen zur Werkstoffcharakterisierung und Durchführung von Schwingversuchen 30 5.1.3.1 Quasi-statischer Zugversuch 30 5.1.3.2 Härtemessung 31 5.1.3.3 Versuchsdurchführung im Einstufen-Schwingfestigkeitsbereich 32 5.1.3.4 Rechnerische Ermittlung von Festigkeitskennwerten auf Basis experimentell ermittelter Kenngrößen 37 5.2 Numerischer Modellaufbau 37 6 Werkstoffuntersuchungen 40 6.1 Werkstoffkennwerte für Untersuchungen zur Gestaltfestigkeit 40 6.2 Werkstoffkennwerte für Untersuchungen zur Nutaufweitung 43 7 Untersuchungen zur Gestaltfestigkeit von PFV 46 7.1 Beanspruchung und Versagen 46 7.2 Experimentelle Untersuchungen 48 7.2.1 Basisversuche: PFV ohne Übermaß zwischen Welle und Nabe 48 7.2.2 Einfluss eines Übermaßes zwischen Welle und Nabe 51 7.2.3 Referenzversuche an blindgehärteten Wellen aus 18CrNiMo7-6 53 7.2.4 Einfluss des Wellendurchmessers (Größeneinfluss) 54 7.2.5 Einfluss der Nabenwandstärke 57 7.2.6 Untersuchungen zum Versagensmechanismus 59 7.2.7 Versuche im Zeitfestigkeitsbereich 63 7.2.8 Versuche mit wechselnder Belastung 65 7.2.9 Versuche mit trockener Verbindung 66 7.2.10 Fraktografische Analyse 68 7.3 Numerische Untersuchungen 73 7.3.1 Tribo-mechanische Schädigung 73 7.3.2 Einfluss des Übermaßes auf die tribo-mechanische Schädigung 76 7.3.3 Einfluss der Nabenwandstärke 76 7.3.4 Untersuchung zur Rissinitiierung an freier Oberfläche (Form B) 78 8 Untersuchungen zur maximal zulässigen Nutaufweitung 84 8.1 Plastische Nutaufweitung als Ausfallkriterium 84 8.2 Basisversuche 87 8.3 Anheben des Grundniveaus auf Basis der zulässigen Nutaufweitung 88 8.4 Absicherungsversuche mit 10 Mio. Lastwechseln 91 8.5 Übermaß zwischen Welle und Nabe – Reibschlussfaktor KR 92 8.5.1 Quasi-statische Untersuchungen 93 8.5.2 Dynamische Untersuchungen mit Übermaß und schwellender Torsion 95 8.6 Einfluss ausgewählter Parameter auf die zulässige Nutaufweitung 97 8.6.1 Lastspitzenhäufigkeitsfaktor fL 97 8.6.2 Lastrichtungswechselfaktor fW 100 9 Auswertung und Interpretation der Untersuchungen 101 9.1 Festigkeit der Welle 101 9.1.1 Neujustierung der Kerbwirkungszahlen 101 9.1.2 Einbindung relevanter Einflussgrößen 104 9.1.2.1 Berücksichtigung des Übermaßes zwischen Welle und Nabe 104 9.1.2.2 Weitere untersuchte Einflussparameter 109 9.1.2.3 Diskussion zum Versagensort 111 9.1.2.4 Untersuchungen zur Zeitfestigkeit 111 9.1.3 Beurteilung der lokalen tribologischen Beanspruchung 112 9.1.4 Beurteilung der lokalen spannungsmechanischen Beanspruchung 116 9.2 Plastische Deformation der Nut 117 9.3 Einfluss des Wellenwerkstoffes auf den Ausfallmechanismus 121 10 Zusammenfassung und Ausblick 124 Literaturverzeichnis 128 Anhang 137 Anhang A 137 Anhang B 141 Anhang C 142 Anhang D 145