Cette thèse concerne l'étude de la dynamique instable du front de détachement d'un ruban adhésif lors de son pelage à vitesse constante depuis un substrat plan. Nous avons en particulier mis en évidence le rôle essentiel de l'inertie du ruban sur cette instabilité.Dans un premier temps, nous avons réalisé une étude expérimentale des différentes dynamiques macroscopiques du front, observé par imagerie rapide, en fonction de la vitesse et de l'angle de pelage. Un régime constitué d'oscillations sinusoïdales en vitesse a alors été mis en évidence à la transition entre le pelage régulier et l'instabilité de stick-slip. Un modèle théorique, prenant en compte l'inertie du ruban, et sa résolution numérique ont permis de retrouver les différentes dynamiques observées, ainsi que les caractéristiques de ces oscillations.D'autre part, l'instabilité de stick-slip microscopique, récemment découverte, a également été étudiée. Nous avons caractérisé l'amplitude des avancées saccadées en fonction de la vitesse et de l'angle de pelage, mais également des propriétés physiques du ruban (masse et module de flexion). Son évolution avec ces différents paramètres est en accord avec une modélisation dynamique du front de détachement, couplant énergie de courbure et énergie cinétique du ruban. / This thesis presents the study of the unstable dynamics of the detachment front of an adhesive tape peeled at constant velocity from a flat surface. We could specifically highlight the essential role of the ribbon inertia on this instability.On one hand, we have performed an experimental study of the different front dynamics at macroscopic scales, observed by fast imaging, as a function of the peeling velocity and peeling angle. We could find a novel dynamical regime with sinusoidal oscillations of the detachment front velocity at the transition between regular peeling and stick-slip motion. A theoretical model taking into account the ribbon inertia, and its numerical resolution allow to explain the different dynamics observed, and furthermore, the characteristics of those velocity oscillations.On the other hand, the recently discovered microscopic stick-slip instability has also been studied. We have characterized the amplitude of the corresponding slips as a function of the peeling velocity and peeling angle, but also, as a function of the ribbon properties (mass and bending modulus). We show that a dynamical model coupling bending and kinetic energy of the ribbon can explain its evolution with these different parameters.

abstract: There is a need to understand spatio-temporal variation of slip in active fault zones, both for the advancement of physics-based earthquake simulation and for improved probabilistic seismic hazard assessments. One challenge in the study of seismic hazards is producing a viable earthquake rupture forecast—a model that specifies the expected frequency and magnitude of events for a fault system. Time-independent earthquake forecasts can produce a mismatch among observed earthquake recurrence intervals, slip-per-event estimates, and implied slip rates. In this thesis, I developed an approach to refine several key geologic inputs to rupture forecasts by focusing on the San Andreas Fault in the Carrizo Plain, California. I use topographic forms, sub-surface excavations, and high-precision geochronology to understand the generation and preservation of slip markers at several spatial and temporal scales—from offset in a single earthquake to offset accumulated over thousands of years. This work results in a comparison of slip rate estimates in the Carrizo Plain for the last ~15 kyr that reduces ambiguity and enriches rupture forecast parameters. I analyzed a catalog of slip measurements and surveyed earth scientists with varying amounts of experience to validate high-resolution topography as a supplement to field-based active fault studies. The investigation revealed that (for both field and remote studies) epistemic uncertainties associated with measuring offset landforms can present greater limitations than the aleatoric limitations of the measurement process itself. I pursued the age and origin of small-scale fault-offset fluvial features at Van Matre Ranch, where topographic depressions were previously interpreted as single-event tectonic offsets. I provide new estimates of slip in the most recent earthquake, refine the centennial-scale fault slip rate, and formulate a new understanding of the formation of small-scale fault-offset fluvial channels from small catchments (<7,000 m2). At Phelan Creeks, I confirm the constancy of strain release for the ~15,000 years in the Carrizo Plain by reconstructing a multistage offset landform evolutionary history. I update and explicate a simplified model to interpret the geomorphic response of stream channels to strike-slip faulting. Lastly, I re-excavate and re-interpret paleoseismic catalogs along an intra-continental strike-slip fault (Altyn Tagh, China) to assess consistency of earthquake recurrence. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2016

Cette thèse de doctorat présente une étude essentiellement expérimentale de l'instabilité de stick-slip lors du pelage d'adhésifs. Nous avons développé différents dispositifs expérimentaux permettant d'observer directement la dynamique de rupture saccadée du pelage. Les expériences sont réalisées à vitesse imposée dans différentes géométries : l'adhésif est pelé directement depuis son rouleau, ou depuis un substrat plan à angle imposé. D'une part, nous avons mis en évidence d'importants effets dynamiques, que les modèles théoriques actuels ne permettent pas d'expliquer. D'autre part, nous avons montré l'effet crucial de l'angle de pelage sur l'instabilité, qui est fortement réduite (en amplitude et en gamme d'existence) pour de grands angles. De plus, une nouvelle approche théorique, prenant en compte l'inertie du ruban, permet de comprendre en partie ces résultats expérimentaux. Enfin, nous démontrons que l'instabilité de stick slip est multi-échelle, en mettant en évidence la présence d'une instabilité secondaire, à des échelles temporelles et spatiales plus faibles que le stick-slip observé habituellement. Alors que l'instabilité principale est causée par des variations d'énergie élastique d'élongation, cette instabilité secondaire est pilotée par un relâchement de l'énergie de courbure du ruban / This thesis presents a mainly experimental study of the stick-slip instability during the peeling of adhesive tape. We developed different experimental set-ups, allowing us to observe directly the jerky dynamics during peeling. The experiments are conducted at an imposed velocity and different geometries : the adhesive is peeled directly from a roller, or from a flat substrate at a fixed angle. On the one hand, we highlight the existence of strong dynamical effects, which cannot be understood with the existing theoretical models. On the other hand, we show the crucial effect of the peeling angle on the instability, which is strongly reduced at large angles (both its amplitude and range of existence decrease). Besides, a new theoretical approach, taking into account the ribbon inertia, can allow us to understand partially the experimental observations. Finally, we show that the stick-slip instability is multi-scale : a secondary instability can occur at spatial and temporal scales smaller than the usually observed stick-slip. While the main instability is due to variations of the stretching elastic energy, this secondary instability is driven by the release of the bending energy stored in the ribbon

Except for aerodynamics forces, all vehicle excitation forces are generated at the tyre-road interface. Considering low speed applications, such as terramechanics where the aerodynamics force are negligible, the road-tyre interaction is of extreme importance. Crucial variables which govern the forces generated at the tyre-road interface are tyre side-slip angle, tyre longitudinal slip ratio and terrain pro le. Solutions to measure these variables exist for smooth hard roads but the solutions experience challenges on rough and o -road terrain. Digital Image Correlation is concerned with tracking the changes of a scene in a sequence of images or in images obtained from multiple viewpoints. These methods are frequently used in micro and nano-scale mechanical testing due to its ease of implementation and use as well as its non-contact approach. As a result these techniques are being implemented in many elds from material testing, physics, lm animations and engineering. The aim of this thesis is to investigate the applications of Digital Image Correlation in vehicle dynamics using cost e cient o -the-shelf digital cameras and lenses. The following three vehicle dynamic problems are investigated: The measurement of the vehicle side-slip angle, longitudinal slip-ratio of a pneumatic tyre and high delity terrain pro ling. The vehicle side-slip angle can be used as a measure of the vehicle stability and therefore be used to improve the e ectiveness of vehicle stability controllers. The tyre side-slip angle is also a vital measurement in characterising the lateral force characteristics of pneumatic tyres. A planar measuring method using Digital Image Correlation is shown to accurately measure the side-slip angle. The method is expanded by developing two additional algorithms which can measure all translational and rotational velocities. These methods are validated on both smooth surfaces and rough o -road terrain. A method is also implemented whereby the longitudinal slip ratio of a tyre can be measured using a single camera. Therefore, doing away with the conventional method of using three independent measurement systems. Features in the contact patch, encompassing both the tyre and the road, are tracked in a sequence of images. The features are classi ed into features lying on the tyre, road and outliers using a clustering algorithm. This enables the system to determine the tyre and road velocities from which the slip ratio is determined. High delity terrain pro ling is performed using a calibrated stereographic rig to obtain a three dimensional point cloud of the scene which is being viewed. The point cloud generated at one sample contains a grid of points encompassing a large area with points spaced both laterally and longitudinally. Overlapping point clouds are generated and joined using various registration techniques. The joined point clouds are sub-sampled to obtain a regularised grid of point containing a single point cloud of non overlapping points. The proposed techniques create new possibilities in the eld of vehicle dynamics. Enabling the side-slip angle to be measured in rough of road conditions while providing additional measurements. The longitudinal slip ratio which is measured directly at the contact patch could pave the way for better understanding the mechanism of the longitudinal tyre force generation. The inexpensive road pro ling systems enables multiple sensors to be used in terramechanics tests to determine the impact of a vehicle on the environment. The thesis presents the mere tip of the ice berg concerning digital image correlation used in vehicle dynamics with many more possibilities waiting to be discovered. / Thesis (PhD)--University of Pretoria, 2015. / tm2015 / Mechanical and Aeronautical Engineering / PhD / Unrestricted

This paper is a bachelor thesis in machine design where screaming screw tightenings are discussed. The research was initiated with a preliminary study in screw mechanics and the tightening process, as well as the stick-slip phenomenon. Furthermore, interviews were conducted with people at Scania and Atlas Copco who have relevant experience in screaming screw tightenings. These interviews strengthened the theory that screaming is caused by stick-slip. The natural frequency of a screw joint with a M8 x 60 mm screw and M8 M6M nut were approximated with FEM-analysis in Ansys. This in order to provide data for comparison with measured screams in future practical tests. The initial hypothesis that stick-slip causes scream was considered plausible since the natural frequency for the screw joint’s torsional oscillation is within the audible range. / Denna rapport är ett kandidatexamensarbete i maskinkonstruktion där skrikande skruvdragningar undersöks. Undersökningen inleddes med en förstudie i skruvens mekanik och åtdragningsprocessen. Stick-slip-fenomenet har även undersökts i förstudien. Vidare har intervjuer gjorts med personer som har erfarenhet inom området på Scania och Atlas Copco. Dessa intervjuer stärker teorin om att skrikfenomenet orsakas av stick-slip. Egenfrekvenser för ett skruvförband med dimensionerna M8 x 60 mm för skruven och M8 M6M för muttern togs fram genom en FEM-analys i Ansys. Detta för att i framtida praktiska tester kunna jämföra dessa frekvenser med uppmätta skrik. Den ursprungliga hypotesen om att stick-slip orsakar skrik bedömdes rimlig då egenfrekvensen för skruvförbandets torsionssvängning faller inom det hörbara intervallet.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第24171号 / 理博第4862号 / 新制||理||1695(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)准教授 西村 卓也, 教授 宮﨑 真一, 准教授 深畑 幸俊 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

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In this thesis, the superconductive and superresistive properties of thin percolating films of lead nanoclusters are presented. The samples were created by depositing clusters from an inert gas aggregation cluster source onto substrates held at either room temperature or 10K. Observations of the characteristic behaviours of the samples were made through R(T ) and V (I) measurements. Several interesting features were observed - smooth and discrete steps in the R(I) curves, hysteresis between increasing and decreasing bias currents, and non-zero resistances at superconducting temperatures. Explanations are proposed in terms of theoretical models of several phenomena - phase slips, phase slip centres and hotspots - which have seen little prior application to percolating systems in literature.

Nowadays sealing systems are commonly designed by means of hydrodynamic and elastohydrodynamic theories. Although the analytical as well as the computational approaches have improved in meaning full manner since the last decades: For small sealing gaps, in the order of micrometers and below, a discrepancy between experimental investigated and theoretically predicted leakage flows occur. As a cause for the discrepancy a breakdown of the no slip boundary condition is suspected. Since in small sealing gaps the continuum hypothesis is violated and molecular effects have to be considered. One fundamental quantity to take molecular affects into account is the slip length. Within this paper a new measurement apparatus to evaluate the slip length for hydraulic applications is presented. The adjustable gaps between two planar surfaces are in the order of magnitude of 1 μm. In a first step the slip length for the system steel-oil –steel is investigated at three different temperatures: 18°C, 22°C and 25°C. The measured slip lengths are in the order of magnitude of ~100 nm.

<p>The fiber suspensions in the production line from wood topaper are subjected to many types of chemical and mechanicalprocesses, in which the flow of the suspension is of vitalimportance. The flow of the suspension determines the degree ofuniformity of the fibers through the processing, which inreturn affects the properties of the fiber suspension. In orderto optimise the process, thorough knowledge of the suspensionflow is necessary, both on the level of suspension, fibernetworks and individual fibers. Knowledge of the fibersuspension behaviour combined with commercial CFD simulationprovides an efficient design method for any unit operation inthe papermaking process.</p><p>This work concentrates on macroscopic modeling of thebehaviour of fiber suspensions from 0.5-5% dry content, purefiber suspensions without fillers or additives. Any mechanismscausing the characteristic behaviour of the pulp suspensionhave not been included, they are only included through theirinfluence on the suspension parameters. Excluded mechanismsare, for instance, the fiber-fiber coupling mechanisms that arethe reason for the formation of fiber networks and parts offiber network, flocs.</p><p>By combining a rheology model for the bulk suspension, awall function that accounts for the slip layer and finallyintroducing turbulence, a model has been created that is ableto simulate the flow of most fiber suspensions. The flow of thesuspension is not constrained to any particular flowconditions; the models discussed in this work aim at describingthe behaviour of the suspension for all flow rates and flowtypes. The models are developed under simple flow conditions,where all variables can be controlled, but the models areintended for usage within the industry-based flows in real pulpand papermaking applications.</p><p><b>Keywords:</b>rheology, fiber, suspension, CFD, model, wall,slip, turbulence</p>