Dissertação (Mestrado em Engenharia Mecânica) - Centro Universitário FEI, São Bernardo do Campo, 2018

No description available.

AN ABSTRACT OF THE THESIS OF Jacob Boone, for the Master of Science degree in Mechanical Engineering, presented on 10/28/2010, at Southern Illinois University Carbondale. TITLE: DESIGN, CONSTRUCTION, AND EVALUTAION OF UNIVERSAL FRICTION TESTER MAJOR PROFESSOR: Dr. Peter Filip Many different types of friction testers are currently available for testing specific frictional applications. Of these machines very few have versatility, and of the ones that do, the amount of versatility is limited. Since friction is a property specific to each system, all operating parameters need to match the specific application as closely as possible in order to obtain accurate data. This requires many research facilities to have several specific friction testers in order to provide the necessary testing capabilities. The goal of this project was to design a Universal Friction Tester (UFT) with enough versatility to reproduce most types of sliding friction situations. This was accomplished by providing a wide range of testing capabilities through the use of interchangeable system components. Results show that the UFT provides quality data over its entire operating range. It was shown that normal pressure, sliding speed, temperature and system stiffness all have drastic effects on frictional performance. By using a borosilicate glass disc, the friction surface was viewed in-situ during testing. This allowed insights into true surface temperature and contact area. In conclusion, the UFT can successfully take the place of several friction testers and thus provide many friction research capabilities while requiring fewer resources. The wide range of testing capabilities will allow the UFT to be used as a research tool for many types of advanced friction studies. Some of these may include true surface temperatures, true contact area, influence of conditions on stick-slip phenomenon, and thermo-elastic instabilities.

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.

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

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.

The research reported in this thesis builds on a novel model developed at the University of Minnesota to analyze the self-excited vibrations that occur when drilling with polycrystalline diamond cutter bits. The lumped parameter model of the drilling system takes into consideration the axial and the torsional vibrations of the bit. These vibrations are coupled through a bit-rock interaction law. At the bit-rock interface, the cutting process combined with the quasihelical motion of the bit leads to a regenerative effect that introduces a coupling between the axial and torsional modes of vibrations and a state-dependent delay in the governing equations, while the frictional contact process is associated with discontinuities in the boundary conditions when the bit sticks in its axial and angular motion. The response of this complex system is characterized by a fast axial dynamics superposed to the slow torsional dynamics. A two time scales analysis that uses a combination of averaging methods and a singular perturbation approach is proposed to study the dynamical response of the system. An approximate model of the decoupled axial dynamics permits to derive a pseudo analytical expression of the solution of the axial equation. Its averaged behavior influences the slow torsional dynamics by generating an apparent velocity weakening friction law that has been proposed empirically in earlier works. The analytical expression of the solution of the axial dynamics is used to derive an approximate analytical expression of the velocity weakening friction law related to the physical parameters of the system. This expression can be used to provide recommendations on the operating parameters and the drillstring or the bit design in order to reduce the amplitude of the torsional vibrations. Moreover, it is an appropriate candidate model to replace empirical friction laws encountered in torsional models used for control. In this thesis, we also analyze the axial and torsional vibrations by basing the model on a continuum representation of the drillstring rather than on the low dimensional lumped parameter model. The dynamic response of the drilling structure is computed using the finite element method. While the general tendencies of the system response predicted by the discrete model are confirmed by this computational model (for example that the occurrence of stick-slip vibrations as well as the risk of bit bouncing are enhanced with an increase of the weight-on-bit or a decrease of the rotational speed), new features in the self-excited response of the drillstring are detected. In particular, stick-slip vibrations are predicted to occur at natural frequencies of the drillstring different from the fundamental one (as sometimes observed in field operations), depending on the operating parameters. Finally, we describe the experimental strategy chosen for the validation of the model and discuss results of tests conducted with DIVA, an analog experimental set-up of the lumped parameter model. Some results of the experiments conducted in an artificial rock seem to validate the model studied here although the same experiments obtained with natural rocks were unsuccessful. Different problems with the design of the experimental setup were identified. By using the outcome of the analysis of the uncoupled dynamics, we could provide critical recommendation to elaborate and to design a simpler and stiffer analog experiment (TAZ) used to study the self excitation of the axial dynamics that ultimately lead to the excitation of the torsional dynamics.

none

Downhole vibrations lead to downhole failures and decrease the rate of penetration (ROP). The bottom hole assembly (BHA) static and dynamic design is a key factor in optimizing drilling operations. The BHA should be designed to minimize the vibration levels in the axial, lateral, and torsional directions. This would be achieved by avoiding rotating the drillstring in the speeds that are nearby the natural frequency of BHA. The complexity associated with current BHA components requires using advanced computational tools that are capable of solving complex and time-consuming equations. Finite Element Analysis (FEA) is the most used technique in analyzing vibration behavior of the drillstring by mesh discretizing of a continuous body into small elements. This thesis will study the dynamic behavior of different BHA designs for Manifa and Karan fields of Saudi Aramco to optimize the drilling operations. The FEA software that will be used to conduct these studies is called Vibrascope™, which was developed by NOV. The software will determine the critical speeds of the drillstring that should be avoided to prevent resonance of the BHA, which will lead to severe downhole vibration. / text

Friction Stir Welding (FSW) is a solid-state joining process that is of special interest in joining aluminum and other alloys that are traditionally difficult to fusion weld. The energy required for this joining process is transmitted to the work-pieces through a rotating FSW tool. Modeling attempts, aimed at perfecting the process, rely on assumptions of the contact conditions present between the work-pieces and the FSW tool. Various studies have attempted to define these contact conditions. Both theoretical and experimental studies indicate the contact conditions between the work-piece and weld tool are unknown and may vary during the FSW process. To provide insight into the contact conditions, the objective of this study is to characterize the FSW nugget in terms of swept volume as indicated by the cross-sectional area and symmetry of the FSW nugget over a range of processing conditions.