Theoretical and experimental investigations of the friction behavior of automotive shock absorbers

Reibung in Automobil-Schwingungsdämpfern setzt sich aus zwei Reibungstypen zusammen: Die beabsichtigte viskose Flüssigkeitsreibung dämpft geschwindigkeitsabhängig die Fahrwerksschwingungen, während die ungewollte Festkörperreibung zwischen den aneinander reibenden Dichtungen und Führungen des Dämpfers entsteht. Die letztere, sogenannte statische Reibung beeinträchtigt den Fahrkomfort und (bei hohem Reibniveau) die Fahrsicherheit. Die Verminderung der statischen Reibung ist daher ein übliches Ziel in der Dämpferentwicklung. In dieser Dissertation wird eine Methode zur Reibungssimulation vorgestellt, welche die Optimierung der Dämpferreibung früh im Entwicklungsprozess ermöglicht, wodurch Zeit und Kosten für die Untersuchung realer Prototypen deutlich gesenkt werden können. Zur Ermittlung der Parameter, welche in relevanter Weise das Reibverhalten des Dämpfers mitbestimmen, werden neuartige Einzelreibstellenprüfstände entwickelt und aufgebaut, da bereits existierende Dämpferreibungsprüfstände die tatsächlichen Betriebsbedingungen im Gesamtdämpfer nur unzureichend wiedergeben. Die Integrität dieses Experimentalkonzeptes wird durch Reibmessungen am Gesamtdämpfer validiert. Die Einzelreibstellenmessungen werden ausgewertet, woraufhin ein Ansatz zur Reibmodellierung aufgrund des Reibverhaltens entwickelt wird. Da Dämpferreibung in hohem Maße geometrieabhängig und die Variation von Bauteilgeometrie ein üblicher Konstruktionsprozess ist, wird 3D-FEM-Struktursimulation verwendet, um die Verformung der Dämpferbauteile durch Montage und unter veränderlichen Betriebsbedingungen zu bestimmen. In den jeweiligen Kontaktzonen der FEM-Simulation wird ein dynamisches Reibmodell implementiert und mittels Einzelreibstellenmessungen parametriert. Im Anschluss an die Parametrierung des Gesamtreibmodells mit Geometriedaten, Betriebsbedingung, Materialdaten und Reibmodellparametern werden Einzelreibstellensimulationen durchgeführt, ausgewertet und gegen sowohl Einzelreihstellen- als auch Gesamtdämpfermessungen validiert. Es stellt sich heraus, dass die in dieser Arbeit vorgestellte Simulationsmethode die Vorhersage des Reibverhaltens übereinstimmend mit den anfangs auf geführten Anforderungen erlaubt. Die Anwendung dieser Methode ermöglicht es somit, ein weites Feld von dämpferreibungsrelevanten Parametern mit signifikant erhöhter Entwicklungseffizienz zuverlässig zu untersuchen.Friction in automotive shock absorbers is composed of two friction types: The intended viscous fluid friction generates the speed-dependent counter force to damp the chassis vibrations, while the unwanted solid body friction is generated by the rubbing of the damper's seals and guides during stroking. The latter so-called static friction impairs ride comfort and (at high levels) driving safety. Lowering static friction is therefore a common target in the shock absorber design process. In this dissertation, a friction simulation method is introduced, which allows for the optimization of damper friction early in the design stage, aiming to significantly decrease time and cost for the setup and experimental analysis of real prototypes. To determine the parameters which have a relevant impact on the damper's friction behavior, this dissertation presents the design and setup of novel single friction point test rigs, since existing damper friction measurement setups do not sufficiently resemble the real operating conditions of a full damper. To prove the integrity of this experimental concept, it is validated against full damper friction measurements. The single friction point measurements are analyzed with regard to their friction behavior, on the base of which a friction modeling approach is developed. Since damper friction is highly dependent on geometry, and the variation of the shape of the damper parts is common in the design process, 3D structural FEM is used to determine the deformations of the damper parts resulting from mounting and varying operation conditions. In the respective contact zones, a dynamic friction model is applied to the FEM simulation and parameterized based on the single friction point measurements. Subsequent to the parameterization of the overall friction model with geometry data, operation conditions, material properties and friction model parameters, single friction point simulations are performed, analyzed and validated against both single friction point and full damper measurements. lt is shown that the simulation method introduced within this work allows for friction prediction coincident with the above-mentioned requirements. Consequently, its application makes it possible to reliably investigate a wide range of parameters relevant to damper friction with significantly increased development efficiency

Models for the dynamic simulation of tank track components

This project has been sponsored by QinetiQ Limited (QinetiQ); whose aim it is to model the dynamics of a prototype high-speed military tracked vehicle. Specifically their objective is to describe the mechanism by which force inputs are transmitted from the ground to the vehicle’s hull. Many track running gear components are steel and can be modelled as simple lumped masses or as linear springs without internal damping. These present no difficulty to the modeller. However tracked vehicle running gear also has nonlinear components that require more detailed descriptions. Models for two rubber components, the road wheel tyre and track link bush, and a model for the suspensions rotary damper, are developed here. These three components all have highly nonlinear dynamic responses. Rubber component nonlinearities are caused by the materials nonlinear elastic and viscoelastic characteristics. Stiffness is amplitude dependent and the material exhibits a significant amount of internal damping, which is predominantly Coulombic in nature but also relaxes overtime. In this work, a novel method for measuring the elastic and viscoelastic response of Carbon Black Filled Natural Rubber components has been devised and a ‘general purpose’ mathematical model developed that describes the materials response and is suited to use in multibody dynamic analysis software. The vehicle’s suspension rotary damper model describes three viscous flow regimes (laminar, turbulent and pressure relief), as a continuous curved response that relates angular velocity to damping torque. Hysteresis due to the compression of entrapped gas, compliance of the dampers structure and compression of damper oil is described by a single non-parametric equation. Friction is considered negligible and is omitted from the model. All components are modelled using MSC.ADAMS TM multibody dynamic analysis software. The models are shown to be easily implemented and computationally robust. QinetiQ’s requirement for ‘practical’ track running gear component models has been met.EThOS - Electronic Theses Online ServiceQinetiQ LimitedGBUnited Kingdo

A research project to develop and evaluate a technical education component on materials technology for orientation to space-age technology

A project was initiated to develop, implement, and evaluate a prototype component for self-pacing, individualized instruction on basic materials science. Results of this project indicate that systematically developed, self-paced instruction provides an effective means for orienting nontraditional college students and secondary students, especially minorities, to both engineering technology and basic materials science. In addition, students using such a system gain greater chances for mastering subject matter than with conventional modes of instruction

Subject-adjustable computational modelling for the analysis of human head–neck motions in rear-end impacts

Whiplash Associated Disorder (WAD) is a general term used to describe minor injuries to the neck, mostly as a result of a rear-end motor vehicle collision. Although the injury is defined as minor, the long-term symptoms such as neck pain, stiffness, headache, or concentration difficulties, result in high costs to the economy, healthcare services and individuals. Consequently, there has been significant amount of research undertaken to understand and prevent WAD, covering experimental and computational studies. However, whiplash injuries are difficult to detect since diagnostic tools such as X-rays, CT (Computed Tomography) scans or MRI (Magnetic Resonance Imaging) are not suitable to identify the location or the extent of the injury. Also, the injury mechanisms are not fully understood; hence mathematical criteria are used as surrogates to estimate the likelihood of injury. In the present research, a biofidelic, subject-adjustable head-and-neck model (i.e. the model is adjustable for individual subject characteristics) has been developed for rear-end impact whiplash analysis. Existing literature is used to develop the overall research framework (methodology), which has three main objectives: first to explain the importance of personalised protection investigations, second to evaluate the suitability of existing data for a subject-adjustable model, and third to define the required steps in the design of such a model.To generate the geometry of the model, previously published cascading equations capable of predicting the main vertebrae dimensions based on the subject characteristics age, gender and height are used. Also, in line with previous work, seven cervical neck segments represent the seven cervical vertebrae and all surrounding cervical tissues properties. The mass and moment of inertia properties of each segment are lumped into each respective segment. The intervertebral behaviour for two adjacent segments is described by non-linear spring-damper functions, which change according to subject specific characteristics. The model is driven by specification of the first thoracic vertebra (T1) motion.The model combines existing data and methods from different sources, utilising available data in the public domain. New procedures and techniques are incorporated to create a homogeneous model, which is adaptable to a wide range of subjects. The developed computational model is not simply a linear scaling of a master-model to other dimensions, but rather uses prediction equations to create the desired anthropometric model. The anthropometric model predictions for body part dimensions and inertia properties are successfully verified using anthropometric surveys available in the literature.Using lumped and non-linear stiffness and damping equations for the intervertebral joints, and without modelling separate muscles, the model is dynamically calibrated for different experimental sled test data available in the open domain. The joint equations and their coefficients are derived based on published joint data measurements on Post Mortem Human Subjects (PMHS); a scaling of these coefficients is applied to match the overall head-and-neck kinematics of the computational model to the experimental sled test kinematics. For each experimental study, the global head kinematics of the model was calibrated successfully to mimic the head kinematics.The model has been modelled to represent subjects with different anthropometric characteristics, involving a novel relationship between intervertebral joint coefficients and anthropometric subject specifications. The observed effect of each change of anthropometric subject characteristic is evaluated independently using time-history diagrams; then the observed effect of multiple changes of anthropometric subject characteristics is assessed using multi-dimensional response surfaces for the response’s highest magnitude.The analysis of the proposed model has revealed that existing work involving the use of lumped parameter models is not as robust as claimed. This is because existing work has always been evaluated using a low number of validation graphs, i.e. using only the graphs which gave good validation results. The proposed model has been comprehensively evaluated and its limitations are addressed. The developed model had to merge different studies (different ethnical backgrounds, different subject types, etc.) together to create an adjustable model; this is because of the limited available data. The final model is the most homogeneous model currently possible. In addition, there is also limited relevant experimental data for full validation of the model, which is not ideal. Nevertheless, reliable results for the comparison of global head kinematics compared with several experimental sled test studies have been obtained for the average male subject model. Also, using the proposed model the dynamic effects resulting from anthropometric subject differences have been evaluated; these effects are almost perfectly linear relationships for each subject characteristic change. Potential applications for the developed model are the injury assessment based on mathematical whiplash injury criteria, head-restraint optimisation to minimise injury risk and the improvement of neck biofidelity in anthropometric test devices.</div

Ultrasonic Histotripsy for Cell Therapy

Liver transplantation is the mainstay of the treatment for end stage liver diseases including metabolic and congenital liver diseases. The number of suitable donor organs is, however, limited. Intra-portal hepatocytes transplantation has been considered as a bridging therapy to liver transplantation but has shown a mixed clinical outcome with limited success including low level of engraftment of transplanted hepatocytes. To enhance the level of cell engraftment, this thesis introduces an alternative and novel approach to traditional intra-portal cell therapy mediated by High Intensity Focused Ultrasound (HIFU) histotripsy. The proposed novel strategy is to create damage to the recipient liver by producing a number of cavities inside the liver parenchyma through histotripsy and then delivering donor hepatocytes into the cavities. The aim of histotripsy is to mechanically fractionate soft tissue as an alternative to thermal ablation for therapeutic applications. While a number of studies have demonstrated the efficacy of histotripsy for fractionating solid tumours, the exact mechanisms underpinning this phenomenon are poorly understood. The main objectives of this thesis are to (a) investigate the major mechanisms involved in histotripsy and (b) demonstrate the feasibility of the proposed new cell therapy. A high-speed camera with a passive cavitation detection (PCD) system were used to observe the dynamics of bubbles produced in optically transparent tissue phantoms exposed to HIFU fields. Numerical studies on the bubble dynamics and both ex- and in vivo liver experiments were conducted with histological and serological analyses. Boiling bubbles were generated in a localised super-heated region and cavitation clouds were subsequently induced ahead of the expanding bubble. This process was repeated with HIFU pulses and eventually resulted in a tadpole shaped lesion. The in vivo experimental results together with histological observations showed that direct injection of cells inside the cavity facilitated successful uptake, proliferation and integration of the transplanted hepatocytes in the recipient liver. A week after the transplantation, the plasma albumin level was partially restored to 50% of the normal level in Nagase analbuminemic rats (serum albumin level was initially nil) by cell therapy after HIFU histotripsy. This novel method of intra-hepatic hepatocyte transplantation might be an invaluable tool for cell therapy in the future

Aeronautical engineering: A continuing bibliography with indexes (supplement 272)

This bibliography lists 719 reports, articles, and other documents introduced into the NASA scientific and technical information system in November, 1991. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment, and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics

Velocity dependent rheologies in seismotectonic scale modelling: Characterization and Implementation in a new analogue modelling scheme

Large earthquakes along lithospheric fault zones associated with major plate boundaries pose a significant threat to structures and people. Although the number of large earthquakes (moment magnitude $M_w > 7.0$) is low, they still account for the majority of fatalities caused by seismic activity and associated consequences (tsunamis, landslides,...). Their scarcity leads to incomplete statistiscal models that rely on few data points. As a result, the conditions and processes that lead to earthquakes of this size are still not completely resolved. To improve the current real-world earthquake catalog, I attempt to model seismotectonic deformation experimentally. Simplified laboratory sized analog models of strike-slip and subduction zones are used to reproduce the dynamics, kinematics and statistics of earthquakes. The laboratory experiments are accompanied by analytical considerations and will serve as a testbed for numerical simulations. For this purpose a new analogue modelling scheme is designed in this thesis and improved based on the findings. In a first step, the rheological properties of several silicone polymers are studied to evaluate their suitability for long-term laboratory use and usefulness for seismotectonic analogue models. Silicone polymers of differing composition and origin are tested with state of the art rheometric methods. All tested silicones show a transition from Newtonian to power-law rheology with increasing shear rate. As a result, the effective viscosity drops in a similar manner to the lower crust. Consequently, I use one of the tested silicone oils as an analogue for the lower crust, which is assumed to show Maxwell behaviour under the influence of seismic activity. A further advantage of the silicone oils is their long-term stability and chemical similarity over multiple batches. To model the frictional behaviour of a fault zone I used glass beads, which exhibit rate-and-state-friction under the targeted experimental conditions. Intensive material tests have shown, that a very simplified granular fault zone, only consisting of glass beads, can already show a large number of slip behaviours. Many stick-slip cycles are produced using an annular shear cell. Depending on the experimental parameters, such as loading rate and stiffness, the granular fault zone shows creep, oscillating slip and stick-slip. In some cases a characteristic separation of small slow events and large fast events is observed. This is proposed to be the result of competing micromechanical processes that lead to the reorganization of the granular packaging. Furthermore, the recurrence and magnitude of the larger events is strongly affected by transients and slow events during the interseismic phase. The analogue earthquakes in this study are several orders of magnitude faster than the interseismic loading rate. The separation of scales which was found for the granular stick-slip events and the resulting effect on the system behaviour requires continuous monitoring of the experiment over the complete seismic cycle. This is done using digital image correlation of images taken during the experiment. Because the duration of each experiment is in the order of a few hours, and the required acquisition rate for the fastest processes is in the order of several Hz, the amount of data generated per experiment is very high. To circumvent this, a dynamic triggering algorithm is developed to reduce the amount of data by almost 95\%. The shear stress during an experiment is used as an input for the triggering system. In combination with a dynamically accessible buffer of images on the monitoring computer, only images that show relevant information are extracted. A comparison of the experimental findings with existing studies shows a good agreement with natural examples and several analytical descriptions of fault zones. As a next step the experimental setup is going to be developed further with the findings from this thesis and numerical simulations are going to be used for cross-validation.Große Erdbeben stellen eine signifikante Gefahr für Gebäude und Menschen entlang großer Plattengrenzen dar. Obwohl die absolute Zahl von besonders großen Beben (Moment Magnitude $M_w >7.0$) klein ist, sind sie für einen Großteil der Todesfälle durch seismische Aktivität und ihre Auswirkungen (Tsunamis, Erdrutsche,...) verantwortlich. Das seltene Auftreten führt zu unvollständigen, statistischen Modellen, welche auf relativ wenigen Datenpunkten basieren. Daher sind die Bedingungen und Prozesse, welche zu Erdbeben dieser Größe führen noch nicht komplett verstanden. Um die bisher bestehenden Erdbebenkataloge zu ergänzen, modelliere Ich experimentell seismotektonische Prozesse. Die Dynamik, Kinematik und Statistik von Erdbeben wird durch vereinfachte Labormodelle von Blattverschiebungen simuliert. Die Experimente werden von analytischen Überlegungen begleitet und sollen zukünftig als Testobjekte für numerische Simulationen dienen. Zu diesem Zweck beschreibt die vorliegende Arbeit die Entwicklung eines neuen Schemas zur Analogmodellierung und gibt Vorschläge zu dessen späteren Verbesserung. In einem ersten Schritt werden die rheologischen Eigenschaften verschiedener Silikonpolymere untersucht, um deren Eignung zur langjährigen Verwendung und Anwendbarkeit in seismotektonischen Modellen zu prüfen. Silikonpolymere unterschiedlicher Zusammensetzung und Herkunft werden mit modernen, rheometrischen Analyseverfahren auf ihre Tauglichkeit geprüft. Alle getesten Silikone zeigen einen Umschlag von Newtonischer zu exponentieller Rheologie mit steigender Scherrate. Dies führt zu einer verringerten effektiven Viskosität, welches analog zum Verhalten der duktilen Unterkruste ist. Somit verwende Ich eines der Silikone als Analogmaterial für die duktile Unterkruste, welche eine Maxwell-Rheologie unter dem Einfluss von seismotektonischer Deformation zeigt. Desweiteren zeigt sich, dass Silikonöle aufgrund ihrer besonderen Langzeitstabilität und chemischen Ähnlichkeit über mehrere Produktionschargen, besonders gut für die angedachten Experimente eignen. Um die spröden Reibungseigenschaften von Störungzonen zu modellieren, verwende Ich Glasperlen, welche unter den angepeilten Laborbedingungen einen ausgeprägten Haftgleiteffekt zeigen. Intensive Materialprüfungen legen nahe, dass sehr stark vereinfachte, granulare Störungszonen aus Glasperlen, bereits eine große Vielfalt von verschiedenartigen Gleitphasen (analoge Erdbeben) hervorruft. Mittels Ringscherversuchen wird eine große Menge von abwechselnden Haft- und Gleitphasen simuliert. In Abhängigkeit der Rahmenbedingungen zeigt die analoge Störungszone langsames Kriechen, oszillierendes Rutschen und schnelles Gleiten. In manchen Versuchen kann eine zeitliche Separation von kleinen, langsamen Ereignissen und großen, schnellen Ereignissen beobachtet werden. Dies entsteht sehr wahrscheinlich durch das Zusammenspiel verschiedener, mikromechanischer Prozesse welche die granulare Packungsdichte beeinflussen und verändern. Desweiteren, wird das Wiederauftreten und die Magnitude der analogen Beben stark von transienten und langsamen Prozessen während der Haftphase beeinflusst. Die untersuchten analogen Erdbeben, sind häufig mehrere Größenordungen schneller als die Belastungsrate und die Prozesse während der Haftphase. Auch die zeitliche Separation und deren Folgen sind sehr wichtig für das Verhalten des Gesamtsystems. Folglich muss das Experiment kontinuierlich über den gesamten Zyklus überwacht werden. Dies wird durch Bilder und Kraftmessungen gewährleistet, welche während dem Experiment aufgenommen und im Anschluss mittels Bildkorrelation ausgewertet werden. Da die Gesamtdauer eines Experiments zum Teil mehrere Stunden umfasst und die notwendige Aufnahmegeschwindigkeit der Bilder bei über 10 Hz liegt, entstehen während eines Experimentes sehr große Datenmengen, welche nur zu einem geringen Prozentsatz für die weitere Analyse benötigt werden. Um dies zu Vermeiden wurde ein dynamischer Auslösermechanismus entwickelt, welcher die Menge der Daten um fast 95\% reduziert. Als Vorlage zum Algorithmus dient die Kraftmessung, welche die Scherkräfte während des Experiments aufzeichnet. In Kombination mit einem dynamisch ansteuerbaren Zwischenspeicher für Bilddaten im Aufnahmerechner werden lediglich die für die Auswertung relevanten Bilder extrahiert und für die Analyse gespeichert. Die Ergebnisse der Experimente zeigen eine gute Übereinstimmung mit bestehenden Studien und analytischen Beschreibungen der Deformation entlang von Störungszonen. Zukünftig soll das Analogexperiment mit den Ergebnissen aus dieser Studie weiter verbessert werden und numerische Simulationen sollen zur Vergleichsprüfung herangezogen werden

Investigating the effects of variety on the piston rod manufacturing process at Gabriel SA (Pty) Ltd

Bibliography: leaves 145-147.This thesis investigates the effects of variety on the manufacturing operations system of a automotive component (shock absorber) manufacturer, Gabriel South Africa Pty Ltd. Effective ways to manage this variety are also considered. By variety is meant the total number of possible states that a system can have. The measure of variety can also be considered as the extent of complexity of a system. The variety of product, people (from different cultures, backgrounds, etc.), processes machines and equipment, etc. and a continually changing environment creates a complex situation in which management decisions have to be made. Over the last three years, 1992 to 1994, Gabriel SA Pty Ltd has implemented world class manufacturing initiatives, for example, cellular manufacture, kanban, employee involvement programs, strategic business units, a Total Quality Management System, etc., but the anticipated results of increased production throughput did not occur. A situation has developed where changes had been implemented and there is now a difference between the actual and expected results. This thesis investigates possible causes for this difference. In order to conduct a rigorous and structured inquiry into the problem situation a theoretical research framework was developed. This framework was developed from the ideas of the American philosopher Charles Sanders Peirce (CSP) and that of Chris Argyris. Checkland's, Ackoff's et. al. views on system thinking were also used to form this framework