Development of a new mechano-chemical model in boundary lubrication

A newly developed tribochemical model based on thermodynamics of interfaces and kinetics of tribochemical reactions is implemented in a contact mechanics simulation and the results are validated against experimental results. The model considers both mechanical and thermal activation of tribochemical reactions instead of former thermal activation theories. The model considers tribofilm removal and is able to capture the tribofilm behaviour during the experiment. The aim of this work is to implement tribochemistry into deterministic modelling of boundary lubrication and study the effect of tribofilms in reducing friction or wear. A new contact mechanics model considering normal and tangential forces in boundary lubrication is developed for two real rough steel surfaces. The model is developed for real tribological systems and is flexible to different laboratory experiments. Tribochemistry (e.g. tribofilm formation and removal) and also mechanical properties are considered in this model. The amount of wear is calculated using a modified Archard’s wear equation accounting for local tribofilm thickness and its mechanical properties. This model can be used for monitoring the tribofilm growth on rough surfaces and also the real time surface roughness as well as changes in the λ ratio. This model enables the observation of in-situ tribofilm thickness and surface coverage and helps in better understanding the real mechanisms of wear

Advances in Vibration Analysis Research

Vibrations are extremely important in all areas of human activities, for all sciences, technologies and industrial applications. Sometimes these Vibrations are useful but other times they are undesirable. In any case, understanding and analysis of vibrations are crucial. This book reports on the state of the art research and development findings on this very broad matter through 22 original and innovative research studies exhibiting various investigation directions. The present book is a result of contributions of experts from international scientific community working in different aspects of vibration analysis. The text is addressed not only to researchers, but also to professional engineers, students and other experts in a variety of disciplines, both academic and industrial seeking to gain a better understanding of what has been done in the field recently, and what kind of open problems are in this area

Specific energy consumption of metal cutting with thin abrasive discs

The aim of this research is to provide an in-depth understanding of energy consumption in abrasive disc cutting processes. The specific energy consumed in cutting is measured,analysed, and then characterised in to three components. To this end, an experimental device is built using an Arduino-controlled grinder to measure the specific energy consumed by cutting at different feed rates. Using a model, the experimental data is validated and the Specific Energy Consumed is separated into three energy components: sliding, ploughing and specific cutting energy. Furthermore, the influence of cutting conditions and material properties significantly influenced the specific energy consumption and its components. To analyse the effect of grain shape and the relative dependence of the different components of the Specific Energy Consumed as a function of material removal rate, integral models of specific ploughing energy, specific sliding energy and specific cutting energy are developed. Conventional and super abrasive cubitron abrasive grains were used. Cutting with pyramidal abrasive discs (cubitron) was used for the determination of the relative components of the specific energy consumed. It was found that the specific ploughing energy is more sensitive to the change in material removal rate compared to the sliding energy. Due to the fast shearing and precisely shaped cubitron grains, the transition from sliding to a specific shear regime was so fast for some materials that the magnitude of the ploughing energy was found to be negligible.However, the model implementation for some materials showed that the absence or presence of ploughing energy also depends on the rate of material removed. Finally, the development of a cutting grain model is presented which will allow the study of the chip compression ratio which is not possible to characterise by means of a single cutting grain in metal cutting with thin abrasive discs. This latest development is the beginning of a study of chip formation in the primary cutting zone of an abrasive grain. This research provides a machine and a methodology to characterise cutting with commercially available abrasive discs in terms of the Specific Energy Consumed parameter.El objetivo de esta investigación es proporcionar un conocimiento profundo sobre el consumo de energía en los procesos de corte con discos abrasivos. Se mide y analiza la energía específica consumida en el corte, caracterizando dicha energía en tres componentes. Para ello se construye un dispositivo experimental que utiliza una amoladora controlada por un Arduino, para medir la energía específica consumida por el corte a diferentes velocidades de alimentación. Utilizando un modelo, se validaron los datos experimentales y se separa la Energía Específica Consumida en tres componentes energéticos: deslizamiento, arado y energía de corte específica. Además, la influencia de las condiciones de corte y las propiedades del material influyeron significativamente en el consumo de energía específico y sus componentes. Para analizar el efecto de la forma del grano y la dependencia relativa de las diferentes componentes de la Energía Específica Consumida en función de la tasa de remoción de material. Se desarrollan modelos integrales de energía de arado específica, energía de deslizamiento específica y energía de corte específica. Se utilizaron granos abrasivos convencionales y súper abrasivos de Cubitrón. El corte con discos abrasivos de granos piramidales (cubitron) se utilizaron para la determinación de las componentes relativas de la energía específica consumida. Se encontró que la energía de arado específica es más sensible al cambio en la tasa de remoción de material en comparación con la energía de deslizamiento. Debido a los granos de Cubitrón de corte rápido y de forma precisa, la transición de deslizamiento a un régimen de corte específico fue tan rápida para algunos materiales que la magnitud de la energía de arado resultó ser insignificante. Sin embargo, la implementación del modelo para algunos materiales demostró que la ausencia o presencia de energía de arado también depende de la tasa de material removido. Por último se presenta el desarrollo de un modelo de grano de corte que permitirá estudiar la relación de compresión de la viruta que no es posible caracterizar a través de un solo grano de corte en el corte de metales mediante discos abrasivos delgados. Este último desarrollo es el comienzo de un estudio de la formación de viruta en la zona primaria de corte de un grano abrasivo. Esta investigación proporciona una máquina y una metodología para caracterizar el corte con disco abrasivos, disponibles comercialmente, en términos del parámetro Energía Específica Consumida.Postprint (published version

Integrated control and health management. Orbit transfer rocket engine technology program

To insure controllability of the baseline design for a 7500 pound thrust, 10:1 throttleable, dual expanded cycle, Hydrogen-Oxygen, orbit transfer rocket engine, an Integrated Controls and Health Monitoring concept was developed. This included: (1) Dynamic engine simulations using a TUTSIM derived computer code; (2) analysis of various control methods; (3) Failure Modes Analysis to identify critical sensors; (4) Survey of applicable sensors technology; and, (5) Study of Health Monitoring philosophies. The engine design was found to be controllable over the full throttling range by using 13 valves, including an oxygen turbine bypass valve to control mixture ratio, and a hydrogen turbine bypass valve, used in conjunction with the oxygen bypass to control thrust. Classic feedback control methods are proposed along with specific requirements for valves, sensors, and the controller. Expanding on the control system, a Health Monitoring system is proposed including suggested computing methods and the following recommended sensors: (1) Fiber optic and silicon bearing deflectometers; (2) Capacitive shaft displacement sensors; and (3) Hot spot thermocouple arrays. Further work is needed to refine and verify the dynamic simulations and control algorithms, to advance sensor capabilities, and to develop the Health Monitoring computational methods

Enhance ZDDP tribofilm growth and fatigue lifetime of rolling bearings by Laser Surface Texturing

Laser surface texturing (LST) is a fast and precise surface engineering method capable of improving the frictional performances of machine elements, thus contributing to an increase in energy efficiency. However, not many studies have carried out research of LST in the boundary lubrication regime, likely due to concerns of higher contact stresses that can occur with the increasing surface roughness. This study aims to improve the fatigue lifetime of rolling bearings in the boundary lubrication condition by LST combined with ZDDP-added lubrication. Firstly, the ZDDP antiwear tribofilm was characterized. The composition of the tribofilm and the difference between the blue- and the brown-colored region was revealed. Moreover, the analyses by high resolution methods indicated a sulfur enrichment at the interface between the tribofilm and the steel substrate. Secondly, the LST patterns were verified to reduce wear due to the capacity of lubricant storage and the enhanced growth of ZDDP tribofilm. The pressure distribution on the textured surface was calculated by a contact simulation, and the increase of normal stress led to a promotion of the tribofilm. Finally, the rolling bearings with the LST patterns demonstrated an increase in fatigue life.Die Laseroberflächenstrukturierung (eng.: Laser Surface Texturing (LST)) ist ein schnelles und präzises oberflächentechnisches Verfahren, welches es erlaubt die Reibung von Maschinenelementen zu reduzieren und somit zur Steigerung der Energieeffizienz beiträgt. Außerdem können die LST-Strukturen die Verwendung eines üblichen Verschleißschutzadditivs wie Zinkdialkyldithiophosphat (ZDDP) unterstützen. Allerdings ist der Einsatz von LST im Grenzreibungsregime noch nicht etabliert. Ziel dieser Arbeit war es, die Lebensdauer von Wälzlagern unter Grenzreibung durch eine Kombination aus LST und ZDDP-Einsatz zu verlängern. Zunächst wurde die chemische Beschaffenheit der Verschleißschutz-Triboschicht charakterisiert. Messungen mittels Atomsonden-Tomographie zeigen eine Anreicherung von Schwefel in der Grenzschicht zwischen Grund und Gegenkörper. Darüber hinaus wurde nachgewiesen, dass die LST-Strukturen den Verschleiß aufgrund von Schmiermittelspeicherung und einer verstärkten Triboschichtbildung verringern. Die Druckverteilung auf einer strukturierten Oberfläche wurde durch eine Kontaktsimulation berechnet, und die Zunahme der Normalspannung führt zu einer Förderung des Triboschichtbildung. Schließlich zeigten die Wälzlager mit den LST-Strukturen eine dreifache Ermüdungslebensdauer

Slip in radial cylindrical roller bearings and its influence on the formation of white etching cracks

Ungünstige Betriebsbedingungen und unzureichende Radialkräfte führen zu Schlupf in Radial-Zylinderrollenlagern. Das kann zu verschiedenen Ausfallmechanismen, wie Anschmierung, Fressschäden, Abplatzen und auch sogenannten White Etching Cracks (WEC) führen, die bereits nach einem Bruchteil der berechneten Lagerlebensdauer auftreten können. In dieser Arbeit wird durch systematische Tests der Einfluss der Lagerbetriebsbedingungen (Radialkraft, Drehzahl und Öldurchfluss), sowie der Ausführung des Lagers (Lager- und Käfigtyp, Material, Führung und Toleranzklassen) auf die Entstehung des Wälzkörper- und Satzschlupfs untersucht. Die Wälzkörper vollrolliger Lager in der lastfreien Zone werden verzögert und sind in der Beschleunigungsphase einem vollständigen Rollenschlupf ausgesetzt. Für mit Käfig ausgestattete Zylinderrollenlager übertrifft der einteilige den zweiteiligen Käfig durch eine geringere Schlupfneigung, besonders unter begrenztem Öldurchfluss. Rollengeführte Käfige zwingen die Rollen dazu mit dem rotierenden Innenring zu interagieren, wodurch weniger Schlupf verursacht wird. Polyamid als Käfigwerkstoff bietet Gewichteinsparungen, wird aber bei hohen Lagertoleranzen nicht empfohlen, da es deformiert und somit einen höheren Schlupf bewirkt. Bei moderaten Lagertoleranzen tragen mehr Rollen zur Belastungsübertragung bei. Das kann zu höherem Rollenschlupf als bei hohen Toleranzen führen, da verringerte Traktionskräfte auf die Rollen wirken. Wird ein Lager jedoch durch eine enge Toleranzklasse (TC) vorgespannt, kann der Schlupf unter jeglichen Betriebsbedingungen verhindert werden. Der Einfluss von Schlupf auf die Bildung von WEC am Innen- und Außenring eines Zylinderrollenlagers wurde in insgesamt vier Dauerlaufversuchen mit einem zweiphasigen Belastungsschema untersucht. Während der Niedriglastphase wird das Lager bei erhöhtem Schlupf betrieben und danach einer hohen Lastphase ausgesetzt, während der Ermüdungsrissfortschritt von WEC auftreten kann. Es wurde festgestellt, dass Betriebsbedingungen mit hohem Schlupf weniger kritisch für die WEC-Bildung (an beiden Lagerringen) sind. Die sehr geringe Radialkraft, die in der Niedriglastphase aufgebracht wird, um einen hohen Schlupf zu ermöglichen, führt zu einer geringen Flächenpressung, die nicht WEC-kritisch ist. Ein weiterer Grund ist die längere Regenerationszeit zwischen zwei Überrollungen, die bei einem hohen Sollschlupf auftreten. Kritischer sind die dynamischen Kraftverhältnisse für die stehenden Lagerringe. Sie würden den Rollenschlupf unter der wechselnden Lastzonenbreite akkumulieren, was WEC-kritischer ist. Obwohl die vollrolligen Lager einen hohen Satzschlupf und 100%igen Rollenschlupf in der Lastzone erleiden, zeigten sie auch nach mehr als 3400 Teststunden, unter den für Käfiglager sehr kritischen Prüfbedingungen, keine Anzeichen eines WEC-Ausfalls.Unfavorable operating conditions and inadequate radial force cause slip to occur in radial cylindrical roller bearings. This can also lead to several failure mechanisms such as smearing, scuffing, spalling, and White Etching cracks (WEC) that can occur at a small percentage of the calculated bearing life. In this work, through systematic testing, the influence of the bearing operating conditions (radial force, speed, and lubricant flow rate) as well as the bearing’s design (bearing type, cage type, material, guidance as well as the clearance class) on the development of the roller- and the rolling set slip was studied. The rollers of the full complement bearing stall in the load-free zone, and they suffer from a 100% roller slip at the acceleration zone. For caged bearings, a single-part cage outperforms the two-part cages by having lower slip tendency under restricted oil flow rates. Cages that are roller-guided force the rollers to interact more with the rotating inner ring and thus suffer from an overall lower slip. For the cage material, Polyamide cages offer weight savings. However they are not recommended under elaborated clearance as they would deform and cause high slip. Under moderate clearance, more rollers contribute to the load transfer. This leads to higher roller slip than under higher clearance level due to the decrease in traction forces acting on each roller. However, preloading a bearing by using the TC clearance class while using a tight fitting for both rings my lead to the elimination of the slip under any operating conditions. The influence of slip on the formation of WEC on the inner and outer rings of a cylindrical roller bearing was studied by conducting a total of four endurance tests using a two-phase loading scheme. In the low-load phase, a slip-rich environment is introduced to the bearing during which lubricant smearing can take place. After that, a high load phase is introduced to the bearing during which, fatigue crack propagation of WEC is enabled. It was found that high-slip operating conditions are less critical for the WEC formation on both bearing rings. The very low radial force that must be used in the low load phase to allow such a high slip to occur would result in a low contact pressure that is not WEC-critical. Another reason is the longer regeneration time between two overrollings occurring at a high set slip. Dynamic force conditions are more critical for the stationary bearing rings. They would accumulate the roller slip under the changing load zone width which is more WEC-critical. Although suffering from high set slip and 100% roller slip in the load zone, full complement bearings didn’t show any sign of WEC failure even after testing them for more than 3400 hours under very critical testing conditions for caged bearings

A Wearer-Centred Framework to Design for Wearability in Animal Biotelemetry

In a technological era, monitoring animals for scientific, husbandry, or caring reasons is often done by using tracking systems attached to the animals’ bodies. Remote data acquisition from animals has enhanced the knowledge about their biology and ecology. However, there is evidence that carrying biotelemetry tags affects the welfare of animal wearers and interferes with the validity of recorded data. On welfare and scientific grounds, animal scientists have advocated for the re-design of physical and functional aspects of tags, proposing guidelines aimed at minimising device-induced impacts. However, such guidelines are dispersed and difficult to apply systematically. Hence, there is a need for an approach to systematising the design of animal-borne tags in order to minimise their impact on the wearer. This thesis addresses such a challenge. It draws on the concept of wearability and proposes it as a design goal to develop devices that afford a better wearer experience (WX) for animals. The thesis develops a wearer-centred design framework (WCF) and applies it to demonstrate its usefulness to systematically design for good wearability. Specifically, after the framework’s elements were derived by analysing relevant information in the biotelemetry and interaction design literature, the framework was administered to teams of workshop participants who implemented it to perform a requirements analysis for a cat-tracking device. Workshop requirements served to produce a feline-centred prototype which was tested with cat wearers to investigate their experience of wearing it and thus evaluate its wearability. Outcomes show improvements of the prototype in relation to off-the-shelf devices which were tested in a parallel study. This study established a baseline for investigating a cat WX and highlighted various wearability issues with the off-the-shelf tags. Lastly, this research demonstrates that designers can systematically design for wearability using the WCF therefore supporting the thesis that the reduction of device-related impacts is achievable

A particle finite element method for fluid-related problems in civil engineering

The work presented in this Thesis is a set of developments focused on the Particle Finite Element Method (PFEM) and its applicability in several fields in Civil Engineering. The PFEM had already been proven to be a powerful tool for the free surface flows with large deformation and domain separation, but the application to actual engineering problems requires many more advances. The interaction between the fluid and many solids contacting with each other, the erosion of soils and the transport of small particles are some of these advances, which are main topics addressed in this document. Apart from them, other developments related with the fluid solution are included, which are intended to get deeper than ever before in the practical use of PFEM.El treball que es presenta en aquesta Tesi és un conjunt de desenvolupaments centrats en el Particle Finite Element Method (PFEM) i en la seva aplicació a diversos camps de l'enginyeria civil. El PFEM ja havia demostrat ser una eina potent pels fluxes amb superfície lliure amb grans deformacions i separació de dominis, però l'aplicació a problemes d'enginyeria reals requereix molts més avenços. La interacció entre el fluid i molts sòlids que contacten els uns amb els altres, l'erosió de sòls i el transport de partícules petites són alguns d'aquests avenços, que són els principals temes tractats en aquesta Tesi. Apart d'aquests, s'inclouen altres desenvolupaments relacionats amb la solució del fluid, que miren d'arribar més profunditat que mai abans en l'ús pràctic del PFEM i la seva implementació. Primer es presenta el PFEM, es descriuen els desenvolupaments de l'autor millorant la solució de la dinàmica de fluids i altres capacitats simples que s'hi han afegit. Després, tres capítols principals es centren en a) l'algoritme d'interacció fluid-estructura amb contacte b) l'erosió de sòls c) el transport de partícules. A continuació altres aplicacions del mètode s'expliquen, així com una llista dels projectes d'investigació amb els quals aquesta tesi ha tingut vincle.Postprint (published version

A history of wear and wear prevention 1700-1940

Much of the present knowledge of the processes involved in the wear of materials has been derived since the end of the Second World War. This thesis shows, however, that many of the basic concepts of wear were understood, at least empirically, prior to 1940. Factors which influenced the rate of wear of components in machines began to be investigated during the second half of the last century, and particular combinations of sliding materials were chosen to give an adequate wear life for their applications. As background, the first two chapters describe the work on sliding and rolling friction during the eighteenth and nineteenth centuries. The third chapter present evidence which shows how the empirical understanding of wear developed up to 1940. This covers wear in both sliding and rolling contact, the relationship between wear and hardness as well as wear under abrasive conditions. The next chapter shows how the concept of the real area of contact, as opposed to the apparent area, emerged from studies of the electrical resistance between two metals in contact. With this technique, measurements of the real area of contact between surfaces under various loads were made in the late nineteen thirties. The chapter also traces the development of instruments for assessing the roughness of surfaces during the same decade. Chapters 5, 6 and 7 deal with wear prevention. Chapter 5 shows how developments in plain bearings kept pace with the duties imposed on them and describes some special forms, such as the "anti-friction" pivot and the marine thrust bearing. Data is also provided on the way in which the loads and speeds of bearings increased from 1700 to 1900. Chapter 6 deals with fluid lubrication and with the pioneering work of G.A. Hirn. Hirn's experiments were the first to demonstrate convincingly the complete separation of surfaces by a film of fluid. In chapter 7 the advances in metallurgy which enabled improved bearing metals to be made are outlined. In particular, the origins of the production of high-lead bronzes is described. These alloys proved to be highly wear resistant. Some aspects of white metals (both lead and tin based) are also described. The emphasis in the thesis is on the practical steps which were taken to mitigate the detrimental aspects of wear and to develop wear resistant materials, particularly for sliding bearings. The evidence presented shows that whilst separation of surfaces by a fluid film is the ideal means of preventing wear,in many instances lubrication conditions were far from ideal

Mathematical Modeling and Simulation in Mechanics and Dynamic Systems

The present book contains the 16 papers accepted and published in the Special Issue “Mathematical Modeling and Simulation in Mechanics and Dynamic Systems” of the MDPI “Mathematics” journal, which cover a wide range of topics connected to the theory and applications of Modeling and Simulation of Dynamic Systems in different field. These topics include, among others, methods to model and simulate mechanical system in real engineering. It is hopped that the book will find interest and be useful for those working in the area of Modeling and Simulation of the Dynamic Systems, as well as for those with the proper mathematical background and willing to become familiar with recent advances in Dynamic Systems, which has nowadays entered almost all sectors of human life and activity