Machine Learning in Tribology

Tribology has been and continues to be one of the most relevant fields, being present in almost all aspects of our lives. The understanding of tribology provides us with solutions for future technical challenges. At the root of all advances made so far are multitudes of precise experiments and an increasing number of advanced computer simulations across different scales and multiple physical disciplines. Based upon this sound and data-rich foundation, advanced data handling, analysis and learning methods can be developed and employed to expand existing knowledge. Therefore, modern machine learning (ML) or artificial intelligence (AI) methods provide opportunities to explore the complex processes in tribological systems and to classify or quantify their behavior in an efficient or even real-time way. Thus, their potential also goes beyond purely academic aspects into actual industrial applications. To help pave the way, this article collection aimed to present the latest research on ML or AI approaches for solving tribology-related issues generating true added value beyond just buzzwords. In this sense, this Special Issue can support researchers in identifying initial selections and best practice solutions for ML in tribology

Cold Micro Metal Forming

This open access book contains the research report of the Collaborative Research Center “Micro Cold Forming” (SFB 747) of the University of Bremen, Germany. The topical research focus lies on new methods and processes for a mastered mass production of micro parts which are smaller than 1mm (by forming in batch size higher than one million). The target audience primarily comprises research experts and practitioners in production engineering, but the book may also be of interest to graduate students alike

Correlating Raman scattering signatures with microstructural properties of tribological surfaces

This thesis focuses on advancing the knowledge on fundamental structural and physicalchemical processes in the contact of relative moving surfaces using Raman spectroscopy. With this advancement, a step towards monitoring wear and friction in real-time applications is performed. In this thesis, Raman scattering signatures are correlated with their spatial distribution at worn metallic surfaces and their microstructural properties are investigated. It is shown that tribological material typically contains oxides and is formed by micro- or nano-sized particles. Furthermore, the properties and the tribological behavior of, in particular, MoS2 and amorphous carbon films are sensitive to the deposition process, post-processing and the surrounding atmosphere. In detail, the spatial distribution of hematite and magnetite Raman modes is used to detect heavily worn steel surfaces, the Raman signatures of incorporated oxygen in tungsten carbide coatings are exploited to determine the coating’s degree of wear and the different chemical behavior of third-body MoS2 particles from deposited MoS2 films are utilized as indicator for the degree of wear of the respective coatings. Furthermore, deposition parameters reducing the probability for sp3 formation in amorphous carbon films, deposition parameters shifting the S/Mo ratio in MoS coatings and changing their bond lengths are identified. Additionally, influences on the MoS inter-layer spacing, strain-relaxation and a basal reorientation process are investigated. The thesis closes with a chapter on tribofilm formation in steel-steel contacts, where nano-sized hematite, magnetite and amorphous carbon particles form the tribofilm. Here, the accumulation of amorphous carbon in pitting areas is observed and an estimation of the flash temperatures is given. Furthermore, atmospheric oxygen is identified to select the reaction pathway for tribofilm formation. Taking these results into account, the tribological properties may be tailored to the desired application. In order to simplify the analysis of the spectral data, a software package is developed, which allows for a fast correlation of spectral information with surface properties. The software package also combines the Raman scattering data with chemometrical methods, providing a fast insight into huge sets of data and supporting the results obtained by conventional analysis.Im Mittelpunkt dieser Arbeit steht die Vertiefung der Kenntnisse über grundlegende strukturelle und physikalisch-chemische Prozesse im Kontakt von relativ zueinander bewegten Oberflächen mittels Raman-Spektroskopie. Mit diesem Wissensgewinn wird ein Schritt zur Verschleiß- und Reibungsüberwachung in Echtzeitanwendungen vollzogen. In der vorliegenden Arbeit wird die räumliche Verteilung von Raman-Signaturen mit verschlissenen metallischen Oberflächen korreliert und ihre mikrostrukturellen Eigenschaften untersucht. Es wird gezeigt, dass das tribologische Material typischerweise Oxide enthält und aus mikrooder nanoskaligen Partikeln besteht. Darüber hinaus sind die Eigenschaften und das tribologische Verhalten insbesondere von MoS2- und amorphen Kohlenstoffschichten empfindlich gegenüber dem Abscheidungsprozess, der Nachbearbeitung und der umgebenden Atmosphäre. Im Detail wird die räumliche Verteilung der Hämatit- und Magnetit-Raman-Moden zur Detektion stark verschlissener Stahloberflächen genutzt, die Raman-Signaturen von in Wolframkarbidbeschichtungen eingebautem Sauerstoff zur Bestimmung des Abnutzungsgrades der Beschichtung genutzt und das von abgeschiedenen MoS2-Schichten verschiedene chemische Verhalten von Drittkörper MoS2-Teilchen wird als Indikator für den Verschleißgrad der jeweiligen Beschichtung genutzt. Darüber hinaus werden Abscheidungsparameter identifiziert, die die Wahrscheinlichkeit der sp3-Bildung in amorphen Kohlenstoffschichten reduzieren, sowie Abscheidungsparameter, die das S/Mo-Verhältnis in MoS-Schichten verschieben und deren Bindungslängen verändern. Zusätzlich werden Einflüsse auf den MoS- Schichtabstand, Spannungsrelaxation und ein basaler Reorientierungsprozess untersucht. Die Arbeit schließt mit einem Kapitel zur Tribofilmbildung in Stahl-Stahl-Kontakten, wobei nanoskalige Hämatit-, Magnetit- und amorphe Kohlenstoffpartikel den Tribofilm bilden. Hier wird die Akkumulation von amorphem Kohlenstoff in Bereichen mit Grübchenbildung beobachtet und eine Abschätzung der Blitztemperaturen gegeben. Außerdem wird Luftsauerstoff als entscheidend für den Reaktionsweg der Tribofilmbildung identifiziert. Unter Berücksichtigung dieser Ergebnisse können die tribologischen Eigenschaften auf die gewünschte Anwendung zugeschnitten werden. Um die Analyse der spektralen Daten zu vereinfachen, wurde ein Softwarepaket entwickelt, das eine schnelle Korrelation der spektralen Informationen mit den Oberflächeneigenschaften ermöglicht. Das Softwarepaket erlaubt auch die Kombination der Streutechnik mit chemometrischen Methoden, die einen schnellen Einblick in große Datensätze geben und die durch konventionelle Analyse erhaltenen Ergebnisse unterstützt.

Development studies of lubricating fluids to accelerate removal of material from silicon nitride

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The superior qualities of ceramics such as high hardness, chemical stability and wear resistance make them promising tribological materials for machine elements, for example, pumps, bearings and heat engines. Ceramics are hard and brittle, therefore, machining such materials is time-consuming, difficult and expensive. A low cost machining process that can remove material rapidly while maintaining a good surface finish is required. The general aim of the studies presented is to find a correlation between the wear mechanisms and surface modifications induced by interactions of tribochemical nature and to identify the most effective combination of parameters involved in producing high material removal rates of ceramics. This study concentrates on silicon nitride, as this material has most potential for use in industry. The influence of lubricant chemistry on the friction and wear of silicon nitride is investigated using a ball-on -plate tribotester and a modified four-ball machine. A wide variety of liquid lubricants and additives supplied by Castrol International are tested to evaluate the role of the chemical characteristics of the lubricant on the friction and wear of silicon nitride. Surface and chemical analysis results reveal that by using different chemistries of liquids, the material removal rate and the surface finish of the silicon nitride can be significantly altered. The highest material removal rate is obtained when using the ester base fluid T80884 + 0.3% triethanol amine. This gives an increase by four fold when compared to the material removal rate obtained with the industrial reference slurry Kemet. The topography of the silicon nitride ball after the grinding test is found to be very smooth indicating that the predominant mechanism of material removal rate could be due to a tribochemical reaction occurring at the contact interface.This study is funded by Castrol International Ltd

Toward commercial realisation of whole field interferometric analysis

The objective of this work was to produce an instrument which could undertake wholefield inspection and displacement measurement utilising a non-contacting technology. The instrument has been designed to permit operation by engineers not necessarily familiar with the underlying technology and produce results in a meaningful form. Of the possible techniques considered Holographic Interferometry was originally identified as meeting these objectives. Experimental work undertaken 'provides' data which confirms the potential of the technique for solving problems but also highlights some difficulties. In order to perform a complete three dimensional displacement analysis a number of holographic views must be recorded. Considerable effort is required to extract quantitative data from the holograms. Error analysis of the experimental arrangement has highlighted a number of practical restrictions which lead to data uncertainties. Qualitative analysis of engineering components using Holographic Interferometry has been successfully undertaken and results in useful analytical data which is used in three different engineering design programmes. Unfortunately, attempts to quantify the data to provide strain values relies upon double differentiation of the fringe field, a process that is highly sensitive to fringe position errors. In spite of this, these experiments provided the confidence that optical interferometry is able to produce data of suitable displacement sensitivity, with results acceptable to other engineers.....

Laser Cladding for use in Extreme Tribological Interfaces

Coatings are common in engineering applications for protecting the surface of components, either from exposure to environmental conditions or from contact with other components. Laser cladding is a coating technique which allows for thicker coatings of various alloys that enable high load bearing interfaces to operate at a wider range of loads or for longer, for example by increasing durability. This is of great benefit to the railways industry as well as other heavy industries, such as the steel industry. Laser clad coatings have been used extensively in other industries such as oil and gas for increasing the durability of drilling components; in mining and earth moving equipment, for increasing the durability of the components that come in contact with hard soil and rocks. Both are extreme interfaces. In this study, new interfaces and extreme conditions for new industries are investigated, by highlighting the laser clad coating advantages, when used under extreme conditions. The extreme test conditions have not been investigated in published literature, especially with the use of laser clad coatings. This project evaluated the performance of laser cladding coatings on railway components such as the wheel and rail. Other interfaces found in machinery in the steel industry were considered, specifically in the rolling of steel. A variety of interfaces were evaluated by modelling and testing, such as rolling-sliding, high pressure water jet erosion and impact. Three clad materials were identified as suitable for the chosen interfaces, martensitic stainless steel (MSS), Stellite 6 (Co-Cr) and a two-layer clad of Inconel 625 with Technolase. The clad parameters were fixed, resulting in constant material grades, allowing the coatings used in different interfaces to be comparable. The materials choice was based on published research on similar interfaces. Tests were performed on existing test rigs for rolling-sliding and bending tests. The impact test was performed on a rig modified specifically for this study, while a bespoke rig was built for the erosion test. Metallographic techniques were used for all materials, to prepare the samples for characterisation using optical and electron microscopy, as well as nanoindentation and microhardness. Pre- and post-test material analysis was performed. The use of computer modelling was considered mainly for the generation of test parameters, while the results from testing were compared to existing data. Key findings highlight that the use of the selected clad materials under the chosen extreme interfaces can have a positive effect on the durability of the coating, mainly by increasing the wear resistance properties of the coating. Furthermore, the two-layer clad coating showed promising results in stopping crack propagation to the substrate. The test results can be used in predictive tools by researchers in academia, as well as in industry, as a way of introducing laser cladding applications to interfaces of engineering products. Furthermore, the performance of the chosen materials indicates that this study may be used as the basis for selecting similar clad coatings for pilot trials or large scale testing