Current research projects
Propagation of Surface Initiated Rolling Contact Fatigue Cracks in Bearing Steel
Researcher: Dr Pawel Rycerz
Supervisor: Dr Amir Kadiric, Professor Andrew Olver
Surface initiated rolling contact fatigue, leading to a surface failure known as pitting, is a life limiting failure mode in many modern machine elements, particularly rolling element bearings. Most research on rolling contact fatigue considers total life to pitting. Instead, this work studies the growth of rolling contact fatigue cracks before they develop into surface pits in an attempt to better understand crack propagation mechanisms.
A triple-contact disc machine will be used to perform pitting experiments on bearing steel samples under closely controlled contact conditions in mixed lubrication regime. Crack growth across the specimen surface will be monitored and crack propagation rates extracted. The morphology of the generated cracks will be observed by preparing sections of cracked specimens at the end of the test.
Application of Mixed Thermal Elastohydrodynamic Lubrication Model in Journal and Sliding Bearing Systems
Biomimetic Tribology: Exploiting natural lubrication mechanisms for mechanical systems
Researcher: Murali Manoj
Supervisor: Dr Marc Masen, Dr Philippa Cann
The replacement of oil-based lubricants with biodegradable water-based lubricants has been a long-standing unfulfilled ambition. The physical instabilities and poor wear performance associated with water-based lubricants has led to minimal adoption within mechanical systems. However, many water-based lubrication systems exist within nature that are capable of providing extremely low friction and minimal wear.
This project aims to explore these natural lubrication mechanisms with the intention of exploiting their behaviour for application within mechanical systems. This will lead to the development of a biolubricant that is capable of providing suitable friction and wear characteristics for a multitude of applications. The biolubricant will be tuned to be compatible with materials that are likely to be adopted into many of the systems around us in the future. This allows for application of the lubricant within novel systems previously unexplored that may come to the forefront in the near future. Nature exhibits countless complex lubrication mechanisms and biological methods to achieve targeted lubrication. Hence, the focus is towards creating a biolubricant which is capable of local activation at a contact, thereby providing a local high viscosity zone with a bulk low viscosity and reducing energy losses due to churning or fluid shear. Some of the lubricant additive possibilities to be explored are proteins, cationic surfactant micelles and polymer-colloids amongst others.
Brain Mimicking Hydrogels
Researcher: Zhengchu Tan
Supervisor: Professor Daniele Dini
The characterisation of the mechanical response of real soft tissues, such as brain, liver and cartilage, is immensely important as it allows us to understand the way they respond under a variety of different loads. Hence, ways to reduce damage to living tissues during real life scenarios can be identified and developed. However, real tissue is difficult to obtain and test due to accessibility. Therefore, there is a huge advantage in developing an accurate synthetic tissue phantom that is easier to procure and produce. This has led to the popularity of hydrogels, which have been developed into tissue mimicking materials due to their biocompatibility and stiffness tunability.
This project focuses on the development of a composite hydrogel (CH) constituting of poly(vinyl) alcohol (PVA) and phytagel that is able to match the complex viscoelastic behaviour of brain. The CH can be tuned to achieve different stiffness and relaxation responses by varying the concentrations of each hydrogel component, which allows the material to mimic other soft tissues.
Consequently, a mechanically accurate tissue phantom material opens the doors to many applications in the study of mechanobiology and regenerative medicine. This project investigates cell viability of the CH substrate, therefore extending the range of applicability to explore a variety of different mechanical loads affects cells seeded on a CH substrate These experiments include impact tests, needle insertion tests and tribological tests to match the high strain rate behaviour of brain for the study of TBI, fracture behaviour of liver during surgery and tribological behaviour of cartilage, respectively.
Contact Mechanics of Soft and Complex Biological Tissues (BIOCONTACT)
In the last decade, a number of medical and bio-engineering challenges, requiring a deep understanding of the phenomena occurring at biological interfaces, have boosted scientific interest in the field of biological contact mechanics. The MSCA-awarded BIOCONTACT project will develop an innovative methodology to tackle bio-lubricated contacts involving soft tissues in the presence of complex fluids, enhancing the understanding of these interactions, by pursuing new models and numerical methodologies, specifically suited for this class of problem. This approach is key to provide long-term societal benefits by solving long-standing issues including the prevention of hospital bedsores, the mechanical compatibility of prosthetic implants or contact lens, and the optimization of surgical procedures and tools.
In particular, our vision is to first build a mechanical model for biological soft tissues that specifically relies on constitutive laws for multi-layered linear viscoelastic materials. This model will be then implemented in a newly developed contact mechanics solver, based on improved Boundary Element Method schemes that we have recently proposed, able to capture specific chemo-mechanical local responses. Interfacial interactions will adopt an atomistic and molecular description, thus relying on interfacial mean potentials modelling. In the framework of inverse analysis, the material properties of individual layers will be tuned to best replicate the experimental behavior captured using an innovative procedure which, probing the materials at different dimensional scales, is able to extract mechanical properties of the different layers composing the tissue.
Finally, in order to provide a complete and widely applicable tool, solid-liquid interaction will be addressed by coupling the contact solver with a lubrication model, based on non-Newtonian Reynolds theory. The development of this ready-to-use numerical tool will foster the uptake of my proposed methodologies for use in the above mentioned complex cases of industrial and medical relevance.
Coupled Fluid-Mechanical Modelling of the Brain
Researcher: Andrea Bernardini
Supervisor: Professor Daniele Dini
The brain is composed of two main types of tissues, namely grey and white matter. In this project, we focus on the latter, which is where glioblastoma is localised (i.e. where the EDEN system will infuse medication). The white matter is comprised of several types of cells and components which make it possible to theorise it as an anisotropic mechanical entity. Segmentation of the components from SEM images enables the 3-D reconstruction of the representative units to be modelled and then analysed via FEA.
A coupled fluid-mechanical model of the brain will be developed by modelling the mechanical behaviour of such tissue and its interaction with the fluidic environment in which it is submerged. This will enable the prediction of diffusive phenomena and patterns in the enhanced drug delivery in order to optimise the surgical procedure and the point of cancer-drug dosing.
Damage initiation and evolution of rolling-sliding lubricated contacts exposed to transversal vibrations
Researcher: David Uribe Saenz de Camara
Supervisor: Dr Amir Kadiric, Prof. Daniele Dini
Rolling-element bearings are undoubtedly one of the most abundant machine components found in any equipment or machinery. There is a rising demand for an improved performance and higher efficiency along longer service lives. The reliability of these components has considerably increased in the last decades, and yet there are circumstances when they fail prematurely below 10% of their rated life.
The aim of this project is to improve the fundamental understanding of the damage acceleration that occurs under transient conditions such as vibrations. Damage accumulation experiments will be performed using a triple-contact disc rig, under closely controlled laboratory conditions in the elastohydrodynamic and mixed lubrication regimes. Other potential research topics of significant interest include the investigation of how these transient conditions may alter bearing performance throughout the service life.
Degraded Oil Performance
Researcher: Sarah Bellingham
Supervisor: Dr Amir Kadiric
Design Principles for Low-Friction Polymer Brushes as a Synthetic Analogue of Cartilage
Researcher: Mohamed Abdelbar
The articular cartilage found covering the ends of bones in the synovial joints of mammals exhibit exceptional tribological properties, giving a low friction response (μ = 0.001) even when subjected to normal loads exceeding 100 atm. The goal of this project is to use coarse-grained molecular dynamics in order to study the system focusing on the architecture of the polymers on the surface and thus provide rational design principles for cartilage analogues.
Developing Acoustic Emission Monitoring to Assess Lubricant Performance
Researcher: Daniel Owens
Supervisor: Dr Tom Reddyhoff
This project aims to address how frictional events lead to acoustic emission and how this information can be utilised to provide non-invasive tools that can monitor and improve the efficiency and durability of automotive piston contacts.
The acoustic emission from single asperity contacts will be studied to gain an in-depth understanding of the generation mechanisms. A range of lubricants and additives will be tested to characterise their effects on noise emission and then further tests will be conducted on engine components to assess the effectiveness of the monitoring technique in practical applications.
Development of Novel Mechatronic Suspension Systems
Researcher: Dr. Min Yu
Supervisors: Professor Daniele Dini
Experimental and road testing of Series Active Variable Geometry Suspension (SAVGS) and the Parallel Active Link Suspension (PALS).
EDEN2020 (An Enhanced Delivery Ecosystem for Neurosurgery)
Due to an aging population and the spiralling cost of brain disease in Europe and beyond, EDEN2020 aims to develop the gold standard for one-stop diagnosis and minimally invasive treatment in neurosurgery. Supported by a clear business case, it will exploit the unique track record of leading research institutions and key industrial players in the field of surgical robotics to overcome the current technological barriers that stand in the way of real clinical impact.
Finite Element Method (FEM) Modelling of the Skin-Surface Interface
Supervisor: Dr Marc Masen, Professor Daniele Dini
This project involves numerically modelling of the skin-surface interface in order to better understand the sensations of touch and perception. This involves developing finite element method (FEM) models of multi-layered soft tissue to observe the stress/strain fields in the vicinity of mechanoreceptors.
Friction of 3D Printed Materials
Friction Reduction and Optimisation of Tribological Interactions via Microtexturing and Superhydrophobic Surfaces
Researcher: Jun Wen
Supervisor: Dr Tom Reddyhoff, Prof. Daniele Dini
The aim for this PhD project is to reduce friction in hydrodynamic bearings using surface treatments. The application will be targeted first is micro-scale bearings to explore the lubrication of Micro-Electro-Mechanical-Systems (MEMS). Due to the small size and the functions they can perform, MEMS devices have the potential to significantly impact our way of life, but are currently limited by severe problems of friction and wear that occur at the micro-scale.
To address this problem, the way of entrapping air pockets on the bearing surfaces by surface modification will be used. An important and highly novel aspect of the project will be to use silicon fabrication techniques, including Deep Reactive Ion Etching (DRIE), to produce surface features which will act to anchor the gaseous regions in place. Then, the models of bubble interface interactions will be combined with the hydrodynamic bearing lubrication model in order to validate and optimize the experimental results. This will also help to explore the possibility of bubble/cavitation induced friction reduction in other application such as macro-scale hydrodynamic bearings.
Hydrodynamic Lubrication Modelling using MD-CFD Hybrid Methods
Researcher: Eduardo Ramos Fernandez
The field of nanotribology has remained slightly detached from mainstream macro-scale tribology, focusing primarily on specialized nano-scale applications. At the macro- and mesoscopic levels, continuum models are often able to correctly model fluids. However, at smaller scales, continuum models do not consider the atomic nature of matter and can sometimes fail to capture the essential physics. In such cases, explicit molecular models must be employed, for example to model a liquid-solid interface.
The development of a truly multi-scale approach, which spans nano- to macro-scales, is a decisive step forward in understanding engineering tribological interfaces. Hybrid methods, where atomistic simulations such as molecular dynamics (MD) and continuum computational fluid dynamics (CFD) inter-operate, offer a solution that combines the strengths of both paradigms. The aim of this project is to model contact-lubrication problems with a multi-scale simulation methodology taking advantage of an in-house coupling software (CPL_library) that has been developed in the group in the past years.
Implementing Lubrication in Micro-Electro-Mechanical Systems (MEMS)
Researcher: Peng Wang
Supervisor: Dr Tom Reddyhoff
Micro-electro-mechanical systems (MEMS) are tiny (sub-millimetre) machines, which have arisen from advances in semiconductor fabrication. Due to their low cost, high tolerances, and ability to combine sensors and actuators with microprocessors, MEMS have the potential to profoundly affect our way of life. However, high friction and wear problems mean that current commercial MEMS designs are confined to non-, or very low sliding devices.
This project aims to demonstrate how low viscosity liquids combined with friction modifier additives are an effective means of the lubricating MEMS devices. This has so far only been achieved in lab-based tests; therefore the current aim is to implement this type of lubrication in an actual MEMS device. To do this, the project is using semiconductor fabrication techniques to build micro-hydrodynamic bearings which will be incorporated and tested in a MEMS turbine energy harvester.
In addition to the goal of producing a MEMS turbine that runs on hydrodynamic micro-bearings, a number of more fundamental avenues of research, involving tribology and silicon MEMS, are being explored. These include a feasibility study into the development of sliding MEMS with textured surfaces.
This project is a collaboration with the Optical and Semiconductor Devices Group at Imperial College.
Influence of Catalyst Binder Chemistry on the Microstructure of Polycrystalline Diamond During Liquid Phase Sintering
Researcher: Branislav Dzepina
Supervisor: Professor Daniele Dini
Sponsor: Element Six
The main problem of polycrystalline diamond cutters (PDCs) used in oil and gas drilling is the brittle nature of the diamond cutting face. Premature fracture during a drilling operation results in ineffective rock cutting. Repair of the fractured cutters requires complete removal of the drill head and string. The subsequent down-time imposes a great monetary burden to the driller. It is thus important to be able to manipulate the behaviour of the cutter to prevent or delay the onset of long cracks which lead to catastrophic brittle failure.
One possible way to affect the properties of the diamond cutter is through manipulation of the microstructure. To this end, the project proposes the development of a Monte Carlo model to simulate the evolution of the microstructure during high-pressure high-temperature (HPHT) liquid phase sintering. In order to enable inputs for the model, molecular dynamics simulation and HPHT experimentation will be conducted. It is anticipated that the proposed simulation will not only identify new mechanisms for the diamond sintering model, but also allow microstructural prediction given key input variables.
This project forms part of the Diamond Science and Technology CDT.
Infrared Microscopy to Study In-Contact Friction Behaviour
Researcher: Jia Lu
The overall aim of this PhD project is apply infrared microscopy to a range of sliding interfaces in order to increase our understanding of the in-contact mechanisms that give rise to heat generation.
The first task is measuring the temperature distribution of the oil within an elastohydrodynamic contact. This involves using an infrared camera and microscope with a number of filters to record the radiation emitted from a contact between a metal ball and transparent sapphire disc. The radiation data obtained in this way is calibrated and processed using Planck’s Law and combined with film thickness measurements in order to separate the temperature of the two bounding surfaces from that of the film of oil.
Once achieved, results will then be used to test theories that predict oil temperature rheology.
In addition to, effect of surface coatings and lubricant additives on in-contact temperature and rheology will be studied using this technique.
Investigation of Tribocharging and Triboemission by Atomistic Simulations
Researcher: Dr Alessandra Ciniero
The aim of this project is to investigate the mechanisms by which phenomena known collectively as “triboemission” (i.e. the emission of photons electrons and charged particles due to rubbing) occur. This is important because triboemission may be responsible for certain tribochemical processes such as lubricant degradation. Ab intio molecular dynamics techniques will be used to model tribocharging and triboemission during sliding.
Lubrication and Fluid Load-Support in Hydrogels for Cartilage Substitutes
Researcher: Elze Porte
Sponsor: Imperial College London
This research focuses on gaining a better understanding of the lubrication mechanisms in articular cartilage. Currently, there is no thorough understanding of the relationship between the lubrication of the material, its fluid load support, and its mechanical properties.
Hydrogels have been suggested as promising substitute materials for cartilage because of their specific mechanical and tribological properties. This makes them suitable substitutes for use in lubrication experiments and, ultimately, as a potential cartilage replacement material in the surgical treatment of osteoarthritis
Fluid exudation from the bulk material into the loaded region is believed to provide the fluid load support and lubrication. To study the lubricating mechanisms of hydrogels as cartilage substitutes, contact and lubrication experiments are done on the newly developed Biotribometer (PCS Instruments, London UK). The obtained knowledge can be used to improve the existing hydrogel structures.
Machine-Learning Pattern Recognition Prototype for Liquid Foams
Researcher: Dr Li Shen
Supervisor: Professor Daniele Dini, Dr Tom Reddyhoff
This project is an EPSRC Impact Acceleration Account (IAA) entitled “Machine-Learning Pattern Recognition Prototype for liquid foams”. The IAA grant supports the development of a potentially marketable project to create impact away from a strictly academic setting. The project aims to develop a foaming rig and a Machine-Learning analysis algorithm that will enable a consistent quantitative analysis of the foaming process in beverages and oil lubricants.
Mechanochemical Behaviour of ZDDP
Researcher: Dr Jie Zhang (Jason)
Supervisor: Professor Hugh Spikes
It has recently been shown that tribofilm formation by the widely-used antiwear additive zinc dialkyl dithiophosphate (ZDDP) is driven by the applied shear stress present in rubbing contacts rather than by the energy dissipated in these contacts. This means that ZDDP reaction results from the stretching and breaking of molecular bonds under stress, i.e. mechanochemistry; an insight that enables relationships between molecular structure and reactivity to be developed. This project studies the impact of applied shear stress on ZDDP film formation under both full film and boundary lubrication conditions to support the principle that ZDDP reaction is controlled by mechanochemistry.
Mechanochemistry of Lubricant Additives
Sponsor: Afton Chemical, TSM-CDT
The aim of this project is to utilise molecular simulations to investigate the mechanochemical behaviour of lubricant additive molecules. Classical molecular dynamics simulations will be employed to study the stresses on additive molecules under shear. First-principles modelling frameworks will also be developed to accurately model lubricant reactivity in order to study their breakdown inside tribological contacts. By understanding the mechanochemical breakdown of current additives new and more effective additives can be designed from the molecular level.
Micro-Mechanical Model Development for Predicting the Effect of Microstructure on Bulk Behaviour of Aerated Soft Solids
Researcher: Georgios Samaras
Soft food systems are often used in confectionery products, such as emulsion or foam fillings, to provide consumers with a unique experience. Traditionally, the mechanical and rheological properties of these systems are studied in combination with sensory evaluation to describe their in-mouth flow properties. However, oral processing of food is very complex and several multi-scale mechanisms take place at the same time in the mouth. This is especially noticeable when dealing with more complex systems, e.g. when hard particles (inclusions) are included within a semi solid system, or products with different micro- and macroscopic structure, e.g. aerated systems. This hinders predictions of the in-mouth behaviour of the food. Knowledge of this behaviour is crucial as it is directly linked to sensory perception.
The aim of the project is to develop a multi-scale thermo-mechanical computational model for simulating the interaction between aerated fluid and solid structures. This includes first bite model for fracture and progressive damage of product into particles and subsequent shearing of particles in tongue/palate contact whilst they heat up, flow, mix with saliva and form cohesive bolus. Necessary rheological experiments, in compression and shear of boluses, will be developed to provide data for validating simulations.
Modelling Polycrystalline Diamond Cutting Tools Failure
Researcher: Mahdieh Tajabadi Ebrahimi
Element Six (E6) is the world's leading manufacturer of synthetic diamond for hard abrasive materials. Synthetic diamonds are used throughout many industrial applications such as cutting, grinding, drilling, and polishing. Polycrystalline diamond (PCD) is one of the E6 products that is formed by sintering diamond powders in the presence of the metallic catalyst. PCDs fail by cracking of diamond crystals under extreme conditions. The theory of fracture, indicates that the dislocations, impurities, and any imperfections present inside the diamond grains can affect their mechanical properties. PCDs contain various imperfections that might cause failure by producing nano-cracks in the system. The objective of the project is to shed light on the mechanisms that lead to these failures, involving different scale. Techniques at different length scale will be used to characterise possible mechanisms of nano-cracks initiation and propagation into macro-cracks inside the system.
Modelling the Sealing Behaviour of Windscreen Wipers
Researcher: Qian Wang (Alexis)
The interaction between rubber wiper blades and vehicles’ windscreens is of great significance in car industries. As the interplay between mechanical, physical and chemical properties of the mating surfaces under various lubricating conditions are complex, a comprehensive model is needed to predict the behaviour of the blades and sealing provided by the wiper.
To this end, this project focuses on simulating the in-contact fluid film behaviour and predicting the sealing performance. Both the material nonlinearity and geometric nonlinearity will be considered to closely mimic the behaviour of wiper blades. The FSI (Fluid Solid Interaction) solver will be used to capture the friction in the transition from boundary lubrication to hydrodynamic lubrication.
Modelling Transmission Efficiency in Electric Vehicles
Researcher: Joseph Shore
Supervisor: Dr Amir Kadiric, Prof. Daniele Dini
Range extension is one of the most important research areas in the development of Electric Vehicles (EVs). Current EVs have significantly shorter ranges per battery charge than a typical Internal Combustion Engine (ICE) vehicle has with a full tank. This, along with consumer concerns regarding lengthy charge times and limited charging point availability has limited the penetration of EVs into the market. Although improvements in battery technology has significantly improved vehicle range in recent years, we are approaching the theoretical maximum energy density achievable with lithium-ion batteries. Therefore, we must look elsewhere to improve range. Improving transmission efficiency is one way to do this.
In conventional ICE vehicles, power losses are dominated by the engines, which typically have efficiencies below 40%. In comparison, Electric Motors (EMs) have efficiencies in the 90% range. Transmission losses therefore make up a much greater proportion of the overall vehicle losses than in ICE vehicles, being the second greatest source after battery charging. Therefore, improvement in transmission efficiency could significantly exchange vehicle range. There are a number of challenges when selecting components and lubricants for an EV. The torque-speed characteristics of EMs are significantly different to ICEs and the higher speeds achieved by EMs result in significant churning losses. These high speeds also result in significant shear heating, reducing the lubricant viscosity and increasing the risk of component failure.
EMs typically operate at maximum torque near zero speed and as such, the need of a clutch is negated. The torque-speed characteristics of EMs also allow EV transmissions to operate with just a single ratio gear reduction, greatly simplifying the design. However, the transmission will therefore be required to run at a much wider range of input speeds than an ICE vehicle transmission. This presents challenges when selecting a lubricant, as any chosen lubricant must have a significant enough viscosity to enable it to provide an adequate film thickness at lower speeds, whilst not being so viscous as to cause excessive churning losses at high speeds.
The aim of this project is to develop an accurate computational model to predict the different losses in EV transmissions, including gear losses, bearing losses and churning losses. This will provide a valuable design tool for automotive manufacturers, allowing them to better optimise transmission designs and thereby improve the vehicle range.
Molecular Behaviour at Surfaces and Interfaces
Researcher: Dr James Ewen
Recent advances in eperiments and simulations at the micro/nanoscale have demonstrated that behaviour at these scales often governs macroscopic tribological phenomena. In particular, molecular simulations can now be used to accurately model the behaviour of lubricant and additve molecules inside tribological contacts. In this project, moleular simulations will be used to give unique insights into various important open questions in tribology; from the mechanohemical dissociation of ZDDP molecules to the friction and flow of fluid molecules under EHL conditions.
Molecular Simulations of Interfaces under Extreme Conditions
Sponsor: Baker Hughes
The molecular-level interactions between lubricants and engineering surfaces are not fully understood. The aim of this project is to conduct molecular simulations to investigate the behaviour of lubricated surfaces under extreme temperature, pressure, and sliding velocity conditions. An understanding of this behaviour is required to design advanced materials and molecules for drilling applications. The ultimate goal is to develop a true multi-scale (atomistic to continuum), multi-physics tribological model for drilling problems.
First, molecular simulations will be conducted on existing well-defined systems of lubricants and surfaces under thermomechanical loading to study their effectiveness and breakdown. With this initial framework in place, it will be used to accelerate future development and yield effective formulated lubricants and engineered surfaces for drilling applications.
Origins of Micropitting in Gears
Supervisor: Dr Amir Kadiric
Micropitting is a form of rolling contact fatigue associated with hardened gears and rolling element bearings. It consists of tiny pits on the scale of 10s of microns which can cover large portions of the face of the gear and raceway of the bearings. These pits can lead to loss of tooth profile and provide an initiation point of other types of rolling contact fatigue such as spalling. The mechanism by which micropits are formed is not well understood and there is a real need to produce models to predicate the useable life of components which may suffer from it.
To better understand the mechanism behind micropitting, experiments are being undertaken on a PCS MicroPitting Rig (MPR). Preventative measures and ways to predict the life of gears after micropitting has occurred are also being investigated.
Polymeric Additives in Lubricants for Electric Vehicle Powertrains
Researcher: Amran Mohamed
Supervisor: Dr Janet Wong, Dr Luca di Mare
Scuffing in Non-Conformal Contacts
Short Crack Propagation of Surface Initiated Rolling Contact Fatigue Cracks in Bearing Steel
Researcher: Bjoern Kunzelman
Supervisor: Dr Amir Kadiric, Prof. Daniele Dini
Surface initiated rolling contact fatigue, leading to a surface failure known as pitting, is a life limiting failure mode in many modern machine elements, particularly rolling element bearings. Based on a prior study which investigated the crack propagation until pitting, this study focuses on short crack propagation. Short crack propagation induced by rolling contact fatigue is characterised by a relatively slow crack propagation and frequent crack arrests.
A triple-disc contact machine will be used to determine the major parameters which influence short crack growth (e.g. surface topography, fluid film properties, microstructure, etc.). Simple models shall then be derived and validated with the experiments.
Structure Breakdown During Oral Processing of Aerated Chocolates
Researcher: Dimitrios Bikos
Aerated chocolate products are popular consumer items associated with positive textural and sensory attributes. Among other microstructural features such as cocoa solids, sugar particles, etc. aerated chocolate consists of bubbles as well. Interaction between bubbles and particles occur during the structure build-up and structure breakdown process and therefore it needs to be investigated. Therefore, a multidisciplinary approach is taken to predict how microbubbles impact on the rheological, thermal and lubrication processes through progressive structure breakdown in the mouth. However, the effect of the aerated microstructure on the chocolate’s behavior during both industrial and oral processes is a very complex research field. During oral processing, food first fractures into particles, which interact with saliva to form a bolus, which is then swallowed. During this process, mechanical and thermal loads are applied whilst the effect of the contact with the oral cavity is also crucial in determining the consumer’s taste experience. Chocolate changes phase as it melts further complicating the behavior. However, the effect of aeration on industrial processing or manufacturing of chocolate cannot be neglected. Specifically, the effect of bubbles on the thermal properties of the chocolate is to be determined such that manufacturing can be controlled to ensure that chocolate will have the desirable textural and sensorial attributes.
Surface Deposition of Carbonaceous Materials
Researcher: Dr Sophie Campen
Supervisor: Dr Janet Wong
Fouling by carbonaceous deposits poses a serious and costly problem for the oil production industry. In upstream, midstream and downstream oil production, carbonaceous deposits frequently consist of asphaltene. Asphaltene is the densest, most polar fraction of crude oil and is generally stable in the reservoir. However, changes in environmental conditions, in particular pressure, but also temperature, shear rate and solvency of the crude oil base stock can lead to asphaltene being destabilised. Destabilisation of asphaltene, resulting in its precipitation from liquid crude is believed to be responsible for the formation of thick deposits that can completely plug the wellbore. Asphaltene is defined by its solubility: soluble in aromatic solvents like toluene, but insoluble in n-alkanes like heptane. Being a solubility class of compounds means that by definition, asphaltene is polydisperse. This makes cross-study comparisons challenging since crude oils from different sources possess different chemistries and hence display different deposition behaviours.
The aim of this project is to achieve a fundamental understanding of the mechanisms that govern asphaltene deposition. This will allow for better informed decisions on the most effective pathways to preventing fouling, for example through additive chemistry and smart surface coatings. Asphaltene deposition will be investigated experimentally using a quartz crystal microbalance. This technique allows us to measure in situ the deposited mass as a function of time.
Funded by BP, this study forms part of larger project within the International Centre for Advanced Materials and involves collaboration with partner members at Imperial College London, the University of Manchester, the University of Cambridge, and the University of Illinois at Urbana-Champaign.
The Effect of Shear Stress on Lubricant Behaviour
Researcher: Stephen Jeffreys
The aim of the project is to investigate the effect of shear stress on lubricant behaviour, particularly in high-pressure high-shear environments such as those found in elastohydrodynamic (EHD) contacts. Here it is critical to gain an understanding of the rheological properties at a molecular level, considering the local structure of the lubricant. Given the severity of operating conditions lubricants can reveal unusual phenomena where the Newtonian assumption may be inadequate. An inaccurate description of the flow limits our understanding of lubricant rheology which affects the ability to theorize novel ways of controlling friction. This impacts the overall goal to manipulate the tribological performance of engineering systems and improve efficiency.
The Effects of Surface Texture in Reciprocating Bearings
Researcher: Dr Sorin-Cristian Vladescu
Supervisor: Dr Tom Reddyhoff
Sponsor: Ford Motor Company
The research project is conducted in collaboration with the Ford Motor Company, and evaluates the how textured surfaces, produced using Laser Surface Texturing (LST), can improve the tribological performances of an internal combustion engine components. Particular focus is on the reciprocating contact between the cylinder liner and piston rings, since this accounts for the approximately 4% of the overall fuel energy used.
To achieve this goal the project involves simultaneously measuring friction force and film thickness in a reciprocating contact using a test rig designed specifically for this purpose. A range of pocket configurations on the ring-liner pairing are investigated, in order to identify an optimum texture pattern suitable for actual piston ring conditions and also to shed light on the mechanisms that are occurring.
The Self-Assembly of Organic Friction Modifier Solutions
Researcher: Ben Fry
Organic friction modifiers (OFMs) are used to reduce friction in the boundary regime. This happens through self-assembled monolayers (SAMs) of the OFMs onto the surface. This project looks at the formation and properties of the SAMs in idealised systems and relate them to friction data to get a better understanding of the mechanism of the OFMs friction reducing properties.
The main techniques to observe the structure and growth of these monolayer are atomic force microscopy (AFM) and spectroscopic ellipsometry. With these combined techniques, a picture of how the monolayer is formed on the surface from a dilute solution can be created.
Transfer Film Formation of High-Performance Polymers
Researcher: Kian Kun Yap
A metal-polymer sliding interface can self-lubricate due to the transfer film formation mechanism. It is therefore ideal for applications where liquid lubricants are inapplicable, for example, in the aerospace, pharmaceutical, and semiconductor industry. It is well known that linear polymers such as PTFE and UHMWPE can form thin and stable transfer film which is excellent in friction reduction. However, most high-performance polymers (HPPs) have highly complex chemical structures and hence do not obey the oversimplified textbook explanation for the transfer film formation mechanism. This project aims to elucidate the transfer film formation of HPPs and specifically polyimides, utilising in-situ and real-time surface characterisation techniques (e.g. spatiotemporal mapping as shown in the figure) during the polyimides/stainless steel sliding. With the support from DuPont, the chemical properties of polyimides can be customised as a strategy to better understand the fundamental mechanism of self-lubrication.
Tribofilm Properties of ZDDP-Containing Oils
Researcher: Mao Ueda
Supervisor: Professor Hugh Spikes
Zinc dialkyl dithiophosphate (ZDDP) is widely used as an anti-wear additive in engine oils. The tribofilms formed by ZDDP have been extensively investigated using friction and wear tests as well as surface analysis. However, the influence of ZDDP film properties on film durability and ultimately tribological performance remains unclear. The aim of this project is to uncover these relationships, as well as to investigate the effect of co-additives on ZDDP performance.
Tribology of Calcium Complex Greases
Researcher: Rory McAllister
Electrification of the automotive sector is putting even more emphasis on low-friction bearing lubricants, and the burgeoning battery market has driven up the price of lithium, a raw material in >70% of lubricating greases. There is, therefore, a need to replace the standard lithium grease thickener with a cheaper, equally effective alternative.
This project aims to investigate the performance of novel calcium complex grease formulations provided by Shell. Rolling contact tests will be performed with both lubricant degradation and inlet starvation controlled to emulate realistic bearing conditions. Techniques such as infrared spectroscopy will be used to analyse the rolled tracks in order to understand the mechanisms of grease lubrication.
Tribology of Dry Wire Drawing
Researcher: Marie-Louise Schlichting
Supervisor: Dr Marc Masen, Dr Amir Kadiric
The wire drawing process involves significant friction forces at the wire-die contact and hence, resulting shear stresses at the wire surface that affect the quality of the wire. Adding lubrication to the contact influences friction between the wire and the die and therefore, wire quality and die wear. Especially in dry wire drawing under high speed conditions, friction has detrimental effects. The aim of this PhD project is to optimise wire quality and die life by characterising the friction and lubrication conditions in dry wire drawing for given lubricant formulation, speeds, roughness and contact pressures.
Understanding and Prevention of False Brinelling Failure Mode in Rolling Element Bearings
Researcher: Rachel Januszewski
Supervisor: Dr Amir Kadiric
False brinelling is a type of surface damage that most commonly occurs in non-conformal, nominally stationary contacts that are subjected to externally generated vibration. All machine elements that rely on non-conformal, rolling-sliding contacts in their operation can suffer from false brinelling, but it is most commonly observed in rolling element bearings, especially in stand-by equipment stored near running machines and in the transport of automotive vehicles by rail or sea.
False brinelling is a specific type of a more general contact damage mechanism of fretting, often referred to as fretting corrosion. The underlying mechanisms causing fretting and false brinelling are thought to be similar, but false brinelling in rolling bearings has an added complication that the oscillatory motion is not pure sliding but also involves rolling of rolling elements on bearing raceways.
The aim of the proposed research is firstly, to gain a better understanding of the factors that drive the onset and progression of false-brinelling damage and secondly, to provide potential preventative measures, be it through the improvements in bearing design or lubricant formulation.
Understanding the Mechanisms Driving Crack Initiation
Researcher: Chiara Bertuccioli
Supervisor: Dr Amir Kadiric
Rolling contact fatigue (RCF) involves initiation and subsequent propagation of cracks due to cyclic stresses caused by a rolling-sliding contact, which eventually leads to the creation of a surface pit and component failure. RCF is a life-limiting failure mode of many engineering components including rolling bearings, gears and cams. Despite its obvious practical and economic importance, the fundamental mechanisms behind RCF are not fully understood.
The overarching aim of this project is to gain a fundamental understanding of the mechanisms that drives crack initiation and early propagation implementing the use of modern analytical techniques to study the material’s microstructural effects on RCF mechanisms.
Understanding Viscosity Modifier Additive Performance
Researcher: Eliane Gendreau
Viscosity modifiers are polymers added to lubricants to control viscosity. Effective viscosity modifiers are crucial in the automotive industry to facilitate the use of base oils with lower viscosity which can reduce hydrodynamic losses and thus increase fuel efficiency. The aim of the project is to investigate how the architecture of polymeric viscosity modifiers affects lubricant rheology. Techniques such as fluorescence spectroscopy will be used to study the effect of polymer architecture on thier temperature and shear responses inside hydrodynamic contacts.