Imperial College London

Dr Tom Reddyhoff

Faculty of EngineeringDepartment of Mechanical Engineering

Reader in Tribology
 
 
 
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Contact

 

+44 (0)20 7594 3840t.reddyhoff Website

 
 
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Location

 

670City and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

113 results found

Miyazaki M, Nakano K, Tadokoro C, Vladescu S-C, Reddyhoff T, Sasaki S, Tsujii Yet al., 2021, Enhancing durability of concentrated polymer brushes using microgrooved substrates, WEAR, Vol: 482, ISSN: 0043-1648

Journal article

Dou P, Jia Y, Zheng P, Wu T, Yu M, Reddyhoff T, Peng Zet al., 2021, Review of ultrasonic-based technology for oil film thickness measurement in lubrication, Tribology International

Journal article

Yu M, Reddyhoff T, Dini D, Holmes A, O'Sullivan Cet al., 2021, Using ultrasonic reflection resonance to probe stress wave velocity in assemblies of spherical particles, IEEE Sensors Journal, ISSN: 1530-437X

A high-sensitivity method to measure acousticwave speed in soils by analyzing the reflected ultrasonic signalfrom a resonating layered interface is proposed here.Specifically, an ultrasonic transducer which can be used to bothtransmit and receive signals is installed on a low-high acousticimpedance layered structure of hard PVC and steel, which in turnis placed in contact with the soil deposit of interest. The acousticimpedance of the soil (the product of density and wave velocity)is deduced from analysis of the waves reflected back to thetransducer. A system configuration design is enabled bydeveloping an analytical model that correlates the objectivewave speed with the measurable reflection coefficient spectrum.The physical viability of this testing approach is demonstratedby means of a one-dimensional compression device that probesthe stress-dependence of compression wave velocity of differentsizes of glass ballotini particles. Provided the ratio of thewavelength of the generated wave to the soil particle size issufficiently large the data generated are in agreement with dataobtained using conventional time-of-flight measurements. Inprinciple, this high-sensitivity approach avoids the need for thewave to travel a long distance between multiple transmitterreceiver sensors as is typically the case in geophysical testingof soil. Therefore it is particularly suited to in-situ observation ofsoil properties in a highly compact setup, where only a single transducer is required. Furthermore, high spatialresolution of local measurements can be achieved, and the data are unaffected by wave attenuation as transmitted insoil.

Journal article

Dou P, Wu T, Luo Z, Yang P, Peng Z, Yu M, Reddyhoff Tet al., 2021, A finite-element-aided ultrasonic method for measuring central oil film thickness in a roller-raceway tribo-pair, Friction, ISSN: 2223-7690

Roller bearings support heavy loads by riding on an ultra-thin oil film (between the roller and theraceway), the thickness of which is critical as it reflects the lubrication performance. Ultrasonicinterfacial reflection, which facilitates a non-destructive measurement of oil film thickness, has beenwidely studied. However, insufficient spatial resolution around the rolling line contact zone remainsa barrier, despite the employment of miniature piezoelectric transducers. In this paper, a finiteelement-aided method is utilized to simulate wave propagation through a three-layered structureof roller-oil-raceway under elastohydrodynamic lubrication (EHL), with nonlinear characteristicsof i) the deformed curvature of the cylindrical roller and ii) the non-uniform distribution of fluid bulkmodulus along the circumference of the oil layer taken into account. A load- and speed-dependentlook-up table is then developed to establish an accurate relationship between the overall reflectioncoefficient (directly measured by an embedded ultrasonic transducer) and the objective variable ofcentral oil film thickness. Moreover, the proposed finite-element-aided method is verifiedexperimentally in a roller-raceway test rig, with the ultrasonic measured oil film thicknessessentially corresponding to the calculated values by EHL theory.

Journal article

Hu S, Reddyhoff T, Li J, Cao X, Shi X, Peng Z, deMello AJ, Dini Det al., 2021, Biomimetic water-repelling surfaces with robustly flexible structures, ACS Applied Materials and Interfaces, Vol: 13, Pages: 31310-31319, ISSN: 1944-8244

Biomimetic liquid-repelling surfaces have been the subject of considerable scientific research and technological application. To design such surfaces, a flexibility-based oscillation strategy has been shown to resolve the problem of liquid-surface positioning encountered by the previous, rigidity-based asymmetry strategy; however, its usage is limited by weak mechanical robustness and confined repellency enhancement. Here, we design a flexible surface comprising mesoscale heads and microscale spring sets, in analogy to the mushroomlike geometry discovered on springtail cuticles, and then realize this through three-dimensional projection microstereolithography. Such a surface exhibits strong mechanical robustness against ubiquitous normal and shear compression and even endures tribological friction. Simultaneously, the surface elevates water repellency for impacting droplets by enhancing impalement resistance and reducing contact time, partially reaching an improvement of ∼80% via structural tilting movements. This is the first demonstration of flexible interfacial structures to robustly endure tribological friction as well as to promote water repellency, approaching real-world applications of water repelling. Also, a flexibility gradient is created on the surface to directionally manipulate droplets, paving the way for droplet transport.

Journal article

Hu S, Cao X, Reddyhoff T, Shi X, Peng Z, deMello AJ, Dini Det al., 2021, Flexibility-patterned liquid-repelling surfaces, ACS Applied Materials and Interfaces, Vol: 13, Pages: 29092-29100, ISSN: 1944-8244

Droplets impacting solid surfaces is ubiquitous in nature and of practical importance in numerous industrial applications. For liquid-repelling applications, rigidity-based asymmetric redistribution and flexibility-based structural oscillation strategies have been proven on artificial surfaces; however, these are limited by strict impacting positioning. Here, we show that the gap between these two strategies can be bridged by a flexibility-patterned design similar to a trampoline park. Such a flexibility-patterned design is realized by three-dimensional projection micro-stereolithography and is shown to enhance liquid repellency in terms of droplet impalement resistance and contact time reduction. This is the first demonstration of the synergistic effect obtained by a hybrid solution that exploits asymmetric redistribution and structural oscillation in liquid-repelling applications, paving the rigidity-flexibility cooperative way of wettability tuning. Also, the flexibility-patterned surface is applied to accelerate liquid evaporation.

Journal article

Haimov E, Chapman A, Bresme F, Holmes A, Reddyhoff T, Urbakh M, Kornyshev Aet al., 2021, Theoretical demonstration of a capacitive rotor for generation of alternating current from mechanical motion, Nature Communications, Vol: 12, Pages: 3678-3678, ISSN: 2041-1723

Innovative concepts and materials are enabling energy harvesters for slower motion, particularly for personal wearables or portable small-scale applications, hence contributing to a future sustainable economy. Here we propose a principle for a capacitive rotor device and analyze its operation. This device is based on a rotor containing many capacitors in parallel. The rotation of the rotor causes periodic capacitance changes and, when connected to a reservoir-of-charge capacitor, induces alternating current. The properties of this device depend on the lubricating liquid situated between the capacitor’s electrodes, be it a highly polar liquid, organic electrolyte, or ionic liquid – we consider all these scenarios. An advantage of the capacitive rotor is its scalability. Such a lightweight device, weighing tens of grams, can be implemented in a shoe sole, generating a significant power output of the order of Watts. Scaled up, such systems can be used in portable wind or water turbines.

Journal article

Zimmer M, Vladescu S-C, Mattsson L, Fowell M, Reddyhoff Tet al., 2021, Shear-Area Variation: A Mechanism that Reduces Hydrodynamic Friction in Macro-Textured Piston Ring Liner Contacts, Tribology International, ISSN: 0301-679X

Journal article

Yu M, Zhang J, Joedicke A, Reddyhoff Tet al., 2021, Experimental investigation into the effects of diesel dilution on engine lubrication, Tribology International, Vol: 156, Pages: 1-9, ISSN: 0301-679X

The dilution of lubricant due to contamination with diesel fuel is an increasingly prevalent, potentially importantand poorly understood issue. Thisstudy addressestwo fundamental questions: 1) How doesthe change in lubricantrheology due to diesel dilution affect engine lubrication? 2) How is the chemical performance of lubricantcomponents (base oil and performance additives) impacted by diesel dilution under different lubrication regimes(boundary/full film, hydrodynamic/elastohydrodynamic). This is achieved by testing three lubricant samples: 1)neat fully formulated 0W-30 engine oil, 2) fully formulated 0W-30 oil diluted with diesel at a concentration of15%, denoted “0W-30D”, and 3) neat, fully-formulated 0W-16, with the same base oil components andperformance additives as the 0W-30, but blended to give a viscosity equal to that of the diluted an equivalent“0W-30D”. Tribometer tests, including 1) low pressure, low shear viscosity, 2) Ultra-high Shear Viscosity (USV),3) elastohydrodynamic film thickness, 4) Stribeck friction and 5) boundary friction and wear, are then conducted.To further emulate engine lubrication conditions, Stribeck curve measurements are performed on the threelubricants using a journal bearing test rig, fitted with a connecting-rod and commercial diesel engine shells.Results suggest that diesel dilution only slightly affects chemical additive performance (with friction modifiersbeing more inhibited than anti-wear additives) but does reduce both viscosity and film thickness. However, caremust be taken in using viscometrics to predict dilution behaviour because 1) the pressure viscosity coefficient isalso affected by diesel dilution which has implications for elastohydrodynamically lubrication contacts, 2) shearthinning means that viscosity modifier additives effects lose their functions at high shear rates; whereas dieselcontamination affects viscosity behaviour throughout the whole shear rate range.

Journal article

Vlădescu S-C, Bozorgi S, Hu S, Baier SK, Myant C, Carpenter G, Reddyhoff Tet al., 2021, Effects of beverage carbonation on lubrication mechanisms and mouthfeel, Journal of Colloid and Interface Science, Vol: 586, Pages: 142-151, ISSN: 0021-9797

The perception of carbonation is an important factor in beverage consumption which must be understood in order to develop healthier products. Herein, we study the effects of carbonated water on oral lubrication mechanisms involved in beverage mouthfeel and hence taste perception. Friction was measured in a compliant PDMS-glass contact simulating the tongue-palate interface (under representative speeds and loads), while fluorescence microscopy was used to visualise both the flow of liquid and oral mucosal pellicle coverage.When carbonated water is entrained into the contact, CO2 cavities form at the inlet, which limit flow and thus reduce the hydrodynamic pressure. Under mixed lubrication conditions, when the fluid film thickness is comparable to the surface roughness, this pressure reduction results in significant increases in friction (>300% greater than under non-carbonated water conditions). Carbonated water is also shown to be more effective than non-carbonated water at debonding the highly lubricious, oral mucosal pellicle, which again results in a significant increase in friction. Both these transient mechanisms of starvation and salivary pellicle removal will modulate the flow of tastants to taste buds and are suggested to be important in the experience of taste and refreshment. For example this may be one reason why flat colas taste sweeter.

Journal article

Reddyhoff T, Ewen J, Deshpande P, Frogley M, Welch M, Montgomery Wet al., 2021, Macroscale superlubricity and polymorphism of long-chain n-alcohols, ACS Applied Materials and Interfaces, Vol: 13, Pages: 9239-9251, ISSN: 1944-8244

Simple n-alcohols, such as 1-dodecanol, show anomalous film-forming and friction behaviors under elastohydrodynamic lubrication (EHL) conditions, as found inside bearings and gears. Using tribometer, diamond anvil cell (DAC), and differential scanning calorimetry (DSC) experiments, we show that liquid 1-dodecanol undergoes a pressure-induced solidification when entrained into EHL contacts. Different solid polymorphs are formed inside the contact depending on the temperature and pressure conditions. Surprisingly, at a moderate temperature and pressure, 1-dodecanol forms a polymorph that exhibits robust macroscale superlubricity. The DAC and DSC experiments show that superlubricity is facilitated by the formation of lamellar, hydrogen-bonded structures of hexagonally close-packed molecules, which promote interlayer sliding. This novel superlubricity mechanism is similar to that proposed for the two-dimensional materials commonly employed as solid lubricants, but it also enables the practical advantages of liquid lubricants to be maintained. When the pressure is increased, 1-dodecanol undergoes a polymorphic transformation into a phase that gives a higher friction. The DAC and DSC experiments indicate that the high-friction polymorph is an orthorhombic crystal. The polymorphic transformation pressure coincides with the onset of a dimple formation in the EHL films, revealing that the anomalous film shapes are caused by the formation of rigid orthorhombic crystals inside the contact. This is the first demonstration of a macroscale superlubricity in an EHL contact lubricated by a nonaqueous liquid that arises from bulk effects rather than tribochemical transformations at the surfaces. Since the superlubricity observed here results from phase transformations, it is continuously self-replenishing and is insensitive to surface chemistry and topology. This discovery creates the possibility of implementing superlubricity in a wide range of machine components, which would resul

Journal article

Dou P, Wu T, Jia Y, Peng Z, Yu M, Reddyhoff Tet al., 2021, High-accuracy incident signal reconstruction for in-situ ultrasonic measurement of oil film thickness, Mechanical Systems and Signal Processing, Vol: 156, Pages: 107669-107669, ISSN: 0888-3270

Journal article

Yu M, Zhang J, Reddyhoff T, 2021, Characterizing Fuel Dilution Effects on Rheological and Tribological Behavior of Engine Lubricant, the 7th World Tribology Congress (WTC2021)

Conference paper

Bahshwan M, Myant CW, Reddyhoff T, Pham MSet al., 2020, The role of microstructure on wear mechanisms and anisotropy of additively manufactured 316L stainless steel in dry sliding, Materials and Design, Vol: 196, ISSN: 0264-1275

Wear control, which relies on understanding the mechanisms of wear, is crucial in preserving the life of mechanical components and reducing costs. Additive manufacturing (AM) techniques can produce parts with tailored microstructure, however, little has been done to understand how this impacts the mechanisms of wear. Here we study the impact of initial grain arrangement and crystal orientation on the wear mechanisms of austenitic stainless steel (SS) in dry sliding contact. Specifically, the anisotropic sliding wear behavior of as-built, AM-ed 316L SS is compared against annealed, wire-drawn counterparts. We describe, in-detail, how the sliding wear mechanisms of delamination, abrasion, oxidation, and plastic deformation are attributed to the initial surface microstructure under different loading conditions using a number of techniques. This new understanding sheds light on how different AM-induced microstructures affect wear, thereby allowing for better utilization of this technology to develop components with enhanced wear properties.

Journal article

Yu M, Shen L, Mutasa T, Dou P, Wu T, Reddyhoff Tet al., 2020, Exact analytical solution to ultrasonic interfacial reflection enabling optimal oil film thickness measurement, Tribology International, Vol: 151, Pages: 1-10, ISSN: 0301-679X

The ultrasonic reflection from a lubricated interface has been widely analyzed to measure fluid film thickness, with different algorithms being applied to overcome measurement accuracy and resolution issues. Existing algorithms use either the amplitude or the phase angle of the ultrasonic interfacial reflection. In this paper, a new algorithm (named the “exact model – complex”) that simultaneously utilizes both the amplitude and the phase of the complex ultrasonic reflection coefficient is proposed and mathematically derived. General procedures for theoretical analysis in terms of measurement accuracy and uncertainty are proposed and applied to the new algorithm, the beneficial features of which (as compared to other existing algorithms) can be summarized as: 1) a direct calculation, instead of an iterative approximation, 2) guaranteed maximum measurement accuracy, and 3) acceptable measurement uncertainty. None of the existing methods have showed this combination of benefits. Moreover, two groups of raw data from previous experimental studies are utilized to further validate the practical feasibility of the new algorithm. Overall, the proposed “exact model – complex” algorithm fully exploits the potential of ultrasonic reflection for oil film thickness measurement, with an accurate and a convenient calculation suited to practical implementation.

Journal article

Wen J, Dini D, Reddyhoff T, 2020, Design and optimization of a liquid ring thrust bearing, Tribology International, Vol: 149, ISSN: 0301-679X

Liquid menisci at millimeter length scales and smaller exhibit large Laplace pressures. To utilise these effects, liquid ring bearings have recently been developed, which consist of liquid rings confined between alternate superhydrophobic and hydrophilic patterns. We present a detailed experimental and theoretical performance analysis of such bearings. For a single, 100 μm thickness, liquid ring, the maximum supporting force is 0.13 N, which decreases with increasing the ring misalignment. The frictional torque increases linearly with rotational speed until a critical Reynolds number is reached. Above this, an instability occurs due the concave liquid ring meniscus, which further increases friction. These results show how liquid ring bearings can be optimised.

Journal article

Hu S, Cao X, Reddyhoff T, Puhan D, Vladescu S-C, Wang J, Shi X, Peng Z, deMello AJ, Dini Det al., 2020, Liquid repellency enhancement through flexible microstructures, Science Advances, Vol: 6, Pages: 1-7, ISSN: 2375-2548

Artificial liquid-repellent surfaces have attracted substantial scientific and industrial attention with a focus on creating functional topological features; however, the role of the underlying structures has been overlooked. Recent developments in micro-nanofabrication allow us now to construct a skin-muscle type system combining interfacial liquid repellence atop a mechanically functional structure. Specifically, we design surfaces comprising bioinspired, mushroom-like repelling heads and spring-like flexible supports, which are realized by three-dimensional direct laser lithography. The flexible supports elevate liquid repellency by resisting droplet impalement and reducing contact time. This, previously unknown, use of spring-like flexible supports to enhance liquid repellency provides an excellent level of control over droplet manipulation. Moreover, this extends repellent microstructure research from statics to dynamics and is envisioned to yield functionalities and possibilities by linking functional surfaces and mechanical metamaterials.

Journal article

Hu S, Reddyhoff T, Puhan D, Vladescu S-C, Shi X, Dini D, Peng Zet al., 2020, Droplet manipulation of hierarchical steel surfaces using femtosecond laser fabrication, Applied Surface Science, Vol: 521, Pages: 146474-146474, ISSN: 0169-4332

Journal article

Lu J, Reddyhoff T, Dini D, 2020, A study of thermal effects in EHL rheology and friction using infrared microscopy, Tribology International, Vol: 146, ISSN: 0301-679X

Infrared microscopy is used to obtain through-thickness oil temperature measurements from EHL contacts between different surface materials (steel, silicon nitride and zirconia) for the lubricants Santotrac 50 and PAO4. The measurement technique was first adapted to overcome focussing issues due to the partially transparent zirconia surface. Results were used to infer in-contact rheological behaviour of the lubricants. Santotrac 50 shows significant shear localisation under all conditions with the position of the shear heating zone being highly affected by the contact surfaces' thermal properties. For PAO4, the shear profile depends on the contact surfaces’ thermal properties with moderate to high surface conductivities favouring uniform shearing, whereas highly insulating surfaces (zirconia) cause shear localisation at the surface for both lubricants. These results are used to interpret friction measurements and show how the thermal properties of surfaces can be used to control rheology and friction. This paper is prefaced by a review of thermal EHL theory upon which our analysis is based.

Journal article

Wen J, Reddyhoff T, Hu S, Puhan D, Dini Det al., 2020, Exploiting air cushion effects to optimise a superhydrophobic/hydrophilic patterned liquid ring sealed air bearing, Tribology International, Vol: 144, ISSN: 0301-679X

A thrust bearing consisting of an air cushion formed within a liquid ring has been developed, which takes advantage of the Laplace pressure induced by the liquid/air surface tension. As forces induced by Laplace pressure and surface tension scales down much more slowly than gravity and inertial forces, such a bearing has great potential when scaled down to the micro-scale. The liquid ring between the rotor and the stator of the bearing is anchored there by alternating hydrophilic and superhydrophobic patterns. An important discovery is that the performance of this bearing is greatly enhanced by the sealed cushion of air within the ring. This air cushion and thin liquid ring arrangement mean that the solid/solid contact of the bearing is replaced by solid/air and solid/liquid contact which significantly reduces the friction and wear. The factors which affects the performance of the bearing have been studied both experimentally and numerically providing results that can be used to optimise the design of this new type of bearing.

Journal article

Yin L, Reddyhoff T, Nowell D, 2020, Detailed investigation of brake squeal - Improvement of the squeal test rig and comparison between results and predictions, Pages: 2155-2163

Brake squeal is a long-standing problem in the vibration and tribology fields. This irregular noise causes irritation for vehicle users and passers-by, who may think that the brake components are problematic, although the brake system is working as designed. This study investigates brake squeal through a combination of experiment and simulation. An improved version of the pin-on-disc test rig is developed for squeal testing. Complex eigenvalue analysis is used to extract instability from the finite element model and different friction laws are examined in order to improve prediction.

Conference paper

Yin L, Reddyhoff T, Nowell D, 2020, Y Detailed investigation of brake squeal - Improvement of the squeal test rig and comparison between results and predictions, International Conference on Noise and Vibration Engineering (ISMA) / International Conference on Uncertainty in Structural Dynamics (USD), Publisher: KATHOLIEKE UNIV LEUVEN, DEPT WERKTUIGKUNDE, Pages: 2155-2163

Conference paper

Hu S, Cao X, Reddyhoff T, Puhan D, Vladescu S-C, Wang Q, Shi X, Peng Z, deMello AJ, Dini Det al., 2019, Self-compensating liquid repellent surfaces with stratified morphology, ACS Applied Materials and Interfaces, Vol: 12, Pages: 4174-4182, ISSN: 1944-8244

Artificial liquid repellent surfaces have recently attracted vast scientific attention; however, achieving mechanical robustness remains a formidable challenge before industrialization can be realized. To this end, inspired by plateaus in geological landscapes, a self-compensating strategy is developed to pave the way for the synthesis of durable repellent surfaces. This self-compensating surface comprises tall hydrophobic structural elements, which can repel liquid droplets. When these elements are damaged, they expose shorter structural elements that also suspend the droplets and thus preserve interfacial repellency. An example of this plateau-inspired stratified surface was created by 3D direct laser lithography micro-nano fabrication. Even after being subjected to serious frictional damage, it maintained static repellency to water with a contact angle above 147 and was simultaneously able to endure high pressures arising from droplet impacts. Extending the scope of nature-inspired functional surfaces from conventional biomimetics to geological landscapes, this works demonstrates that the plateau-inspired self-compensating strategy can provide an unprecedented level of robustness in terms of sustained liquid repellency.

Journal article

Ciniero A, Fatti G, Righi MC, Dini D, Reddyhoff Tet al., 2019, A combined experimental and theoretical study on the mechanisms behind tribocharging phenomenon and the influence of triboemission, Tribology Online, Vol: 14, Pages: 367-374, ISSN: 1881-218X

This work describes recent research into the mechanisms behind tribocharging and the influence of triboemission. The term tribocharging is a type of contact-induced electrification and refers to the transfer of charge between rubbing components. The term triboemission, on the other hand, refers to emission of electrons, ions and photons generated when surfaces are rubbed together. The understanding of tribocharging is of wide interest for several industrial applications and in particular the combination of tribocharging and triboemission may be important in lubricated contacts in the formation of boundary lubricant films. We report the use of a unique vacuum measurement system that enables to measure surface charge variations while simultaneously recording triboemission events during the sliding of a diamond tip on silica specimens. Results show for the first time that tribocharging and triboemission behavior are linked and depend on the surface wear. The contribution of contact-induced electrification to the charging of the surface is then described by means of density functional theory (DFT). Results give insight into the transfer of charge from the SiO2 amorphous surface (silica) to the C(111) surface (diamond ) and into the variation of charging during simulated sliding contact.

Journal article

Reddyhoff T, 2019, LUBRICANT COMPOSITIONS, WO2019193368

Patent

Carpenter G, Bozorgi S, Vladescu S, Forte A, Myant C, Potineni R, Reddyhoff T, Baier Set al., 2019, A study of saliva lubrication using a compliant oral mimic, Food Hydrocolloids, Vol: 92, Pages: 10-18, ISSN: 0268-005X

Due to ethical issues and the difficulty in obtaining biological tissues, it is important to find synthetic elastomers that can be used as replacement test media for research purposes. An important example of this is friction testing to understand the mechanisms behind mouthfeel attributes during food consumption (e.g. syrupy, body and clean finish), which requires an oral mimic. In order to assess the suitability of possible materials to mimic oral surfaces, a sliding contact is produced by loading and sliding a hemispherical silica pin against either a polydimethyl siloxane (PDMS), agarose, or porcine tongue sample. Friction is measured and elastohydrodynamic film thickness is calculated based on the elastic modulus of the samples, which is measured using an indentation method. Tests were performed with both saliva and pure water as the lubricating fluid and results compared to unlubricated conditions.PDMS mimics the tongue well in terms of protein adhesion, with both samples showing significant reductions in friction when lubricated with saliva versus water, whereas agarose showed no difference between saliva and water lubricated conditions. This is attributed to PDMS's OSi(CH3)2- group which provides excellent adhesion for the saliva protein molecules, in contrast with the hydrated agarose surface. The measured modulus of the PDMS (2.2 MPa) is however significantly greater than that of tongue (3.5 kPa) and agarose (66–174 kPa). This affects both the surface (boundary) friction, at low sliding speeds, and the entrained elastohydrodynamic film thickness, at high speeds.Utilising the transparent PDMS sample, we also use fluorescence microscopy to monitor the build-up and flow of dyed-tagged saliva proteins within the contact during sliding. Results confirm the lubricous boundary film forming nature of saliva proteins by showing a strong correlation between friction and average protein intensity signals (cross correlation coefficient = 0.87). This demonstrates

Journal article

Tufail K, Gangopadhyay AK, Skipp D, Reddyhoff T, Vladescu S-C, Stark RPet al., 2019, A bore portion for receiving a reciprocating piston, US20200095951

Patent

Hu S, Cao X, Reddyhoff T, Puhan D, Huang W, Shi X, Peng Z, Dini Det al., 2019, Three-dimensional printed surfaces inspired by bi-Gaussian stratified plateaus, ACS Applied Materials and Interfaces, Vol: 11, Pages: 20528-20534, ISSN: 1944-8244

Wettability of artificial surfaces is attracting increasing attention for its relevant technological applications. Functional performance is often achieved by mimicking the topographical structures found in natural flora and fauna; however, surface attributes inspired by geological landscapes have so far escaped attention. We reproduced a stratified morphology of plateaus with a bi-Gaussian height distribution using a three-dimensional direct laser lithography. The plateau-inspired artificial surface exhibits a hydrophobic behavior even if fabricated from a hydrophilic material, giving rise to a new wetting mechanism that divides the well-known macroscopic Wenzel and Cassie states into four substates. We have also successfully applied the plateau-inspired structure to droplet manipulation.

Journal article

Geng Z, Puhan D, Reddyhoff T, 2019, Using acoustic emission to characterize friction and wear in dry sliding steel contacts, Tribology International, Vol: 134, Pages: 394-407, ISSN: 0301-679X

© 2019 Acoustic emission (AE) was recorded during tribological tests on 52,100 steel specimens under different loads. AE signals were transformed to the frequency domain using a Fast Fourier Transform and parameters such as power, RMS amplitude, mean frequency, and energy were analyzed and compared with friction coefficient and wear volume measurements. Results show that certain acoustic frequencies reflect friction while others reflect wear. If frequencies are chosen optimally, AE and friction signals are highly correlated (Pearson coefficients >0.8). SEM and Raman analysis reveal how plastic deformation and oxide formation affect friction, wear and AE simultaneously. AE recordings contains more information than conventional friction and wear volume measurements and are more sensitive to changes in mechanism. This all demonstrates AE's potential as a tool to monitor tribological behavior.

Journal article

Vladescu S-C, Fowell M, Mattsson L, Reddyhoff Tet al., 2019, The effects of laser surface texture applied to internal combustion engine journal bearing shells - An experimental study, TRIBOLOGY INTERNATIONAL, Vol: 134, Pages: 317-327, ISSN: 0301-679X

Journal article

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