Publications

Journal article

Bernardini A, Trovatelli M, Klosowski M, Pederzani M, Zani D, Brizzola S, Porter A, Rodriguez y Baena F, Dini Det al., 2022,

Reconstruction of ovine axonal cytoarchitecture enables more accurate models of brain biomechanics

, Communications Biology, Vol: 5, ISSN: 2399-3642

There is an increased need and focus to understand how local brain microstructure affects the transport of drug molecules directly administered to the brain tissue, for example in convection-enhanced delivery procedures. This study reports a systematic attempt to characterize the cytoarchitecture of commissural, long association and projection fibres, namely the corpus callosum, the fornix and the corona radiata, with the specific aim to map different regions of the tissue and provide essential information for the development of accurate models of brain biomechanics. Ovine samples are imaged using scanning electron microscopy combined with focused ion beam milling to generate 3D volume reconstructions of the tissue at subcellular spatial resolution. Focus is placed on the characteristic cytological feature of the white matter: the axons and their alignment in the tissue. For each tract, a 3D reconstruction of relatively large volumes, including a significant number of axons, is performed and outer axonal ellipticity, outer axonal cross-sectional area and their relative perimeter are measured. The study of well-resolved microstructural features provides useful insight into the fibrous organization of the tissue, whose micromechanical behaviour is that of a composite material presenting elliptical tortuous tubular axonal structures embedded in the extra-cellular matrix. Drug flow can be captured through microstructurally-based models using 3D volumes, either reconstructed directly from images or generated in silico using parameters extracted from the database of images, leading to a workflow to enable physically-accurate simulations of drug delivery to the targeted tissue.

Journal article

Bonari J, Paggi M, Dini D, 2022,

A new finite element paradigm to solve contact problems with roughness

, International Journal of Solids and Structures, Vol: 253, ISSN: 0020-7683

This article's main scope is the presentation of a computational method for the simulation of contact problems within the finite element method involving complex and rough surfaces. The approach relies on the MPJR (eMbedded Profile for Joint Roughness) interface finite element proposed in [Paggi, M., Reinoso, J., 2020. Mech. Adv. Mater. Struct. 27:1731–1747], which is nominally flat but can embed at the nodal level any arbitrary height to reconstruct the displacement field due to contact in the presence of roughness. Here, the formulation is generalized to handle 3D surface height fields and any arbitrary nonlinear interface constitutive relation, including friction and adhesion. The methodology is herein validated with BEM solutions for linear elastic contact problems. Then, a selection of nonlinear contact problems prohibitive to be simulated by BEM and by standard contact algorithms in FEM are detailed, to highlight the promising aspects of the proposed method for tribology.

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Citations: 11

Journal article

Dou P, Zou L, Wu T, Yu M, Reddyhoff T, Peng Zet al., 2022,

Simultaneous measurement of thickness and sound velocity of porous coatings based on the ultrasonic complex reflection coefficient

, NDT & E International, Vol: 131, Pages: 102683-102683, ISSN: 0963-8695

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Journal article

Yang X, Liu H, Dhawan S, Politis D, Zhang J, Dini D, Hu L, Gharbi M, Wang Let al., 2022,

Digitally-enhanced lubricant evaluation scheme for hot stamping applications

, Nature Communications, Vol: 13, ISSN: 2041-1723

Digitally-enhanced technologies are set to transform every aspect of manufacturing. Networks of sensors that compute at the edge (streamlining information flow from devices and providing real-time local data analysis), and emerging Cloud Finite Element Analysis technologies yield data at unprecedented scales, both in terms of volume and precision, providing information on complex processes and systems that had previously been impractical. Cloud Finite Element Analysis technologies enable proactive data collection in a supply chain of, for example the metal forming industry, throughout the life cycle of a product or process, which presents revolutionary opportunities for the development and evaluation of digitally-enhanced lubricants, which requires a coherent research agenda involving the merging of tribological knowledge, manufacturing and data science. In the present study, data obtained from a vast number of experimentally verified finite element simulation results is used for a metal forming process to develop a digitally-enhanced lubricant evaluation approach, by precisely representing the tribological boundary conditions at the workpiece/tooling interface, i.e., complex loading conditions of contact pressures, sliding speeds and temperatures. The presented approach combines the implementation of digital characteristics of the target forming process, data-guided lubricant testing and mechanism-based accurate theoretical modelling, enabling the development of data-centric lubricant limit diagrams and intuitive and quantitative evaluation of the lubricant performance.

Journal article

Bastola A, Stewart D, Dini D, 2022,

Three-dimensional finite element simulation and experimental validation of sliding wear

, WEAR, Vol: 504-505, ISSN: 0043-1648

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Citations: 7

Journal article

Malik S, O'Sullivan C, Reddyhoff T, Dini D, Holmes Aet al., 2022,

An acoustic 3D positioning system for robots operating underground

, IEEE Sensors Letters, Vol: 6, Pages: 1-4, ISSN: 2475-1472

Underground robots are potentially helpful in many application domains, including geotechnical engineering, agriculture, and archaeology. One of the critical challenges in developing underground robotics is the accurate estimation of the positions of the robots. Acoustic-based positioning systems have been explored for developing an underground 3D positioning system. However, the positioning range is limited due to attenuation in the medium. This letter proposes an underground positioning system that utilizes a novel and easy-to-implement electronic approach for measuringthe acoustic propagation times between multiple transmitters and a receiver. We demonstrate a prototype using four transmitters at the surface and a single buried acoustic sensor as a proof-of-concept. The times of arrival for signals emitted by the different sources are measured by correlating the transmitted and received signals. The distances between the multiple transmitters and a receiver are estimated, and a tri-linearization algorithm is used to estimate the position of the buried sensor in 3D with respect to reference coordinates. The system is tested in a soil tank. The experimental results show that the proposed system is able to estimate the 3D position of buried sensors with an error of less than ±2.5 cm within a measurement field of size 50 cm × 50 cm × 35 cm in X, Y, and Z (width × length × depth). The proposed electronic synchronization approach allows increasing the positioning range of the system by increasing the number of transmittersat the surface. This paves the way for the development of a positioning system for robots operating underground.

Journal article

Ueda M, Spikes H, Kadiric A, 2022,

In-situ observation of the effect of the tribofilm growth on scuffing in rolling-sliding contact

, Tribology Letters, Vol: 70, Pages: 1-21, ISSN: 1023-8883

General reductions in lubricant viscosities in many machine components mean that the role of lubricant additives in forming tribofilms has become increasingly important to provide adequate surface protection against scuffing. However, the relationship between scuffing and the formation and removal of tribofilms has not been systematically demonstrated. In this study, a step-sliding speed scuffing test based on contra-rotation using MTM-SLIM and ETM-SLIM has been employed to observe concurrently tribofilm thickness and the onset of scuffing. The initial sliding speed used was found to significantly affect scuffing performance since it determines the extent to which a tribofilm can form before critical sliding speed conditions are reached. In general, additives that formed thicker tribofilms, especially ZDDPs and triphenyl phosphate, gave effective protection against scuffing, though their protective tribofilms were progressively removed at higher sliding speeds, eventually resulting in scuffing.

Journal article

Yu M, Evangelou S, Dini D, 2022,

Parallel active link suspension: full car application with frequency-dependent multi-objective control strategies

, IEEE Transactions on Control Systems Technology, Vol: 30, Pages: 2046-2061, ISSN: 1063-6536

In this article, a recently proposed at basic level novel suspension for road vehicles, the parallel active link suspension (PALS), is investigated in the realistic scenario of a sport utility vehicle (SUV) full car. The involved rocker-pushrod assembly is generally optimized to maximize the PALS capability in improving the suspension performance. To fully release the PALS functions of dealing with both low- and high-frequency road cases, a PID control scheme is first employed for the chassis attitude stabilization, focusing on the minimization of both the roll and pitch angles; based on a derived linear equivalent model of the PALS-retrofitted full car, an H∞ control scheme is designed to enhance the ride comfort and road holding; moreover, a frequency-dependent multiobjective control strategy that combines the developed PID and H∞ control is proposed to enable: 1) chassis attitude stabilization at 0-1 Hz; 2) vehicle vibration attenuation at 1-8 Hz; and 3) control effort penalization (for energy saving) above 10 Hz. With a group of ISO-defined road events tested, numerical simulation results demonstrate that, compared to the conventional passive suspension, the PALS has a promising potential in full-car application, with up to 70% reduction of the chassis vertical acceleration in speed bumps and chassis leveling capability of dealing with up to 4.3-m/s² lateral acceleration.

Journal article

Chennaoui M, Fowell M, Liang H, Kadiric Aet al., 2022,

A novel set-up for in situ measurement and mapping of lubricant film thickness in a model rolling bearing using interferometry and ratiometric fluorescence imaging

, Tribology Letters, Vol: 70, Pages: 1-17, ISSN: 1023-8883

This paper describes a unique experimental set-up constructed for studies of lubricant behaviour in an operating rolling element bearing including in situ quantitative measurements of film thickness in and around the element-raceway contact. The set-up is based on a deep groove ball bearing in which the outer race is made of sapphire to allow full optical access to the zone in which the rolling elements are loaded against it. This allows direct imaging of lubricant films under both steady-state and transient conditions and at contact pressures and rotational speeds representative of those present in real rolling element bearings. Optical interferometry is used to measure thin EHL films inside the ball–raceway contacts while a specific laser induced fluorescence approach, referred to as ratiometric fluorescence, is implemented to observe the lubricant distribution and quantify its thickness ahead of the ball–raceway contact. Results are presented to validate the accuracy of the method and to investigate the influence of bulk lubricant viscosity and bearing speed on contact film thickness, inlet starvation and lubricant distribution around the ball–raceway contact. To the best of our knowledge, the work described here is the first to directly measure lubricant distribution and EHL film thickness in a ball–raceway contact in an operating radial rolling bearing.

Journal article

Zhang X, Scaraggi M, Zheng Y, Li X, Wu Y, Wang D, Dini D, Zhou Fet al., 2022,

Quantifying wetting dynamics with triboelectrification

, Advanced Science, Vol: 9, ISSN: 2198-3844

Wetting is often perceived as an intrinsic surface property of materials, but determining its evolution is complicated by its complex dependence on roughness across the scales. The Wenzel (W) state, where liquids have intimate contact with the rough surfaces, and the Cassie–Baxter (CB) state, where liquids sit onto air pockets formed between asperities, are only two states among the plethora of wetting behaviors. Furthermore, transitions from the CB to the Wenzel state dictate completely different surface performance, such as anti-contamination, anti-icing, drag reduction etc.; however, little is known about how transition occurs during time between the several wetting modes. In this paper, wetting dynamics can be accurately quantified and tracked using solid–liquid triboelectrification. Theoretical underpinning reveals how surface micro-/nano-geometries regulate stability/infiltration, also demonstrating the generality of the authors’ theoretical approach in understanding wetting transitions. It can clarify the functioning behavior of materials in real environment.

Journal article

Hu S, Cao X, Reddyhoff T, Ding X, Shi X, Dini D, deMello AJ, Peng Z, Wang Zet al., 2022,

Pneumatic programmable superrepellent surfaces

, Droplet, Vol: 1, Pages: 48-55, ISSN: 2769-2159

Morphological transformation of surface structures is widely manifested in nature and highly preferred for many applications such as wetting interaction; however, in situ tuning of artificial morphologies independent of smart responsive materials remains elusive. Here, with the aid of microfluidics, we develop a pneumatic programmable superrepellent surface by tailoring conventional wetting materials (e.g., polydimethylsiloxane) with embedded flexible chambers connecting a microfluidic system, thus realizing a morphological transformation for enhanced liquid repellency based on a nature-inspired rigid-flexible hybrid principle (i.e., triggering symmetry breaking and oscillator coupling mechanisms). The enhancement degree can be in situ tuned within around 300 ms owing to pneumatically controllable chamber morphologies. We also demonstrate that the surface can be freely programmed to achieve elaborated morphological pathways and gradients for preferred droplet manipulation such as directional rolling and bouncing. Our study highlights the potential of an in situ morphological transformation to realize tunable wettability and provides a programmable level of droplet control by intellectualizing conventional wetting materials.

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Citations: 27

Journal article

Yap KK, Fukuda K, Vail JR, Wong J, Masen MAet al., 2022,

Spatiotemporal mapping for in-situ and real-time tribological analysis in polymer-metal contacts

, Tribology International, Vol: 171, Pages: 1-16, ISSN: 0301-679X

Spatiotemporal mapping (SMA) is a graphical technique to visualise the evolution of data with time and space during a process. This paper discusses the benefits of SMA in the field of polymer tribology via two highly different polymer/metal sliding systems. The SMA is found useful for the qualitative and quantitative characterisation and analysis of the transfer phenomena at the contact interface during repeated sliding, e.g., the slide-roll mechanism of transfer lumps, the severe-to-mild wear transition due to the tribo-chemical reaction of PTFE, the accumulation of wear debris, and the formation of friction-reducing back-transfer polyimide films. Additionally, the SMA helps spot various abnormal tribological behaviours, such as the local removal of oxides on a misaligned disc that would otherwise be overlooked.

Journal article

Ueda M, Kadiric A, Spikes H, 2022,

Influence of PMA on the anti-scuffing properties of AW/EP additives

, Tribology International, Vol: 174, Pages: 1-11, ISSN: 0301-679X

Scuffing is becoming a quite common failure mode in gears and bearings. It has been shown that AW/EP additives are effective in preventing scuffing, but only if they are able to form a thick tribofilm before encountering severe scuffing-type conditions. This study has employed a contra-rotating, step-sliding speed scuffing test to explore the impact of PMAs on the ability of ZDDP and a commercial SP additive-containing package to prevent scuffing when subjected to immediately severe conditions. It is found that some PMAs can greatly enhance the anti-scuffing performance of these AW/EP additives. They do this by forming thick, adsorbed boundary films that can withstand high speed sliding conditions and protect the rubbing surfaces long enough for tribofilms to form.

Journal article

Yuan T, Zhan W, Jamal A, Dini Det al., 2022,

On the microstructurally driven heterogeneous response of brain white matter to drug infusion pressure

, Biomechanics and Modeling in Mechanobiology, Vol: 21, ISSN: 1617-7959

Delivering therapeutic agents into the brain via convection-enhanced delivery (CED), a mechanically controlled infusion method, provides an efficient approach to bypass the blood–brain barrier and deliver drugs directly to the targeted focus in the brain. Mathematical methods based on Darcy’s law have been widely adopted to predict drug distribution in the brain to improve the accuracy and reduce the side effects of this technique. However, most of the current studies assume that the hydraulic permeability and porosity of brain tissue are homogeneous and constant during the infusion process, which is less accurate due to the deformability of the axonal structures and the extracellular matrix in brain white matter. To solve this problem, a multiscale model was established in this study, which takes into account the pressure-driven deformation of brain microstructure to quantify the change of local permeability and porosity. The simulation results were corroborated using experiments measuring hydraulic permeability in ovine brain samples. Results show that both hydraulic pressure and drug concentration in the brain would be significantly underestimated by classical Darcy’s law, thus highlighting the great importance of the present multiscale model in providing a better understanding of how drugs transport inside the brain and how brain tissue responds to the infusion pressure. This new method can assist the development of both new drugs for brain diseases and preoperative evaluation techniques for CED surgery, thus helping to improve the efficiency and precision of treatments for brain diseases.

Journal article

Collard B, Giuliani F, Ingenbleek G, Verbist G, Dini Det al., 2022,

A fracture mechanics analysis of the micromechanical events in finite thickness fibre push-out tests

, Theoretical and Applied Fracture Mechanics, Vol: 121, Pages: 103441-103441, ISSN: 0167-8442

Understanding the micromechanical events of interfacial failure in fibre reinforced composites is vital to accurately characterising micromechanical properties and, consequently, the macroscopic properties of the composite. A fracture mechanics model of the fibre push-out test is developed, with an emphasis on the effect of sample thickness and residual stresses on the mechanisms of interfacial crack advancement. The model is applied to both a SiC-SiC ceramic matrix composite and a SiC-Ti metal matrix composite. The model demonstrates that previous assumptions about the micromechanical events of interfacial cracking are consistent with the measured values of interfacial fracture energy for ceramic matrix composites. Moreover, the model can identify the range of geometries for which different micromechanical cracking mechanisms occur simultaneously in a given material system. Identifying this range is important in choosing the sample geometry for fibre push-out testing because the interaction of advancing cracks affects the measurement of interfacial fracture energy by classical models.

Journal article

Campen S, Fong J, Song W, Wong Jet al., 2022,

Thermal degradation of n-hexadecane base oil and its impact on boundary friction and surface adsorption

, Tribology International, Vol: 170, ISSN: 0301-679X

The chemical and physical properties of lubricants can alter during use. High temperatures may cause thermal autooxidation of the base oil, which could impact the performance of lubricant additives. Here, the effect of high temperature on the properties of n-hexadecane base oil is investigated. n-Hexadecane undergoes an irreversible transition from high to low boundary friction at 122–134 °C when heated in air. FTIR, UV–vis and NMR spectroscopy indicate the presence of carbonyl- and hydroxyl-containing oxidation products (carboxylic acids, alcohols, esters, ketones and aldehydes). ATR-FTIR shows that iron carboxylates form exclusively inside and around the rubbed friction surface. QCM-D is used to investigate the adsorption of degradation products onto an iron(III) oxide surface and reveals that almost half the adsorbed mass is effectively irreversibly adsorbed.

Journal article

Dou P, Wu T, Luo Z, Yang P, Peng Z, Yu M, Reddyhoff Tet al., 2022,

A finite-element-aided ultrasonic method for measuring central oil film thickness in a roller-raceway tribo-pair

, Friction, Vol: 10, Pages: 944-962, 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

Dou P, Zheng P, Jia Y, Wu T, Yu M, Reddyhoff T, Liao W-H, Peng Zet al., 2022,

Ultrasonic measurement of oil film thickness in a four-layer structure for applications including sliding bearings with a thin coating

, NDT & E International, Pages: 102684-102684, ISSN: 0963-8695

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Journal article

Beamish S, Reddyhoff T, Hunter A, Dwyer-Joyce RSet al., 2022,

A method to determine acoustic properties of solids and its application to measuring oil film thickness in bearing shells of unknown composition

, MEASUREMENT, Vol: 195, ISSN: 0263-2241

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Citations: 1

Journal article

Zhang J, Ewen J, Spikes H, 2022,

Substituent effects on the mechanochemical response of zinc dialkyldithiophosphate

, Molecular Systems Design & Engineering, Vol: 7, Pages: 1045-1055, ISSN: 2058-9689

Mechanochemistry is known to play a key role in the function of some lubricant additives, such as the tribofilm growth of zinc dialkyldithiophosphate (ZDDP). This raises the intriguing possibility of tailoring the mechanochemical response of additives by modifying their alkyl substituents. Here, we study the tribofilm formation rate of ZDDPs containing several different alkyl groups on steel surfaces from a high-friction base oil. We use macroscale tribometer experiments under full-film elastohydrodynamic lubrication conditions to enable careful control of the temperature and stress during tribofilm growth. We show how the chain length and the presence of branches or bulky cycloaliphatic groups can lead to large differences in the temperature- and stress-dependencies of the tribofilm formation rate, which can be explained through variations in packing density, steric hindrance, and stress transmission efficiency. Our rate data are successfully fitted using the Bell model; a simple modification of the Arrhenius equation that is commonly employed to model the kinetics of mechanochemical processes. Using this model, we observe large differences in the activation energy, pre-exponential factor, and activation volume for the various ZDDPs. Our findings show how structure–performance relationships can be identified for lubricant additives, which may be useful to optimise their molecular structure.

Journal article

Ewen J, Maffioli L, Smith E, Daivis P, Dini D, Todd Bet al., 2022,

Slip and stress from low strain-rate nonequilibrium molecular dynamics: The transient-time correlation function technique

, The Journal of Chemical Physics, Vol: 156, Pages: 1-11, ISSN: 0021-9606

We derive the transient-time correlation function (TTCF) expression for the computation of phase variables of inhomogenous confined atomistic fluids undergoing boundary-driven planar shear (Couette) flow at constant pressure. Using nonequilibrium molecular dynamics simulations, we then apply the TTCF formalism to the computation of the shear stress and the slip velocity for atomistic fluids at realistic low shear rates, in systems under constant pressure and constant volume. We show that, compared to direct averaging of multiple trajectories, the TTCF method dramatically improves the accuracy of the results at low shear rates and that it is suitable to investigate the tribology and rheology of atomistically detailed confined fluids at realistic flow rates.

Journal article

Bikos D, Samaras G, Charalambides M, Cann P, Masen M, Hartmann C, Vieira J, Sergis A, Hardalupas Yet al., 2022,

Experimental and numerical evaluation of the effect of micro-aeration on the thermal properties of chocolate

, Food and Function, Vol: 13, Pages: 4993-5010, ISSN: 2042-6496

Thermal properties, such as thermal conductivity, specific heat capacity and latent heat, influence the melting and solidification of chocolate. The accurate prediction of these properties for micro-aerated chocolate products with varying levels of porosity ranging from 0% to 15% is beneficial for understanding and control of heat transfer mechanisms during chocolate manufacturing and food oral processing. The former process is important for the final quality of chocolate and the latter is associated with sensorial attributes, such as grittiness, melting time and flavour. This study proposes a novel multiscale Finite Element Model to accurately predict the temporal and spatial evolution of temperature across chocolate samples. The model is evaluated via heat transfer experiments at temperatures varying from 16 °C to 45 °C. Both experimental and numerical results suggest that the rate of heat transfer within the micro-aerated chocolate is reduced by 7% when the 15% micro-aerated chocolate is compared to its solid counterpart. More specifically, on average, the thermal conductivity decreased by 20% and specific heat capacity increased by 10% for 15% micro-aeration, suggesting that micro-pores act as thermal barriers to heat flow. The latter trend is unexpected for porous materials and thus the presence of a third phase at the pore’s interface is proposed which might store thermal energy leading to a delayed release to the chocolate system. The developed multiscale numerical model provides a design tool to create pore structures in chocolate with optimum melting or solidifying response.

Journal article

Rahman M, Shen L, Ewen J, Dini D, Smith Eet al., 2022,

The intrinsic fragility of the liquid-vapor interface: a stress network perspective

, Langmuir: the ACS journal of surfaces and colloids, Vol: 38, Pages: 4669-4679, ISSN: 0743-7463

The evolution of the liquid-vapour interface of a Lennard-Jones fluid is examined with molecular dynamics simulations using the intrinsic sampling method. Results suggest, in agreement with capillary wave theory, clear damping of the density profiles as the temperature is increased. We identify a linear variation of the space-filling nature (fractal dimension) of the stress-clusters at the intrinsic surface with increasing surface tension, or equivalently, with decreasing temperature. A percolation analysis of these stress networks indicates that the stress field is more disjointed at higher temperatures. This leads to more fragile interfaces that result in a reduction in surface tension at higher temperature.

Journal article

Kadiric A, Shore J, Christodoulias AI, Kolekar AS, Lockwood FEet al., 2022,

Prediction of electric vehicle transmission efficiency using a new thermally coupled lubrication model

, SAE Technical Papers, Pages: 1-20, ISSN: 0148-7191

We present a new method to predict the power losses in electric vehicle (EV) transmission systems using a thermally coupled gearbox efficiency model. Friction losses in gear teeth contacts are predicted using an iterative procedure to account for the thermal coupling between the tooth temperature, oil viscosity, film thickness, friction, and oil rheology during a gear mesh cycle. Crucially, the prediction of the evolution of the coefficient of friction (COF) along the path of contact incorporates measured lubricant rheological parameters as well as measured boundary friction. This allows the model to differentiate between nominally similar lubricants in terms of their impact on EV transmission efficiency. Bearing and gear churning losses are predicted using existing empirical relationships. The effects of EV motor cooling and heat transfers in the heat exchanger on oil temperature are considered. Finally, heat transfer to the surroundings is accounted for so that the evolution of gearbox temperature over any given drive cycle can be predicted. The general approach presented here is applicable to any automotive gearbox while incorporating features specific to EVs. The model predictions are compared to real road measurements made on a popular current EV, and good agreement is shown over a range of road conditions. It should be noted that at high input speeds, the current model somewhat overpredicts the gearbox losses due to limitations in existing empirical bearing and churning loss models. Analyses of transmission losses breakdown at constant input power show that at low speeds/high torques, it is the losses in the gear meshes and high-load bearings that are most significant whereas at high speeds/low torques the losses in high-speed input shaft bearings, as well as gear churning losses, become more important. It is shown that the gearbox losses can account for 15-25% of the overall power losses in an EV depending on road conditions; a much higher proportion than in

Journal article

Vladescu S-C, Tadokoro C, Miyazaki M, Reddyhoff T, Nagamine T, Nakano K, Sasaki S, Tsujii Yet al., 2022,

Exploiting the Synergy between Concentrated Polymer Brushes and Laser Surface Texturing to Achieve Durable Superlubricity

, ACS APPLIED MATERIALS & INTERFACES, Vol: 14, Pages: 15818-15829, ISSN: 1944-8244

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Citations: 10

Journal article

Desai N, Masen M, Cann P, Hanson B, Tuleu C, Orlu Met al., 2022,

Modernising Orodispersible Film Characterisation to Improve Palatability and Acceptability Using a Toolbox of Techniques

, PHARMACEUTICS, Vol: 14

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Citations: 2

Journal article

Yuan T, Gao L, Zhan W, Dini Det al., 2022,

Effect of particle size and surface charge on nanoparticles diffusion in the brain white matter

, Pharmaceutical Research, Vol: 39, Pages: 767-781, ISSN: 0724-8741

PurposeBrain disorders have become a serious problem for healthcare worldwide. Nanoparticle-based drugs are one of the emerging therapies and have shown great promise to treat brain diseases. Modifications on particle size and surface charge are two efficient ways to increase the transport efficiency of nanoparticles through brain-blood barrier; however, partly due to the high complexity of brain microstructure and limited visibility of Nanoparticles (NPs), our understanding of how these two modifications can affect the transport of NPs in the brain is insufficient.MethodsIn this study, a framework, which contains a stochastic geometric model of brain white matter (WM) and a mathematical particle tracing model, was developed to investigate the relationship between particle size/surface charge of the NPs and their effective diffusion coefficients (D) in WM.ResultsThe predictive capabilities of this method have been validated using published experimental tests. For negatively charged NPs, both particle size and surface charge are positively correlated with D before reaching a size threshold. When Zeta potential (Zp) is less negative than -10 mV, the difference between NPs’ D in WM and pure interstitial fluid (IF) is limited.ConclusionA deeper understanding on the relationships between particle size/surface charge of NPs and their D in WM has been obtained. The results from this study and the developed modelling framework provide important tools for the development of nano-drugs and nano-carriers to cure brain diseases.

Journal article

Heyes DM, Dini D, 2022,

Intrinsic viscuit probability distribution functions for transport coefficients of liquids and solids

, JOURNAL OF CHEMICAL PHYSICS, Vol: 156, ISSN: 0021-9606

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Citations: 1

Journal article

Jamal A, Yuan T, Galvan S, Castellano A, Riva M, Secoli R, Falini A, Bello L, Rodriguez y Baena F, Dini Det al., 2022,

Insights into infusion-based targeted drug delivery in brain: perspectives, challenges and opportunities

, International Journal of Molecular Sciences, Vol: 23, Pages: 3139-3139, ISSN: 1422-0067

Targeted drug delivery in the brain is instrumental in the treatment of lethal brain diseases, such as glioblastoma multiforme, the most aggressive primary central nervous system tumour in adults. Infusion-based drug delivery techniques, which directly administer to the tissue for local treatment, as in convection-enhanced delivery (CED), provide an important opportunity; however, poor understanding of the pressure-driven drug transport mechanisms in the brain has hindered its ultimate success in clinical applications. In this review, we focus on the biomechanical and biochemical aspects of infusion-based targeted drug delivery in the brain and look into the underlying molecular level mechanisms. We discuss recent advances and challenges in the complementary field of medical robotics and its use in targeted drug delivery in the brain. A critical overview of current research in these areas and their clinical implications is provided. This review delivers new ideas and perspectives for further studies of targeted drug delivery in the brain.

Journal article

Trovatelli M, Spediacci C, Castellano A, Bernardini A, Dini D, Malfassi L, Pieri V, Falini A, Ravasio G, Riva M, Bello L, Brizzola S, Zani DDet al., 2022,

Morphometric study of the ventricular indexes in healthy ovine BRAIN using MRI.

, BMC Veterinary Research, Vol: 18, Pages: 97-97, ISSN: 1746-6148

BACKGROUND: Sheep (Ovis aries) have been largely used as animal models in a multitude of specialties in biomedical research. The similarity to human brain anatomy in terms of brain size, skull features, and gyrification index, gives to ovine as a large animal model a better translational value than small animal models in neuroscience. Despite this evidence and the availability of advanced imaging techniques, morphometric brain studies are lacking. We herein present the morphometric ovine brain indexes and anatomical measures developed by two observers in a double-blinded study and validated via an intra- and inter-observer analysis. RESULTS: For this retrospective study, T1-weighted Magnetic Resonance Imaging (MRI) scans were performed at 1.5 T on 15 sheep, under general anaesthesia. The animals were female Ovis aries, in the age of 18-24 months. Two observers assessed the scans, twice time each. The statistical analysis of intra-observer and inter-observer agreement was obtained via the Bland-Altman plot and Spearman rank correlation test. The results are as follows (mean ± Standard deviation): Indexes: Bifrontal 0,338 ± 0,032 cm; Bicaudate 0,080 ± 0,012 cm; Evans' 0,218 ± 0,035 cm; Ventricular 0,241 ± 0,039 cm; Huckman 1693 ± 0,174 cm; Cella Media 0,096 ± 0,037 cm; Third ventricle ratio 0,040 ± 0,007 cm. Anatomical measures: Fourth ventricle length 0,295 ± 0,073 cm; Fourth ventricle width 0,344 ± 0,074 cm; Left lateral ventricle 4175 ± 0,275 cm; Right lateral ventricle 4182 ± 0,269 cm; Frontal horn length 1795 ± 0,303 cm; Interventricular foramen left 1794 ± 0,301 cm; Inte

Journal article

Yu M, Reddyhoff T, Dini D, Holmes A, O'Sullivan Cet al., 2022,

Acoustic emission enabled particle size estimation via low stress-varied axial interface shearing

, IEEE Transactions on Instrumentation and Measurement, Vol: 71, ISSN: 0018-9456

Acoustic emission (AE) refers to a rapid release of localized stress energy that propagates as a transient elastic wave and is typically used in geotechnical applications to study stick-slip during shearing, and breakage and fracture of particles. This article develops a novel method of estimating the particle size, an important characteristic of granular materials, using axial interface shearing-induced AE signals. Specifically, a test setup that enables axial interface shearing between a one-dimensional compression granular deposit and a smooth shaft surface is developed. The interface sliding speed (up to 3mm/s), the compression stress (0-135kPa), and the particle size (150μm-5mm) are varied to test the acoustic response. The start and end moments of a shearing motion, between which a burst of AE data is produced, are identified through the variation of the AE count rates, before key parameters can be extracted from the bursts of interests. Linear regression models are then built to correlate the AE parameters with particle size, where a comprehensive evaluation and comparison in terms of estimation errors is performed. For granular samples with a single size, it is found that both the AE energy related parameters and AE counts, obtained using an appropriate threshold voltage, are effective in differentiating the particle size, exhibiting low fitting errors. The value of this technique lies in its potential application to field testing, for example as an add-on to cone penetration test systems and to enable in-situ characterization of geological deposits.

Journal article

Bahshwan M, Gee M, Nunn J, Myant CW, Reddyhoff Tet al., 2022,

In situ observation of anisotropic tribological contact evolution in 316L steel formed by selective laser melting

, Wear, Vol: 490-491, Pages: 1-12, ISSN: 0043-1648

A consensus on the tribological performance of components by additive-versus conventional manufacturing has not been achieved; mainly because the tribological test set-ups thus far were not suited for investigating the underlying microstructure's influence on the tribological properties. As a result, utilization of additive manufacturing techniques, such as selective laser melting (SLM), for tribological applications remains questionable. Here, we investigate the anisotropic tribological response of SLM 316L stainless steel via in situ SEM reciprocating micro-scratch testing to highlight the microstructure's role. As-built 316L SLM specimens were compared against annealed wire-drawn 316L. We found that: (i) microgeometric conformity was the main driver for achieving steady-state friction, (ii) the anisotropic friction of the additively manufactured components is limited to the break-in and is caused by the lack of conformity, (iii) the cohesive bonds, whose strength is proportional to frictional forces, are stronger in the additively manufactured specimens likely due to the dislocation-dense, cellular structures, (iv) low Taylor-factor grains with large dimension stimulate microcutting in the form of long, thin sheets with serrated edges. These findings uncover some microstructurally driven tribological complexities when comparing additive to conventional manufacturing.

Journal article

Weiand E, Ewen J, Koenig P, Roiter Y, Page S, Angioletti-Uberti S, Dini Det al., 2022,

Coarse-grained molecular models of the surface of hair

, Soft Matter, Vol: 2022, ISSN: 1744-683X

We present a coarse-grained molecular model of the surface of human hair, which consists of a supported lipid monolayer, in the MARTINI framework. Using coarse-grained molecular dynamics (MD) simulations, we identify a lipid grafting distance that yields a monolayer thickness consistent with both atomistic MD simulations and experimental measurements of the hair surface. Coarse-grained models for fully-functionalised, partially damaged, and fully damaged hair surfaces are created by randomly replacing neutral thioesters with anionic sulfonate groups. This mimics the progressive removal of fatty acids from the hair surface by bleaching and leads to chemically heterogeneous surfaces. Using molecular dynamics (MD) simulations, we study the island structures formed by the lipid monolayers at different degrees of damage in vacuum and in the presence of polar (water) and non-polar (n-hexadecane) solvents. We also use MD simulations to compare the wetting behaviour of water and n-hexadecane droplets on the model surfaces through contact angle measurements, which are compared to experiments using virgin and bleached hair. The model surfaces capture the experimentally-observed transition of the hair surface from hydrophobic (and oleophilic) to hydrophilic (and oleophobic) as the level of bleaching damage increases. By selecting surfaces with specific damage ratios, we obtain contact angles from the MD simulations that are in good agreement with experiments for both solvents on virgin and bleached human hairs. To negate the possible effects of microscale curvature and roughness of real hairs on wetting, we also conduct additional experiments using biomimetic surfaces that are co-functionalised with fatty acids and sulfonate groups. In both the MD simulations and experiments, the cosine of the water contact angle increases linearly with the sulfonate group surface coverage with a similar slope. We expect that the proposed systems will be useful for future molecular dynamics si

Journal article

Ueda M, Wainwright B, Spikes H, Kadiric Aet al., 2022,

The effect of friction on micropitting

, Wear, Vol: 488-489, Pages: 1-13, ISSN: 0043-1648

Micropitting is a type of surface fatigue damage that occurs in rolling-sliding contacts operating under thin oil film conditions. It is caused by stress fluctuations, brought about by surface asperity interactions, which lead to initiation and propagation of numerous surface fatigue cracks and subsequent loss of material. Despite its increasing importance to gear and bearing reliability, the mechanisms of micropitting are poorly understood. This is particularly the case concerning the effects of friction on micropitting which are difficult to study under controlled conditions. This is because it is difficult to isolate the friction effects from other influential factors, in particular from the build-up of any anti-wear tribofilm and its subsequent effect on the running-in of counterface roughness that is known to strongly affect micropitting through its influence on severity of asperity stresses. This paper presents new data on the impact of friction on micropitting obtained using a new test methodology. Micropitting tests were conducted using a ball-on-disc MTM rig with the additional functionality to continuously monitor the growth of tribofilm during the test. Friction was varied by using custom-made oils containing different concentrations of MoDTC. Crucially, the effect of friction was isolated from the effect of counterface roughness running-in by introducing the MoDTC blend only after the running-in period was completed with a ZDDP solution alone. This approach eliminates the influence of MoDTC on ZDDP anti-wear tribofilm growth in early stages and hence ensures the same running-in takes place in each test. This gives similar asperity pressure history, regardless of the amount of MoDTC present.Resultsshow that friction has a very significant impact on micropitting; for example, the extent of micropitting was reduced by a factor of 10 when friction coefficient was reduced from about 0.1 to 0.04. Lower friction results in fewer surface cracks which grow at a s

Journal article

Ueda M, Spikes H, Kadiric A, 2022,

Influence of black oxide coating on micropitting and ZDDP tribofilm formation

, Tribology Transactions, Vol: 65, Pages: 1-21, ISSN: 1040-2004

Micropitting is a type of surface fatigue damage that occurs in rolling-sliding contacts operating under thin oil film conditions. Application of black oxide (BO) coating to steel rubbing surfaces has been suggested as a potential approach to alleviate micropitting. This paper confirms that BO coatings can prevent micropitting and identifies the predominant mechanism by which this occurs.Micropitting tests were carried out using ZDDP solutions in a ball on disc tribometer. Micropitting was preferentially generated on the smooth balls and this was completely prevented by applying a BO coating to the rougher discs, regardless of whether the balls were coated or not. In contrast, when the rough discs were not BO-coated, micropitting was consistently generated on both BO-coated and uncoated balls. BO coating has about one quarter the hardness of the steel used and was found to be very rapidly removed from the surface asperity peaks at the onset of rubbing, despite the presence of ZDDP. This resulted in an almost immediate and very large reduction of the surface roughness of the discs and this prevented high asperity stresses that would normally initiate and propagate the surface fatigue cracks leading to micropitting. Parallel measurement showed that BO did not suppress tribofilm growth, so the ZDDP was able to protect against adhesive wear while not promoting micropitting. The insights presented here can help with the design of components and lubricants that are effective in controlling both sliding wear and micropitting.

Journal article

Puhan D, Jiang S, Wong J, 2022,

Effect of carbon fiber inclusions on polymeric transfer film formation on steel

, Composites Science and Technology, Vol: 217, Pages: 1-10, ISSN: 0266-3538

High performance polymers (HPPs) with good tribological properties are commonly used in dry contacts, wheretheir tribological performance often depends on properties of polymeric transfer materials (transfer layers) oncounterfaces. Most HPPs suffer from high temperature degradation due to frictional heating, leading to excessivedeformation and wear. Incorporating thermally conducting fillers increases their thermal conductivity andmechanical strength. The impact of these fillers on formation and properties of transfer layers, however, isunclear. In this work the effect of short carbon fiber fillers (CFs) on the nature of the transfer layers andtribological performance of polyetheretherketone (PEEK) and polyetheretherketone-polybenzimidizole (PBP)against steel were investigated at temperature up to 300 ◦C. Transfer layers of CF reinforced PEEK and PBPcontain CF-related materials, resulting in a reduction of friction as compared to neat PEEK and PBP, especiallyaround the glass transition temperature of PEEK (Tg− PEEK) when the transfer layer is relatively thick. While theinclusion of CFs increases the bulk thermal conductivity of polymer composites, the average contact temperatureis not affected. Rather, local hot spots are generated. As a result, their transfer layers may have formed morereadily and have undergone more severe degradation than those from neat polymer. At 300 ◦C, the PBP + CFtransfer layer is thin possibly due to abrasion by CFs dislodged from the matrix. The improvement in the wearresistance due to CF inclusion is observed with PBP up to 300 ◦C due to its improved mechanical strength. PEEK+ CF however suffers higher wear than PEEK below Tg− PEEK. Above Tg− PEEK, a thick transfer layer is formed andthe wear of PEEK + CF reduces.

Journal article

Fellows AP, Puhan D, Wong J, Casford M, Davies Pet al., 2022,

Probing the nanoscale heterogeneous mixing in a high-performance polymer blend

, Polymers, Vol: 14, ISSN: 2073-4360

The blend of polyetheretherketone (PEEK) and polybenzimidazole (PBI) produces a high-performance blend (PPB) that is a potential replacement material in several industries due to its high temperature stability and desirable tribological properties. Understanding the nanoscale structure and interface of the two domains of the blend is critical for elucidating the origin of these desirable properties. Whilst achieving the physical characterisation of the domain structures is relatively uncomplicated, the elucidation of structures at the interface presents a significant experimental challenge. In this work, we combine atomic force microscopy (AFM) with an IR laser (AFM-IR) and thermal cantilever probes (nanoTA) to gain insights into the chemical heterogeneity and extent of mixing within the blend structure for the first time. The AFM-IR and nanoTA measurements show that domains in the blend are compositionally different from those of the pure PEEK and PBI polymers, with significant variations observed in a transition region several microns wide in proximity to domain boundary. This strongly points to physical mixing of the two components on a molecular scale at the interface. The versatility intrinsic to the combined methodology employed in this work provides nano- and microscale chemical information that can be used to understand the link between properties of different length scales across a wide range of materials.

Journal article

Charalambides M, Bikos D, Samaras G, Cann P, Masen M, Hartmann C, German J, Vieira J, Hardalupas Iet al., 2022,

Effect of structure on the mechanical and physical properties of chocolate considering time scale phenomena occuring during oral processing

, Food Structure, Vol: 31, Pages: 1-14, ISSN: 2213-3291

Micro-aeration has been employed by the chocolate industry as a texture and flavour modifier. However, the impact of micro-aeration on oral processing is still not well understood. This study quantifies the mechanical, thermal and tribological behaviour of chocolate materials of different porosity levels. These material properties were then linked to sensory data considering the temporal phenomena of the oral process. In-vivo mastication tests were utilised to define the level of fragmentation of chocolate and coupled with heat transfer numerical models to simulate the melting during oral processing. Micro-aeration affects all material properties resulting in lower fracture stresses, rapid melting and a lower friction coefficient. The sensory results showed that micro-aeration creates a perception of a softer, less sticky chocolate which melts fast inside the mouth, without compromising the sweetness perception. This research adopts an innovative multidisciplinary approach to the physics of chocolates, bringing together the fields of solid mechanics, heat transfer, tribology, and sensory analysis and employing engineering experimental and numerical approaches to provide a link between chocolate structure, material properties and sensory perception. The outcome can contribute a powerful design tool for controlling the perception of sensory attributes for specific chocolate composition.

Journal article

Dou P, Jia Y, Zheng P, Wu T, Yu M, Reddyhoff T, Peng Zet al., 2022,

Review of ultrasonic-based technology for oil film thickness measurement in lubrication

, Tribology International, Vol: 165, ISSN: 0301-679X

Lubricant film thickness is the most informative variable that reflects lubrication conditions and transmission efficiency in the mechanical equipment, therefore its measurement is highly important. Despite a large number of theoretical models that have been developed to describe the lubricant film, complexities and uncertainties in a real tribo-pair contact still hinder the implementation of accurate and robust methods of in-situ film thickness measurements. Recently, ultrasonic-based measurement has been widely studied, showing promising potential owing to its non-destructive characteristics, high sensitivity, and limited physical modifications. This paper comprehensively reviews basic principles of ultrasonic-based oil film measurement; summarizes progress on calculation models and associated signal processing methods; exhibits in-lab demonstrations and in-situ applications; and discusses key technical issues and possible solutions.

Book

Liskiewicz T, Dini D, 2022,

Fretting Wear and Fretting Fatigue: Fundamental Principles and Applications

Fretting Wear and Fretting Fatigue: Fundamental Principles and Applications takes a combined mechanics and materials approach, providing readers with a fundamental understanding of fretting phenomena, related modeling and experimentation techniques, methods for mitigation, and robust examples of practical applications across an array of engineering disciplines. Sections cover the underpinning theories of fretting wear and fretting fatigue, delve into experimentation and modeling methods, and cover a broad array of applications of fretting fatigue and fretting wear, looking at its impacts in medical implants, suspension ropes, bearings, heating exchangers, electrical connectors, and more.

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Journal article

Zhang J, Campen S, Wong J, Spikes Het al., 2022,

Oxidational wear in lubricated contacts – or is it?

, Tribology International, Vol: 165, Pages: 1-9, ISSN: 0301-679X

This study examines the influence of inert gas atmosphere on the wear behaviour of rubbing steel-on-steel contacts lubricated by two hydrocarbon base fluids, isooctane and hexadecane. It is found that for both fluids, wear and mean friction in nitrogen and argon atmospheres are considerably lower than in dry air. As the oxygen content in nitrogen is increased, mean friction and wear both increase, to level out above about 10% oxygen (an O2 partial pressure of 10 kPa). Raman analysis of rubbed surfaces shows the presence of a carbon film on surfaces rubbed in inert gas and at low O2 levels. This film is not observed at high O2 levels.These findings indicate that the prevailing model of oxidational wear in lubricated contacts, that states that wear is greater in air than in inert gas because of corrosion by oxygen, is largely incorrect. Instead, the deleterious effect of oxygen on lubricated wear is primarily due to it preventing the formation of a lubricious, carbon-based boundary film that is generated from hydrocarbon base fluids on rubbing steel surfaces in inert gas conditions.The ability of organic fuels and lubricants to form carbon-based films on rubbing steel surfaces in inert atmospheres may provide a mechanism for reducing friction and wear of fuel- and oil-lubricated machine components. The study also provides a platform from which to design lubricant formulations for use in inert atmospheres.

Journal article

Jamal A, Bernardini A, Dini D, 2022,

Microscale characterisation of the time-dependent mechanical behaviour of brain white matter

, JOURNAL OF THE MECHANICAL BEHAVIOR OF BIOMEDICAL MATERIALS, Vol: 125, ISSN: 1751-6161

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Citations: 6

Journal article

Ayestaran Latorre C, Moore J, Remias J, Spikes H, Dini D, Ewen Jet al., 2021,

Mechanochemistry of phosphate esters confined between sliding iron surfaces

, Communications Chemistry, Vol: 4, Pages: 1-11, ISSN: 2399-3669

The molecular structure of lubricant additives controls not only their adsorption and dissociation behaviour at the nanoscale, but also their ability to reduce friction and wear at the macroscale. Here, we show using nonequilibrium molecular dynamics simulations with a reactive force field that tri(s-butyl)phosphate dissociates much faster than tri(n-butyl)phosphate when heated and compressed between sliding iron surfaces. For both molecules, dissociative chemisorption proceeds through cleavage of carbon−oxygen bonds. The dissociation rate increases exponentially with temperature and stress. When the rate−temperature−stress data are fitted with the Bell model, both molecules have similar activation energies and activation volumes and the higher reactivity of tri(s-butyl)phosphate is due to a larger pre-exponential factor. These observations are consistent with experiments using the antiwear additive zinc dialkyldithiophosphate. This study represents a crucial step towards the virtual screening of lubricant additives with different substituents to optimise tribological performance.

Journal article

Navarro Acero P, Mohr S, Bernabei M, Fernández C, Dominguez B, Ewen Jet al., 2021,

Molecular simulations of surfactant adsorption on iron oxide from hydrocarbon solvents

, Langmuir: the ACS journal of surfaces and colloids, Vol: 37, Pages: 14582-14596, ISSN: 0743-7463

The performance of organic friction modifiers (OFMs) depends on their ability to adsorb onto surfaces and form protective monolayers. Understanding the relationship between OFM concentration in the base oil and the resulting surface coverage is important for improving lubricant formulations. Here, we use molecular dynamics (MD) simulations to study the adsorption of three OFMs─stearic acid (SA), glycerol monoostearate (GMS), and glycerol monooleate (GMO)─onto a hematite surface from two hydrocarbon solvents─n-hexadecane and poly(α-olefin) (PAO). We calculate the potential of mean force of the adsorption process using the adaptive biasing force algorithm, and the adsorption strength increases in the order SA < GMS < GMO. We estimate the minimum area occupied by OFM molecules on the surface using annealing MD simulations and obtained a similar hard-disk area for GMS and GMO but a lower value for SA. Using the MD results, we determine the adsorption isotherms using the molecular thermodynamic theory (MTT), which agree well with one previous experimental data set for SA on hematite. For two other experimental data sets for SA, lateral interactions between surfactant molecules need to be accounted for within the MTT framework. SA forms monolayers with lower surface coverage than GMO and GMS at low concentrations but also has the highest plateau coverage. We validate the adsorption energies from the MD simulations using high-frequency reciprocating rig friction experiments with different concentrations of the OFMs in PAO. For OFMs with saturated tailgroups (SA and GMS), we obtain good agreement between the simulations and the experiments. The results deviate for OFMs containing Z-unsaturated tailgroups (GMO) due to the additional steric hindrance, which is not accounted for in the current simulation framework. This study demonstrates that MD simulations, alongside MTT, are an accurate and efficient tool to predict adsorption isotherms at solid–liquid int

Book chapter

Boidi G, Grützmacher P, Varga M, da Silva MR, Gachot C, Dini D, Profito F, Machado Iet al., 2021,

Tribological performance of random sinter pores vs. deterministic laser surface textures: an experimental and machine learning approach

, Tribology, Editors: Pintaude, Cousseau

This work critically scrutinizes and compares the tribological performance of randomly distributed surface pores in sintered materials and precisely tailored laser textures produced by different laser surface texturing techniques. The pore distributions and dimensions were modified by changing the sintering parameters, while the topological features of the laser textures were varied by changing the laser sources and structuring parameters. Ball-on-disc tribological experiments were carried out under lubricated combined sliding-rolling conditions. Film thickness was measured in-situ through a specific interferometry technique developed for the study of rough surfaces. Furthermore, a machine learning approach based on the radial basis function method was proposed to predict the frictional behavior of contact interfaces with surface irregularities. The main results show that both sintered and laser textured materials can reduce friction compared to the untextured material under certain operating conditions. Moreover, the machine learning model was shown to predict results with satisfactory accuracy. It was also found that the performance of sintered materials could lead to similar improvements as achieved by textured surfaces, even if surface pores are randomly distributed and not precisely controlled.

Journal article

Xu Y, Balint DS, Dini D, 2021,

On the Origin of Plastic Deformation and Surface Evolution in Nano-Fretting: A Discrete Dislocation Plasticity Analysis

, MATERIALS, Vol: 14

Journal article

Amis A, Bartolo MK, Accardi M, Williams A, Newman S, Provaggi E, Dini D, Athwal Ket al., 2021,

Strength of interference screw fixation of meniscus prosthesis matches native meniscus attachments

, Knee Surgery Sports Traumatology Arthroscopy, Vol: 30, ISSN: 0942-2056

PurposeMeniscal surgery is one of the most common orthopaedic surgical interventions. Total meniscus replacements have been proposed as a solution for patients with irreparable meniscal injuries. Reliable fixation is crucial for the success and functionality of such implants. The aim of this study was to characterise an interference screw fixation system developed for a novel fibre-matrix-reinforced synthetic total meniscus replacement in an ovine cadaveric model.MethodsTextile straps were tested in tension to failure (n = 15) and in cyclic tension (70–220 N) for 1000 cycles (n = 5). The textile strap-interference screw fixation system was tested in 4.5 mm-diameter single anterior and double posterior tunnels in North of England Mule ovine tibias aged > 2 years using titanium alloy (Ti6Al4Va) and polyether-ether-ketone (PEEK) screws (n ≥ 5). Straps were preconditioned, dynamically loaded for 1000 cycles in tension (70–220 N), the fixation slippage under cyclic loading was measured, and then pulled to failure.ResultsStrap stiffness was at least 12 times that recorded for human meniscal roots. Strap creep strain at the maximum load (220 N) was 0.005 following 1000 cycles. For all tunnels, pull-out failure resulted from textile strap slippage or bone fracture rather than strap rupture, which demonstrated that the textile strap was comparatively stronger than the interference screw fixation system. Pull-out load (anterior 544 ± 119 N; posterior 889 ± 157 N) was comparable to human meniscal root strength. Fixation slippage was within the acceptable range for anterior cruciate ligament graft reconstruction (anterior 1.9 ± 0.7 mm; posterior 1.9 ± 0.5 mm).ConclusionThese findings show that the textile attachment-interference screw fixation system provides reliable fixation for a novel ovine meniscus implant, supporting

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, Vol: 21, Pages: 22489-22498, 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

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

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Citations: 3

Journal article

Boidi G, Grützmacher PG, Kadiric A, Profito FJ, Machado IF, Gachot C, Dini Det al., 2021,

Fast laser surface texturing of spherical samples to improve the frictional performance of elasto-hydrodynamic lubricated contacts

, Friction, Vol: 9, Pages: 1227-1241, ISSN: 2223-7704

Textured surfaces offer the potential to promote friction and wear reduction by increasing the hydrodynamic pressure, fluid uptake, or acting as oil or debris reservoirs. However, texturing techniques often require additional manufacturing steps and costs, thus frequently being not economically feasible for real engineering applications. This experimental study aims at applying a fast laser texturing technique on curved surfaces for obtaining superior tribological performances. A femtosecond pulsed laser (Ti:Sapphire) and direct laser interference patterning (with a solid-state Nd:YAG laser) were used for manufacturing dimple and groove patterns on curved steel surfaces (ball samples). Tribological tests were carried out under elasto-hydrodynamic lubricated contact conditions varying slide-roll ratio using a ball-on-disk configuration. Furthermore, a specific interferometry technique for rough surfaces was used to measure the film thickness of smooth and textured surfaces. Smooth steel samples were used to obtain data for the reference surface. The results showed that dimples promoted friction reduction (up to 20%) compared to the reference smooth specimens, whereas grooves generally caused less beneficial or detrimental effects. In addition, dimples promoted the formation of full film lubrication conditions at lower speeds. This study demonstrates how fast texturing techniques could potentially be used for improving the tribological performance of bearings as well as other mechanical components utilised in several engineering applications.

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