Imperial College London

ProfessorDanieleDini

Faculty of EngineeringDepartment of Mechanical Engineering

Professor in Tribology
 
 
 
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Contact

 

+44 (0)20 7594 7242d.dini Website

 
 
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Location

 

669City and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

400 results found

Feng Z, Yu M, Evangelou S, Jaimoukha I, Dini Det al., 2022, Feedforward PID Control of Full-Car with Parallel Active Link Suspension for Improved Chassis Attitude Stabilization, IEEE Conference on Control Technology and Applications

Conference paper

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

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, ISSN: 0021-9606

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, Pages: 111643-111643, ISSN: 0020-7683

Journal article

Heyes DM, Dini D, 2022, Intrinsic viscuit probability distribution functions for transport coefficients of liquids and solids., J Chem Phys, Vol: 156

A reformulation of the Green-Kubo expressions for the transport coefficients of liquids in terms of a probability distribution function (PDF) of short trajectory contributions, which were named "viscuits," has been explored in a number of recent publications. The viscuit PDF, P, is asymmetric on the two sides of the distribution. It is shown here using equilibrium 3D and 2D molecular dynamics simulations that the viscuit PDF of a range of simple molecular single component and mixture liquid and solid systems can be expressed in terms of the same intrinsic PDF (P0), which is derived from P with the viscuit normalized by the standard deviation separately on each side of the distribution. P0 is symmetric between the two sides and can be represented for not very small viscuit values by the same gamma distribution formulated in terms of a single disposable parameter. P0 tends to an exponential in the large viscuit wings. Scattergrams of the viscuits and their associated single trajectory correlation functions are shown to distinguish effectively between liquids, solids, and glassy systems. The so-called viscuit square root method for obtaining the transport coefficients is shown to be a useful probe of small and statistically zero self-diffusion coefficients of molecules in the liquid and solid states, respectively. The results of this work suggest that the transport coefficients have a common underlying physical origin, reflecting at a coarse-grained level the traversal statistics of the system through its high-dimensioned potential energy landscape.

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, ISSN: 0724-8741

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

Xu Y, Balint D, Greiner C, Dini Det al., 2022, On the origin of plasticity-induced microstructure change under sliding contacts, Friction, ISSN: 2223-7704

Discrete dislocation plasticity (DDP) calculations are carried out to investigate the response of a single crystal contacted by a rigid sinusoidal asperity under sliding loading conditions to look for causes of microstructure change in the dislocation structure. The mechanistic driver is identified as the development of lattice rotations and stored energy in the subsurface, which can be quantitatively correlated to recent tribological experimental observations. Maps of surface slip initiation and substrate permanent deformation obtained from DDP calculations for varying contact size and normal load suggest ways of optimally tailoring the interface and microstructural material properties for various frictional loads.

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

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

Patino Ramirez F, Dini D, O'Sullivan C, 2022, Explaining the Response of Granular Materials to Shear Deformation Using Statistics and Network Analysis

Working paper

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

Yu M, Evangelou S, Dini D, 2021, Parallel active link suspension: full car application with frequency-dependent multi-objective control strategies, IEEE Transactions on Control Systems Technology, 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

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

Book chapter

Xu Y, Balint D, Dini D, 2021, On the origin of plastic deformation and surface evolution in nano-fretting: a discrete dislocation plasticity analysis, Materials, Vol: 14, Pages: 1-14, ISSN: 1996-1944

Discrete dislocation plasticity (DDP) calculations were carried out to investigate a single-crystal response when subjected to nano-fretting loading conditions in its interaction with a rigid sinusoidal asperity. The effects of the contact size and preceding indentation on the surface stress and profile evolution due to nano-fretting were extensively investigated, with the aim to unravel the deformation mechanisms governing the response of materials subjected to nano-motion. The mechanistic drivers for the material’s permanent deformations and surface modifications were shown to be the dislocations’ collective motion and piling up underneath the contact. The analysis of surface and subsurface stresses and the profile evolution during sliding provides useful insight into damage and failure mechanisms of crystalline materials subject to nano-fretting; this can lead to improved strategies for the optimisation of material properties for better surface resistance under micro- and nano-scale contacts.

Journal article

Jamal A, Bernardini A, Dini D, 2021, 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

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, 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

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.

Journal article

Wang X, Bao L, Wen J, Dini D, Zhang J, Sun L, Yang W, Zhou F, Liu Wet al., 2021, Anomalous boundary behavior in non-newtonian fluids at amphiphobic surfaces, Tribology International, Vol: 165, Pages: 1-7, ISSN: 0301-679X

In this work, the effect of amphiphobic surfaces on the rheological behavior and boundary slip of the shear thickening fluids (STFs) was investigated. The experimental results suggested the viscosities were diminished, shear thickening was delayed and weakened, and an ultrahigh drag reduction was obtained. Furthermore, slip length was observed to vary with shear rate. Dissipative particle dynamics (DPD) simulations were adopted to further investigate these specific rheology and slip behavior. The simulation results conformed with experiments and established a linear relationship between the slip length and viscosity. We consider this study could be a conducive practical reference for the investigation of boundary slip in complex fluids and possibly a crucial protocol for analyzing STFs’ manipulation.

Journal article

Vidotto M, Bernardini A, Trovatelli M, De Momi E, Dini Det al., 2021, On the microstructural origin of brain white matter hydraulic permeability, Proceedings of the National Academy of Sciences of USA, Vol: 118, ISSN: 0027-8424

Brain microstructure plays a key role in driving the transport of drug molecules directly administered to the brain tissue, as in Convection-Enhanced Delivery procedures. The proposed research analyzes the hydraulic permeability of two white matter (WM) areas (corpus callosum and fornix) whose three-dimensional microstructure was reconstructed starting from the acquisition of electron microscopy images. We cut the two volumes with 20 equally spaced planes distributed along two perpendicular directions, and, on each plane, we computed the corresponding permeability vector. Then, we considered that the WM structure is mainly composed of elongated and parallel axons, and, using a principal component analysis, we defined two principal directions, parallel and perpendicular, with respect to the axons’ main direction. The latter were used to define a reference frame onto which the permeability vectors were projected to finally obtain the permeability along the parallel and perpendicular directions. The results show a statistically significant difference between parallel and perpendicular permeability, with a ratio of about two in both the WM structures analyzed, thus demonstrating their anisotropic behavior. Moreover, we find a significant difference between permeability in corpus callosum and fornix, which suggests that the WM heterogeneity should also be considered when modeling drug transport in the brain. Our findings, which demonstrate and quantify the anisotropic and heterogeneous character of the WM, represent a fundamental contribution not only for drug-delivery modeling, but also for shedding light on the interstitial transport mechanisms in the extracellular space.

Journal article

Bhamra J, Ewen J, Ayestaran Latorre C, Bomidi J, Bird M, Dasgupta N, van Duin A, Dini Det al., 2021, Interfacial bonding controls friction in diamond–rock contacts, The Journal of Physical Chemistry C: Energy Conversion and Storage, Optical and Electronic Devices, Interfaces, Nanomaterials, and Hard Matter, Vol: 125, Pages: 18395-18408, ISSN: 1932-7447

Understanding friction at diamond–rock interfaces is crucial to increase the energy efficiencyof drilling operations. Harder rocks usually are usually more difficult to drill; however, poorperformance is often observed for polycrystalline diamond compact (PDC) bits on soft calcitecontaining rocks, such as limestone. Using macroscale tribometer experiments with adiamond tip, we show that soft limestone rock (mostly calcite) gives much higher frictioncoefficients compared to hard granite (mostly quartz) in both humid air and aqueousenvironments. To uncover the physicochemical mechanisms that lead to higher kinetic frictionat the diamond–calcite interface, we employ nonequilibrium molecular dynamics simulations(NEMD) with newly developed Reactive Force Field (ReaxFF) parameters. In the NEMDsimulations, higher friction coefficients are observed for calcite than quartz when watermolecules are included at the diamond–rock interface. We show that the higher friction inwater-lubricated diamond–calcite than diamond–quartz interfaces is due to increasedinterfacial bonding in the former. For diamond–calcite, the interfacial bonds mostly formthrough chemisorbed water molecules trapped between the tip and the substrate, while mainlydirect tip-surface bonds form inside diamond–quartz contacts. For both rock types, the rate ofinterfacial bond formation increases exponentially with pressure, which is indicative of astress-augmented thermally activated process. The mean friction force is shown to be linearlydependant on the mean number of interfacial bonds during steady-state sliding. Theagreement between the friction behaviour observed in the NEMD simulations and tribometerexperiments suggests that interfacial bonding also controls diamond–rock friction at themacroscale. We anticipate that the improved fundamental understanding provided by thisstudy will assist in the development of bit materials and coatings to minimise friction byre

Journal article

Gamaniel SS, Dini D, Biancofiore L, 2021, The effect of fluid viscoelasticity in lubricated contacts in the presence of cavitation, Tribology International, Vol: 160, ISSN: 0301-679X

In this work we study the influence of fluid viscoelasticity on the performance of lubricated contacts in the presence of cavitation. Several studies of viscoelastic lubricants have been carried out, but none of them have considered the possibility of the presence of cavitation. To describe the effect of viscoelasticity, we use the Oldroyd-B model. By assuming that the product between ϵ, i.e. the ratio between vertical and horizontal length scales, and the Weissenberg number (Wi), i.e. the ratio between polymer relaxation time and flow time scale, is small, we can linearise the viscoelastic thin film equations, following the approach pioneered by "Tichy, J., 1996, Non-Newtonian lubrication with the convected Maxwell model." Consequently, the zeroth-order in ϵWi corresponds to a Reynolds equation modified to describe also the film cavitation through the mass-conserving Elrod-Adams model. We consider the flow of viscoelastic lubricants using: (i) a cosine profile representing a journal bearing unwrapped geometry, and (ii) a pocketed profile to model a textured surface in lubricated contacts. The introduction of viscoelasticity decreases the length of cavitated region in the cosine profile due to the increasing pressure distribution within the film. Consequently, the load carrying capacity increases with Wi by up to 50% in the most favorable condition, confirming the beneficial influence of the polymers in bearings. On the other hand for the pocketed profile, results show that the load can increase or decrease at higher Wi depending on the texture position in the contact. The squeeze flow problem between two plates is also modeled for viscoelastic lubricants considering an oscillating top surface. For this configuration a load reduction is observed with increasing Wi due to the additional time needed to reform the film at high Wi. Furthermore, if viscoelastic effects increase, the cavitation region widens until reaching a value of Wi for which a full-film ref

Journal article

Yu M, Cheng C, Evangelou S, Dini Det al., 2021, Series active variable geometry suspension: full-car prototyping and road testing, IEEE-ASME Transactions on Mechatronics, ISSN: 1083-4435

In this paper, afull-car prototype of the recently proposed mechatronic suspension, Series Active Variable Geometry Suspension (SAVGS), is developed for on-road driving experimental proof of concept, aiming to be adopted by suspension OEMs (original equipment manufacturers) as an alternative solution to fully active suspensions. Particularly, mechanical modifications are performed to both corners of the front double-wishbone suspensionof a production car, with active single-links attached to the upper-ends of the spring-damper units, while both corners of the rear suspension remain inthe original (passive) configurations.The mechanical modifications involve innovatively designed parts to enable the desired suspension performance improvements, while maintaining ride harshness at conventional levels.Areal-time embedded system is further developed to primarily implement:1) power supply, data acquisition and measurementsof the vehicle dynamics related variables, and 2) robust control application for the ride comfort and road holding enhancement, which is based on a derived linearized model of the full-car dynamics and a newly synthesizedH-infinity control scheme. Results obtained from on-road driving experiments are inessential agreement with numerical simulation results also produced. Overall, the full-car prototypeof SAVGS demonstrates promising suspension performance,with anaverage 3 dB attenuation (or equivalently 30% reduction) of the chassis vertical acceleration at aroundthe human-sensitive frequencies (2-5Hz),as compared to the original vehicle with the passive suspension system. More importantly, the prototype also indicatesthe practicality of the solution, as the SAVGS retrofit to a real car is achieved by simple mechanical modifications, compact actuator packaging, smallmass increment(21.5kg increase with respect to the original vehicle), limited power usage

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

Wen J, Dini D, Hu H, Smith ERet al., 2021, Molecular droplets vs bubbles: Effect of curvature on surface tension and Tolman length, PHYSICS OF FLUIDS, Vol: 33, ISSN: 1070-6631

Journal article

Terzano M, Spagnoli A, Dini D, Forte AEet al., 2021, Fluid-solid interaction in the rate-dependent failure of brain tissue and biomimicking gels, Journal of The Mechanical Behavior of Biomedical Materials, Vol: 119, ISSN: 1751-6161

Brain tissue is a heterogeneous material, constituted by a soft matrix filledwith cerebrospinal fluid. The interactions between, and the complexity of eachof these components are responsible for the non-linear rate-dependent behaviourthat characterizes what is one of the most complex tissue in nature. Here, weinvestigate the influence of the cutting rate on the fracture properties ofbrain, through wire cutting experiments. We also present a model for therate-dependent behaviour of fracture propagation in soft materials, whichcomprises the effects of fluid interaction through a poro-hyperelasticformulation. The method is developed in the framework of finite straincontinuum mechanics, implemented in a commercial finite element code, andapplied to the case of an edge-crack remotely loaded by a controlleddisplacement. Experimental and numerical results both show a toughening effectwith increasing rates, which is linked to the energy dissipated by thefluid-solid interactions in the process zone ahead of the crack.

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

Boidi G, Profito FJ, Kadiric A, Machado IF, Dini Det al., 2021, The use of Powder Metallurgy for promoting friction reduction under sliding-rolling lubricated conditions, Tribology International, Vol: 157, ISSN: 0301-679X

This work exploits the use of different sintering manufacturing techniques for obtaining superior performances in lubricated point contacts. Disc and ball specimens were manufactures varying porosity and pore characteristics. The effect of surface pores in sintered materials was evaluated based on the frictional behaviour under different sliding-rolling conditions and lubrication regimes. Furthermore, lubricant film thicknesses were measured using interferometric technique. Test results showed that the decrease of porosity generally improves tribological performance. Low porosity surfaces can promote friction reduction compared to non-porous reference materials in specific configurations and operating with similar specific lubricant thickness values. This work contributes to an improved understanding of how randomly distributed micro-irregularities could change lubrication conditions, potentially increasing the efficiency of lubricated mechanical systems.

Journal article

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