Friction Level Research Articles

The Environmental and Economic Importance of Mixed and Boundary Friction

One route to reducing global CO2 emissions is to improve the energy efficiency of machines. Even small improvements in efficiency can be valuable, especially in cases where an efficiency improvement can be realized over many millions of newly produced machines. For example, conventional passenger car combustion engines are being downsized (and also downspeeded). Increasingly, they are running on lower-viscosity engine lubricants (such as SAE 0W-20 or lower viscosity grades) and often also have stop–start systems fitted (to prevent engine idling when the vehicle is stopped). Some of these changes result in higher levels of mixed and boundary friction, and so accurate estimation of mixed/boundary friction losses is becoming of increased importance, for both estimating friction losses and wear volumes. Traditional approaches to estimating mixed/boundary friction, which employ real area of contact modelling, and assumptions such as the elastic deformation of asperities, are widely used, but recent experimental data suggest that some of these approaches underestimate mixed/boundary friction losses. In this paper, a discussion of the issues involved in reliably estimating mixed/boundary friction losses in machine elements is undertaken, highlighting where the key uncertainties lie. Mixed/boundary lubrication losses in passenger car and heavy-duty internal combustion engines are then estimated and compared with published data, and a detailed description of how friction is related to fuel consumption in these vehicles, on standard fuel economy driving cycles, is given. Knowing the amount of fuel needed to overcome mixed/boundary friction in these vehicles enables reliable estimates to be made of both the financial costs of mixed/boundary lubrication for today’s vehicles and their associated CO2 emissions, and annual estimates are reported to be approximately USD 290 billion with CO2 emissions of 480 million tonnes.

How are romantic cross-class relationships sustained?

How are romantic relationships across class maintained under broader conditions of class inequality? This article draws on in-depth interviews with 38 people who have partnered across class in Australia. It examines the emotional and interpersonal labour required to preserve such relationships within a highly differentiated class structure that is widely obscured in public and political life. We find, first, that for people in committed cross-class relationships where this difference was openly acknowledged, class difference was acutely felt and described in highly emotional, imprecise terms. Second, this heightened awareness of class difference stimulated elevated levels of class friction and class dissonance within these relationships. We detail these experiences, as they were narrated to us, before examining certain interviewees' efforts to understand and resolve these complexities. We highlight the collaborative work undertaken by one couple in particular to navigate feelings of class discomfort and class dissonance. Third, by focussing on the emotional terrain of intimate cross-class negotiations, we stress moments which have the potential to disrupt assumptions about class hierarchies and modes of moral distinction that take place within these relationships. Proceeding to tentatively valorise different forms of value-making and recognition within cross-class relationships, we also pay attention to the role of class in enabling this very capacity for adaptation.

Acceleration-based friction coefficient estimation of a rail vehicle using feedforward NN: validation with track measurements

Low friction can lead to poor adhesion conditions between the rail and wheel, which is detrimental to rail vehicle operation and safety. Up to date knowledge of the rail-wheel friction level is currently not available across rail networks, meaning planning mitigation strategies is difficult. This paper presents a real-time friction coefficient estimation algorithm based on a feed-forward neural network (FNN). Unlike conventional methods, the FNN does not depend on slip/adhesion curves or creep force models, and only requires wheelset longitudinal acceleration and speed. The wheelset acceleration and friction measurements are obtained by running a two-car rail vehicle on a friction-modified track with five different levels of friction conditions at four different vehicle speeds. Four different FNNs are trained for four speed conditions, and their estimation performance were validated by training multiple FNNs and testing them in each speed case using new sets of data. Validation results show that the average mean absolute errors from the four FNNs remains below 0.0083.

Effect of Surface Chemistry on the Squeeze-Thin Film and Friction of Boundary Films.

An approach combining adsorption characterization and lubricity effectiveness of amine-based friction modifier molecules has been performed using chemically controlled surfaces, coated either with cobalt or carbon, while keeping the surface roughness constant and sub-nanometric. Through squeeze measurements and numerical modeling, we have identified the mechanical properties of both adsorbed amine films, as a function of the surface on which they were formed. On the one hand, we were able to evidence that the fluid structuring at the vicinity of the adsorbed boundary film differed as a function of the latter mechanical properties, directly resulting from its molecular organization. On the other hand, we showed that the coverage ratio of the monolayer associated with the shear elastic modulus of the boundary film governed the friction level. Changing the surface chemistry while keeping the roughness constant controls the final organization in the boundary layer, the correlated mechanical properties, and the level of friction dissipation.

Numerical and experimental investigation of a new model of friction damper in diagonal brace under cyclic loading

Owing to the performance of prefabricated friction dampers, which are rapidly increasing, the resistance of structural systems against earthquakes increases and depreciates the energies generated by earthquakes in the structure. It is important to use passive control systems to control the vibrations of a structure at a single level. However, in the design, they cannot depreciate the incoming energy from earthquakes at different levels. Friction dampers focus on displacement variables and are mostly used in steel structures according to the rules of a Coulomb damper or a friction brake that converts kinetic energy into heat through friction. In this study, a new type of friction damper, called a flat cylindrical friction damper, was designed using brake pads in a diagonal brace. The performance and seismic resistance of this system, as well as the amount of energy loss, were investigated. In this study, 18 laboratory tests were conducted using the universal device to check the research variables, their hysteresis diagrams were shown, and the configuration of the damper was designed such that grooved bolt connections and twin steel cables of different sizes and thicknesses were used. Moreover, the way the internal and external components are placed in the damper is such that innovation in tension and pressure has been created. In addition, the movement of the cylindrical element in the damper increased the amount of friction, owing to the presence of two types of brake pads with friction coefficients of 0.11 and 0.16 and the bolt connections. This demonstrates the damper performance under different sliding forces at different friction levels. The geometric dimensions, thickness of the brake pad, number and size of bolts, diameter of cables, sliding force, and location of the damper were among the variables investigated in this study. Brake pads, steel cables, and bolt connections are important and economically affordable. The seismic performance of the intended frame was investigated using 80 different damper models and the placement of the research variables. The desired optimal models were modelled using Abaqus software, analysed, and designed. This system aims to reduce the relative horizontal displacement of floors and increase the amount of energy absorption. An increase in theaxial-force created in multiple loading cycles always causes damage to damper components and frames. In this study, we used a special multi-level geometry to reduce the axial-force created in the damper, the relative displacement of the frame, and damages in the elements, as well as increase the ductility. The results show that the friction surfaces of steel plates and brake pads is very high due to the displacement and damping of the cables. Additionally, with the consumption of energy and its absorption by the damper in cyclic loads, displacement is easily controlled. The seismic response of the structures in terms of frame and damper displacement, base shear forces, and energy absorption is also observed. Numerical studies confirmed that the intended damper is an independent seismic-resistant member in critical building structures when high seismic performance or seismic resilience during moderate and strong earthquakes is desirable.

Tribological behavior of DLC film models in base oils: Analysis of influence of sp3/sp2 ratio and hydrogen content

DLC coatings have been proven in formulated oils used in the automotive industry. The development of electric cars and its consequences on the future of the internal combustion engine makes it increasingly necessary that these coatings take their place in other applications where lubrication is generally of lower quality such as for example strips cold rolling where DLC shows significant potential both for production and finishing cold rolling. As a result, the interest of the behavior of these coatings in base oils takes on a new dimension. In this study, we explore the influence of the composition and the sp3/sp2 ratio on tribological behavior of DLC coatings in mineral and synthetic base oils. Hydrogenated DLC films deposited by conventional PECVD with various levels of hydrogen measured by Elastic Recoil Detection Analysis (ERDA) and non-hydrogenated DLC films deposited by PLD in the nanosecond mode (ns-PLD) and by cathodic arc evaporation, thus allowing to have different sp3/sp2 ratios confirmed by Multiwavelength Raman spectrometry, are tested and compared. The tests are performed on a ball-on-flat device with coated balls to better evaluate wear level. The behavior of highly hydrogenated DLC is of particular interest; with a very high level of durability in both base oils and friction level which comparatively varies between low and very low depending on the base oil.

Interfacial crack-tip fields in beaded fiber composites

Beaded fiber composites represent ingenious design strategies capable of resolving the conflicts between strength and toughness in most engineering materials. Although intermittent beading holds great potential for improving mechanical properties, the underlying mechanisms responsible for strengthening and toughening of beaded fiber composites are largely unknown. In this study, we explore near-tip fields of an interface crack between the fiber and the polymeric bead, which is associated with fiber-bead debonding in the course of fiber pullout. The post-yield strain softening followed by strain hardening of polymer matrix, and friction between the bead and matrix are accounted for in the numerical analyses. It is found that pullout of fibers leads to development of multiple shear bands near the tip of the interface crack between the fiber and bead, and coalescence of shear bands gives rise to a zone of high plastic strain. Compared with the low level of friction between the bead and matrix, the bead-matrix interface with high friction coefficient can generate a larger zone of high plastic strain, increasing the propensity of interfacial debonding between the fiber and bead. Furthermore, we have revealed the role of thin coating of carbon nanotubes (CNT). Adding a CNT coating on the fiber enables the emergence of a small zone of high plastic strain near the interface crack tip and reduces the shear stress levels, thereby delaying bead debonding. Additionally, the introduction of CNT coating facilitates stress transfer from the bead to fiber, leading to high pullout force. The findings of this study provide important mechanistic insight into the design principles of beaded fiber composites.

The (Un)ideal Physicist: How Humans Rely on Object Interaction for Friction Estimates.

To estimate object properties such as mass or friction, our brain relies on visual information to efficiently compute approximations. The role of sensorimotor feedback, however, is not well understood. Here we tested healthy adults (N = 79) in an inclined-plane problem, that is, how much a plane can be tilted before an object starts to slide, and contrasted the interaction group with observation groups who accessed involved forces by watching objects being manipulated. We created objects of different masses and levels of friction and asked participants to estimate the critical tilt angle after pushing an object, lifting it, or both. Estimates correlated with applied forces and were biased toward object mass, with higher estimates for heavier objects. Our findings highlight that inferences about physical object properties are tightly linked to the human sensorimotor system and that humans integrate sensorimotor information even at the risk of nonveridical perceptual estimates.

A Generalised Method for Friction Optimisation of Surface Textured Seals by Machine Learning

Friction behaviour is an important characteristic of dynamic seals. Surface texturing is an effective method to control the friction level without the need to change materials or lubricants. However, it is difficult to put the manual prediction of optimal friction reducing textures as a function of operating conditions into practice. Therefore, in this paper, we use machine learning techniques for the prediction of optimal texture parameters for friction optimisation. The application of pneumatic piston seals serves as an illustrative example to demonstrate the machine learning method and results. The analyses of this work are based on experimentally determined data of surface texture parameters, defined by the dimple diameter, distance, and depth. Furthermore friction data between the seal and the pneumatic cylinder are measured in different friction regimes from boundary over mixed up to hydrodynamic lubrication. A particular innovation of this work is the definition of a generalised method that guides the entire machine learning process from raw data acquisition to model prediction, without committing to only a few learning algorithms. A large number of 26 regression learning algorithms are used to build machine learning models through supervised learning to evaluate the suitability of different models in the specific application context. In order to select the best model, mathematical metrics and tribological relationships, like Stribeck curves, are applied and compared with each other. The resulting model is utilised in the subsequent friction optimisation step, in which optimal surface texture parameter combinations with the lowest friction coefficients are predicted over a defined interval of relative velocities. Finally, the friction behaviour is evaluated in the context of the model and optimal value combinations of the surface texture parameters are identified for different lubrication conditions.

Simulation of Filter-Cake Formations on Vertical and Inclined Wells Under Elevated Temperature and Pressure

Summary Drilling fluids consist of colloidal suspensions that are made up of solid particles suspended in liquid. The aqueous component of the drilling mud invades a permeable formation due to differential pressure, leaving solid deposits on the drilled formation walls, forming a filter cake. Typical drilling fluids should create a thin, slick filter cake and fluid loss control to seal permeable zones as swiftly as possible. Tight holes, elevated levels of rotational resistance and friction, wellbore obstruction, fluid loss into formations, suboptimal well-log data, and reservoir formation impairment result from thick filter cakes and excessive filtration. Controlling infiltration of fluids to establish a minimal, low-porosity filter cake is frequently required to avoid drilling and production issues. In this study, we used computational fluid dynamics (CFD) to model the development of filter cakes induced by pipe rotation in vertical and inclined wellbore walls under elevated temperature and pressure during deep drilling. Multiple tests validate the basic model for application in both shallow and deep drilling operations. By use of an Eulerian-Eulerian approach to describe drilling fluids as a binary-phase system, including particles in suspension in the non-Newtonian fluid, our research investigates the power-law and Herschel-Bulkley rheological models. These models successfully predict the flow pattern of drilling fluid at the bottom region of deep drilling operations. The study further explores filter-cake formation by examining the influence of overbalanced pressure on filter-cake thickness at various pressures. Drilling simulations, incorporating pipe rotation and eccentricity effects under realistic operating parameters, accurately project filter-cake thickness, aligning closely with experimental measurements and existing CFD literature in this domain.

Dynamic response analysis of linear motion stage with track roller guides

This paper aims at characterizing the role of preload, friction and mass on the dynamic response of the linear motion stage used in the laser marking machine for black granite. A single-axis linear motion stage model was realized in Creo Parametric® CAE software. The mechanism design option was used to create a virtual mechanism with simulation entities for stiffness, friction, mass, damping, and motors. The experimental design was accomplished using Minitab® software to create the Taguchi orthogonal array. The simulation experiments with different values of preload, friction, and mass were conducted. The results show that increasing the linear bearing preload reduced the settling time. Increased elastic deformation increased bearing rigidity, which ultimately helped reduce vibrations and hence settling time. Furthermore, lower levels of friction reduced sticking and slipping, which led to reduced vibration levels and therefore a lower settling time.

The realities of achieving a Smart, Sustainable, and Inclusive shopfloor in the age of Industry 5.0.

The employment of Industry 4.0 technologies in manufacturing has paved the way to interlinked machinery, shop floor flexibility and personalised production. However, despite the amplified level of productivity and efficiency, such advances may also take a toll on the operators’ skills and well-being. Over and above, worker diversification culminates in the novel ideology of Industry 5.0; where a triad is established between sustainability, human-centricity, and resilience within manufacturing. This broadens the horizon for worker diversification, especially for people with disabilities who may be estranged from the manufacturing shop floor due to an absence of accessibility, stigma, and other lingering challenges. In pursuit of comprehending these hurdles in the form of themes, a set of interviews were conducted with designers and engineers from a range of manufacturing companies, followed by a Reflexive Thematic Analysis Exercise. Three umbrella themes and eight sub-themes revealed an apparent level of friction between manufacturing engineers and the potential of recruiting operators with disabilities, a lack of design knowledge in creating inclusive workstations, and an absence of social sustainability with respect to disability employment in manufacturing. Accordingly, two major areas for future work by engineers, designers and academics are also proposed.

Analisis Karakteristik dan Tingkat Hambatan Samping Ruas Jalan D.I. Panjaitan Kota Kendari

Progress inland transportation has not escaped the emergence of new problems from environmental aspects, accidents, and congestion. Traffic congestion occurs due to the imbalance between the growth of vehicles with improved infrastructure, rapid urbanization, low of discipline of road users, and side friction. Land use, type of road, and size of the city result in the characteristics and level of side friction. From these things, research on the analysis of characteristics and level of side friction on the D.I. Panjaitan Road section of Kendari City became interesting. The purpose of this study is to identify the characteristics of side friction and determine the level of side friction. From research and analysis, it was found that side friction that occurs at three observation points is generally caused by the type of activity of stopped vehicles, parking on street, and vehicles come into and exit from the parking area and coming into or leaving the neighborhood. Based on side friction frequency data at three observation points showed the lowest Side Friction Frequency (SFF) of 33.5 and 39.4 events at point T3, then 67.6 and 64.4 at point T2, and the highest at point T3 70.5 and 59.9 events. The data shows that the side friction class on the road is categorized is very low. The low side friction at the observation location is caused by the observation time carried out during the decline in community activities due to the implementation of health protocols due to the increase in Covid-19 cases

Incep-FrictionNet-Based Pavement Texture Friction Level Classification Prediction Method

Pavement skid resistance is crucial for driving safety, and pavement texture significantly impacts skid resistance performance. To realize the application of pavement texture data in assessing pavement skid resistance performance, this paper proposes a convolutional neural network model based on the InceptionV4 module to predict the pavement friction level from the pavement texture dataset. The surface texture data of indoor test-rutted slabs were collected using a portable laser scanner. The surface friction coefficient of rutted slabs was measured using a pendulum tribometer. After data pre-processing, a total of nine types of texture data that are in the range of 0.4 to 0.8 skid resistance levels are selected at an interval of 0.05 for training, validation, and testing of the network model. The same dataset and training parameters were also used to train a conventional convolutional network model for comparison. The results showed that the proposed network model achieved 97.89% classification accuracy on the test set, which was 11.94 percentage points higher than the comparison model. This demonstrates that the proposed model in this paper can evaluate pavement friction levels by non-contact scanning of textures and has higher evaluation accuracy.

The Cold-Brittleness Regularities of Low-Activation Ferritic-Martensitic Steel EK-181

The behavior of the EK-181 low-activation ferritic-martensitic reactor steel (Fe–12Cr–2W–V–Ta–B) in the states with different levels of strength and plastic properties after traditional heat treatment (THT) and after high-temperature thermomechanical treatment (HTMT) in the temperature range from −196 to 25 °C, including the range of its cold brittleness (ductile–brittle transition temperature, DBTT) is studied. The investigations are carried out using non-destructive acoustic methods (internal friction, elasticity) and transmission and scanning electron microscopy methods. It is found that the curves of temperature dependence of internal friction (the vibration decrement) of EK-181 steel after THT and HTMT are similar to those of its impact strength. Below the ductile–brittle transition temperature, it is characterized by a low level of dislocation internal friction. The temperature dependence curves of the steel elastic modulus increase monotonically with the decreasing temperature. In this case, the value of Young’s modulus is structure-sensitive. A modification of the microstructure of EK-181 steel as a result of HTMT causes its elastic modulus to increase, compared to that after THT, over the entire temperature range under study. The electron microscopic studies of the steel microstructure evolution near the fracture surface of the impact samples (in the region of dynamic crack propagation) in the temperature range from −196 to 100 °C reveal the traces of plastic deformation (increased dislocation density, fragmentation of the martensitic structure) at all of the temperatures under study, including those below the cold brittleness threshold of EK-181 steel.

Friction in orthodontics

Friction is a fundamental aspect of orthodontic movement. Researchers and clinicians must be acquainted with its biomechanical and physical principles, as well as the potential alterations that may occur with the use of diverse materials. This literature review presents an approach of the physical principles at work in frictional mechanics, an analysis of the friction, at macro and microscopic level, of different orthodontic materials; describes the influence of friction on tooth movement and presents an update on friction research and its relationship to various materials.

Design friction in autonomous drive—exploring transitions between autonomous and manual drive in non-urgent situations

In the ongoing turn to automation, the growing trend towards the design of conditionally and highly automated vehicles (C/HAV) is evident. In a CAV, the driver no longer needs to partake in the driving. However, the vehicle might send a takeover request (TOR) when the CAV’s system reaches its operational boundaries, i.e. a call for a transition from autonomous to manual drive. Previous research on TORs has focused on the context of urgent situations, e.g. hazards and unpredictable events. Furthermore, it has been noted that drivers’ situation awareness (SA) deteriorates after being in autonomous drive. However, less is known about TORs in non-urgent situations. Motivated by this need, the study explores how design friction can serve as a guiding concept for transferring control between autonomous and manual drive in non-urgent situations to increase situation awareness. Design friction is defined as elements of interactions that steer attention and guides the driver to take informed decisions. The work resulted in prototypes that leveraged design friction as part of a takeover sequence. The proposed design was empirically evaluated in a fixed-base medium-fidelity driving simulator. The results indicated that the level of friction might have been too extensive, as some annoyance was expressed. However, participants claimed to feel calm and aware of their surroundings at the moment of regaining control of the vehicle. This suggests that design friction is a promising tool for guiding concept design to enhance transitions from autonomous to manual drive.

Total mesialization of the mandibular dentition using amini-implant-supported device : Afinite element analysis.

Total mandibular arch mesialization using mini-implants is challenging due to anatomic limitations. The aim of this study was to introduce amini-implant-supported device for total mesialization of the mandibular dentition and to analyze the biomechanical properties of the device. Finite element models were constructed to explore the effect of friction and force direction on the force transmission efficiency of the device. In addition, the three-dimensional displacement of each tooth was evaluated with two force application points (2 or 8 mm hooks) under three force conditions (symmetric: 150 g of force on both sides, or asymmetric: 100 and 200 g of force on each side). The force transmission efficiency was 66.7% under afriction coefficient of 0.15 and parallel pushing and pulling forces. The force transmission efficiency was 65.90 and 66.63% when the pushing force was 15° away from the pulling force on the sagittal and horizontal planes, respectively. The mandibular dentition moved mesially with agreater tendency for incisor labial crown tipping, mesial molar rotation and buccal second molar crown tipping when using the 8 mm hook compared to that when using the 2 mm hook. Rigid archwires resulted in more consistent tooth mesialization than stainless steel archwires. Asymmetric forces resulted in asymmetric dental arch mesialization. The forces transmitted by the presented mini-implant-supported device varied depending on the friction level and force direction. The device should be able to achieve symmetric or asymmetric total mesialization of the mandibular dentition.

Mechanical seal friction condition monitoring based on bispectral characteristics

PurposeThe purpose of this paper is to investigate the monitoring of the friction condition of mechanical seals.Design/methodology/approachAcoustic emission signals from the friction of the seal end face were obtained, and their bispectral characteristics were extracted. The variation of non-Gaussian information with the degree of friction was investigated, and by combining bispectral characteristics with information entropy, a bispectral entropy index was established to represent the friction level of the seal end face.FindingsIn the start-up stage, the characteristic frequency amplitude of the micro-convex body contact is obvious, the friction of the end face is abnormal, the complexity of the system increases in a short time and the bispectral entropy rises continuously in a short time. In the stable operation stage, the characteristic frequency amplitude of the micro-convex body contact varies with the intensity of the seal face friction, the seal face friction is stable and the bispectral entropy fluctuates up and down for a period of time.Originality/valueThe bispectral analysis method is applied to the seal friction monitoring, the seal frequency domain characteristics are extracted, the micro-convex body contact characteristic frequency is defined and the bispectral entropy characteristic index is proposed, which provides a certain theoretical basis for the mechanical seal friction monitoring.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2023-0242/

Friction Coefficient Dynamics of Tribological Coatings from Engine Lubricants: Analysis and Interpretation

Even today, there is no full understanding of the relationship between the physical, chemical, and mechanical properties and the behavior of the lubricating films formed in tribological systems. Most of the published scientific research measures and reports the overall values of friction and wear, but the information given via statistical signals in the tribological tests is, in general, dismissed, leaving a hole in the study of the dynamics of tribological systems. In this work, an experimental study of statistical friction data, coating characteristics, and tribological performance is carried out using a pin-on-disk tribometer to test some metallic samples coated with lubricant films under several experimental conditions. The results indicate that long deposition times at high deposition temperatures of coatings from engine oil develop low-friction intervals, which fall until 20% of the uncoated coefficient friction. However, an unexpected and unfavorable behavior of the coatings was observed for the short deposition times and high temperature. In these conditions, the developed friction profiles reached a maximum level of friction that was 20% more than the uncoated coefficient friction. Moreover, it was found that the proper analysis and interpretation of the statistical data, in combination with the characterization of the coatings, describes the dynamics of the interactions between the bodies in contact and reveals the transitions of the surfaces with non-homogeneous properties throughout their depth.