Friction Measurements Research Articles

Friction hysteretic behavior of supported atomically thin nanofilms

Hysteretic friction behavior has been observed on varied 2D nanofilms. However, no unanimous conclusion has yet been drawn on to the exact mechanism or relative contribution of each mechanism to the observed behavior. Here we report on hysteretic friction behavior of supported atomically thin nanofilms studied using atomic force microscopy (AFM) experiments and molecular dynamics (MD) simulations. Load dependent friction measurements were conducted on unheated and heated samples of graphene, h-BN, and MoS2 supported by silica substrates. Two diverging friction trends are reported: the unheated samples showed higher friction during unloading than during loading, and the heated samples showed a reversed hysteresis. Further, the friction force increased sub-linearly with normal force for heated samples, compared with unheated samples. Tapping mode AFM suggested that the interaction strength of the substrate was increased with heating. Roughened substrates in the MD simulations that mimicked strong/weak interaction forces reproduced the experimental observations and revealed that the evolution of real contact area in different interface interaction situation caused the diverging behaviors. Surface roughness and interaction strength were found to be the key parameters for controlling the out-of-plane deformation of atomically thin nanofilms.

Protein-induced delubrication: How plant-based and dairy proteins affect mouthfeel

Understanding how certain proteins cause astringency is necessary in order to improve the mouthfeel and popularity of plant-based foods. To this end, we studied protein interactions during oral processes using a PDMS-PDMS interface lubricated by ex-vivo human saliva. Friction measurements and in-contact imaging were implemented, while food consumption was simulated by introducing model plant and animal-based proteins. All but one of the protein samples caused an increase in measured friction and this correlated with astringency ratings from a human taste panel. This is attributed to delubrication as the salivary pellicle is removed, since food proteins interact with salivary proteins thus disrupting their adhesion. This interaction is shown to occur both on the surface and in the bulk of the fluid. However, the debonding of the pellicle requires frictional shear stress (i.e., rubbing) . Food proteins in isolation are themselves shown to be surface-active and form boundary films, which can adhere following removal of the pellicle. The mechanical action of protein particles in the delubrication process was isolated by filtering and shown to account for a moderate (<33%) increase in friction magnitude accompanied by a significant (>90%) increase in frictional noise. The flow and deformation of these particles was also visualised thus demonstrating how the microscale breakdown of food can be studied. • Tribological measurements combined with in-contact fluorescence imaging were used to study the breakdown of the salivary pellicle by food proteins within a simulated tongue-palate interface. • During salivary pellicle formation, salivary proteins agglomerations are trapped at the inlet and act to feed the contact. • Measured friction increase resulting from the introduction of food protein onto a saliva film on PDMS agreed with that from a biological tongue and correlated with astringency ratings from a human taste panel. • Both plant-based and dairy proteins can cause astringency by interacting with saliva proteins thus reducing their adhesion to the surface. This interaction is shown to occur both on the surface and in the bulk of the fluid. • Shear stress is required to remove the weakly bound saliva proteins to cause delubrication. • The role of insoluble food protein particles entrainment in astringency is to cause abrasive wear that increases the average friction coefficient and contributes to significant frictional noise.

Knot-inspired optical sensors for slip detection and friction measurement in dexterous robotic manipulation

Knot-inspired optical sensors for slip detection and friction measurement in dexterous robotic manipulation

Doprinos triboloških testova sveobuhvatnoj karakterizaciji medicinskih i kozmetičkih proizvoda

Tribology investigates the events that happen on the surfaces of two substances/objects that are in direct or indirect contact through assessing friction, lubrication and/or wear. In particular, friction measurements could provide the information on the textural characteristics of (per)oral pharmaceutical preparations and contribute to the understanding of palatability. On the other hand, tribological tests have been more intensively used to characterize topical preparations (pharmaceutical, cosmetic), giving a thorough insight into the tactile and texture properties of these preparations. However, these tests are often combined with rheological, textural, and certain biophysical approaches. Additionally, the materials used for constructing artificial joints and articular cartilages are true tribological systems, developed and optimized in order to have properties that resemble the natural ones. Since tribological studies can be used to assess a wide range of drug dosage forms and products in general, the equipment used may be quite diverse. Accordingly, a special section of this work is committed to the description of the testing equipment's specifications and the applied protocols. The investigation of recently regulatory discovered phenomena, such as transformation/metamorphosis of the vehicle/base of topical preparations, have brought tribology back into focus as a potential assessment method.

Methodology for Obtaining Optimal Sleeve Friction and Friction Ratio Estimates from CPT Data

Cone penetration testing (CPT) is a cost effective and popular tool for geotechnical site characterization. CPT consists of pushing at a constant rate an electronic penetrometer into penetrable soils and recording cone bearing (qc), sleeve friction (fc) and dynamic pore pressure (u) with depth. The measured qc, fs and u values are utilized to estimate soil type and associated soil properties. A popular method to estimate soil type from CPT measurements is the Soil Behavior Type (SBT) chart. The SBT plots cone resistance vs friction ratio, Rf [where: Rf = (fs/qc)100%]. There are distortions in the CPT measurements which can result in erroneous SBT plots. Cone bearing measurements at a specific depth are blurred or averaged due to qc values being strongly influenced by soils within 10 to 30 cone diameters from the cone tip. The qcHMM algorithm was developed to address the qc blurring/averaging limitation. This paper describes the distortions which occur when obtaining sleeve friction measurements which can in association with qc blurring result in significant errors in the calculated Rf values. This paper outlines a novel and highly effective algorithm for obtaining accurate sleeve friction and friction ratio estimates. The fc optimal filter estimation technique is referred to as the OSFE-IFM algorithm. The mathematical details of the OSFE-IFM algorithm are outlined in this paper along with the results from a challenging test bed simulation. The test bed simulation demonstrates that the OSFE-IFM algorithm derives accurate estimates of sleeve friction from measured values. Optimal estimates of cone bearing and sleeve friction result in accurate Rf values and subsequent accurate estimates of soil behavior type.

On the lubricating efficiency of high-performance powder metallurgy lubricants

Frictional characteristics of an iron-based mixture were studied using a specifically designed friction test bench allowing (after prior compaction) the measurement of the friction coefficient during the sliding of a compact on a slab simulating the die surface. Temperature and sliding velocity were controlled. An experimental campaign was conducted with four high-performance lubricants and a conventional EBS wax, based on a single FL-4400 mix formulation. The experimental parameters included: mix temperatures from 40 to 80 °C; density of 7.20 g ⋅ cm −3 ; normal pressure of 244 MPa; sliding distance 80 mm; sliding velocity 20 mm ⋅ s −1 . The analyses focused on the evolution of the friction coefficient and the compact’s surface degradation. Two methods were compared: single testing with slab cleaning between each test, and repeated testing. After multiple repetitions, a steady state was established with a sliding distance beyond which degradation became critical. The degradation depended on the lubricant and experimental conditions. The difference between lubricants became more obvious, some of them proving an enhanced ability to create long-range lubrication. This study aims at better understanding how the friction coefficient evolves during the ejection of a production part. • High-performance lubricants increase the sliding distance before surface degradation. • The maximum sliding distance before degradation was estimated using a friction test. • Repeated testing improves the quality and repeatability of friction measurements. • Lubrication properties evolve with the number of compaction cycles.

In Situ Observation of Hyaluronan Molecular Weight Effectiveness within Articular Cartilage Lubrication

Degradation of the articular cartilage (AC) structure due to osteoarthritis significantly influences its friction and lubrication mechanisms. Injection with exogenous hyaluronic acid (HA) is one of the ways to slow down the progress of these changes. The present paper aims to determine the effect of HA on the friction and lubrication processes of the synovial joint model. The main emphasis is placed on the effect of HA molecular weight (MW) on the coefficient of friction (COF) and the interactions between HA and other constituents of synovial fluid (SF). Frictional measurements between the AC surface and the glass were performed with simultaneous in situ observation of the contact zone by fluorescence microscopy. Using this methodology, a decrease in AC COF with an increase in the fluorescence intensity emitted from contact with HA was observed, while the phenomenon was found to be MW-dependent. These findings demonstrate that high-MW HA is more effective within a resumption of healthy AC lubrication due to a better adhesion to the AC surface.

Body mapping of skin friction coefficient and tactile perception during the dynamic skin-textile interaction

The clothing fabric and skin interact continuously across the many regions of users′ bodies during wear, which can lead to both physical skin damage and discomfort. Therefore, this investigation aimed to explore the regional differences in skin friction, tactile perception, and sensitivity in both females and males during the skin-textile interaction. The static and dynamic friction coefficient and textile perception (texture, stickiness, pleasantness, and discomfort) were measured across the 36 selected testing body areas by using a friction measurement device. The results revealed there was a significant difference in skin friction, tactile perceptions, and sensitivity across the various body regions. The anterior neck had the highest skin friction in both females and males, and participants generally rated higher texture perception in their anterior aspects compared to posterior and lateral regions. There was no significant difference in skin friction, tactile perception ratings, and sensitivity between females and males. Practitioner summary: This study sought to examine regional variations in skin friction, tactile perception, and sensitivity during the skin-textile interaction. There was a significant difference in skin friction, tactile perceptions, and sensitivity across the various body regions and no significant sex effect on skin friction, tactile perception ratings, and sensitivity.

Security Agencies and Human Right Violations in Nigeria

It is no news that Nigeria, which is arguably the giant of Africa, is known for human rights violations. From its years of military authoritarianism which witnessed the killing of several human rights activists, and since the return to democratic rule, the country’s human rights narrative has not changed. Government authorities and law enforcement agents (the police) frequently engage in various human rights violations, notably unlawful killings, torture, ill-treatment of no crime suspects, forced evictions, interference with the rights to peaceful assembly and freedom of association, and violence against women and children are widespread across the country. This has created worrisome threats to lives and government seems to be grappling with the situation, hence there is some measure of friction between the activities of security agencies and human right in Nigeria. It is against this backdrop that pertinent questions are asked on how well security agencies could be operated without infringement on fundamental human rights and what are the probable mechanisms that could be adopted by security agencies without abuse of human rights in Nigeria. Answers to these questions instigated this research work. This study exemplified the extent of human rights abuses in Nigerian democratic governance. It equally highlighted causes and the effects of human rights abuses in Nigeria and made recommendations on how to prevent its occurrences in the future. Secondary sources of data thus become the hub of its methodology. The study adopted system theory by Gabriel Almond as its theoretical framework.

Abrasion testing of fibre rope on impermeable fabrics for wave energy converter systems

The NetBuoy system is being developed as means of providing low cost buoyancy, typically for use in the wave energy converter (WEC) sector where many devices rely on large, heavy and expensive fabricated steel hulls/structures to absorb the incoming wave energy.The NetBuoy system is an elegant concept in that it utilises an air pressurised impermeable buoyant pod to provide structural rigidity, which is restrained by a synthetic fibre rope net. This provides a structure that is cheaper to produce than steel equivalents and has additional benefits in terms of ease of transport to site and maintenance. However, there are a number of considerations relating to the performance of the buoy and the containing net. It is important that the net does not damage the buoy (which might lead to loss of buoyancy) as wave action may cause relative movement between net and buoy. Equally, the net must retain integrity so that the buoy does not come free from its tether (creating a shipping hazard and loss of device).This paper describes a novel test method developed to investigate the performance of a range of impermeable elastomer membranes (buoy materials) when abraded against a polyester fibre rope. It discusses the methodology of the tests and provides results of testing on a number of elastomer membrane materials, considering both wear volumes and measurement of friction between the rope and the membrane material as a means of assessing performance. Of the five materials assessed, a clear ranking of abrasive resistance in the elastomers was found on test with EPDM and Neoprene being clearly better than all other materials. Natural rubber performed well, whilst Hypalon and Nitrile were found to be least resistant to abrasion from the rope. In all tests the rope was largely unaffected by the abrasion.

Dynamic and static friction measurements of elastomer footwear blocks on ice surface

This study conducted friction experiments of three elastomer block materials on ice (low pressure injection of polyurethane (PU), injection moulding of a thermoplastic polyurethane (TPU) and vulcanization of rubber (RU)), with a linear tribometer operating under four different ambient air temperatures (−10 to 0 °C) and six different sliding velocities (0.3–5 m/s). At low temperatures (−10 °C and −5 °C), the RU material showed the highest dynamic and static friction. However, at high temperatures (−2 °C and 0 °C) the PU revealed the highest dynamic friction and highest static friction at 0 °C. We discuss the physical phenomena’s of elastomer friction on ice and in relation to the application of footwear slipping on ice.

Systematic error in the internal friction measurement of coatings for gravitational wave detectors

Low internal friction coatings are key components of advanced technologies such as optical atomic clocks and high-finesse optical cavity and often lie at the forefront of the most advanced experiments in Physics. Notably, increasing the sensitivity of gravitational-wave detectors depends in a very large part on developing new coatings, which entails developing more suitable methods and models to investigate their loss angle. In fact, the most sensitive region of the detection band in such detectors is limited by the coating thermal noise, which is related to the loss angle of the coating. Until now, models which describe only ideal physical properties have been adopted, wondering about the use of one or more loss angles to describe the mechanical properties of coatings. Here we show the presence of a systematic error ascribed to inhomogeneity of the sample at its edges in measuring the coating loss angle. We present a model for disk-shaped resonators, largely used in loss angle measurements, and we compare the theory with measurements showing how this systematic error impacts on the accuracy with which the loss model parameters are known.

Direct measurement of skin-friction in shock/boundary-layer interaction flows

The direct measurement of skin friction at high speed is extraordinarily complicated due to the interference from various extraneous forces and the short test-time of high-speed facilities. The present study deals with the design and performance assessment of a skin friction sensor in a hypersonic flowfield with shock-boundary layer interaction, which is a predominant high-speed flow phenomenon. The experiment was conducted in the IIT Bombay Shock Tunnel (IITB-ST); the sensor was exposed to a flow with freestream Mach number, total enthalpy, and Reynolds number of 8.4, 0.69 MJ/kg, and 2.60 × 106 m−1, respectively. The shock-boundary layer interaction was induced by an oblique shock impinged on a flat plate, with a flow turn angle of 15°. The low magnitude average skin friction could be measured with an uncertainty of ±21%. The comprehensive study conducted confirmed the suitability of the skin friction sensor for high-speed applications in impulse facilities.

Orthodontic Bracket Friction Affected by Design Selection Material and Manufacturing Process

One of the problems in orthodontic treatment is friction. Some of the factors that support friction are archwire material, archwire dimensions, bracket material, surface roughness, type of ligation, environmental humidity, and bracket position, angulation angle between bracket and wire, changes in the surface of the archwire and bracket. The aim of this study is to analyse the difference in friction between the two branded bracket designs and a new patented bracket (patent no. IDP000069597). The production method for this new bracket is different, however, uses the same material of 17-4 PH stainless steel. There are three groups in this research, one sample of bracket each from two different branded and one sample of a new bracket design. All three groups were tested for microstructure, then tested for measurement of friction between bracket slots and archwire. The microstructure of the two branded brackets has a martensitic phase that is not as dense as the new bracket, which is due to the different manufacturing method processes. The two branded brackets use the metal injection molding method, while the new brackets use the investment casting method. The friction test results show that there are significant differences between the three groups of brackets. One of the branded brackets (A) has the lowest friction, but branded bracket (B) does not have different friction with the new bracket. Differences in design and manufacturing methods of orthodontic bracket affect the friction between orthodontic brackets and archwires even though they use the same material.

Influence of hyaluronic acid on intra-articular friction – a biomechanical study in whole animal joints

BackgroundCartilage is a mechanically highly stressed tissue in the human body and an important part of synovial joints. The joint cartilage is lubricated by synovial fluid with hyaluronic acid (HA) as main component. However, in joints with osteoarthritis HA has a lower concentration and molecular weight compared to healthy joints. In recent years, the intra-articular injection of therapeutic HA lubricant, has become a popular therapy. The effect of HA application on the friction of a complete joint with physiological movement needs to be further determined.MethodsThe aim of the present study was to evaluate the lubrication effect of the joint by three lubricants (NaCl, fetal calf serum (FCS) and HA) and their effect on the friction in nine complete ovine carpo-metacarpal joints. The joints were mounted on a material testing machine and a physiological movement with 10° rotation was simulated with ascending axial load (100 – 400 N). Specimens were tested native, with cartilage damage caused by drying out and relubricated. Dissipated energy (DE) as a measure of friction was recorded and compared.ResultsInvestigating the effect of axial load, we found significant differences in DE between all axial load steps (p < .001), however, only for the defect cartilage. Furthermore, we could document an increase in DE from native (Mean: 15.0 mJ/cycle, SD: 8.98) to cartilage damage (M: 74.4 mJ/cycle, SD: 79.02) and a decrease after relubrication to 23.6 mJ/cycle (SD: 18.47). Finally, we compared the DE values for NaCl, FCS and HA. The highest values were detected for NaCl (MNorm = 16.4 mJ/cycle, SD: 19.14). HA achieved the lowest value (MNorm = 4.3 mJ/cycle, SD: 4.31), although the gap to FCS (MNorm = 5.1 mJ/cycle, SD: 7.07) was small.ConclusionsWe were able to elucidate three effects in joints with cartilage damage. First, the friction in damaged joints increases significantly compared to native joints. Second, especially in damaged joints, the friction increases significantly more with increased axial load compared to native or relubricated joints. Third, lubricants can achieve an enormous decrease in friction. Comparing different lubricants, our results indicate the highest decrease in friction for HA.

Effective pavement skid resistance measurement using multi‐scale textures and deep fusion network

AbstractPavement skid resistance measurement is a fundamental component of roadway management and maintenance. Most traditional approaches rely on manual operations or heavy devices, which lead to a labor‐intensive, inefficient, and vulnerable testing environment. Precise laser scanning technology lays a solid foundation for effective and continuous pavement friction measurement. This paper proposed an automated pavement friction estimation model using 3D point cloud data and a deep neural network. The fine‐grained texture data of over 800 pavement sections with various anti‐skidding abilities were collected. The impact of the multi‐scale textures on pavement friction was separated and analyzed via two‐dimensional wavelet decomposition. A multi‐input fusion network with deep aggregation modules was designed to fuse the features of sub‐images generated by wavelet decomposition. The results show that the average prediction error is 0.0935, outperforming most state‐of‐the‐art models. The impact of different texture scales on friction estimation is then revealed. The proposed method provides a new tool for effective and large‐scale pavement friction evaluation.

Intercalation leads to inverse layer dependence of friction on chemically doped MoS2

We present results of atomic-force-microscopy-based friction measurements on Re-doped molybdenum disulfide (MoS2). In stark contrast to the widespread observation of decreasing friction with increasing number of layers on two-dimensional (2D) materials, friction on Re-doped MoS2 exhibits an anomalous, i.e. inverse, dependence on the number of layers. Raman spectroscopy measurements combined with ab initio calculations reveal signatures of Re intercalation. Calculations suggest an increase in out-of-plane stiffness that inversely correlates with the number of layers as the physical mechanism behind this remarkable observation, revealing a distinctive regime of puckering for 2D materials.

Evaluation of locked-wheel skid trailer and SCRIM friction measurements at NCAT test track

ABSTRACT This study aimed to evaluate the repeatability of locked-wheel skid trailer (LWST) and sideway-force coefficient routine investigation machine (SCRIM) measurements and investigate the influences of test speed and test temperature on the friction measurements. This study selected 14 test sections from the NCAT Test Track with different surface texture and friction characteristics. The LWST and SCRIM tests were conducted at different test speeds and test times (or temperatures) on the two consecutive days. The repeatability analysis indicates that both LWST skid number (SN) and SCRIM reading (SR) measurements were most repeatable at a test speed of 50 mph and tangent section. The SN measured in the late afternoon and SR measured at noon were more repeatable than those measured at other times. This study recommended an acceptable precision of friction measurement be within 2.5 SN or 3 SR units. In addition, this study concluded that the SN and SR had a good linear correlation. The statistical regression analysis demonstrates that test speed, air temperature, pavement mean profile depth, and pavement type were significant variables affecting asphalt pavement friction. The developed regression models for SN and SR were helpful to correct the friction measurements to a reference speed or temperature.

Nanoscale friction force on thin films of polymer blends and silane layers matrix

In this paper, nanoscale friction measurements are obtained from the Atomic Force Microscope (AFM) cantilever tip interaction with the layer of polymer blends of Polymethyl Methacrylate (PMMA)/ Polystyrene (PS) (2:1 and 1:2 ratios), and silane (C8, C12 and C18) layers at different proportion. The contrast of these polymer blends is investigated from the simultaneous recording of the topographic and lateral forces imaging. The resonance frequency excitation method and the wedge calibrations are used to quantify the normal and the lateral force constant respectively. Then, the quantitative frictional forces are calculated from the obtained normal and lateral force constants. The nanonewton (nN) frictions are found to be dependent on the nano-dynamic properties of the tip-sample interaction, the proportion of the polymer matrix and silane layers, and the scan speed.

Recrystallization in Ti5553 and Ti4733 detected by mechanical spectroscopy

This paper proposes a new way to detect recrystallization in beta-metastable alloys Ti5553 and Ti4733. Samples of these alloys were cold rolled and thermally treated. Internal friction was measured during heat cycles using a torsion pendulum. A correlation between recrystallization and sharp peak in internal friction specra was shown. The mechanism of dissolution of alpha phase triggering the recrystallization is proposed. In subsequent temperature cycles, the internal friction high temperature background decreases and stabilizes after three cycles. This is attributed with secondary recrystallization leading to grain growth. The size of the grains for different recrystallization time and temperature was measured and is coherent with the mechanical spectroscopy results. This result tends to prove that internal friction measurement can be used to optimize recrystallization treatment in beta metastable titanium alloys.