Higher Friction Values Research Articles

Friction and wear behavior of a mechanical oscillating strip system used for interproximal enamel reduction: a quantitative and qualitative scanning electronic microscope evaluation.

To evaluate wear and friction properties of oscillating strips in order to validate the importance of a standardized interproximal enamel reduction (IPR) sequence to preserve their efficiency and lifetime. Fifteen complete oscillating IPR sequences were tested by means of tribological tests (Linear Reciprocating Tribometer, C.S.M. Instruments, Peseaux, Switzerland). Fifteen single 0.2-mm metallic strips underwent a long continuous cycle of 240 minutes. Strip surface roughness and waviness measurements were assessed by means of a contact probe surface profiler (TalySurf CLI 2000; Taylor Hobson, Leicester, UK) and TayMap software. Statistical analysis was performed with independent-samples t-test. Significance was at the P < .05 level. Scanning electronic microscopy analysis of strip surfaces was conducted with an FEI Quanta 200 (Hillsboro, Ore) in high vacuum at 30.00 kV. Resin strips revealed a significant reduction in surface roughness (Ra, Rt, RDq) and a significant increase in waviness parameters (Wa, Wt). Rt and RDq values significantly decreased upon use of the metallic strips. Significantly higher values of Wa (+ 2.84 µm) and Wt (+0.1 µm) were observed only for the 0.2-mm metallic strips. Higher friction values were observed when the metallic strips were tested singularly rather than within the entire sequence. Lower Ra and Rt values were revealed when 0.2-mm metallic strips were tested up to 240 minutes. The application of a standardized oscillating sequence allows for more efficient wear performance of the strips with a significant impact on their abrasive power and lifetime.

The Combination of Glucocorticoids and Hyaluronic Acid Enhances Efficacy in IL-1β/IL-17-Treated Bovine Osteochondral Grafts Compared with Individual Application.

Patients with knee osteoarthritis often receive glucocorticoid (GC) or hyaluronic acid (HA) injections to alleviate symptoms. This study evaluated the impact of Triamcinolone Hexacetonide (a GC), HA, and a combination of both on bovine osteochondral grafts exposed to IL-1β and IL-17 in an ex vivo culture. Metabolic activity increased with GC treatment. GCs and GCs/HA counteracted cytokine effects, with gene expressions similar to untreated controls, while HA alone did not. However, HA improved the coefficient of friction after two weeks. The highest friction values were observed in GC-containing and cytokine-treated groups. Cytokine treatment reduced tissue proteoglycan content, which HA could mitigate, especially in the GC/HA combination. This combo also effectively controlled proteoglycan release, supported by reduced sGAG release. Cytokine treatment led to surface cell death, while GCs, HA, or their combination showed protective effects against inflammation. The GC/HA combination had the best overall results, suggesting its potential as a superior treatment option for osteoarthritis.

Parametric analysis of masonry arches following a limit analysis approach: Influence of joint friction, pier texture, and arch shallowness

Among the most characteristic structures in historical constructions for crossing large spans are the masonry vaulted structures by utilizing their geometric stability to safely transfer the loads to supports with regard to their negligible tensile strength. The ability of masonry piers to bear such transferred stresses and safely convey them to the support is directly related to their structural integrity, as well as to a number of other factors. Using an in-house limit analysis code, a study on the crucial parameters impacting the safety level of piers under the thrust of arches is performed. Parameters such as pier texture, joint friction angle, and arch shallowness, namely, shallow, semi-circular, and pointed arches, were investigated under three load scenarios: horizontal and concentrated vertical live load applied at mid-span and quarter-span. The main findings of this work show that all studied parameters have a significant influence on the structure response. Higher friction values, sharper arches, and piers that follow the rule of art result in higher collapse multipliers. Furthermore, this work emphasizes the importance of accounting for the sliding mechanism and masonry texture, parameters that are often neglected.

Mechanical and tribological properties of C/C–SiC ceramic composites with different preforms

Abstract The C/C–SiC composites were fabricated by the liquid silicon infiltration method. The mechanical and tribological properties of C/C–SiC composites were assessed and compared based on different C/C densities and the carbon fiber textile architecture. The results demonstrated that the bending and shear strengths of C/C–SiC were lower than those of C/C composites, which resulted from the carbon fibers being corroded during the process of infiltration of liquid silicon. In contrast to C/C composites, the compressive strength of C/C–SiC exhibited higher values due to the presence of SiC ceramics. Moreover, the mechanical strength of C/C composites increased gradually with the increase of the C/C preform density. The tribological properties of various C/C–SiC composites showed a stable friction phase at an intermediate braking stage. When the density of C/C preforms was around 1.78 g/cm3, the C/C–SiC composites exhibited excellent friction coefficients (0.438 and 0.465), and low wear rates (linear and weight wear rates were 0.450 µm/time and 0.123 g/cycle, respectively). Furthermore, the C/C–SiC composites fabricated with non-woven carbon fiber needling preforms showed relatively a higher friction value and wear rate than those of C/C–SiC with PANOF integral C/C preforms. Therefore, C/C–SiC composites have been considered promising friction materials for braking system applications.

Experimental identification of the fractional parameter of the fractional derivative standard linear solid model for fiber-reinforced rubber concrete

This paper studies the influence of different factors, such as polymer and fiber type and aging, on the internal friction and fractional parameter, which are determined for rubber concrete and fiber-reinforced rubber concrete by means of the Resonant Frequency and Damping Analyzer (RFDA Basic) implementing the Impulse Excitation Technique (IET). Both materials contained low molecular weight cis-polybutadiene rubber SKDN-N as the main binder. Another type of binding material has been used for further investigation of internal friction phenomena in polymer concrete. Namely, low molecular weight polybutadiene rubber (BR) of mixed microstructure was utilized to produce the samples for the experimental program. Two different types of fiber are used: metal and polymer fiber. It has been found that the addition of steel fiber reduces internal friction in the material, whereas propylene fiber acts as additional damping material and increases internal friction. BR-based concrete and fiber-reinforced concrete show rather high values of internal friction, i.e. behave more viscoelastically. BR-based concrete performs higher values of the fractional parameter, and, therefore, more obvious viscoelastic properties. Introduction of steel fiber in the mixture reduces the fractional parameter, since it plays the role of additional bonds in the material structure. However, addition of propylene fiber increases fractional parameter in both, SKDN-N and BR-based concretes. It can be explained by additional damping effect of the polymer fiber. The obtained results are compared with those for the reference specimens made of ordinary Portland cement concrete, and a certain influence of the selected parameters on the internal friction of the considered materials are established.

Acoustic signature identification of damage and wear mechanisms in a steel/glass sliding contact

The tribological behavior of a steel/glass ball-on-flat contact was studied by synchronizing the friction measurements with an acoustic emission device and a vision system. The results highlight two distinct friction regimes identified with low and high friction values. Their transition is characterized by a modification of acoustic emission signals. In addition, two main damage and wear mechanisms are identified: the creation and propagation of Hertzian cracks visible on the glass surface and the constitution of an interfacial layer of debris. The different accommodation mechanisms, activated successively or simultaneously, are identified for acoustic emission frequencies between 300 and 700 kHz. Eventually, this approach allows a real-time wear mechanisms identification and gives better insights about acoustic emission signals in relation to tribological systems.

Theoretical study of the process of balls rolling with a diameter of 40 mm on a ball rolling mill

The following calibration scheme for rolling round steel is used for producing thermally hardened grinding balls with a diameter of 40 mm at JSC SSGPO for 320 variety rolling mill: a round billet with a diameter of 40 mm is produced from the initial billet of 120 × 120 mm. In the last developed scheme the square billet 150x150 mm is used as an initial billet for whole mill where the round steel with diameter of 40 mm is obtained from the above mentioned billet and then this round steel is used for production of balls with a diameter of 40 mm. Computer simulation of the ball rolling process in the Simufact Forming program was performed. The results of strain state distribution showed that the maximum processing level in the surface layers of balls is observed, while the stress state distribution showed that in the surface layers prevail high compressive stresses up to −400 MPa. Such stress-strain state leads to formation of gradient structure in the ball cross-section, where the surface layers will have more high mechanical properties. That is the most optimal result for details worked in condition of high values of friction.

Effect of Non-linear Radiation on MHD Mixed Convection Flow of a Micropolar fluid Over an Unsteady Stretching Sheet

The current analysis explores the results of non-linear radiation on an unsteady stretching mixed Micropolar fluid. Issue modelling leads to a framework of PDE, reworked by transformations into non-linear ODEs. The Homotopy analysis methodology is applied to resolve the matter. The diagrams address the impact of the Magnetic parameter, unsteadiness parameter, Eckert number, Micropolar parameters, buoyancy parameters, Radiation parameter, Temperature ratio and Schmidt number on velocity, temperature, and concentration gradients. Amount of Nusselt number will increase in massive Prandtl number values, within the case of the high values of the unsteadiness parameter skin friction, wall couple stress and Sherwood decrease.

Numerical analysis on the three-dimensional flow and heat transfer of multiple nanofluids past a Riga plate

This examination is passed on to decide the properties of three-dimensional flow of H 2 O/NaC 6 H 9 O 7 base liquid with F e 3 O 4 /Al 2 O 3 nanoparticles confined by a Riga plate. Mathematical model is detailed as PDEs and afterward transmuted into ODEs with the assistance of similarity transformations. The subsequent system is numerically dealt with the aid of the Runge-Kutta procedure bolstered by shooting technique. Highlights of the flow field and thermal field are exemplified quantitatively through plots. Results for the local skin friction coefficient and local Nusselt number are registered and examined tabularly. It is induced that the modified Hartmann number and stretching ratio parameter ameliorate the velocity profile. Additionally, it is likewise explained that H 2 O − Al 2 O 3 nanofluid has high skin friction values and the rate of heat transfer of NaC 6 H 9 O 7 − Al 2 O 3 nanofluid is more desirable.

Investigation of the friction coefficient evolution and lubricant breakdown behaviour of AA7075 aluminium alloy forming processes at elevated temperatures

The lubricant behaviour at elevated temperatures was investigated by conducting pin-on-disc tests between P20 tool steel and AA7075 aluminium alloy. The effects of temperature, initial lubricant volume, contact pressure and sliding speed on the lubricant behaviour (i.e. evolutions of the coefficient of friction (COF) and the breakdown phenomenon) were experimentally studied. The evolutions of COF at elevated temperatures consisted of three distinct stages with different friction mechanisms. The first stage (stage I) occurred with low friction when the boundary lubrication was present. The second stage (stage II) was the transition process in which the COF rapidly increased as the lubricant film thickness decreased to a critical value. In the final plateau stage (stage III), lubricant breakdown occurred and intimate contact at the interface led to high friction values. At the low friction stage (stage I), the value of COF increased with increasing temperature. The increase in temperature, contact pressure and sliding speed as well as the decrease in initial lubricant volume accelerated the lubricant breakdown.

Evolution of the coefficient of lateral earth pressure at rest with interparticle friction: a numerical study

The grain-scale nature of evolution of the coefficient of lateral earth pressure at rest (K0) with interparticle friction (µp) is poorly understood. This study aims to use discrete element method simulations of vertical one-dimensional compression on both face centred cubic (FCC) samples and random monodisperse (RM) samples to link K0 and µp, and the results show that K0 increases with reductions in interparticle friction. Although K0 is dependent upon the sample density, patterns of evolutions with strain levels are likely to be unchanged with initial confining pressures. The stress-induced fabric becomes more anisotropic for samples with high values of the interparticle friction. The percentage of particles with a high value of the normal contact force increases with increasing strain levels as the interparticle friction increases in the simulations.

Tailoring damping properties by electron irradiation in Ni-Mn-Ga shape memory alloys in a wide high-temperature range

Damping devices need to maintain a high internal friction value in a wide high-temperature range in an aviation environment. Damping behavior is sensitive to defects including vacancies, interstitials, and dislocations. Electron irradiation is an effective method to introduce defects into materials to tailor the damping properties. The relaxation internal friction peak value increases first and then decreases with the increase of irradiation dose in Ni54Mn25Ga21 alloy. The peak value increases from 0.04 to 0.055 by 37.5% after irradiated by 1.2 MeV electrons at 2 × 1017 e/cm2. It derives from the effect of dislocations on the interaction between interstitials and twin boundaries. The high isothermal internal friction remains stable with a large working temperature range of 160 ℃ from 50 ℃ to 210 ℃. This research provides a new method to obtain high damping Ni54Mn25Ga21 alloy with a wide high-temperature range.

Combined effects of contact friction and particle shape on strength properties and microstructure of sheared granular media.

We present a systematic numerical investigation concerning the combined effects of sliding friction and particle shape (i.e., angularity) parameters on the shear strength and microstructure of granular packings. Sliding friction at contacts varied from 0 (frictionless particles) to 0.7, and the particles were irregular polygons with an increasing number of sides, ranging from triangles to disks. We find that the effect of local friction on shear strength follows the same trend for all shapes. Strength first increases with local friction and then saturates at a shape-dependent value. In contrast, the effect of angularity varies, depending on the level of sliding friction. For low friction values (i.e., under 0.3), the strength first increases with angularity and then declines for the most angular shapes. For high friction values, strength systematically increases with angularity. At the microscale, we focus on the connectivity and texture of the contact and force networks. In general terms, increasing local friction causes these networks to be less connected and more anisotropic. In contrast, increasing particle angularity may change the network topology in different directions, directly affecting the macroscopic shear strength. These analyses and data constitute a first step toward understanding the joint effect of local variables such as friction and grain shape on the macroscopic rheology of granular systems.

Effect of Low-Fluorescence Anti-Seize Lubricant on Rheological Properties of Water-Based Drilling Fluid

Water-based drilling fluids generally may cause high friction and torque values. Lubricants are usually chosen as friction reducers. In this paper we investigate the effect of a low-fluorescence anti-seize lubricant JXFQ-6 on rheological properties of the water-based drilling fluid at high temperatures. Rheological properties of different samples are evaluated according to the American Petroleum Institute (API) standards. The experimental results show that rheological behavior of the water-based drilling fluids is maintained in the presence of JXFQ-6 ranging from 1.0 to 10.0 wt.% at a temperature as high as 150°C.

The effect of bed roughness uncertainty on tidal stream power estimates for the Pentland Firth.

Uncertainty affects estimates of the power potential of tidal currents, resulting in large ranges in values reported for sites such as the Pentland Firth, UK. Kreitmair et al. (2019, R. Soc. open sci. 6, 180941. (doi:10.1098/rsos.191127)) have examined the effect of uncertainty in bottom friction on tidal power estimates by considering idealized theoretical models. The present paper considers the role of bottom friction uncertainty in a realistic numerical model of the Pentland Firth spanned by different fence configurations. We find that uncertainty in removable power estimates resulting from bed roughness uncertainty depends on the case considered, with relative uncertainty between 2% (for a fully spanned channel with small values of mean roughness and input uncertainty) and 44% (for an asymmetrically confined channel with high values of bed roughness and input uncertainty). Relative uncertainty in power estimates is generally smaller than (input) relative uncertainty in bottom friction by a factor of between 0.2 and 0.7, except for low turbine deployments and very high mean values of friction. This paper makes a start at quantifying uncertainty in tidal stream power estimates, and motivates further work for proper characterization of the resource, accounting for uncertainty inherent in resource modelling.

Controlled atmosphere dependent tribological properties of thermally annealed ultrananocrystalline diamond films

Tribological properties of ultrananocrystalline diamond (UNCD) films were investigated in the ambient atmospheric and high-vacuum in the dynamic transition of tribo-atmospheric condition. The UNCD film with trans-polyacetylene (t-PA) phase showed high friction value in the ambient atmospheric condition and this value became significantly less in the transition of atmosphere to high-vacuum. In contrast, thermally annealed similar UNCD film showed ultralow friction value in the ambient atmospheric condition and this value was high in the transition to high-vacuum tribo-condition. The UNCD film with t-PA phase oxidized in the ambient atmospheric tribological condition which was the main reason for high friction. However, intrinsic hydrogen present in the UNCD films passivated the dangling bonds in high-vacuum tribological condition. Chemical passivation of carbon dangling bonds was efficient for thermally annealed UNCD film in the ambient atmosphere and such passivation was restricted in the high-vacuum. Chemical analysis of the wear track was investigated by the Auger X-ray and X-ray photoelectron spectroscopies for revealing the comprehensive friction mechanisms.

Friction Coefficients for Slide-In Bridge Construction Using PTFE and Steel Sliding Bearings

Slide-in bridge construction (SIBC) has been used in accelerated bridge construction (ABC) for the last decade. Slide-in bridge construction is carried out using bearing pads consisting of polytetrafluoroethylene (PTFE) and steel sliding surfaces. In this study, coefficient of friction (COF) measurements were made with variable surface roughness, lubrication type, sliding speed, and contact pressure. Among three tested surfaces, the rough rolled stainless steel and the carbon steel produced COF values much higher than those of stainless steel with a #2B surface. Unlubricated and graphite-lubricated surfaces resulted in very high friction values, whereas the values for soap, grease, and oil were comparably lower. The oil and grease tests gave the lowest friction values, 0.90–4.04% and 0.67–5.15%, for the studied contact pressures, respectively, and are recommended for future use. Higher contact pressures typically resulted in lower COF values. Overall, the currently recommended COF values underpredict the COF compared with the results from this study. However, for higher contact pressures, this study found lower COF (e.g., for high pressure of 55 MPa, 2% versus 0.9–1.44%) compared with current recommendations and the opposite for low contact pressures (e.g., for 11 MPa, 2.71% versus 4.04–5.66%). Unlubricated sliding surfaces are not recommended due to the large scatter in comparable data in this study and the literature.

Nano-Al (OH)3 and Mg (OH)2 as flame retardants for polypropylene used on wires and cables

While materials sustainability is mostly considered in terms of their long-time aging, fires are more important—while polymers are flammable. We have developed flame retardants (FRs) for polypropylene (PP) with varied FR concentrations since PP is a very widely used polymer. Stearic acid (SA) has been added to increase filler–matrix interactions and filler dispersion in the matrix. Effects of filler types, particle size, and their concentrations on fire resistibility of different composite samples have been determined via limiting oxygen index tests and burning times. As expected, the oxygen index increases with increasing concentration of either FR. The highest value of the index is seen for 10 wt% 50 nm Al (OH)3 sample. Mixing the two hydroxides does not provide a synergy effect. The longest burning time is seen for 5 wt% 50 nm Al (OH)3 + 7 wt% SA, longer than the time for pure PP sample by 137%. Neat PP has a relatively high dynamic friction value, while addition of 5% SA results in the lowest friction value of all. The highest tensile modulus is seen for PP with 7.5 wt% 15 nm Al (OH)3 particle addition. Thermogravimetric analysis shows high thermal stability for PP with 5% each of Al (OH)3 and Mg (OH)2. Scanning electron microscopy shows that the surfaces of Al (OH)3-containing samples are slightly rougher than those with Mg (OH)2. Energy dispersive X-ray spectroscopy shows uniform distribution of both Al and Mg atoms in the composites.

Surface degradation mechanisms in precipitation-hardened high-entropy alloys

Design of high-entropy alloys with complex microstructures presents a unique opportunity to combine the best of solid solution strengthening and precipitation hardening. These alloys are potentially disruptive for several high-performance applications including aerospace, oil and gas, nuclear industry, and next-generation tribology. This study presents the thermo-mechanical treatment, microstructural evolution, and surface degradation resistance in precipitation hardenable Al0.3Cu0.3Ti0.2CoCrFeNi high-entropy alloy. The heat-treated alloy consisted of fine precipitates of L12 and L21, strengthening the face-centered cubic solid solution matrix. Potentiodynamic polarization showed nano-galvanic coupling between the intermetallic particles and the matrix. Phase-specific nano-indentation showed that hard intermetallic particles caused three-body wear and higher friction values during sliding wear. The microstructure was correlated with processing conditions and resulting surface degradation resistance using transmission electron microscopy imaging and analysis.

Friction-Active Surfaces Based on Free-Standing Anchored Cellulose Nanofibrils.

A specific feature of fibrous surfaces is the dependence of their mechanical properties on the alignment of the fibers. Vertically aligned fibers enhance friction and adhesion, whereas horizontal fibers are known to act as a lubricant reducing the friction. Many plants form a specific fibrous mucilage cover around their seeds upon hydration. This mucilage consists of cellulose, hemicelluloses, and strongly hydrophilic pectins. We show that the controlled critical-point drying of hydrated seed mucilage of three exemplary seed mucilage-rich plant species results in the exposure of free-standing cellulose nanofibers with a very high aspect ratio and anchored to the seed surface. The structural dimensions of the cellulose nanofibers are similar to the vertically aligned carbon nanotubes and the contact elements in the adhesion system of the gecko that show an outstanding high dry friction and adhesion. Tribological experiments demonstrate very high average friction coefficients when sliding a smooth and stiff probe over the surface of such arrays of dry free-standing cellulose nanofibrils in the range from 1.4 to 1.8. The high friction values most likely arise from bending of the single cellulose fibers and their alignment with the counterpart surface in close contact. We suggest the potential of free-standing cellulose nanofibrils of plant seed mucilage as a natural and ecologically friendly material where high contact forces to surfaces in dry environments are desired.