Low Friction Materials Research Articles

Screening of low-friction two-dimensional materials from high-throughput calculations using lubricating figure of merit

Two-dimensional materials are excellent lubricants with inherent advantages. However, superlubricity has been reported for only a few of these materials. Unfortunately, other promising two-dimentional (2D) materials with different physical properties cannot be discovered or applied in production; thus, energy consumption can be greatly reduced. Here, we carry out high-throughput calculations for 1,475 2D materials and screen for low-friction materials. To set a standard, we propose, for the first time, a geometry-independent lubricating figure of merit based on the conditions for stick-slip transition and our theory of Moiré friction. For the efficient calculation of this figure of merit, an innovative approach was developed based on an improved registry index model. Through calculations, 340 materials were found to have a figure of merit lower than 10−3. Eventually, a small set of 21 materials with a figure of merit lower than 10−4 were screened out. These materials can provide diverse choices for various applications. In addition, the efficient computational approach demonstrated in this work can be used to study other stacking-dependent properties.

Shaking table tests on seismic performance of a five-story reinforced concrete frame structure with MoS2 sliding bearings and steel dampers

The seismic performance of friction isolated structure is greatly affected by the friction coefficient, and the combination of low friction material and limit device is an available option. Via the Motion State module simulating the friction conditions and the Bouc Wen model describing the restoring characteristic of the steel dampers, a single-degree-of-freedom model was established to investigate the influence of the friction coefficient and limit stiffness on the isolation effect. Then, for the evaluation of the seismic performance of the proposed isolation system with molybdenum disulfide (MoS2) sliding bearings and steel dampers, the shaking table tests of a 1/5 scaled five-story reinforced concrete frame structure model, subjected to three ground motions with different peak ground acceleration, were implemented to obtain the isolation layer drift, absolute acceleration, inter-story shear and damage energy of the structure under the testing conditions of free sliding, limited sliding, multi-dimensional seismic excitation, and top additional layer sliding. It is found that the ideal friction coefficient for sliding isolated structure is 0.03–0.07, and the corresponding reasonable elastic stiffness of steel dampers is (0.2–0.5) Ks that is the stiffness of the structural standard story, and the proposed MoS2 sliding bearing presents remarkable low-friction characteristic with a friction coefficient of 0.04–0.05. The appropriate steel dampers can reduce the isolation layer drift without obviously increasing the acceleration. The low-frequency components in the ground motion significantly increase the isolation layer drift, while the high-frequency components cause the superstructure acceleration to show a K-shaped distribution along the height. Moreover, the proposed isolated system can be effectively used for structural protection under multi-dimensional earthquakes, the sliding additional layer on the roof can be considered as the second defense line in the structural seismic design, and the seismic energy the superstructure bears can directly estimate the seismic isolation effect that is consistent with the analysis result of dynamic response.

Effect of internal and external damping in the reduction of non-exhaust particulate matter emissions in a low metallic friction material formulation

Friction-induced vibrations in an automotive braking system are of serious concern, leading to different repercussions. Numerous conventional and unconventional methods have been proposed to curb these vibrations, which are also observed to be directly related to generating non-exhaust particulate matter emissions. In this study, an in-house formulated friction material, tested in the form of pins, was subjected to internal damping by adding rubber content from 0 to 3 wt% and external damping by wrapping the different pins in rubber tape. The DMTA showed a decrease in storage modulus and an increase in loss factor with the increase in rubber content. The pin density decreased with the increase in the rubber content. Dry sliding friction, wear, emissions, and vibrations tests were conducted on a pin on disc tribometer with relevant attachments to measure emissions and vibrations. A large drop in vibrations was observed with the rubber content, irrespective of external damping. On the other hand, a significant reduction in wear, emissions, and vibrations was observed with the sample containing the highest rubber addition and with the damping tape. This study showed the feasibility of employing the combination of internal and external damping, emphasizing the optimum rubber content in friction material formulations.

Force on a sphere suspended in flowing granulate.

We investigate the force of flowing granular material on an obstacle. A sphere suspended in a discharging silo experiences both the weight of the overlaying layers and drag of the surrounding moving grains. In experiments with frictional hard glass beads, the force on the obstacle was practically flow-rate independent. In contrast, flow of nearly frictionless soft hydrogel spheres added drag to the gravitational force. The dependence of the total force on the obstacle diameter is qualitatively different for the two types of material: It grows quadratically with the obstacle diameter in the soft, low-friction material, while it grows much weaker, nearly linearly with the obstacle diameter, in the bed of glass spheres. In addition to the drag, the obstacle embedded in flowing low-friction soft particles experiences a total force from the top as if immersed in a hydrostatic pressure profile, but a much lower counterforce acting from below. In contrast, when embedded in frictional, hard particles, a strong pressure gradient forms near the upper obstacle surface.

Wear resistant PEEK composites with great mechanical properties and high thermal conductivity synergized with carbon fibers and h‐BN nanosheets

AbstractIt is well known that carbon fiber (CF) reinforced PEEK (polyether‐ether‐ketone) (defined as “PEEK/CF”) composites have excellent properties and have been widely used in diverse fields. Meanwhile, hexagonal boron nitride (h‐BN), as an excellent nano reinforcing agent, is often incorporated into polymer to improve its mechanical strength and thermal conductivity. Herein, PEEK matrix was regulated by adding high‐strength CF as the load‐bearing phase and 2D h‐BN sheets as the solid lubricant and thermally conductive fillers prepared by melt blending to achieve the multi‐scale packing of uniform mixing. The results show that h‐BN is well dispersed in PEEK matrix and improves the interfacial bonding between CF and PEEK matrix, exhibiting a good synergistic effect in enhancing tensile properties of composites. PEEK composite with 20 wt% CF and 4 wt% h‐BN (referred as P/20C/4B) exhibits the highest tensile strength (176.05 MPa) and thermal conductivity (0.396 W/(m·K)), which are 97.54% and 126.3% over those of pure PEEK (89.12 MPa; 0.175 W/(m·K)), respectively. In addition, PEEK composite with 10 wt% CF and 4 wt% h‐BN (referred as P/10C/4B) has excellent tribological properties with a friction coefficient of 0.15, the lowest fiction temperature (30.5°C) and a relative low wear rate of 1.62 × 10−6 mm3/(N·m) among them. The synergitic effects of h‐BN and CF on mechanical, tribological properties and thermal conductivity of PEEK composites provides a very broad prospect in their application of low frictional and wear resistant polymeric materials.

Overview in Technical Synthesis and Applications of Zr2AC (A= In, Sn, Pb, Al, S and Se) MAX phases: a brief review

Zr2AC MAX phases are ternary carbide family with layered structures combining of the outstanding characteristics of metals and ceramics. This review study provides an overview of Zr2AC MAX phase formation mechanisms, applications, and the correlation between Zr2AC MAX phase formation mechanisms and performance in applications such solar coatings, oxidation resistance, high temperature applications, and nuclear applications. Zr2InC MAX phase has low friction and wear materials that can be used for variety applications for significant technology such as electrical spinning connections and rotating bearings. More examples, the Zr2SnC MAX phase uses for self-healing of cracks and oxidation resistance. The Zr2PbC MAX phases are elastic and electrically anisotropic in nature and appropriate for high temperature applications, optoelectronic devices, and coating materials. Studying the optical characteristics of the Zr2SeC has shown its potential for application as a shielding material in order to decrease the heating of solar. The Zr2SC is suitable for use in high-temperature technologies, such as thermal barrier coating material TBC. The Zr2AlC phase is the most attractive among all non-synthesizable ternary MAX phases, particularly for the nuclear industry. There are a lot of challenges during fabrication of the MAX phase, including synthesis temperature, the MAX phase purity, and the secondary phase (impurities). In harsh external conditions, the defect density has a substantial impact on the MAX phase's stability and thus, the methods of defect formation and migration have a considerable impact on the phases' radiation resistance and self-healing capabilities.

Investigation on Low Metallic NAO Brake Friction Material for Minimization of Non-Exhaust Pollution

Investigation on Low Metallic NAO Brake Friction Material for Minimization of Non-Exhaust Pollution

Supramolecular repair of hydration lubrication surfaces

<h2>Summary</h2> Although advances in coating technologies have allowed us to match—or even exceed—the lubricity of Nature's low-friction surfaces, the performance of synthetic materials inevitably diminishes over time as the surfaces are worn and damaged by irreversible breakage of covalent bonds. Synthetic systems lack the bespoke repair mechanisms that replenish hydration lubrication surfaces in Nature. Here, we demonstrate dynamic repair of low-friction surfaces prepared through a surface-selective self-assembly strategy. Monolayers of lubricating polymers associate with functionalized surfaces through strong and specific host–guest interactions, leading to hydration lubrication surfaces with low coefficients of friction (0.024–0.028). Following friction-induced dissociation of the polymers, the polymer-to-surface interaction is restored by the reformation of host–guest complexes, thus repairing the monolayer, renewing the lubricity, and reducing the effects of wear. Such dynamically restored low-friction materials will be an essential tool in decreasing global energy use—a fifth of which is expended overcoming friction.

Scaling Relationship Between the Wavelength of Longitudinal Ridges and the Thickness of Long Runout Landslides on the Moon

AbstractThe formation mechanism of longitudinal ridges in long runout landslides has been proposed to require ice and/or clay minerals, as low friction materials would allow the spreading of the deposit, causing the development of longitudinal ridges by tensile deformation of the slide. The necessity of ice in the formation of longitudinal ridges has been challenged by the finding that the wavelength of longitudinal ridges is 2–3 times the thickness of the deposit in both ice‐free laboratory experiments on rapid granular flows and in a martian and terrestrial long runout landslide, suggesting a scale‐ and environment‐independent mechanism. We conduct morphometric analysis of the longitudinal ridges in two landslides on the Moon, considered ice‐free throughout its geological history: the Tsiolkovskiy crater landslide, and the Light Mantle avalanche in Taurus‐Littrow Valley. We show that Tsiolkovskiy crater landslide exhibits a scaling relationship between the wavelength of its longitudinal ridges and the thickness of its deposit that is consistent with previous studies, supporting the idea that ice is not a necessary condition for the development of longitudinal ridges. As the Tsiolkovskiy crater landslide is laterally confined, it demonstrates that neither the development of longitudinal ridges nor the occurrence of the scaling relationship between the wavelength of the ridges and the thickness of the deposit depend on the lateral spreading of the deposit. Finally, we use the Light Mantle to test the use of the scaling relationship as a tool to estimate the thickness of the deposit when classical geomorphological methods are not applicable.

Role of OH Termination in Mitigating Friction of Diamond-like Carbon under High Load: A Joint Simulation and Experimental Study.

Diamond-like carbon (DLC) has recently attracted much attention as a promising solid-state lubricant because it exhibits low friction, low abrasion, and high wear resistance. Although we previously reported the reason why H-terminated DLC exhibits low friction based on a tight-binding quantum chemical molecular dynamics (TB-QCMD) simulation, experimentally, the low-friction state of H-terminated DLC is not stable, limiting its application. In the present work, our TB-QCMD simulations suggest that H/OH-terminated DLC could give low friction even under high loads, whereas H-terminated DLC could not. By using gas-phase friction experiments, we confirm that OH termination can indeed provide much more stable lubricity than H termination, validating the predictions from simulations. We conclude that H/OH-terminated DLC is a new low-friction material with high load capacity and high stable lubricity that may be suitable for practical use in industrial applications.

Experimental evaluation of extra-stroke displacement capacity for Curved Surface Slider devices

Curved Surface Slider (CSS) devices have been widely used in recent years for the reduction of seismic vulnerability of structural systems. Recent risk assessment studies have revealed that base isolated systems can be characterized by higher seismic risk with respect to their fixed-base counterparts. It is believed that this unexpected outcome is, partly, due to the definition of collapse condition that has traditionally been adopted for base isolated structures, which is somewhat stricter than for many other structural systems. More specifically, in most circumstances, a base isolator is assumed to collapse once the sliding pad reaches maximum geometrical displacement, which corresponds to the edge of the sliding surface.This paper summarizes the results of an experimental program that investigated the response of CSS devices under extreme seismic loading, with focus on base isolation devices stressed beyond their nominal capacity. A full-scale Double CSS prototype with three different low-friction materials was tested with cyclic signals and in the context of a hybrid simulation. A low value of peak sliding velocity has been assumed, in comparison to realistic values experienced during earthquake excitations, in order to be able to control the stability of the force response for the whole duration of the performed tests. The results collected were able to assess the effective response of CSS devices, when design geometrical characteristics are overcome within specific defined limits, and to formulate suitable numerical models to deal with extra-stroke response of DCSS in dynamic analysis.

Dressings for preventing pressure ulcers: how do they work?

Pressure ulcers (PUs) negatively affect quality of life (QoL) and cause problems for patients, such as pain, distress and often specific difficulties with treatments used to manage the wound. Thus, it is important to implement appropriate prevention strategies in order to achieve high-quality care, thereby reducing the burden of PUs on patients, the healthcare system and society as a whole. PU development arises due to the adverse effects of pressure, shear, friction and moisture at the skin/surface interface. Preventive interventions typically include risk assessment, reducing pressure and minimising shear and friction. More recently, certain wound dressings, as a potential additional protective strategy for preventing PUs, have been introduced. This review explores the mechanisms of action of dressings for preventing PUs. Findings from the review indicate that decreasing frictional forces transmitted to the patient's skin is achieved by use of a dressing with an outer surface made from a low friction material. Furthermore, the ability of dressings to absorb and redistribute shear forces through good adhesion to the skin, high loft and lateral movement of the dressing layers is important in reducing shear forces. This is achieved when the dressing reduces pressure transmitted to the patient's tissues by the propriety of high loft/thickness and padding that allows a degree of cushioning of bony prominences. Further, dressings may reduce humidity at the skin/dressing interface, i.e., the dressing is absorbent and/or permits moisture to evaporate quickly. As part of an established PU prevention protocol, dressings may help decrease PU incidence.

Friction and wear reduction by graphene nano platelets for hybrid nano Aluminium matrix composite under dry sliding conditions

Friction losses and wear losses are the main failure reasons in the internal combustion (IC) engine components i.e., cylinder liner and piston. So, it demands lightweight self-lubricating low friction and wear-resistant materials to increase the efficiency and reduce the emission issue of the IC engine. In this concern, tribological tests are performed on self-lubricating aluminium composites samples reinforced with 6 wt.% of γ-Al2O3 and Graphene Nano Platelets (GNP) with varying concentration (0.5 wt.% - 5 wt.%), using ball-on-disc tribo-configuration under dry sliding conditions. The scope of this study is to investigate the anti-friction and anti-wear properties of GNP as reinforcement in the hybrid nanocomposite. The hybrid nanocomposite samples are fabricated using Spark Plasma Sintering (SPS) fabrication route. From the results, it is reported that friction and wear reduction percentage is 37.43 % and 51.64 %, respectively for the hybrid nanocomposite with 5 wt. % GNP. It is attributed to the inclusion of GNP, which reduces the Coefficient of Friction (COF) and improves wear resistance of the composite significantly.

Method for Improving the Aircraft Hydraulic Drives Ability to Work

Abstract One of the approaches to ensure friction stability in hydraulic precise pairs can be coating their components with low-friction materials with the friction coating method using a metal, e.g. brass. The article presents the method of applying brass on the steel surface of a hydraulic pair using friction. It discusses the technology of brass plating of hydraulic precise pairs and the results of laboratory tests involving friction-brasses hydraulic precise pairs. The factors impacting the quality of brass-coating process of hydraulic precise pairs and the requirements set for hydraulic precise pairs subject to friction-brassing were also discussed.

Comparison of dry sliding behavior and wear mechanism of low metallic and copper-free brake pads

Rising environmental concerns and implementing restrictions on the use of copper in friction materials (FM) make it mandatory for manufacturers to look for a reliable replacement. Two commercial pads: 1) low metallic FM contains 7 wt.% copper fibers and 2) low metallic FM contains thermal graphite (TG), and cellulose fibers as replacements for copper were studied. The two FMs showed almost identical thermal behavior. However, Cu-contained FM exhibited a bit more thermal stability. The fade ratio and recovery ratio in the first fade and recovery stages showed almost the same values. Moreover, in the second fade, change from 86% to 78% and second recovery change from 90% to 77%, respectively, for Cu-contained and Cu-Free FMs.

Influence of Ag alloying on the morphology, structure, mechanical properties, thermal stability and oxidation resistance of multilayered TiSiN/Ti(Ag)N films

Self-lubricant films combine the intrinsic properties of high oxidation resistance coatings with lubricious elements deposited as monolayer and/or multilayered configuration, offering an opportunity to design green coating materials. The present paper reports the influence of Ag additions (range 0–3.2 at.%), considered as low friction material, on the morphology, structure, mechanical properties, thermal stability and oxidation resistance of multilayered TiSiN/TiN(Ag) films deposited by sputtering. The surface morphology of the coatings progressively changed from a well-defined cauliflower structure to a tetrahedral and pyramid-like structure and the cross-section morphology became more compact with Ag incorporation. A decrease of coating's hardness and Young's modulus was observed with Ag additions, due to the incorporation of the soft silver on the structure. The coatings showed excellent thermal stability and revealed a good control to the Ag diffusion towards the surface in protective atmosphere. Ag additions did not affect the onset oxidation point of films. However, the oxidation resistance of the films was reduced with Ag inclusion, due to its additional transportation during the oxidation process, promoting additional paths for ions diffusion, giving rise to a less protective Ti-Si-O layer and contributing to the formation of big crystals of rutile on the top.

The Methods to Unlock Molybdenum Disulfide

Author(s): Rodriguez, Anthony | Abstract: In today’s world, we’ve invented many new technologies that have allowed us to map out the earth’s surface but just as we can map out surfaces in a large scale, we can also map out surfaces in a very small scale such as in nanometers. Thus, giving us opportunities to study a discover various materials such as molybdenum disulfide (MoS2) crystalline flakes. MoS2 being a material that has a similar yet different structure to graphene, low friction when compared to SiO2 (a low friction material as is), and provides many potential applications that can be implemented into aerospace as a solid lubricant. But like any fellow researcher studying a material, each has their own methods/techniques that they use to obtain results. In our proposal, we will cover the research that has taken place to provide a consensus of MoS2’s potential application as a solid lubricant in aerospace to its low frictional properties in the nanometer scale. And the technologies we’ll be looking into to access for our methods/techniques for researching will be Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), X-Ray Photoelectric Spectroscopy (XPS), X-Ray Diffraction (XRD), and Tribometers at the University of California, Merced (UC Merced).

Effect of load on the friction and wear properties of aluminum hybrid composite/chromium plated chrome steel tribopair under boundary lubrication conditions

Friction and wear loss are the main reason that contribute to the failure in the IC engine components. This emerges the demand for the light weight, low friction and wear resistant material to enhance the efficiency and to reduce the emission problem in the IC engine components. In this concern, tribological test are performed on the hybrid aluminium matrix composites (Al–Si/Al2O3/GNP) composite fabricated using non-conventional rapid Spark Plasma Sintering (SPS) against chromium plated chrome steel ball under boundary lubrication conditions at room temperature using Ball-on-disc tribometer configuration. Friction & wear studies are conducted under high loading conditions ranging 100 N–300 N with 120 m sliding distance, 30 Hz frequency, 2 mm stroke length. From the study, it is reported that coefficient of friction (COF) as well as the wear significantly reduces; attributed to SAE20W50 engine oil lubricant with GNP Nano particles used as the secondary reinforcement (solid lubricant) in the hybrid composite. Ultra-mild adhesion and abrasion are the dominating wear mechanisms for the hybrid composite samples.

Coating Cutting Blades with Thin-Film Metallic Glass to Enhance Sharpness

In this study, we sought to enhance the cutting properties of the various blades by coating them with Zr- and Fe-based thin film metallic glasses (TFMGs) to a thickness of 234–255 nm via sputter deposition. In oil-repellency/sliding tests on kitchen blades, the sliding angle and friction forces were as follows: bare blades (31.6°) and (35 µN), Ti-coated blades (20.3°) and (23.7 µN), and Z-TFMG coated blades (16.2°) and (19.2 µN). Comparisons were conducted with bare blades and those with a Teflon coating (a low-friction material commonly used for the coating of microtome blades). We also found that the Teflon coating reduced the cutting forces of an uncoated microtome blade by ~80%, whereas the proposed Z-TFMG achieved a ~51% reduction. The Z-TFMG presented no indications of delamination after being used 30 times for cutting; however, the Teflon coating proved highly susceptible to peeling and the bare blade was affected by surface staining. These results demonstrate the efficacy of the TFMG coating in terms of low friction, non-stick performance, and substrate adhesion. The performance of Z-TFMG and F-TFMG was also evaluated in split-thickness skin graft surgery using dermatome blades aimed at elucidating the influence of TFMG coatings on the healing of surgical incisions. When tested repeatedly on hairless skin, the surface roughness of uncoated blades increased by approximately 70%, whereas the surface roughness of TFMG-coated blades increases by only 8.6%. In the presence of hair, the surface roughness of uncoated blades increased by approximately ~108%, whereas the surface roughness of TFMG-coated blades increases by only ~23%. By Day 7, the wounds produced using TFMG-coated blades were noticeably smaller than those produced using uncoated blades, and these effects were particularly evident in hairy samples. This is a clear demonstration of the efficacy of TFMG surface coatings in preserving the cutting quality of surgical instruments.

Effectiveness of low binding frictional materials: Evaluation of the binding frictional resistance of improved superelastic nickel-titanium alloy wires with different bracket combinations

Introduction: This study aimed to evaluate the binding frictional resistance of improved superelastic nickel- titanium alloy wires (ISW) with different bracket combinations and to verify the effectiveness of low binding frictional materials by applying them in orthodontic treatment. Materials and Methods: Straight stainless steel wire (SSW; 0.016 × 0.022-inch) and straight ISW (0.016 × 0.022- inch) were set to each displaced bracket, and the tensile resistance load was measured. The maximum tensile resistance load was statistically compared using the Tukey test. For exemplification, we treated a typical extraction case of Angle Class I crowding malocclusion with lip protrusion using lower binding frictional materials, which were selected based on tensile test results. Results: The SSW and metal bracket combination had the largest maximum tensile resistance load, and the ISW and metal slot-equipped plastic bracket combination had the smallest load (P &lt; 0.01). In a patient treated using lower binding frictional materials, the active treatment period was 9 months. Satisfactory patient results were obtained without using reinforced anchorage. Conclusions: Binding frictional resistance varies, depending on the archwire and bracket combination. In a multibracket appliance, selecting materials with as low a binding frictional resistance as possible may make a more effective treatment.