High Friction Research Articles

Bioengineered lubricin alters the lubrication modes of cartilage in a dose-dependent manner.

The low friction nature of articular cartilage has been attributed to the synergistic interaction between lubricin and hyaluronic acid in the synovial fluid (SF). Lubricin is a mucinous glycoprotein that lowers the boundary mode coefficient of friction of articular cartilage in a dose-dependent manner. While there have been multiple attempts to produce recombinant lubricin and lubricin mimetic cartilage lubricants over the last two decades, these materials have not found clinical use due to challenges associated with large scale production, manufacturing, and purification. Recently, a novel method using codon scrambling was developed to produce a stable, full-length bioengineered equine lubricin (eLub) in large reproducible quantities. While preliminary frictional analysis of eLub and other recombinantly produced forms revealed they can lubricate cartilage, a complete tribological characterization is lacking, with previous studies evaluating the friction coefficient only at a single dose or a single speed. The objective of this study was to analyze the dose-dependent tribological properties of eLub using the Stribeck framework of tribological analysis. Recombinantly produced eLub at doses greater than 1.5 mg/mL exhibits friction coefficients on par with healthy bovine SF, and a maximal 5 mg/mL dose exhibits a nearly 50% lower friction coefficient than healthy SF. eLub also modulates the shift in lubrication mode of the cartilage from the high friction boundary mode to the low friction minimum mode at high concentrations.

Dynamic fuzzy comprehensive evaluation of wet friction components performance degradation based on G1-CRITIC

High power density wet friction components are crucial in heavy equipment transmission systems, directly influencing equipment reliability. This paper proposes a fuzzy comprehensive evaluation method with combined weighting, which dynamically divides the performance degradation of wet friction components into three stages. It constructs a multi-indicator, multi-level evaluation system, in which the performance degradation data is obtained from the wet clutch accelerated life test. Additionally, we utilize the combined weighting method to dynamically allocate weights for evaluation indicators at different stages and introduce the trapezoidal distribution membership function. The accuracy of the fuzzy comprehensive evaluation model is then verified by using two prediction models as a comparison method. The results indicate that the model achieves an average relative error of 14.79% and a correlation coefficient R2 of 0.9580, indicating higher usability and accuracy than the prediction models. Furthermore, the evaluation indicator weights are more sensitive to pressure variations.

Development of a Load‐Bearing, Terrain‐Adaptive Hexapod Robot With Chebyshev‐Linkage Legs

ABSTRACTThis study introduces an exploratory design for a hexapod load‐carrying robot, aiming to address challenges commonly associated with quadruped robots, including limited load capacity and high control complexity. By leveraging a Chebyshev linkage‐based overconstrained leg‐foot architecture that combines high rigidity and low friction, along with a multi‐drive system for lateral movement, we propose a robot with improved adaptability to diverse terrains, such as snow, sand, puddles, ice, and deserts. This versatility suggests potential applications in areas such as factory inspection, field reconnaissance and transport, and desert exploration. Using static and dynamic analyses, we evaluated the leg structure's stress distribution and motion requirements, employing simulations in Workbench and Adams to cross‐validate our theoretical calculations. The development of a prototype and its subsequent testing under various environmental conditions aimed to demonstrate the design's practicality and the robot's operational capabilities in real‐world settings. Although the findings indicate progress toward enhancing load‐bearing capabilities and terrain adaptability with reduced control complexity, further research and development are necessary to fully realize the potential of such robotic systems in practical applications.

Improve wear resistance of C/C composites as artificial bone using diamond-like carbon coatings

In this study, diamond-like carbon (DLC) coatings and silicon-doped diamond-like (Si-DLC) coatings were prepared on the surface of C/C composites by a combination of plasma-enhanced chemical vapor deposition (PECVD) and magnetron sputtering processes. The film composition, microstructure and atomic bond structure were characterized using X-ray photoelectron spectroscopy, field-emission scanning electron microscopy and Raman spectroscopy. The mechanical properties and friction behavior related to the Si element were investigated using nanoindentation and HT-1000 high temperature friction and wear tester. The biocompatibility of the materials was also evaluated by the MG-63 proliferation test. The results indicate that Si elements were successfully incorporated into the DLC films, bonding with C and O atoms, which altered the thermal stability and microstructure of the coatings, reduced the internal stress of the films, and increased disorder. Compared to C/C composites, all coated layers exhibited lower coefficients of friction, with the formation of transfer layers and graphitization induced by friction contributing to the excellent tribological performance. Both coatings showed no cytotoxicity and demonstrated good biocompatibility. Both coatings are effective in reducing wear and chip losses in C/C composites when used as artificial bones. This work suggests that diamond-like carbon coated C/C composites can be excellent structural materials for human body in biomedical science.

Comparing the Performance of Recycled Calcined Bauxite vs. Locally Available Aggregate as Components in High Friction Surface Treatment Applications

Comparing the Performance of Recycled Calcined Bauxite vs. Locally Available Aggregate as Components in High Friction Surface Treatment Applications

Comminution‐Induced Transient Frictional Behavior in Sheared Granular Halite

AbstractGrain comminution is commonly observed in numerous geological settings. To elucidate the role of grain comminution in dry granular friction, we sheared breakable halite (NaCl) grains using a ring‐shear configuration at a constant slip rate under various normal stresses. We observed transient frictional behaviors: a constant regime exhibiting a high friction coefficient at small slip displacements, and a weakening regime showing a substantial decay in friction at large slip displacements. The characteristic slip lengths for both regimes decreased with normal stress and were characterized by similar exponents. Micro‐X‐ray tomography revealed the evolution of microstructure from distributed grain comminution to progressive shear localization for these two regimes. We propose that the filling processes of comminuted fine particles, during which fine particles saturate and then overflow the shear zone, define transient frictional behaviors. This study may hold significant implications for natural shear systems, given the ubiquity of comminution and localization phenomena.

Simulating Pelvis Kinematics from Belt and Seat Loading in Frontal Car Crash Scenarios: Important Boundary Conditions that Influence the Outcome.

The risk of submarining during automotive crashes, defined by the lap belt sliding off the pelvis to load the abdomen, is predicted to increase in future autonomous vehicles as greater variation in seating position is enabled. Biofidelic tools are required to efficiently design and evaluate new and/or improved safety systems. This study aims to evaluate the pelvis response sensitivity to variations in boundary conditions that directly influence the pelvis loads, deemed important for the submarining outcome, to facilitate a more precise comparison between finite element human body models (FE-HBMs) and post-mortem human subjects (PMHSs). A parameter study, using a one-variable-at-a-time analysis (low/high) of belt friction, seat friction, seat stiffness, and (on/off) for added belt bending stiffness, was performed using a state-of-the-art FE-HBM in four different test scenarios; one stationary, two sleds with upright occupant posture, and one sled with reclined occupant posture. In the stationary scenario, both belt friction and belt bending stiffness influenced the belt folding behavior, which consequently affected the belt-to-pelvis angle at submarining. In the sled scenarios, only seat friction was found to influence the pelvis kinematics and submarining outcome, with the most biofidelic response resulting from both the low (0.2) and high (0.5) friction coefficient depending on the scenario. To reduce uncertainty in boundary conditions affecting the external pelvis loads and increase confidence in FE-HBM to PMHS comparisons, it is recommended that future experiments evaluate the PMHS to seat friction coefficient and that new belt modeling methods that accurately capture belt folding when interacting with soft tissues are developed.

Pearl‐Inspired Colored Carbon Fibers with Electromagnetic Interference and Optical Camouflage Properties

Carbon fibers (CFs) are widely used in cutting‐edge and civilian fields due to their excellent comprehensive properties such as high strength and high modulus, superior corrosion and friction resistances, excellent thermal stability, light weight, and high electrical conductivity. However, their natural ultra‐black appearance is difficult to meet the aesthetic needs of today's civilian sector and the need for optical stealth in the military field. In addition, conventional coloring methods are difficult to effectively adhere to CF surfaces due to high crystallinity and highly inert surface caused by their graphite‐like structure. In this work, inspired by the nacre structural color of pearls, colored CFs with 1D photonic crystal structure are prepared by cyclically depositing amorphous (Al2O3 + TiO2) layers on the surface of carbon CFs through atomic layer deposition (ALD). The obtained CFs exhibit brilliant colors and excellent environmental durability in extreme environments. Moreover, the colored CFs also exhibit high EMI shielding effectiveness (45 dB) and optical stealth properties, which can be used in emerging optical devices and electromagnetic and optical stealth equipment.

Influence of silica and alumina nanoparticles on the wear and mechanical behavior of Indian almond fiber reinforced natural composites

Natural composites are valued for their lightweight, cost-effectiveness, and environmental benefits, but they often fall short in performance compared to conventional materials. To enhance their properties, nanoparticles are added. This study focused on natural composites made from Indian almond fiber, with alumina and silica nanoparticles incorporated. The scope of this research was to develop the Indian almond based materials as industry ready by enhancing its strength with nano-fillers. Four composites were created: C0 (Epoxy/Indian almond), C1 (Epoxy/Indian almond/Silica), C2 (Epoxy/Indian almond/Alumina), and C3 (Epoxy/Indian almond/Silica/Alumina), using a resin-to-fiber ratio of 70:30 and 3 wt% nanoparticles. The inclusion of nanoparticles improved composite performance, with C2 demonstrating superior mechanical and wear properties. Specifically, C2 achieved high tensile strength (84 MPa), flexural strength (122 MPa), impact strength (7.31 kJ/m2), and hardness (86 shore D), along with smallest wear and friction coefficient. HIGHLIGHTS Natural fiber based material was prepared by means of Indian almond fiber in addition to epoxy resin Silica and alumina nano-additives were added for further strengthening of composite Indian almond/Silica/Alumina composite’s functioning was investigated Indian almond/Alumina composite exhibited better tensile, flexural and impact strengths Indian almond/Alumina composite showed high hardness, slightest wear plus low friction coefficient

Identification of non-circular profiles in hydrodynamic journal bearings

Hydrodynamic bearings, especially cylindrical radial plain journal bearings, are widely utilized in industry for their high load capacity and low friction energy losses. However, these bearings are prone to faults such as wear and ovalization, which can deform their circular profile and affect their vibrational response. Detecting these faults is essential to reduce their impact on production. This study introduces a methodology to identify hydrodynamic bearings with non-circular profiles. The bearing model and its numerical solution are implemented using the Finite Volume Method, with the effects of failures incorporated into a rotating system modeled by the Finite Element Method. A dataset is generated to reflect three common failure conditions in industrial applications: wear, ovalization, and a combination of ovalization with wear. The authors used this dataset to train a Multilayer Perceptron (MLP) neural network, which can identify the bearing profile shape based on specific attributes of the dynamic responses. The identification tests for the three fault conditions demonstrated high accuracy, particularly in distinguishing between ovalization and wear.

A Biomimetic Adhesive Disc for Robotic Adhesion Sliding Inspired by the Net-Winged Midge Larva.

Net-winged midge larvae (Blephariceridae) are known for their remarkable ability to adhere to and crawl on the slippery surfaces of rocks in fast-flowing and turbulent alpine streams, waterfalls, and rivers. This remarkable performance can be attributed to the larvae's powerful ventral suckers. In this article, we first develop a theoretical model of the piston-driven sucker that considers the lubricated state of the contact area. We then implement a piston-driven robotic sucker featuring a V-shaped notch to explore the adhesion-sliding mechanism. Each biomimetic larval sucker has the unique feature of an anterior-facing V-shaped notch on its soft disc rim; it slides along the shear direction while the entire disc surface maintains powerful adhesion on the benthic substrate, just like the biological counterpart. We found that this biomimetic sucker can reversibly transit between "high friction" (4.26 ± 0.34 kPa) and "low friction" (0.41 ± 0.02 kPa) states due to the piston movement, resulting in a frictional enhancement of up to 93.9%. We also elucidate the frictional anisotropy (forward/backward force ratio: 0.81) caused by the V-shaped notch. To demonstrate the robotic application of this adhesion-sliding mechanism, we designed an underwater crawling robot Adhesion Sliding Robot-1 (ASR-1) equipped with two biomimetic ventral suckers. This robot can successfully crawl on a variety of substrates such as curved surfaces, sidewalls, and overhangs and against turbulent water currents with a flow speed of 2.4 m/s. In addition, we implemented a fixed-wing aircraft Adhesion Sliding Robot-2 (ASR-2) featuring midge larva-inspired suckers, enabling transit from rapid water surface gliding to adhesion sliding in an aquatic environment. This adhesion-sliding mechanism inspired by net-winged midge larvae may pave the way for future robots with long-term observation, monitoring, and tracking capabilities in a wide variety of aerial and aquatic environments.

Using Thin Ultra-High-Molecular-Weight Polyethylene Coatings to Reduce Friction in Frost-Resistant Rubbers.

Frost-resistant rubbers retain their highly elastic properties over a wide temperature range. They are used in various friction units (e.g., seals), but their high friction coefficient and low wear resistance lead to the need for frequent replacement. In this paper, we propose applying thin (several hundred microns) UHMWPE coatings to formed rubber rings. The application technology depends on the required coating thickness. Friction tests of the coatings and pure UHMWPE were performed using the ball-on-disk (unidirectional sliding) scheme for various loads and velocities. In the experiments, the friction coefficients and temperatures near the contact area were determined. Friction tracks were studied using microscopy methods. The sliding contact of the ball and the two-layer material was modeled to obtain the dependences of the deformation component of friction on the sliding velocity for coatings of different thicknesses. UHMWPE is sensitive to frictional heating, so the thermal problem of determining the temperature in the contact area was also solved. It is shown that the minimum friction coefficient occurs for coatings with a thickness of 600 μm. At the same time, in the case of the 300 μm coating, the surface of the friction track is practically no different from the initial one. Thus, the studied combination of polymers provides antifrictional properties and wear resistance to the surface layer while maintaining the damping properties of rubber.

Biocompatible Hydrogel Coating on Silicone Rubber with Improved Antifouling and Durable Lubricious Properties.

Silicone rubber is widely used in various medical applications. However, silicone rubber is prone to biofouling due to their affinity for lipids and has a high friction coefficient, which can significantly impact their efficacy and performance used as medical devices. Thus, the development of hydrogels with antifouling and lubricious abilities for the modification of silicone rubber is in high demand. We herein prepared a variety of hydrogel coatings mainly based on polyvinylpyrrolidone (PVP) and poly (ethylene glycol) diacrylate (PEGDA). We modified the silicone rubber using the prepared hydrogel coatings and cured it using a heating method. Then, we characterized its surface and evaluated the antifouling property, lubricious property, cytotoxicity, sensitization, and vaginal irritation. The results of water contact angle (WCA), protein adsorption, and friction coefficient indicated the success of the modification of the silicone rubber, leading to a significant decrease in the corresponding test values. Meanwhile, the results of cytotoxicity, sensitization, and vaginal irritation tests showed that the hydrogel coating-modified silicone rubbers have an excellent biocompatibility. This study describes how the silicone rubber could be modified with a biocompatible hydrogel coating. The hydrogel coating-modified silicone rubbers have improved antifouling and durable lubricious properties.

Relationship between Capillary Wettability, Mass, and Momentum Transfer in Nanoconfined Water: The Case of Water in Nanoslits of Graphite and Hexagonal Boron Nitride.

The flow of water confined in nanosize capillaries is subject of intense research due to its relevance in the fabrication of nanofluidic devices and in the development of theories for fluid transport in porous media. Here, using molecular dynamics simulations carried out on 2D capillaries made up of graphite, hexagonal boron nitride (hBN) and a mix of the two, and of sizes from subnanometer to few nanometers, we investigate the relationship between the wettability of the wall capillary, the water diffusion, and its flow rate. We find that the water diffusion is decoupled from its flow properties as the former is not affected either by the height or chemistry of the capillary (except for the subnanometer slits), while the latter is dependent on both. The capillaries containing hBN show a reduced flow rate compared to those that are purely graphitic, likely due to the high friction coefficient between water and hBN. Such resistance to the flow is, however, at its maximum in the smallest capillary and lower for larger ones. Finally, we show that the flow rate values obtained from the Hagen-Poiseuille theory are almost always smaller than those obtained from simulations, indicating that either the slip length or the viscosity of nanoconfined water could be substantially different from the bulk values.

Improving Friction Sensitivity of Molecular Perovskite Energetic Material DAP‐4 by Polymer Binders Coated

AbstractThe high detonation and thermostability of the molecular perovskite energetic material DAP‐4 attracted a lot of interest, but its high friction sensitivity hindered its applicability. It is critical to minimize the friction sensitivity of DAP‐4 for future applications. DAP‐4‐based composites with core‐shell structures coated by polymer binders were devised and manufactured in this study. DAP‐4 was discovered to be polymer binder compatible, and the thermal breakdown temperature remained constant at 380°C. The friction sensitivity of DAP‐4‐based core‐shell composites increased from 36 N (raw DAP‐4) to 60 N (DAP‐4@Estane‐5703, DAP‐4@F2602, and DAP‐4@F2311) when 10% polymer binders were added as shell‐structured layers. Furthermore, their theoretical detonation performance was calculated, and each sample demonstrated superior performance. Among them, the theoretical detonation velocity of DAP‐4@F2602 reached 8081 m/s, and the heat of detonation was 5.118 kJ/kg. This provided proof‐of‐concept work for increasing the mechanical safety of molecular perovskite energetic materials.

An investigation on tribology performance of Abutilon Indicum fibre reinforced polymer composites

This research work investigates the tribological characteristics of Abutilon Indicum Fiber (AIF) reinforced composites with epoxy as the binding agent. The Abutilon Indicum fiber reinforced composites were manufactured by compression molding technique. These composites were fabricated by varying the fiber volume fraction ranging from 5%, 10%, 15% and 20% respectively and considering the fiber length as a fixed factor due to its short length. This research paper illustrates the effects of different fiber volume fractions (5,10,15 and 20%) on the tribological properties such as Specific wear rate (SWR) and Coefficient of friction (µ) of Abutilon Indicum fiber reinforced composites. Sliding wear tests were carried out under dry environment conditions with pin-on-disc wear testing machine. The experiments were performed for each composite with different combinations of testing parameters, sliding loads (10, 20 and 30 N); sliding distances (1,2 and 3 km); sliding speeds (1,2 and 3 m/s). Shore D hardness of 78.22 is determined to be higher for 15% volume fraction of AIF composites. Results conclude that the addition of AIFs in these composites enhanced the tribological performance with good wear resistance in relation with the pure epoxy-based composites with 15% volume fraction of AIFs displaying best results with higher resistance to wear at various operating conditions. Composites produced with 20% volume fraction displays the effects of fiber agglomeration which in turn has an inverse effect on hardness; limits the wear resistance with higher friction and wear rate and such results agree well with the wear debris, pits and contact patches in micrographs. Optimal fiber volume fraction of 15% was suggested in fabrication of composites for usage of AIFs as friction material.

A Tribological Study of CrN and TiBN Hard Coatings Deposited on Cobalt Alloys Employed in the Food Industry

In this work, a comparative study of the tribological performance of two hard coatings, CrN/TiBN, was conducted for research purposes and industrial applications in food products, particularly for food packaging into cans using the double hermetic sealing process. CrN and TiBN coatings were successfully deposited on a base-cobalt metal substrate of a CoCrW commercial alloy using physical vapor deposition by arc evaporation (AEPVD) technology to improve the tribological properties of the commercial alloy, including wear and corrosion resistance, lower coefficient of friction, and overall durability. This research focuses on conducting scratch and abrasion wear resistance tests in dry conditions; specifically, it pursues to evaluate the wear corrosion properties, known as tribocorrosion performance, on CrN/TiBN hard coatings. The experimental results show that the CrN coating (2.9 μm) is slightly thicker than the TiBN coating (2.7 μm), with a 47 N critical load. It also shows a lower coefficient of friction (CoF) in a dry environment, while the TiBN coating showed total detachment and a high coefficient of friction in a dry environment condition. Tribocorrosion testing in brine aqueous solution indicated that CrN coating shows a high friction coefficient with a higher open circuit potential value (Ecorr), and TiBN shows the lowest corrosion potential (Ecorr) and the lowest friction coefficient. This suggests that CrN could provide better corrosion protection for commercial cobalt alloys and improve tool performance during the food canning process in brine environments.

Novel fracturing fluid made of low molecular weight polymer and surfactant achieves proppant full suspension and filling entire area of hydraulic fractures

In large-scale hydraulic fracturing of unconventional reservoirs, high viscosity friction reducers (HVFR) which employ high concentration polymers of high molecular weight can improve proppant suspension, but still lack long-distance and long-time proppant transport capability. Herein, for the first time, we report a fracturing fluid made of self- assembled low molecular weight polymer and a surfactant (LMPS). When using only 0.1 wt% of the polymer, LMPS has a viscosity of 29.6 mPa·s (170 s−1, 25 ℃) and can achieve full suspension of 40/70 mesh sand at 80 ℃. LMPS can form robust short molecular chain networks through numerous self-assembling association sites, rather than relying on entanglement. Notably, it achieves a minimum loss tangent as low as 0.1 in the viscoelastic response, demonstrating its strong elastic characteristics. According to the creep-recovery test, the strain recovery rate (87.9 %) of LMPS at 0.2 wt% polymer concentration far exceeds that of the HVFR with a concentration as high as 10.1 %. This indicates that LMPS has a stronger deformation-resisting ability, thereby preventing proppant settling. Taking advantage of LMPS’ superior proppant suspension capability, proppant can move with the slurry to the whole fracture for placement, while the HVFR provides only 48 % height support of the fractures in the form of dunes. A field trial shows that at a polymer concentration of 0.2 wt%, LMPS can stably transport 20/40 mesh quartz sand under a slurry rate of 2.8 m3/min and a proppant concentration of 635 kg/m3 during the fracturing process.

Effect of radiation on lubrication performance and the consequences for mechanical equipment at CERN

Successful operation of the accelerator complex at CERN relies on Beam Intercepting Devices (BIDs) which are exposed to high doses of radiation and severely restricted maintenance access over their operating life. Instances of lubrication problems have been observed, such as high friction, overheating, corrosion and, in extreme cases, seizure. Understanding the root causes and the mechanisms controlling such failures is key to avoid downtime and improve maintenance schedules and processes. The paper reviews radiation degradation of lubricants and examines their tribological implications. Several examples of lubrication problems observed at CERN are investigated, and preliminary explanations are provided in the light of tests performed on irradiated samples. This highlights the need for better testing protocols and a thorough assessment of the time-varying performance of lubricants operating in the presence of radiation.

Drilling Technology of Large Plumb Ratio Shallow Shale Gas Well

Abstract SY1H is the first shallow shale horizontal well deployed in Jilin Oilfield, with a depth of 1,150m in Qing1 section of the target layer, a designed horizontal section length of 2,000m, and a water-drag ratio of nearly 2:1, so the well is characterised by the difficulty of pressurising with a large digit-drag ratio, the high friction between the drilling and the lower casing, and the shale wall being easy to be destabilised and collapsed. There are no horizontal wells in the neighbouring wells with a section of green as the destination layer, and there is a lack of reference materials, and the stability of the shallow shale is not clear. In order to ensure that the well can be reached and drilled for a long time, a technical route was formulated with the objectives of effectively reducing drilling resistance, increasing drilling pressure, and rapid drilling and completion within the collapse cycle, and technical measures such as equipping with a top drive and a high-grade drilling rig to increase the drilling pressure, oil-based drilling fluids and rotary guiding to reduce drilling resistance and the ability to deal with complex situations, and floating casing process to ensure that casing can be smoothly lowered in place, etc., so as to achieve safe and rapid construction of SY1H and achieve a horizontal section of 2,000m. construction and achieve the geological target of 2000m horizontal section.