As a widely used engineering polymer, epoxy resin has been successfully employed in high-performance components and setups. However, the poor thermal and friction properties of traditional epoxy ...resin greatly limit its application in many extreme environments. In this work, a new kind of epoxy-Ti
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with three-dimensional nanosheets (3DNS) composite which was designed by freeze-drying method showed up excellent thermal and friction properties. As a result, the coefficient of thermal expansion (CTE) of epoxy-Ti
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3DNS 3.0 composites was 41.9 ppm/K at 40 °C, which was lower than that of the traditional epoxy resin (46.7 ppm/K), and the thermal conductivity (TC) was also improved from 0.176 to 0.262 W/(m·K). Meanwhile, epoxy-Ti
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3DNS 1.0 composites showed up the best friction property, with wear rate 76.3% lower than that of epoxy resin. This work is significant for the research of high-performance composite materials.
Low friction coefficients are required for biomaterials in order for them to be used in the repair of articular cartilage. In the present study, polyvinyl alcohol (PVA)/polyvinylpyrrolidone (PVP) ...hydrogels were synthesized with different degrees of polymerization in the PVA and different polymer concentrations. A repeated freezing-thawing method was used to prepare them. The microstructures of the synthesized compositions gave an insight into the effects of the preparation processes and properties of the hydrogel. The influences of PVA polymerization and polymer concentration on the swelling behavior of PVA/PVP hydrogels in phosphate-buffered saline (PBS) were examined. The friction coefficients of PVA/PVP hydrogels against stainless steel were measured using a rotating ball-on-plate tribometer. The testing variables were: (a) polymerization degree of PVA, (b) polymer concentration, (c) lubrication condition (dry, physiological saline, and bovine serum), (d) sliding speed and (e) load. With increasing polymer concentration and polymerization degree of PVA, the inner structures of the hydrogels tended to be denser. An effective drop in swelling ratio was observed for hydrogels in PBS. The friction coefficient increased with an increase in polymerization degree of PVA, while it decreased with an increase of polymer concentration in the low load region and under liquid lubrication. At long testing times, the friction coefficient of hydrogels under dry sliding conditions increased rapidly owing to a lack of the interstitial fluid, while the friction coefficient remained stable during the entire friction test when fluid lubricated. Biphasic lubrication is proposed to be the key reason for maintaining a low friction coefficient level for PVA/PVP hydrogel when sliding against stainless steel.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Lyocell fibers are currently claimed as green fibers with good application prospects, but the major problem of fibrillation restricts further promotion and application. In this study, based on the ...theory of hydration lubrication at the solid/liquid interface, hexamethylene-diisocyanate trimer (HDIt), polyethylene glycol (PEG), and butanone oxime (MEKO) were used to synthesize a reactive hydrophilic triblock polyurethane (RHT-PU). RHT-PU could construct a water lubrication layer on the lyocell fiber surface via H-bonding between polyoxyethylene ether and water molecules, reducing the coefficient of friction (CoF) of the fiber interface in the water. It was found that PEG molecular weight and grafting density had significant effects on the CoF of modified fabrics, with CoFs decreased with increased PEG molecular weight and grafting density. In water, the CoFs of fabrics modified by RHT-PU were reduced from 0.45 to 0.32 and maintained lower CoFs at higher temperature and higher normal loads. After mechanical friction and household washing tests, the surface abrasion of modified fabrics were significantly improved and color fading grade of fabrics raised from 3 grade to 4–5 grade. Construction of water-lubricated interfaces effectively reduced fibrillation.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The synergistic influences of geometrical, mechanical and thermal mismatches between a skin‐contacting medical device and the skin may cause tissue stress concentrations and sharp temperature ...gradients, both of which contribute to the risk for medical device‐related pressure ulcers. In this work, we developed an innovative, integrated experimental bioengineering approach encompassing mechanical stiffness, friction and thermal property studies for testing the biomechanical suitability of a hydrogel‐based dressing in prophylaxis of injuries caused by devices. We characterised the viscoelastic stress relaxation of the dressing and determined its long‐term elastic modulus. We further measured the coefficient of friction of the hydrogel‐based dressing at dressing‐device and skin‐dressing interfaces, using a tilting‐table tribometer. Lastly, we measured the thermal conductivity of the dressing, using a heat‐flow meter and infrared thermography‐based method. All measurements considered dry and moist conditions, the latter simulating skin perspiration effects. Our results revealed that the long‐term stiffness and the thermal conductivity of the hydrogel‐based dressing matched the corresponding properties of human skin for both dry and moist conditions. The dressing further demonstrated a relatively high coefficient of friction at its skin‐facing and device‐facing aspects, indicating minimal frictional sliding. All these properties make the above dressing advantageous for prevention of device‐related injuries.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Air-cooled blast furnace slag is a metallurgical waste that can be used to produce the slag aggregate for pavement subbase. Slag aggregate is much cheaper than natural stone aggregate, but differs in ...heterogeneity in strength (from 2 to 40 MPa), tendency to absorb water, and low resistance to freezing-thawing. The paper suggests the use of methods of enrichment by friction properties, selective crushing, and hydrophobization to increase slag aggregate resistance to freezing-thawing cycles, crushing, and water penetration. Selection of the most strength (low porous) 75 % slag aggregate grains due to enrichment by friction properties decreases the total water absorption of the sample from 4.45 % to 3.64 %, decreases the sample mass loss after tests for resistance to freezing-thawing cycles from 5.05 % to 2.82 %, reduces the aggregate crushing value (ACV) from 30.71 % up to 23.80 %. Hydrophobization of the pre-enriched slag aggregate additionally reduces its water absorption to 1.08–––1.3 %.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The angle of repose is a measure reflecting the internal friction and cohesion properties of a granular material. In this paper, we present an experimental setup and measurements for the angle of ...repose of snow for seven different snow samples over a large range of temperatures. The results show that the angle of repose is dependent on the fall height, the temperature, and the grain size of the snow. These variables are quantified, and their interdependencies are separately studied. With increased snow temperature, the angle of repose increases, and this can be explained by the presence of a liquid layer on ice that can be thermodynamically stable at temperatures below the melting point of water. With decreasing grain size the angle of repose also increases which is expected since the cohesive energy decreases more slowly than the grain mass. For increasing fall height, the snow grains generally accelerate to larger collisional velocities, yielding a smaller angle of repose. In general, the dimensionless cohesion number was found to largely reflect the dependencies of the variables and is therefore useful for understanding what affects the angle of repose. The results demonstrate that the drag force and collision dynamics of ice grains are important for understanding how snow accumulates on a surface, for example if one desires predicting snow accretion by simulating a dispersed cloud of snow.
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•Experimental results for the angle of repose of snow with seven different snow samples.•Temperature dependency was concluded to follow an Arrhenius relationship.•Fall height was shown to be an important experimental parameter.•A size dependency was established where smaller grains yield higher angles.•The cohesion number captures the nonlinear dependencies observed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Carbon fiber-reinforced silicon carbide matrix (C/C-SiC) composites with different SiC contents were fabricated by reactive melt infiltration of silicon with four types of porous C/C composites ...prepared by chemical vapor infiltration. Compared to high-density C/C composites and silicified graphite, the C/C-SiC composites demonstrated an excellent balance of mechanical properties, especially impact toughness. The results show that the porosity of C/C composites is a key factor that affects the SiC content in the C/C-SiC composites. A W18Cr4V steel alloy (hardness 55-60 HRC, roughness 0.8 μm) was used as the material for the friction pair. The friction coefficient of the C/C-SiC composites measured by block-on-ring friction tests is mainly influenced by SiC content and test load. The friction coefficient first increases and then decreases as the SiC content and test load increase, reaching a minimum of 0.011 for 44.22 vol% SiC composite under a load of 80 N. Water also plays an important role in decreasing the friction coefficient. Observations of the worn surface and wear debris indicate that the main wear mechanism of C/C-SiC composites is abrasive wear.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
Full ceramic ball bearings are widely used in extreme and complex conditions, such as ultra-high/low temperature, ultra-high speed, corrosion and insulation, because of their material specificity. In ...order to reveal the friction and lubrication properties, improve the service performance life of all ceramic ball bearings, a mathematical model of the oil lubrication for full ceramic ball bearings has been established in this paper. The distribution rule of the lubricant film in the contact area under different speeds and loads were analysed. The main factors influencing the peak mutation of the lubricant film pressure are clearly defined. The results are compared and analysed by using a ball-disc rolling lubricant film test machine. The study found that the thickness of the lubricant film of a full ceramic ball bearing is positively correlated with the bearing speed and negatively correlated with the bearing loads. The bearing speed has a relatively large effect on the change in the lubricant film thickness. The pressure of the lubricant film in the contact area is positively correlated with the bearing speed, but it is not affected by the bearing load. Unlike metal ball bearings, the thickness and pressure of the lubricant film have a greater relative rate of change in different positions in the contact area of full ceramic ball bearings. With an increase in the bearing speed, the necking-down effect has a greater influence on the peak mutation of the oil pressure. Only one pressure peak occurs in the oil film in the contact area. The results of this paper play an important role in revealing the friction and lubrication properties of full ceramic ball bearings and improving their service performance and life under oil lubrication conditions.
The isotropic pyrocarbon bulk materials were prepared by the fixed-bed chemical vapor deposition method, and the internal structure was composed of ribbon-like structure and spherical structure ...together. The friction behaviors of isotropic pyrocarbon at room temperature were studied by characterizing the microstructure and friction morphology. The frictional properties of isotropic pyrocarbon are greatly influenced by internal ribbon-like pyrocarbon. With a higher content of ribbon-like pyrocarbon, the material produces a moderately rough friction film, which improves the stability of the friction coefficient. Meanwhile, ribbon-like pyrocarbon increases the hardness of the material and reduces its wear rate. In addition, external stress can impact the friction behavior of the material. Increasing the external load causes the friction film to become more continuous and uniform, reducing the overall friction coefficient of the material. When the load is low (50 N and 100 N), the friction coefficient tends to stabilize more quickly. Nevertheless, an excessive load (200 N) will result in the creation of grooves, making it difficult to stabilize the friction coefficient of the material.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The dimension of components in micro/nanoelectromechanical systems (MEMS/NEMS) has been reduced to nanometer. Due to size effects at nanoscale, there is severe adhesion effect in the MEMS/NEMS. As a ...result, improving friction behaviors has become one of the most important ways for MEMS/NEMS to prolong their lives. At macroscale, friction forces of rolling contacts are lower than those of sliding contacts, while there are no comprehensive studies on the friction performance of the nanoscale rolling contacts. Molecular dynamics simulation is used to investigate the friction performance of nanoscale rolling contacts in this work. The dependence of average friction forces on indentation depth and tip size is investigated. The average friction force of the rolling contact is much lower than that of the sliding contact. Increasing the indentation depth causes the increase of the average friction forces, while the tip radius shows little influence. Furthermore, by creating textures with different widths on upper and lower substrates, their influence on the rolling contact performance is studied. Compared with a smooth surface, the textured surfaces can improve the friction properties of nanoscale rolling contacts. The texture width, texture depth, and texture shape influence the friction behaviors greatly.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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