Search Results (3,649)

This paper reports the preliminary experimental studies carried out on an innovative sliding bearing made of polycrystalline diamond, a material with excellent mechanical and chemical characteristics, used mainly in the drilling industry. Bearings crafted from this material do not necessitate lubrication due to their extremely low coefficient of friction and high resistance to wear. For this reason, they are prime candidates for replacing traditional oil bearings, eliminating the need for auxiliary systems and thereby reducing environmental risks. In this regard, an innovative test rig was designed, capable of reaching speeds up to 6000 rpm both in vertical and horizontal configurations thanks to a novel tilting frame. Moreover, with a high modularity it was possible to test three different kinds of radial PCD bearings. Dynamic data were acquired and elaborated to evaluate orbits, acceleration and absorbed torque, to finally compare these different configurations to better understand how dynamic behavior is influenced by bearings’ geometrical characteristics. Full article

In recent years, micro-cutting has been employed to obtain components that are more detailed and/or have great surface quality, regardless of dimensions, like dental implants. In the manufacturing of medical/dental components, titanium and its alloys are biomaterials of great notability. Like in conventional machining, sustainability is a delicate issue because it does not only depend on environmental aspects. One simple solution would be to perform dry machining. However, in the machining of difficult-to-cut materials, like titanium and its alloys, the use of cutting fluids is generally recommended to avoid the high temperature causing damage to the tool and/or machined surface. Concerned with the quality surface that is required for dental components, this work investigates the use of cutting fluid in the micro-cutting of commercially pure titanium. Orthogonal micro-cutting experiments were carried out under dry and wet conditions, using cutting fluid at room and cooled temperatures. To evaluate the lubri-cooling performance, cutting efforts, the friction coefficient, specific cutting energy, and chip formation analysis were compared. The outcomes indicated that, under the test conditions, the use of dry cutting and high feed levels had a positive effect on micro-cutting performance. Full article

The aim of this study was to measure the physical attributes of seeds of selected lilac species and to describe the correlations between these properties and seed mass for seed processing and treatment. Basic physical parameters were measured in the seeds of five lilac species and the results were used to calculate aspect ratios describing seed shape and size. The average values of the measured properties ranged from 3.57 to 5.98 m s⁻¹ for terminal velocity, from 6.20 to 9.61 mm for seed length, from 2.19 to 3.94 mm for seed width, from 0.85 to 1.21 mm for seed thickness, from 5.9 to 19.2 mg for seed mass, and from 32° to 44° for the angle of external friction. Seed mass was bound by the strongest correlations with terminal velocity (Amur lilac, Hungarian lilac, and Pekin lilac), thickness (broadleaf lilac), and width (Japanese tree lilac). Seed thickness followed by terminal velocity were the primary distinguishing features of lilac seeds. Therefore, lilac seeds should be sorted with the use of sieve separators with longitudinal openings or pneumatic separators. These devices effectively sort lilac seeds into fractions with uniform seed mass, which can facilitate the propagation of lilacs in nurseries and the production of high-quality seedlings, thus promoting the sustainable use of natural resources and production materials. In medium-sized and large seed fractions, the coefficient of variation of seed mass can be decreased by up to 50% relative to unsorted seeds. Full article

Ti₃SiC₂/Cu composites were prepared using spark plasma sintering technology, and the effect of the velocity–load bivariate on the tribological behaviors of the Ti₃SiC₂/Cu-45# steel tribo-pair at 800 °C was investigated. The physical change and frictional chemical reaction during the friction process were analyzed based on the morphology characterization and frictional interface phases. The related friction and wear mechanism model was established. The results showed that the influence of velocity and load on the tribological performance of the Ti₃SiC₂/Cu-45# steel tribo-pair was not monotonically linear. When both the velocity and load were large, the coordinated effect of the two led to a low friction coefficient (0.52). At 800 °C, the velocity mainly affected the exfoliation and re-formation of the oxide film on the wear surface of the Ti₃SiC₂/Cu-45# steel tribo-pair, while the load affected the extrusion and fragmentation of the oxide film on the wear surface of the tribo-pair. In the friction process, frictional oxidation was the main influencing factor for the formation of the oxide film. When the velocity and load were small, the main frictional oxide consisted of SiO_2−x and a small amount of CuO. When the velocity reached 1 m/s and the load reached 3 N, the oxide film was partially broken down and flaked off, and the matrix of the Ti₃SiC₂/Cu composite was exposed and oxidized, at which time the oxide film was composed of SiO_2−x, TiO₂, CuO, and Fe₂O₃. Under the synergistic effect of the velocity–load–temperature field, the friction and wear mechanism of the Ti₃SiC₂/Cu-45# steel tribo-pair changed from abrasive wear to frictional oxidation wear with the increase in velocity and load. Full article

Sand solidification of earth-rock dams is the key to flood discharge capacity and collapse prevention of earth-rock dams. It is urgent to find an economical, environmentally friendly, and durable sand solidification technology. However, the traditional grouting reinforcement method has some problems, such as high costs, complex operations, and environmental pollution. Enzyme-induced calcium carbonate precipitation (EICP) is an anti-seepage reinforcement technology emerging in recent years with the characteristics of economy, environmental protection, and durability. The erosion resistance and shear strength of earth-rock dams solidified by EICP need further verification. In this paper, EICP-solidified standard sand is taken as the research object, and EICP-cemented standard sand is carried out by a consolidated undrained triaxial test. A two-stage pouring method is adopted to pour samples, and the effects of dry density, cementation times, standing time, and confining pressure on the shear strength of cemented standard sand are emphatically analyzed. The relationship between cohesion, internal friction angle, and CaCO₃ formation was analyzed. After the optimal curing conditions are obtained through the triaxial shear strength test, the erosion resistance model test is carried out. The effects of erosion angle, erosion flow rate, and erosion time on the erosion resistance of EICP-solidified sand were analyzed through an erosion model test. The results of triaxial tests show that the standard sand solidified by EICP exhibits strain softening, and the peak strength increases with the increase in initial dry density, cementation times, standing time, and confining pressure. When the content of CaCO₃ increases from 2.84 g to 12.61 g, the cohesive force and internal friction angle change to 23.13 times and 1.18 times, and the determination coefficients reach 0.93 and 0.94, respectively. Erosion model test results indicate that the EICP-solidified sand dam has good erosion resistance. As the increase in erosion angle, erosion flow rate, and erosion time, the breach of solidified samples gradually becomes larger. Due to the deep solidification of sand by EICP, the development of breaches is relatively slow. Under different erosion conditions, the solidified samples did not collapse and the dam broke. The research results have important reference value and scientific significance for the practice of sand consolidation engineering in earth-rock dams. Full article

The tensile strength of roots and the friction characteristics of the root–soil interface of tree species are the indicators that play a crucial role in understanding the mechanism of soil reinforcement by roots. To calculate the effectiveness of the reinforcement of soil by tree roots based on essential influencing parameters, typical trees in the coastal region of southeastern China selected for this study were subjected to tests of the tensile mechanical properties of their roots, as well as studies on the friction characteristics of the root–soil interface and the microscopic interfaces. The results indicated that in the 1–7 diameter classes, the root tensile strength of both Pinus massoniana and Cunninghamia lanceolata was negatively correlated with the root diameter in accordance with the power function. The root tensile strength of these two trees, however, was positively correlated with the lignin content but negatively correlated with cellulose and hemicellulose contents. The shear strength at the root–soil interface and the vertical load exhibited a constitutive relationship, which followed the Mohr–Coulomb criterion. As the root diameter increased, both the cohesion and the friction coefficients at the root–soil interface gradually increased, but the growth rate stood at around 15%. The cohesion value of the root–soil interface of the two trees decreased linearly with the increase in soil moisture content within the range of 25 to 45%. At the microinterface, the root surface of C. lanceolata exhibited concave grooves and convex ridges that extended along the axial direction of roots, with their height differences increasing with the enlargement of the root diameter. The rough surface of P. massoniana roots had areas composed of polygonal meshes, with an increase observed in the mesh density with increasing root diameter. Full article

The aim of this article is to provide an analysis of the influence of the type of hard anti-wear coatings on the friction behaviour of DC01 deep-drawing steel sheets. DC01 steel sheets exhibit high formability, and they are widely used in sheet metal forming operations. The tribological properties of the tool surface, especially the coating used, determine the friction conditions in sheet metal forming. In order to carry out the research, this study developed and manufactured a special bending-under-tension (BUT) friction tribometer that models the friction phenomenon on the rounded edges of tools in the deep-drawing process. The rationale for building the tribotester was that there are no commercial tribotesters available that can be used to model the phenomenon of friction on the rounded edges of tools in sheet forming processes. The influence of the type of coating and sheet deformation on the coefficient of friction (CoF) and the change in the topography of the sheet surface were analysed. Countersamples with surfaces prepared using titanium + nitrogen ion implantation, nitrogen ion implantation and electron beam remelting were tested. The tests were carried out in conditions of dry friction and lubrication with oils with different kinematic viscosities. Under dry friction conditions, a clear increase in the CoF value, with the elongation of the samples for all analysed types of countersamples, was observed. Under lubricated conditions, the uncoated countersample showed the most favourable friction conditions. Furthermore, oil with a lower viscosity provided more favourable conditions for reducing the coefficient of friction. Within the entire range of sample elongation, the most favourable conditions for reducing the CoF were provided by uncoated samples and lubrication with S100+ oil. During the friction process, the average roughness decreased as a result of flattening the phenomenon. Under dry friction conditions, the value of the Sa parameter during the BUT test decreased by 20.3–30.2%, depending on the type of countersample. As a result of the friction process, the kurtosis and skewness increased and decreased, respectively, compared to as-received sheet metal. Full article

Gas foil bearings have important and wide applications in high-speed turbomachinery, generating low frictional lubricating gas film in series with underlying elastic foil structures to support the rotor system. Their dynamic performance is of vital significance in maintaining the rotor stability as well as in depressing rotor vibrations. This paper conducts a comprehensive review on dynamic performance studies conducted on gas foil bearings, including research on the dynamic stiffness and damping coefficients, bearing stability, nonlinear vibrations of the rotor–bearing system, and active methods for controlling rotor dynamic motions. This review provides clear observations towards the developments and iterations of the models, methods, and experiments of these studies. Full article

The present study aims to investigate the advantages of diamond-like carbon (DLC) films in reducing friction and lubrication to address issues such as the low surface hardness, high friction coefficients, and poor wear resistance of titanium alloys. Cr-doped DLC films were deposited by high-power impulse magnetron sputtering (HiPIMS) in an atmosphere of a gas mixture of Ar and C₂H₂. The energy of the deposited particles was controlled by adjusting the target powers, and four sets of film samples with different powers (4 kW, 8 kW, 12 kW, and 16 kW) were fabricated. The results showed that with an increase in target power, the Cr content increased from 3.73 at. % to 22.65 at. %; meanwhile, the microstructure of the film evolved from an amorphous feature to a nanocomposite structure, with carbide embedded in an amorphous carbon matrix. The sp²-C bond content was also increased in films, suggesting an intensification of the film’s graphitization. The hardness of films exhibited a trend of initially increasing and then decreasing, reaching the maximum value at 12 kW. The friction coefficient and wear rate of films showed a reverse trend compared to hardness variation, namely initially decreasing and then increasing. The friction coefficient reached a minimum value of 0.14, and the wear rate was 2.50 × 10⁻⁷ (mm³)/(N·m), at 8 kW. The abrasive wear was the primary wear mechanism for films deposited at a higher target power. Therefore, by adjusting the target power parameter, it is possible to control the content of the metal and sp²/sp³ bonds in metal-doped DLC films, thereby regulating the mechanical and tribological properties of the films and providing an effective approach for addressing surface issues in titanium alloys. Full article

Sloshing of liquefied bulk granular cargoes weakens the stability of cargo carriers when at sea. Using the horizontal rectangle baffle is a promising way to restrain its sloshing motion. But the location height and optimal baffle area rate to achieve a better anti-sloshing effect should be studied first. The discrete element method was adopted to establish the simulation model, and the direct shear test was used for verification. Through the static tilt tests, the definite relationship between the effects of moisture content on cargo motion and particle friction coefficients was acquired. Then, liquefied cargo motion in a cargo hold without baffles and with one and two pairs of horizontal baffles was simulated. Based on variations in the cargo gravity center offset and the sloshing-induced force on the cargo hold, the anti-sloshing effect of different settings of the baffles was compared. Results show that the baffles have the ability to restrain cargo sloshing, and this is important for sea transportation safety. The anti-sloshing effect is better when the baffle plane is right on the cargo top surface compared to the other location heights. Further, there is an optimal length–width combination, e.g., a single baffle plane with a length of 0.26 L and a width of 0.46 B, at which a better anti-sloshing effect could be achieved with the smallest baffle area rate. This study could be useful for the practical application of horizontal baffles for bulk granular cargo carriers. Full article

The present investigation addresses the mechanical properties, wear behaviour, and high-temperature oxidation of cermets and hardmetals based on either Ti(C,N) or WC and a metal binder based on Fe15Ni or Fe15Ni10Cr. This study also includes a commercial-grade WC-Co for comparative purposes. The production of these materials involved a powder metallurgy and sinter-HIP processing route under identical conditions. It is found that WC-based materials have superior mechanical properties, including hardness, fracture toughness, transversal rupture strength (TRS), and wear response, compared to Ti(C,N)-based materials. However, the latter show better oxidation behaviour than the former. Notably, WC-FeNi exhibits a higher hardness and TRS than the commercial-grade material (an increase of 7% and 9%, respectively). The difference in wear behaviour is due to the difference in wear mechanisms. In this regard, cermets wear through a tribolayer of Ti and Fe oxides, while hardmetals primarily wear through abrasion from ploughing. Thus, hardmetals exhibit a lower coefficient of friction (COF) and wear rate than cermets. Furthermore, Ti(C,N)-based materials form a protective layer of TiO₂, which enhances their integrity and reduces mass gain. The addition of Cr to the FeNi binder only appears to have a clear effect on the TRS of the materials. Full article

Nitrile butadiene rubber (NBR) and its various composite materials are widely employed as friction materials in mechanical equipment. The use of carbon nanotube (CNT) reinforcement in NBR for improved friction and wear characteristics has become a major research focus. However, the mechanisms underlying the improvement in the friction and wear characteristics of NBR with different CNT contents remain insufficiently elucidated. Therefore, we conducted a combined analysis of NBR reinforced with varying CNT contents through molecular dynamics (MD) simulations and ring–block friction experiments. The aim is to analyze the extent to which CNTs enhance the water-lubricated friction and dry wear properties of NBR and explore the improvement mechanisms through molecular chain characteristics. The results of this study demonstrate that as the mass fraction of CNTs (0%, 1.25%, 2.5%, 5%) increases, the water-lubricated friction coefficient of NBR continuously decreases. Under water-lubricated conditions, CNTs improve the water storage capacity of the NBR surface and enhance lubrication efficiency. In the dry wear state, CNTs help reduce scratch depth and dry wear volume. Full article

This study examines the effects of different addition levels of tungsten (W) content on the microstructure, corrosion resistance, wear resistance, microhardness, and phase composition of coatings made from FeCoCrNiAl high-entropy alloy (HEA) using the laser cladding technique. Using a preset powder method, FeCoCrNiAlW_x (where x represents the molar fraction of W, x = 0.0, 0.2, 0.4, 0.6, 0.8) HEA coatings were cladded onto the surface of 45 steel. The different cladding materials were tested for dry friction by using a reciprocating friction and wear testing machine. Subsequently, the detailed analysis of the microstructure, phase composition, corrosion resistance, wear traces, and hardness characteristics were carried out using a scanning electron microscope (SEM), X-ray diffractometer (XRD), electrochemical workstation, and microhardness tester. The results reveal that as the W content increases, the macro-morphology of the FeCoCrNiAlW_x HEA cladding coating deteriorates; the microstructure of the FeCoCrNiAlW_x HEA cladding coating, composed of μ phase and face-centered cubic solid solution, undergoes an evolution process from dendritic crystals to cellular crystals. Notably, with the increase in W content, the average microhardness of the cladding coating shows a significant upward trend, with FeCoCrNiAlW_0.8 reaching an average hardness of 756.83 HV_0.2, which is 2.97 times higher than the 45 steel substrate. At the same time, the friction coefficient of the cladding coating gradually decreases, indicating enhanced wear resistance. Specifically, the friction coefficients of FeCoCrNiAlW_0.6 and FeCoCrNiAlW_0.8 are similar, approximately 0.527. The friction and wear mechanisms are mainly adhesive and abrasive wear. In a 3.5 wt.% NaCl solution, the increase in W content results in a positive shift in the corrosion potential of the cladding coating. The FeCoCrNiAlW_0.8 exhibits a corrosion potential approximately 403 mV higher than that of FeCoCrNiAl. The corrosion current density significantly decreases from 5.43 × 10⁻⁶ A/cm² to 5.26 × 10⁻⁹ A/cm², which suggests a significant enhancement in the corrosion resistance of the cladding coating. Full article

In this study, a spherical CrCoFeNiMn high-entropy alloy (HEA) powder with uniform size was prepared using gas atomization. High-quality CrCoFeNiMn HEA coatings were then applied to a 316L stainless steel substrate using prepowdered laser cladding. The main focus of the study is on the phase structure composition and stability, microstructure evolution mechanism, mechanical properties, and wear resistance of CrCoFeNiMn HEA coatings. The results show that the CrCoFeNiMn HEA coatings prepared using gas atomization and laser melting techniques have a single FCC phase structure with a stable phase composition. The coatings had significantly higher diffraction peak intensities than the prepared HEA powders. The coating showed an evolution of columnar and equiaxed crystals, as well as twinned dislocation structures. Simultaneously, the microstructure transitions from large-angle grain boundaries to small-angle grain boundaries, resulting in a significant refinement of the grain structure. The CrCoFeNiMn HEA coating exhibits excellent mechanical properties. The microhardness of the coating increased by 66.06% when compared to the substrate, the maximum wear depth was reduced by 65.59%, and the average coefficient of friction decreased by 9.71%. These improvements are mainly attributed to the synergistic effects of grain boundary strengthening, fine grain strengthening, and twinning and dislocation strengthening within the coating. Full article

In this work, multilayer gradient coatings obtained by detonation spraying were studied. To obtain a multilayer gradient coating by detonation spraying, two modes with different numbers of shots of NiCrAlY and YSZ were developed. The presented results demonstrate the effectiveness of creating a gradient structure in coatings, ensuring a smooth transition from metal to ceramic materials. Morphological analysis of the coatings confirmed a layered gradient structure, consisting of a lower metallic (NiCrAlY) layer and an upper ceramic (YSZ) layer. The variation in the contents of elements along the thickness of the coatings indicates the formation of a gradient structure. X-ray analysis shows that all peaks in the X-ray diffraction patterns correspond to a single ZrO₂ phase, indicating the formation of a non-transformable tetragonal primary (t′) phase characteristic of the thermal protective coatings. This phase is known for its stability and resistance to phase transformation under changing operating temperature conditions. As the thickness of the coatings increased, an improvement in their mechanical characteristics was found, such as a decrease in the coefficient of friction, an increase in hardness, and an increase in surface roughness. These properties make such coatings more resistant to mechanical wear, especially under sliding conditions, which confirms their prospects for use in a variety of engineering applications, including aerospace and power generation. Full article