Search Results (133)

Lubrication between the rail gauge face and wheel flange is necessary to improve vehicle performance and reduce component wear. One way to achieve this is to use a solid stick loaded against the wheel flange. This paper details twin-disc testing of eight stick products according to Annex H of EN 15427-2-1:2022 (previously Annex L of EN 16028:2012) and then describes a new assessment methodology using conditions more relevant to field application. EN 15427-2-1:2022 specifies a test involving the application of the product during wheel–rail specimen contact. Once a specified time has elapsed, product application ceases, and performance is assessed as the time taken for the friction coefficient to return to a nominal dry value. This is described as “retentivity”. In the new test, the product is applied whilst wheel and rail are out of contact, to allow the product to build up on the wheel, then the specimens are put into contact, under conditions representing 150 m of continuous, heavy flange contact; this process is repeated a set number of times. The new test showed that products that failed the current friction criteria successfully protect the wheel and rail from wear, which is ultimately the aim of the product application. Full article

In railways, problems in braking and traction can be caused by so-called low-adhesion conditions. Adhesion is increased by sanding, where sand grains are blasted towards the wheel–rail contact. Despite the successful use of sanding in practice and extensive experimental studies, the physical mechanisms of adhesion increase are poorly understood. This study combines experimental work with a DEM model to aim at a deeper understanding of adhesion increase during sanding. The experimentally observed processes during sanding involve repeated grain breakage, varying sand fragment spread, formation of clusters of crushed sand powders, plastic deformation of the steel surfaces due to the high load applied and shearing of the compressed sand fragments. The developed DEM model includes all these processes. Two types of rail sand are analysed, which differ in adhesion increase in High-Pressure Torsion tests under wet contact conditions. This study shows that higher adhesion is achieved when a larger proportion of the normal load is transferred through sand–steel contacts. This is strongly influenced by the coefficient of friction between sand and steel. Adhesion is higher for larger sand grains, higher sand fragment spread, and higher steel hardness, resulting in less indentation, all leading to larger areas covered by sand. Full article

During the service life of automotive panel stamping dies, the surface is often subjected to high loads and repeated friction, resulting in excessive wear. This leads to die failure, reduced machining accuracy, and decreased production efficiency. To enhance the anti-friction and wear-resistant performance of die steel surfaces, this study introduces the concept of biomimetic engineering in surface science. By mimicking microstructural configurations found in nature with outstanding wear resistance, biomimetic functional surfaces were designed and fabricated. Specifically, quadrilateral dimples inspired by the back of dung beetles, pentagonal scales from armadillo skin, and hexagonal scales from the belly of desert vipers were selected as biological prototypes. These surface textures were fabricated on Cr12MoV die steel using high-speed ball-end milling. Finite element simulations and dry sliding wear tests were conducted to systematically investigate the tribological behavior of surfaces with different dimple geometries. The results showed that the quadrilateral dimple surface derived from the dung beetle exhibited the best performance in reducing friction and wear. Furthermore, the milling parameters for this surface were optimized using response surface methodology. After optimization, the friction coefficient was reduced by 21.3%, and the wear volume decreased by 38.6% compared to a smooth surface. This study confirms the feasibility of fabricating biomimetic functional surfaces via high-speed ball-end milling and establishes an integrated surface engineering approach combining biomimetic design, efficient manufacturing, and parameter optimization. The results provide both theoretical and methodological support for improving the service life and surface performance of large automotive panel dies. Full article

The growing demand for sustainable, high-performance composite materials has increased the interest in natural fibers as reinforcements for brake friction materials (BFMs). Silk and Grewia optiva fibers, in particular, have emerged as promising candidates for BFMs due to their good mechanical properties, biodegradability, and availability. To evaluate their potential, friction materials were formulated with 6% Grewia (GF), 6% silk (SF), and a hybrid formulation containing 3% of both fibers (SGF), alongside a reference material reinforced with 6% aramid fiber (AF). These composites were then tested on a braking tribometer using an extended SAE J2522 procedure to assess their performance. The AF formulation showed slightly better wear resistance and the GF formulation showed inferior performance during high-temperature cycles, whereas SF and SGF performed close to the reference formulation (AF) in these sections. In terms of friction stability, SF matched the AF formulation, while GF demonstrated significantly poorer stability. The first high-temperature exposure of the BFMs (Fade 1) served as a critical thermal settlement phase, after which they demonstrated both improved friction stability and repeatable performance characteristics. Finally, this study demonstrates that silk fiber represents a viable, sustainable alternative to aramid in BFMs, exhibiting comparable performance in terms of friction stability and thermal resistance. Full article

The accurate modeling of dynamic soil–structure interaction processes under impact loading is critical for advancing the design of soil-embedded barrier systems. Full-scale crash testing remains the benchmark for evaluating barrier performance; however, such tests are costly, logistically demanding, and subject to variability that limits repeatability. Recent advancements in computational methods, particularly the development of large-deformation numerical schemes, such as the multi-material arbitrary Lagrangian–Eulerian (MM-ALE) and smoothed particle hydrodynamics (SPH) approaches, offer viable alternatives for simulating soil behavior under impact loading. These methods have enabled a more realistic representation of granular soil dynamics, particularly that of the Manual for Assessing Safety Hardware (MASH) strong soil, a well-graded gravelly soil commonly used in crash testing of soil-embedded barriers and safety features. This soil exhibits complex mechanical responses governed by inter-particle friction, dilatancy, confining pressure, and moisture content. Nonetheless, the predictive fidelity of these simulations is governed by the selection and implementation of soil constitutive models, which must capture the nonlinear, dilatant, and pressure-sensitive behavior of granular materials under high strain rate loading. This review critically examines the theoretical foundations and practical applications of a range of soil constitutive models embedded in the LS-DYNA hydrocode, including elastic, elastoplastic, elasto-viscoplastic, and multi-yield surface formulations. Emphasis is placed on the unique behaviors of MASH strong soil, such as confining-pressure dependence, limited elastic range, and strong dilatancy, which must be accurately represented to model the soil’s transition between solid-like and fluid-like states during impact loading. This paper addresses existing gaps in the literature by offering a structured basis for selecting and evaluating constitutive models in simulations of high-energy vehicular impact events involving soil–structure systems. This framework supports researchers working to improve the numerical analysis of impact-induced responses in soil-embedded structural systems. Full article

A separable bamboo-like carbon nanotube-based catalyst was prepared by the spherfication method using sodium alginate and nickel. The spheres were carbonized and then decorated with palladium nanoparticles before they were tested in nitrobenzene hydrogenation. The test was repeated with five different commonly used solvents (methanol, ethanol, isopropanol, tetrahydrofuran, and acetonitrile). According to the results, polar solvents showed a significantly higher aniline yield than the more apolar solvents and exceptional results were reported for ethanol (~100%). The catalyst was reused two more times (four hours each) to check the Pd leaching where the spheres kept their shape (despite the high mechanical friction caused by the mixer) and only a relatively low Pd amount was lost (5.48 rel.%). The catalyst was easily retrievable. Full article

Friction–inertia piezoelectric actuators can perform long-range positioning with nanometer resolution. However, friction and inertia are not easy to control and can influence the actuator’s performance. The present study proposes a friction–inertia-type piezoelectric XY positioning platform with a simple structure, which uses magnets to provide stable normal force and friction. Sliders and rails were used to provide long travel ranges of 80 mm and 70 mm in the X and Y directions, respectively. Compact optical encoders were installed on the platform to enhance the positioning accuracy. With a three-phase positioning strategy involving both stepping and closed-loop methods, the system achieved a positioning accuracy of 3 µm (0.03%) and a repeatability of 325 nm (0.0033%) over a 10 mm long travel range. The positioning resolution was 4.7 nm, which was primarily limited by optical encoder noise under the closed-loop control mode. An astigmatic optical profilometer was used for the wide-range and high-resolution surface imaging of the XY positioning platform. Full article

In this study, a contact–separation triboelectric catalytic device was designed and constructed to systematically investigate the underlying degradation mechanism. The device enabled precise control of the contact–separation process between frictional surfaces. Polytetrafluoroethylene (PTFE) and polyethylene terephthalate (PET) films were selected as the triboelectric pair, and methylene blue (MB) was used as the model organic pollutant. Experimental results demonstrated that the contact–separation process in an aqueous environment effectively promotes the degradation of organic dyes. For an MB solution with an initial concentration of 5 mg/L, a degradation efficiency of 40.34% was achieved within 3 h. Moreover, the device exhibited excellent repeatability and stability, with no significant decline in performance after 15 h of continuous operation. Control experiments confirmed that the degradation originates specifically from the contact–separation interaction between the PTFE and PET surfaces. Free radical quenching experiments identified superoxide radicals (·O₂⁻) and hydroxyl radicals (·OH) as the primary reactive species responsible for degradation. Based on these findings, a microscopic mechanism is proposed: during contact, triboelectric charging generates electrons (e⁻) and holes (h⁺) on the surfaces; upon separation, these charges interact with the solution—e⁻ reduce dissolved oxygen to form ·O₂⁻, while h⁺ oxidize hydroxide ions (OH⁻) to produce ·OH. The combined action of ·O₂⁻ and ·OH ultimately results in the efficient degradation of MB. Full article

Ball screws play an important role in machine tools by converting rotational motion into precise linear motion. This study evaluates and compares ball screws from two companies (TIC and NSK) through simulations and experimentation to assist in the selection process. Simulation results show that TIC exhibits a lower maximum temperature (32.6 °C) and axial deformation (119.3 μm) compared to NSK (34.05 °C and 174 μm, respectively), indicating superior thermal performance and deformation properties. An accelerated life test conducted over 240 h further demonstrates that TIC maintained more stable temperatures during continuous operation. Additional tests on the TIC ball screw include thermal displacement which is 13.5 μm after 2000 cycles of reciprocating motion. Friction torque fluctuation rate which ranges from 11.6% to 19.9%, and test bench positioning repeatability experiment shows a mean deviation of 4.99 μm from the target position. Overall, the results from this work contribute to process optimization by guiding the selection of ball screws based on their thermal performance and durability, ultimately enhancing machine tool accuracy and reliability. Full article

The invasive presence of nanoplastics in various ecosystems makes them a significant environmental problem nowadays. One of the main production mechanisms of nanoplastics is mechanical wear. The combination of friction, abrasion, and shear forces can indeed lead to the progressive fragmentation of polymeric materials. The high surface area–volume ratio of the resulting nanoparticles not only alters the physicochemical properties of the polymers but also leads to increased interaction with biological systems, which raises questions about the persistence of nanoplastics in the environment and their potential toxicity. Despite the growing body of research on microplastics, studies specifically addressing the formation, characterization, and impact of wear-induced nanoplastics remain limited. This article describes current research on the formation mechanisms of nanoplastics generated by mechanical wear, highlighting the tribological processes underlying their release. Advanced characterization techniques used to identify the morphology and composition of these particles are also mentioned. The techniques include atomic force microscopy (AFM), scanning electron microscopy (SEM), and, to some extent, Raman spectroscopy. In the case of AFM, an example of application to the extrusion of nanoplastics from polystyrene surfaces subjected to repeated nanoscratching is also provided. Full article

This study introduces a novel discrete element method (DEM) model for compacted loess, incorporating a bond rate parameter within a linear contact bond model to simulate constitutive damage behavior. This enhancement significantly improves the characterization of structural damage from repeated wet–dry cycles, offering a quantitative method for predicting damage progression. Unlike existing DEM models, our model directly uses a bond rate parameter to quantitatively describe inter-particle bond deterioration, reflecting reduced bonding strength due to pore structure development and the weakening effect of water. Rigorous calibration and validation were performed using comparative experiments. A key innovation is the systematic analysis of microscopic parameters (contact stiffness, friction coefficient, contact strength, and bond rate) and their impact on macroscopic mechanical behavior. Our findings show that decreasing the bond rate significantly reduces the macroscopic mechanical properties, providing valuable insights into the micro–macro relationship. We comprehensively evaluated prediction sensitivity to these parameters. This methodology offers a new perspective on using DEM for predicting crucial civil engineering material properties, providing a valuable reference for incorporating bond rate parameters into future modeling, particularly for long-term geotechnical material behavior under environmental degradation. The model’s accurate representation of wet–dry cycle effects on loess strength improves earth structure design and safety. Full article

A bistable effect on a laminate structure with a piezoelectric patch was tested to harvest kinetic energy. The composite bistable plate was prepared in the autoclave with two different orientations of the glass fibers. The dynamic tests were performed on the universal testing machine using cyclic vertical compression excitation. During the tests, the bottom edge of the plate was clamped firmly while its upper edge was attached with some clearance to enable sliding. In such a configuration, the friction force between the plate and upper clamp element is responsible for the plate excitation. Simultaneously, the plate has enough space to change the shape between the two equilibria. During the harmonic excitation of the testing machine operating mode, a piezoelectric element was placed on the bistable plate and its voltage and normalized power outputs were evaluated. The experiments were repeated with additional mass distribution, which influenced the natural frequency of the plate. Full article

To compare them with PTFE-40# steel tribo-pairs, the tribological properties of textured PEEK-40# (AISI 1040) steel friction pairs were researched under full-film lubrication conditions by manufacturing micro-dimples with different dimensions on the contact surfaces of 1040 steel discs using laser surface texturing (LST). After repeated tribological tests, the coefficients of friction (COFs), wear losses, and wear morphologies of the PEEK-1040 steel friction pairs were measured and analyzed. The results show that micro-dimples do not significantly reduce the average COFs of PEEK-1040 steel friction pairs when lubricated with a sufficient amount of hydraulic oil, but they do reduce the wear losses of most groups. When the dimple diameter was 250 μm, the dimple depth was 5 μm, the area ratio was 6.6%, and the mass loss of the 1040 steel disc was reduced by 90% compared to the smooth reference. In comparison to the behavior of the PTFE-1040 steel tribo-pairs, PEEK-1040 steel friction pairs can provide better tribological performance, whether smooth or dimple-textured. This study offers important insights for the design of seals in machinery. Full article

Surface texturing entails surface alteration through forming, microgrooving, microdimpling, and microchanneling. This is achieved by laser micromachining, in addition to other related methods, of a substrate surface. The present paper describes the surface characteristics obtained after the laser texturing of a biodegradable polymer (Arbofill Fichte) with four and six passes in hexagonal and square patterns. The results of the wettability test indicate that this biodegradable polymer has a surface with a weak hydrophobic characteristic (contact angle near 90°), regardless of the type of texture that is obtained. The underlying material’s wear behavior changes as a result of the surface alteration due to laser surface texturing (LST). The coefficient of friction (COF) values thus increase for all samples. The hexagonal geometry offers greater stability and consistency compared to square geometry, independent of the number of passes. Square geometry is more susceptible to variations, particularly along the Y axis, and may need additional adjustment of the process parameters. The hexagonal structure naturally promotes more uniform leveling due to its tighter and more evenly spread arrangement, even at four texturing passes (4x). However, at six texturing passes (6x), the advantages become more pronounced because of the repeated overlaps in the laser trajectories. The overlap in the hexagonal configuration guarantees that each area of the material receives a relatively consistent energy dose, reducing localized discrepancies. The possibility of using this method to texture surfaces is viable; thus, based on the obtained results, there is the possibility that it can replace non-biodegradable polymers in different sectors. Full article

TiNi-based alloys are widely utilized in various engineering and medical applications. This study presents a newly developed and optimized technology for producing TiNi wires with a diameter of 40 μm utilizing a combined mechano-chemical treatment and drawing process. The resulting thin wires were tested and characterized using multiple methods to determine their structural, phase, and mechanical properties. The structure of the TiNi wires, designed for use as textile implants in reconstructive medicine, features a TiNi metal matrix (B2 and B19′ phases) at the core and a surface oxide layer. A key structural characteristic of these wires is the presence of fine nanograins averaging 15–17 nm in size. No texturizing of the metallic material was observed during repeated plastic deformations throughout the drawing process. The applied mechano-chemical treatment aimed to modify the structure of the wires’ surface oxide layer. Specifically, reducing the thickness and roughness of this layer decreased the friction coefficient of the alloy during drawing, thus significantly reducing the number of breaks during production. At the same time, the cryogenic treatment of the final product was found to stabilize the martensitic phase B19′, which reduces the Young’s modulus by 10 GPa. Consequently, this newly developed methodology enhances the material’s quality and reduces labor costs during production. Full article