Search Results (1,216)

Environmental contamination critically affects the durability and performance of lubricants in machine components. Over long operating periods, particles and water ingress through degraded seals accelerate grease degradation and deteriorate tribological behavior. This study evaluates the effects of SiO₂ particle concentration and water contamination, alone and in combination, on the performance of calcium-based grease in bearing steel contacts. Friction coefficients, grease temperatures, wear, pitting, and vibration signals were analyzed. The results show that an increase in particle concentration raised both friction and temperature, leading to more severe wear and pitting. The addition of 0.6 wt% water reduced fluctuations in friction and temperature, but when combined with high particle concentrations, it significantly worsened wear and pitting. The vibration-based energy ratio correlated strongly with pitting evolution, highlighting its potential as a sensitive parameter for monitoring surface fatigue. These findings provide insights into lubricant degradation under contaminated conditions and offer guidance for improving the reliability of lubricated systems. Full article

This study examined the effects of phosphoric acid (H₃PO₄), polyimide (PI), and lubricants (MoS₂, graphite) on the phase stability, microstructure, and magnetic performance of Fe-5.0 wt.%Si soft magnetic composites (SMCs). Warm compaction (≤550 °C) and annealing at 700 °C were applied to samples prepared under a full factorial design. X-ray diffraction confirmed stable α-Fe(Si) phases without secondary phases. SEM and TEM–EDS revealed interfacial insulating layers mainly composed of Si-O, with localized phosphorus and carbon. Additive composition strongly influenced magnetic and physical properties. Increasing H₃PO₄ and PI reduced the density from 7.50 to 7.27 g/cm³ and lowered the permeability (from 189 at 1 kHz to 156), due to thicker interparticle layers that restricted metallic contact and domain wall motion. In contrast, Q-values rose significantly with frequency: for H₃PO₄ 0.25 wt.% + PI 0.25 wt.% + graphite 0.3 wt.%, Q increased from 0.39 (1 kHz) to 2.91 (10 kHz), reflecting effective eddy current suppression. Lubricant type further influenced performance: graphite consistently outperformed MoS₂, with 0.3 wt.% graphite providing the best balance of high density, permeability, and a frequency-stable Q-value. Overall, Fe-5.0 wt.%Si performance is governed not by bulk phase changes but by the trade-off between densification and insulation at particle interfaces. The optimal combination of low H₃PO₄ and PI with 0.3 wt.% graphite offers practical guidelines for designing high-frequency, high-efficiency motor materials. Full article

Because of their exceptional strength, corrosion resistance, and low weight, materials such as titanium, aluminum, and others are becoming increasingly popular. The application scope of additive manufacturing (AM) in the aerospace sector continues to expand. Because of its high performance and low coefficient of thermal expansion, AlSi10Mg processed by laser-based powder bed fusion (LPBF) is becoming increasingly popular in lightweight aerospace component design. Nonetheless, the AM technique has a number of benefits; poor surface quality is the only drawback, necessitating post-processing. This study aims to focus on the machinability of AlSi10Mg under three distinct environmental conditions (dry, minimum quantity lubrication (MQL), and SL-MQL). The experimental investigations were centered on chip morphology, flank wear (Vb), surface roughness (Ra), and cutting temperature (Tc). SL-MQL reduced the roughness by 53–57% over dry machining and 23–29% over MQL condition, and in a similar way lessened the flank wear by 36–40% over dry machining and 12–15% over MQL condition. In addition, to check the predictive accuracy and optimize machining parameters, four machine learning models were used: Gaussian Process Regression (GPR), Bagging, Multilayer Perceptron (MLP), and Random Forest (RF). In both the training and testing stages, MLP consistently demonstrated superior performance across all parameters in comparison to other algorithms, achieving high levels of accuracy and low error rates. Full article

Electron beam melting (EBM) is an additive manufacturing method that enables the manufacturing of metallic parts. EBM-printed parts require post-processing to meet the surface quality and dimensional accuracy requirements. Machining is one approach that is beneficial for achieving these requirements. However, during machining, particles are emitted and can affect the environment and the operator’s health. This study aims to investigate the concentration of particles emitted during the milling of 3D-printed Ti6Al4V alloy produced by EBM. First, the influence of machining speed and cutting fluids, namely flood and minimum quantity lubricant (MQL), on particle emissions was statistically investigated. Then, the standby time required for the operator to safely open the machine door and interact with the machine within the machining area was studied. In this regard, two scenarios were proposed. In the first scenario, the machine door is open immediately after machining, and the operator waits until the particle concentration is acceptable. In the second, the machine door will be opened only when the particle concentration is acceptable. Statistical findings revealed that cutting fluids have a significant impact on particle emissions, exhibiting distinct patterns for both fine and coarse particles. Irrespective of the scenario, MQL results in higher particle concentration peaks and larger particle sizes, and the operator needs a longer standby time before interacting with the machine. For instance, the standby time in MQL is 328% more than that of the flood system. This study provides insight into sustainable manufacturing by taking into account social factors such as worker health and safety. Full article

Conventional rubber-modified asphalt typically suffers from low rubber content and requires high construction temperatures. This study developed a warm-mix high-content crumb-rubber-modified asphalt (CRMA) with an increased rubber particle content of over 20%; moreover, the optimization of the warm-mixing agent was determined. Its rutting and cracking resistance performances were investigated using a dynamic shear rheometer (DSR) and a bending beam rheometer (BBR). Fourier Transform Infrared (FTIR) and Atomic Force Microscopy (AFM) were used to characterize the aging resistance and microstructural characteristics. The key findings revealed that the optimal dosage of the SDYK-type warm-mix additive (SDYK; a surfactant used to improve the high-temperature stability, low-temperature crack resistance, and anti-aging performance of asphalt) was 0.6% for high-rubber-content CRMA. The combination of warm-mix additives and rubber granules enhanced the aging resistance and elasticity of the asphalt while also contributing to an increase in chemical functional group indicators. The decrease in both the aliphatic chain index and branched alkane index of CRMA indicates that the warm-mix agent and the rubber additive enhanced the aging resistance of the asphalt. The warm-mix agent reduced the roughness of the asphalt, counteracting the roughness-enhancing effect of crumb rubber. This was attributed to the lubrication effect induced by the water film during the mixing process, which promotes a more uniform distribution of the rubber crumb network. This research established a theoretical and experimental basis for the application of high-rubber-content CRMA in large-temperature-difference regions. Full article

The automotive industry is undergoing a transformative shift toward sustainability, driven by stringent environmental regulations, rising energy demands, and the pursuit of enhanced performance and efficiency. Lubricating materials play a pivotal role in reducing friction, wear, and energy losses in automotive systems, yet conventional lubricants, primarily petroleum-based, pose significant ecological and operational challenges. This review examines the development and performance of sustainable and advanced lubricant including bio-based oils, synthetic esters, nanolubricants, and ionic/solid lubricants for automotive applications. Drawing on tribological principles and recent advances in materials science, the article categorizes these lubricants based on source, chemical structure, and tribological behavior. A comparative framework is introduced to evaluate key performance indicators such as viscosity index, thermal stability, oxidation resistance, biodegradability, and compatibility with modern engine designs. The review also highlights emerging trends, including nanotechnology-based additives, green synthesis techniques, and novel antioxidant systems that enhance lubricant functionality and lifespan. Furthermore, a strategic research roadmap is proposed, outlining short-, medium-, and long-term priorities that integrate technical, environmental, and economic dimensions. By bridging foundational science with practical innovation, this article aims to guide researchers, manufacturers, and policymakers toward the adoption of high-performance, eco-compatible lubricants that support the transition to cleaner and more efficient mobility systems. Future directions and challenges in scaling, cost-effectiveness, and lifecycle assessment are discussed to guide innovation in this critical domain. Full article

In a previous experimental study, a high-frequency reciprocating rig tribotester was used to test several base oils, including a mineral oil and a vegetable oil, as well as a blend of the two, with and without the addition of carbon-based nanoparticles. The results showed synergy between certain nanoparticles and the oil blend. As such, in this study, molecular dynamics simulations are conducted on three systems to find the model that most accurately represents the experimental setup. These systems consist of lubricant molecules sandwiched between two iron oxide surfaces. The lubricant molecules represent the three types of lubricant used in the experimental study: hexadecane for the mineral base oil, a mixture of fatty acids for the rapeseed oil, and a mixture of both hexadecane and fatty acids for the oil blend. Three system sizes were considered: the first with 100 molecules, the second with 200 molecules, and the third with 300 molecules. The density, velocity, and temperature profiles, as well as the shear rate and coefficient of friction, are analyzed. The results show that the 300-molecule systems show a similar trend to that observed in the experimental study, with the vegetable oil model having the lowest coefficient of friction, followed by the blend model and finally the hexadecane model. The different analyzed profiles provide valuable insights into the interactions within the lubricant film. Full article

Loss of lubrication in aeronautic drivetrains can lead to catastrophic gearbox failure, and drivetrains must be tested to prove their resistance to loss of lubrication. Research led to a better understanding of the modes of action, interdependencies, and effective measures to optimize drivetrains for a loss of lubrication event. However, there are currently no calculation methods available, so gear design against loss of lubrication is mainly based on experience. This study proposes a novel calculation method that builds upon the scuffing load calculation from ISO/TS 6336-21 to allow for scuffing safety calculation for cylindrical gears facing loss of lubrication. The proposed method synthesizes existing knowledge in the context of loss of lubrication and incorporates further research results concerning the friction, temperature, and scuffing of gears. The calculation method considers relevant gear design aspects and enables estimation of the time-to-failure. A calculation study is used to compare different measures for cylindrical gears facing loss of lubrication. The results demonstrate the remarkable potential for enhancing loss of lubrication performance through increased oil share in the fluid flow, the application of coatings, the adoption of low-loss gear designs, the use of low-friction lubricants, and the incorporation of additives that increase the scuffing temperature. Full article

Three-dimensional printing has emerged as a promising technology in endovascular surgery for the production of patient-specific stent-grafts. Thermoplastic polyurethane (TPU) is widely used for this purpose due to its favourable biocompatibility, hemocompatibility, and mechanical properties. However, its long-term stability under physiological conditions remains uncertain. This study evaluates the ageing behaviour of 3D-printed TPU stent-grafts under accelerated oxidative conditions (20% H₂O₂–0.1 M CoCl₂) over three months, corresponding to approximately 45 months in vivo, and during three months in hydrolytic (0.1 M NaOH) conditions. Mechanical, physicochemical, thermal, and surface properties were periodically analysed. Differential scanning calorimetry revealed a decrease in crystallisation enthalpy of 41% and a reduction in melting enthalpy of 29% after hydrolytic ageing, whereas no decrease was observed after oxidative ageing. Despite these chemical changes, size exclusion chromatography indicated minimal chain scission. However, spectroscopy and microscopy showed minor chain scission and additive migration (antioxidant and lubricant). Nevertheless, tensile testing highlighted that mechanical performance remained within clinically acceptable ranges. These findings demonstrate that 3D-printed TPU vascular implants retain essential properties under prolonged simulated ageing, supporting their safety and durability for vascular applications. Full article

An operational test and degradation analysis of a hydraulic fluid based on synthetic esters was performed in three types of work machines. To enhance its performance, ZDDP anti-wear agents were added. Hydraulic fluids are susceptible to degradation by oxidation; therefore, to ensure the long service life of the equipment, it is essential to monitor their current condition through laboratory analyses during machine operation. Emission spectrometry was used to determine the presence of contaminants and the concentration of additive substances in the oil. Pollution was assessed by cleanliness code analysis according to ISO 4406-2021, alongside Total Acid Number (TAN) analysis and LNF analysis of wear and contamination in lubricants. The combination of cleanliness code analysis and LNF analysis of particle type and origin allows for monitoring not only the count but also the origin of contaminating metallic particles, which increases the probability of correct diagnostics and successful detection and resolution of wear problems. All three machines were still operational at the end of the test interval, meaning the tested hydraulic fluid is a suitable alternative to mineral variants. However, in all three pieces of equipment, it is necessary to replace the hydraulic fluid and flush the system before further operation. Furthermore, we recommend replacing the filter elements and inspecting the internal spaces of rotating parts with an increased potential for wear. From the oil’s perspective, it is advisable to add more anti-wear additives (ZDDP), which are depleted the fastest. Full article

Enhancing the high-temperature tribological performance of protective claddings is crucial for demanding industrial applications. This study focuses on developing hexagonal boron nitride (hBN)-reinforced Ni-based composite claddings to improve wear resistance over a wide temperature range. Ni/WC/CeO₂ cladding layers with varying hBN contents (0.25 wt% and 0.75 wt%) were fabricated on 45 steel substrates via vacuum cladding. Their microstructure, mechanical properties, and tribological behavior under thermal cycling (25–600 °C) were systematically evaluated. Results reveal that the in situ formation of a hard Cr₂B phase, coupled with hBN addition, was key to achieving optimal overall properties. The composite with 0.25 wt% hBN (NWB25) demonstrated optimal overall properties, featuring the lowest porosity (0.1813%) and the highest H/E ratio (0.0405), leading to the best overall tribological performance. A distinct transition from mild to severe wear was observed during the 300 °C-2 stage, resulting from the fracture of a high-temperature tribo-oxidative layer. An hBN content of 0.25 wt% is identified as optimal for balancing solid lubrication and matrix cohesion, thereby achieving superior thermal cycling wear resistance. Higher hBN concentrations promote grain coarsening and increased porosity, which degrade performance. Full article

Additively manufactured (AM) aluminum (Al) alloys are very useful in sectors like automotive, manufacturing, and aerospace because they have unique mechanical properties, such as their light weight, etc. AlSi10Mg made by laser powder bed fusion (LPBF) is one of the most promising materials because it has a high strength-to-weight ratio, good thermal resistance, and good corrosion resistance. But machining AlSi10Mg parts is still hard because they have unique microstructural properties from the way they were produced. This research investigates the machining efficacy of the AM-AlSi10Mg alloy in distinct cutting conditions (dry, flood, chilled air, and minimal quantity lubrication with castor oil). The study assesses how different cooling conditions affect important performance metrics such as cutting temperature, surface roughness, and tool wear. Due to castor oil’s superior lubricating and film-forming properties, MQL (Minimal Quantity Lubrication) reduces heat generation between 80 °C and 98 °C for the distinct speed–feed combinations. The Multi-Objective Optimization by Ratio Analysis (MOORA) approach is used to determine the ideal cooling and machining conditions (MQL, Vc of 90 m/min, and fr of 0.05 mm/rev). The relative closeness values derived from the MOORA approach were used to predict machining results using machine learning (ML) models (MLP, GPR, and RF). The MLP showed the strongest relationship between the measured and predicted values, with R values of 0.9995 in training and 0.9993 in testing. Full article

This article comprehensively reviews the tribological behavior of a Ti-6Al-4V alloy manufactured via electron beam powder bed fusion (EB-PBF), an additive manufacturing process for aerospace and biomedical applications. EB-PBF Ti-6Al-4V demonstrates wear resistance that is superior or comparable to conventional Ti-6Al-4V. The reported average friction coefficient ranges between ~0.22 and ~0.75 during sliding wear in dry and lubricated conditions against metallic and ceramic counterparts when loading 1–50 N under varied surface and heat treatment conditions, and between 1.29 and 2.2 during fretting wear against EB-PBF Ti-6Al-4V itself. The corresponding average specific wear rates show a broad range between ~8.20 × 10⁻⁵ mm³/Nm and ~1.30 × 10⁻³ mm³/Nm during sliding wear. Lubrication reduces the wear rates and/or the friction coefficient. Wear resistance can be improved via machining and heat treatment. Wear anisotropy is reported and primarily attributed to microhardness variations, which can be mitigated through lubrication and post-processing. The effects of applied load and frequency on EB-PBF Ti-6Al-4V are also discussed. The wear resistance at elevated temperatures shows a mixed trend that depends on the counterpart material and the testing methods. Wear mechanisms involve oxide tribo-layer formation, abrasive wear, and adhesive wear. Current limitations, future research directions, and a standardization framework are also discussed. Full article

The range of lubricant applications has broadened to include multiple sectors, aiming to optimize the operational efficiency of mechanical systems. Given their adaptable friction-reducing properties, lubricants have recently been incorporated into energy harvesting technologies such as triboelectric nanogenerators (TENGs). In such devices, lubricants are essential for mitigating wear, facilitating heat dissipation, eliminating contaminants, and prolonging the service life of mechanically actuated energy harvesters. Notably, emerging developments in sliding and rotational-mode TENGs leverage lubricants to improve electrical output while reducing interface degradation. However, despite significant potential, TENGs still face inherent challenges, including interface friction and energy losses from air breakdown. Recent research indicates that these drawbacks can be effectively addressed by the intentional use of polymer-based lubricants, which contribute to maintaining micro/nanostructured surfaces and minimizing air breakdown, thereby enhancing charge storage capability and increasing device robustness. This review systematically examines the categories, physicochemical attributes, and operational roles of polymeric lubricants used in TENG technology. It underscores their combined function is both primary and support materials to augment triboelectric efficiency. In addition, the article assesses how different lubricants impact device performance and durability, providing a critical analysis of their suitability based on the operational benchmarks of lubricant-embedded TENG configurations. Full article

The evolving bitumen market is increasingly complex due to variations in crude sources and transitions in refining processes, affecting the properties of bitumen. Unexpected additions of materials to alter bitumen’s properties could occur, where traditional PEN grade testing fails to detect modifications by inclusion of, for example, Re-refined Engine Oil Bottoms. This is the first study to comprehensively compare REOBs from European vs. North American sources and assess their effects on binder performance in a unified framework, performed by assessing the REOB-modified binders by identification, stability, compatibility, ageing susceptibility, and low-temperature properties. Two series of REOB-modified bitumen were prepared by blending 5, 10, and 15 wt.% REOB into hard grade bitumen. Results showed increased carbonyl formations (likely caused by lubricant additives) and phase instability during storage which can be attributed to saturates exudation. Rheological assessment demonstrated that REOB softens bitumen, although ageing causes a pronounced gain in stiffness. Low temperature rheological measurements showed that REOB-modified bitumen is prone to brittle fracture, suggesting a loss of relaxation properties. This study highlights that REOB is a material of inconsistent nature, with complex interactions with molecular groups of the base bitumen, causing increased ageing, phase instability, and brittle fracture susceptibilities. Full article