Nanoparticles have gained increasing attention as lubricant additives due to their exceptional ability to minimize friction, reduce wear, and enhance thermal stability in tribological systems. Although numerous studies have explored this application, a structured and up-to-date synthesis of the available literature remains necessary. To fulfil this need, the present study conducts a systematic review aimed at consolidating current knowledge on the use and performance of nano additives in lubrication. A thorough search was carried out across two major academic databases—Scopus and Web of Science—targeting peer-reviewed journal articles published between 2023 and 2025. The review process was guided by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) methodology to ensure a transparent and rigorous selection procedure. Following the screening, 129 relevant studies were selected for detailed analysis. Preliminary findings suggest that nanoparticles such as metal oxides, carbon-based nanostructures, and layered materials contribute significantly to improved tribological properties through mechanisms like the formation of tribofilms, rolling effects, and tribochemical interactions. This review not only highlights recent advancements but also points out key research gaps, including variations in experimental methods and the lack of long-term durability studies. Overall, nano additives demonstrate considerable promise for advancing lubrication technology, and further research is essential to support their practical adoption in real-world engineering systems.
This study develops a sliding wear test rig based on the actual operating conditions of engine valve-guide pairs. The rig integrates lateral and oblique loading functionalities to more accurately simulate real load patterns. Key parameters such as temperature, load, and sliding distance are adjustable, simulating sliding tests under high-temperature and heavy-load conditions. The setup effectively simulates the real environment of an engine, enabling consistent and reliable test results. The apparatus exhibits a compact structural layout and low fabrication cost. An experimental study of three different valve-guide pairs was conducted on the rig. The influence of temperature and material pairs on the tribological performance of the valve-guide pair was investigated. Through comprehensive analysis combined with wear mechanism studies, differences in the wear resistance of various pairs were identified. Results indicated that temperature has a significant influence on wear. The pair containing a moderate copper content exhibited optimal wear resistance under all tested temperatures.
The fretting wear scars that form at internal contacts within wire ropes can have a significant influence on fatigue cracking of the rope wires. The nature and progression of this fretting wear is significantly influenced by lubricant and lubrication-related factors. Using a laboratory-scale fretting wear test, the influence of various lubrication-related parameters on the fretting wear of drawn wire was investigated, particularly the importance of base oil viscosity. Because there are many interrelated lubricant properties and influences, multivariate statistical analysis was used to identify the most significant lubrication-related factors on fretting wear. The viscosity of the grease base fluid and the formation of a stable interface layer in the Gross Slip fretting regime during the run-in phase were found to be the most influential factors in long term fretting wear. Galvanised drawn wires were more sensitive to base fluid viscosity than bright drawn wire because extruded zinc and wear debris features restricted lubricant access to the contact, meaning that lower base fluid viscosity, lower bulk viscosity and higher oil bleed improved lubricant supply.
In the present study, the combined influence of surface roughness and Micropolar lubricants on the performance of a hole-entry type hybrid journal bearing is investigated. The Reynolds equation governing Micropolar lubrication for the journal bearing system is suitably modified to incorporate the effects of surface roughness. The resulting governing equations are solved by coupling the capillary restrictor flow equation with a finite element formulation. Different magnitudes of surface roughness and Micropolar lubricant parameters are considered for various surface roughness patterns in order to comprehensively evaluate their impact on the bearing performance characteristics. The analysis demonstrates that surface roughness, when used in conjunction with Micropolar lubricants, significantly alters the hydrodynamic behavior of the bearing. Specifically, the results reveal an 18.9% reduction in bearing flow rate, a 5% increase in the minimum fluid film thickness, and a pronounced enhancement in the stiffness and damping coefficients for a bearing with a longitudinal surface roughness pattern operating under Micropolar lubrication, compared to an equivalent smooth bearing lubricated with a Newtonian fluid. These findings highlight the potential advantages of employing Micropolar lubricants and engineered surface textures in improving the dynamic and load-carrying performance of hybrid journal bearings.
Bionic textures are the designs which are inspired from nature or adopted from biological organisms. These textures are conceived on the mating surfaces to enhance their performance behaviours. In this paper, an attempt has been made to improve the performance of thrust pad bearing employing bionic texture inspired from the honeycomb structure. In the numerical investigation, Reynolds equation incorporating mass conservation algorithm is solved considering thermal effects. The effect of bionic texture attributes such as their dimensions, their extent in circumferential and radial directions on the performance parameters, namely, minimum film thickness and coefficient of friction, has been reported. It has been found that the minimum film thickness enhanced up to 31% and the coefficient of friction reduced up to 30% by conceiving bionic texture on the pad surface in comparison to plain pad. Pin-on-disk experimental test validated that bionic textured disc has lower coefficient of friction than plain disc.
To improve the hardness and wear resistance of 316L stainless steel, which cannot be strengthened through conventional heat treatment, an ultrasonic rolling extrusion method is proposed for surface strengthening. Ultrasonic rolling extrusion experiments are conducted on 316L under different process parameters. To obtain the process parameters for maximum surface hardness, an optimization and prediction model is established using the response surface methodology. The improvement in the tribological performance of 316L is characterized and analyzed through friction and wear tests, metallography, and SEM. The results indicate that the order of process parameters influencing surface hardness is: Static pressure > Feed rate > Spindle speed > Amplitude. The surface hardness of the strengthened 316L increases by 43.6%, and the depth of the refined grain layer reaches 130 mu m. In the water-lubricated ring-on-pin friction and wear tests, the friction coefficient and wear volume of the strengthened 316L decrease by 42.9% and 23.3%, respectively. The wear volume of the paired CFRPEEK also significantly reduces. Additionally, The fatigue wear and abrasive wear resistance of 316L after strengthening is significantly improved. This study demonstrates the effectiveness of the ultrasonic rolling extrusion strengthening method, which is of significant importance for the design and application of water-lubricated friction pairs.
Reciprocating seals in hydraulic actuators are critical to ensuring the performance and reliability of aerospace systems. This review presents a comprehensive overview of their operating conditions, material properties, modeling approaches, and testing methodologies. First, the operational environments of aviation hydraulic reciprocating seals are examined, with particular emphasis on the challenges posed by high pressures, elevated temperatures, and dynamic loading. The properties of candidate materials and temperature-sensitive sealing compounds are analyzed, focusing on material selection criteria tailored to specific application requirements. Macro-scale characteristic modeling, micro-scale lubrication mechanisms, and wear prediction are discussed in detail to enhance understanding of the tribological behavior at the seal interface. The integration of finite element analysis (FEA) with mixed lubrication methods is identified as a promising approach for improving the accuracy of seal performance predictions. Experimental techniques for evaluating macroscopic characteristics, visualizing seal conditions, and assessing service life are also reviewed, and the limitations of current testing methods are critically discussed. These studies provide valuable insights into seal behavior under realistic operating conditions, guiding the optimization of seal design and material selection. Finally, key challenges in the field are highlighted, including wear, leakage, and performance degradation, along with potential directions for future research aimed at enhancing the durability and reliability of reciprocating seals in aviation hydraulic systems.
This study explores the dry sliding wear behaviour of cost-effective, eco-friendly Al6061 aluminium matrix composites (AMCs) reinforced with corn cob ash (CCA), an agro-waste byproduct, via bottom-pouring stir-casting, to overcome the challenges posed by conventional ceramic reinforcements, including strength-to-weight ratio, wear resistance, and cost. The composite was optimised using a multi-response identifier and Taguchi-grey relational analysis (GRA). The test was performed using a Design of Experiments (DoE) L36 orthogonal array with various loads and sliding velocities. The optimal dry sliding wear test parameters were 4% CCA reinforcement, 10 N load, and 1 m/s velocity. Seven different types of machine learning and statistical regression methods were utilised to improve prediction performance. The results showed that the ANFIS and ANN models outperform other models, with R 2 values of 0.99 and 0.956, respectively. The results revealed that combining modern ML models with Taguchi-GRA is an effective approach for producing lightweight, wear-resistant agro-based AMCs, which will help expand their applications in the aerospace and automotive industries.
Sealing rings are widely used in drilling and completion tools, but they are prone to performance degradation under combined high-temperature, high-pressure, and corrosive conditions, leading to sealing failure and leakage. This study investigates the high-temperature corrosion and high-pressure sealing performance of three sealing rings with identical specifications but different material systems: a fluorine rubber ring and two perfluoroether rubber rings, designated as S-FKM, S-FFKM-1, and S-FFKM-2. High-temperature corrosion tests were conducted, and the evolution of material properties was evaluated through systematic characterization of changes in morphology, mass, and hardness before and after corrosion. High-pressure sealing performance was further assessed using a specialized fixture, with sealing reliability determined by monitoring pressure variations. The S-FFKM-2 ring exhibited no cracking at 232 °C, with a mass change of 0.22 % and a hardness variation below 2 Shore A, demonstrating superior high-temperature corrosion resistance. The S-FFKM-1 ring maintained a pressure of approximately 67 MPa after corrosion at 180 °C, indicating excellent high-pressure sealing performance. In contrast, S-FKM showed intermediate behavior in both corrosion and sealing tests, reflecting a more balanced overall performance. The outstanding performance of S-FFKM-2 is attributed to its high tetrafluoroethylene content, while the high perfluoroalkyl vinyl ether and carbon black content in S-FFKM-1 contributes to its superior sealing capability. These findings provide valuable guidance for the selection of materials for high-temperature downhole sealing applications.
Wear and microscopic seepage will be aggravated when reciprocating combined seals used with high water-based liquid owing to its low viscosity and strong permeability. To accurately evaluate the tribological and seepage properties of the combined seal under the high water-based liquid, considering wear and microscopic seepage, a macroscopic friction and leakage model of the Glyd ring is constructed based on the mixed lubrication and film thickness corrected Archard theory, a seepage analysis method based on the two-dimensional Reynolds equation for the microchannel is further proposed by integrating the actual microscopic morphology and macroscopic compression ratio. The friction force and wear thickness tests are carried out for verification. The result shows that the Glyd ring undergoes with a decrease in the amplitude of rough peaks and valleys, characterized by an expansion of the microscopic contact area and a decrease in seepage channel height. The reduction in friction force as wear continues is caused by the combined effects of decreased pre-compression and micro-convex peaks. The traditional Archard model, based on the contact pressure of micro-convex bodies, will overestimate the wear amount. Introducing a lubrication correction coefficient related to film thickness can improve the accuracy of wear assessment. The microscopic seepage of the Glyd ring is approximately 1/130 of the macroscopic leakage, and it will continue to decrease as the wear process. The research results provide a theoretical basis for accurately predicting the leakage and wear characteristics of the Glyd ring and other reciprocating seals.
Supercritical carbon dioxide (sCO 2 ) power cycles are poised to become a promising technology in the energy generation sector, particularly for small modular nuclear reactors. However, current turbomachinery utilizing sCO 2 faces significant challenges due to high leakage rates, which hinder the full potential of this power generation method. These elevated leakage rates not only penalize system efficiencies but also raise environmental issues by increasing CO 2 emissions into the atmosphere. To address these challenges, we propose an elastohydrodynamic (EHD) shaft-end seal as a potential solution. This study presents experimental proof-of-concept data supporting our proposed seal design's effectiveness in minimizing leakage under high-pressure conditions. We constructed a test rig featuring a 2-inch stainless steel static shaft and employed three different seals made from carbon graphite, virgin PEEK, and bearing-grade PEEK materials for evaluation. The experiments were run with inlet pressures reaching up to 13.5 MPa and with initial clearances as narrow as 0.001 inches, encompassing a total of 39 tests conducted across various configurations. The highest recorded leakage rates observed were 4.0 g/s for carbon graphite, 3.6 g/s for virgin PEEK seals, and 8.2 g/s for bearing-grade PEEK; however, these values decreased significantly, dropping to 0.3 g/s, 1.0 g/s, and 3.4 g/s respectively, as pressure rose to its maximum level. All tested seals exhibited throttling behavior characterized by bell-shaped mass flow rate profiles throughout their operation range. These findings indicate that the EHD seal could have a potential application within sCO 2 turbomachinery systems.
To address the issues of inherent stress concentration in the O-ring and excessive deformation of the thin-walled C-ring in a Stirling engine's conventional cap-type piston rod seal, a novel sealing configuration incorporating a toothed slip ring is proposed to improve structural adaptability. A two-dimensional axisymmetric finite element model was developed to analyse the stress distribution and wear behaviour of the proposed seal under reciprocating motion, and its performance was compared with the original cap-type seal. The results show that under steady-state operation, the maximum von Mises stress in the toothed slip ring was reduced by approximately 45.9% and 54.6% during the forward and return strokes, respectively, and that in the O-ring was reduced by approximately 11.6% and 10.5%, significantly improving the overall stress state of the sealing assembly. Subsequently, distinguishing this work from conventional single-parameter studies, a coupled regression-based design approach was employed to optimise the O-ring compression ratio, the cross-sectional width of the toothed slip ring, and the interference fit. The optimisation results indicate that with an O-ring compression ratio of 15%, a toothed slip-ring width of 0.754 mm, and an interference fit of 0.03 mm, the wear rate at the sealing interface is minimised. Compared to the initial design, this optimal configuration achieves reductions in wear rate of approximately 21.7% in the forward stroke and 8.9% in the return stroke. These findings provide insights and practical guidelines for designing high-performance piston rod seals, minimizing friction-induced damping, and enhancing the service life and dynamic stability of Stirling engines.
As internal combustion engines advance toward higher power density and lower emissions, the reliability of piston ring-cylinder liner tribological pairs becomes increasingly critical. In this study, the wear behavior of a molybdenum-sprayed piston ring against a nitrided cylinder liner was investigated under varying sliding time, temperature, and load using a simulated wear test. Anti-scuffing performance was further evaluated by interrupting oil supply under severe conditions (40 MPa, 220 degrees C), where the pair sustained operation for an average of 110 min. The results provide insight into the tribological characteristics of this material pairing for high-performance engine applications.
Condition monitoring can help to detect faults of rotating machinery early and thereby prevent failures. Rolling elementbearings are one of the most important machine elements to be monitored. This study focusses on rolling element bearingfault detection and localization using high-frequency, structure-borne sound, so-called acoustic emissions (AE) sensors on adedicated roller bearing test bench. One the one hand, the high-frequency signals (range 20-1000 kHz) are analyzed and onthe other hand, a demodulation algorithm is employed to down-sample the signals to frequency range of common bearingfrequencies (<= 10 kHz) to allow a state-of-the-art fault localization using spectral analysis of these signals. The AE results arealso compared to the commonly used spectral analysis of vibration signals using conventional, piezo-electric accelerationsensors (<= 10 kHz). The results show that AE is on par with vibration signals for fault localization and outperforms vibrationin detecting very small surface damages and starved-lubrication conditions.
Premature bearing failures are frequently reported in lightly built rotating machinery such as ceiling fans, despite the use of high-quality rolling element bearings and the absence of classical rolling-contact fatigue damage. Field inspections typically reveal fretting marks on bearing outer races, lubricant discoloration, elevated vibration levels, and localized heating near bearing housings, yet conventional vibration-based diagnostics fail to identify discrete fault signatures. This study investigates the hidden structural cause of such failures through combined experimental measurements and numerical contactmechanics analysis using a commercially representative ceiling fan system. Bearing housing support rigidity was systematically varied by modifying housing thickness, spot-weld density, and rib reinforcement. Experimental results show that compliant housing configurations exhibit 40–60% higher RMS vibration levels and bearing housing temperature rises of 8–12°C compared with reinforced configurations under identical operating conditions. Finite element analysis reveals that reduced housing stiffness produces non-axisymmetric bearing seat ovalisation, resulting in highly non-uniform contact pressure distributions and peak contact stress increases of approximately 30%. These pressure gradients promote micro-slip and fretting-type behaviour at the bearing–housing interface, generating frictional heat and broadband vibration amplification rather than classical defect frequencies. The combined evidence establishes housing compliance as a primary root cause of premature bearing degradation in lightly supported rotating systems. The findings explain why such failures are often misattributed to bearing quality and why traditional fault-frequency diagnostics are ineffective. Structural reinforcement of bearing housings is shown to be a more effective reliability measure than modification of bearing clearance or replacement of bearings.
The conical bearings are capable of supporting combined radial and axial loads, their performance at higher semi-cone angles-particularly under heavy thrust loads-has received minimal attention in the literature. Therefore, this study aims to achieve improved bearing performance of conical hybrid thrust bearing (CHTB) lubricated with Magneto-Rheological (MR) lubricant under heavy thrust load requirements. In this paper, the modified Reynolds equation governing the bearing fluid domain is discretized using the finite element method (FEM) and solved via the Newton-Raphson technique. The flow behaviour of the MR lubricant is modelled using the Dave equation, based on the Bingham plastic rheological model. The effect of restrictor design parameter, axial shaft position and semi-cone angle is systematically investigated to examine the static and dynamic behaviour of the bearing. A parametric study of recess dimensions is also performed, and the optimum recess geometry is identified based on stiffness characteristics. The numerical results indicate that the use of MR lubricant, particularly at lower shaft positions and higher semi-cone angles, significantly enhances load capacity, maximum lubricant pressure, lubricant flow rate, and damping coefficient. Also, at a particular value of restrictor design parameter, the stiffness coefficient provides the optimum performance. The findings provide important insights into the coupled influence of restrictor design parameter, axial shaft position and semi-cone angle of conical hybrid thrust bearing (CHTB) operating with both Newtonian and MR lubricants.
To investigate the dynamic characteristics of the stern bearing lubrication film during rudder maneuvers, this study employs the displacement superposition method to describe the bidirectional deformation and geometric posture of the stern bearing. A lubrication model is developed, and a computational method for determining dynamic parameters is proposed. The model is solved numerically to analyze the effects of varying operating conditions and structural parameters. Results indicate that increases in both vertical and horizontal loads enhance the lubrication film's dynamic parameters, with vertical loads exerting a stronger influence, and that the stern bearing is more sensitive to vertical displacement disturbances. Compared to right rudder maneuvers, left rudder maneuvers produce greater dynamic parameters in the lubrication film. Further analysis reveals that increasing the length-to-diameter ratio reduces dynamic parameters, whereas increasing the clearance ratio enhances them, and that both ratios have a pronounced effect on parameters associated with vertical displacement.
Water-lubricated bearings are critical components in marine propulsion systems. They must reliably sustain load transmission and accommodate vibration propagation under demanding operating conditions. Bearing performance directly affects propulsion efficiency, operational reliability, and onboard noise emissions. This study proposes a novel laminated water-lubricated bearing design to mitigate propulsion-shaft noise and improve crew survivability. A coupled fluid-structure-acoustic (FSA) model is developed to characterize the bearing response under representative operating conditions. The effects of key operating and structural parameters on lubrication performance and noise radiation are systematically quantified. In addition, the influence of soft-hard material combinations on fluid-structure interactions is examined, elucidating the relationship between bearing deformation and the resulting stress-strain response across different scenarios. The results advance the understanding of multiphysics coupling in water-lubricated bearings and provide a theoretical basis for optimizing and deploying modern laminated bearings, thereby underscoring their engineering significance.
A significant portion of the energy used to propel a vehicle is dissipated as rolling resistance (RR) in the tire-road interaction. Largely due to the hysteretic losses resulting from the cyclical deformations of the tire's viscoelastic material as the tread engages with asperities of different wavelengths, RR depends on the tire and pavement surface characteristics. However, factors related to vehicle and ambient conditions also play a role. In particular, specifics of battery electric vehicles (BEVs) like the increased tire load and different torque performance compared to equivalent-sized internal combustion engine vehicles are expected to increase the RR and induced energy consumption. This paper investigates the relationship between the pavement surface characteristics and the RR in a passenger BEV. To this end, experimental measurements of the RR were performed in conditions close to real driving. They involved an instrumented BEV equipped with two dynamometric wheels acting as tribometers, driven on a test track featuring several asphalt pavement sections of diverse texture and roughness levels, and differing in age and wearing course. Standardized descriptors of these surface properties were then correlated with the corresponding measured RR coefficients. Different segmentation strategies were applied to derive the values of the metrics. The results (1) validate correlations previously observed in drum- and trailer-based measurements and (2) reveal how local variations in pavement surface characteristics influence RR. These findings may support road pavement managers in the design of pavement management strategies that potentialize the environmental benefits offered by passenger BEVs.
The process of additive manufacturing (AM) and fuzed deposition modeling (FDM, in particular), has become a promising approach to manufacturing complex products with biodegradable materials like polylactic acid (PLA). Nevertheless, the tribological performance of FDM-printed PLA components is still a severe limitation of functional use. This research experimentally studied the tribological performances of the PLA + and carbon-fiber-reinforced PLA (PLA Pro CF) fabricated through FDM. Pin-on-disk tribometer A group trial of cylindrical specimens was conducted in line with the standards of ASTM G99- 04. Five key printing parameters, layer thickness, raster angle, material type, infill pattern, and infill percentage were varied across 24 experimental runs. ANOVA and multi-criteria decision-making using the Combined Compromise Solution (CoCoSo) method wase employed to analyze surface roughness, frictional force, coefficient of friction (COF), and wear. The results indicate that raster angle (26.36%) and infill percentage (17.01%) are the most influential parameters affecting tribological performance. The optimal parameter combination, layer thickness of 0.2 mm, raster angle of 30 degrees, PLA + material, full honeycomb infill pattern, and 50% infill, resulted in a 40.28% reduction in surface roughness, 22.21% reduction in frictional force, 28.22% reduction in coefficient of friction (COF), and 9.17% reduction in wear compared to the average of all experimental runs. This optimal configuration represents the best compromise among all considered performance responses. FESEM analysis showed that PLA + had an abrasive-adhesive wear whereas PLA Pro CF had enhanced wear resistance owing to the strength of carbon fiber. The findings demonstrate that carbon fiber reinforcement significantly enhances the tribological performance of FDM-printed PLA components.
