Search Results (26)

The instability of a film falling down a vertical plate with lateral walls, which is the base configuration describing the structured packing geometry, is numerically investigated via the lubrication theory. The solid substrate wettability is imposed through the disjoining pressure, while the assumption of a tiny, precursor film thickness allows for modelling a moving contact line. Contact angles up to ${60}^{\circ }$, which falls in the range of structured packing applications, are investigated, thanks to the full implementation of the capillary pressure instead of the small slope approximation. Parametric computations are run for a film falling down a vertical plate bounded by lateral walls, changing the plate width and the flow characteristics. An in-house, finite volume method (FVM) code, previously developed in FORTRAN language and validated in the case of film instability and rivulet flow, is used. The number of observed rivulets, triggered by the instability induced by the lateral walls, is traced for each computation. The numerical results suggest that rivulets with a given wavelength, equal to the one provided by the linear stability analysis, are generated, but only those characterized by a wavelength greater than a minimum threshold, which depends on the substrate wettability, induce partial dewetting of the domain. This allowed for the development of a simplified, statistically based model to predict the effective interface area and the rivulet holdup (required to estimate the mass transfer rate in absorption/distillation applications). Compared to the literature models of the structured packing hydrodynamics, which usually assume a continuous wetting layer, the influence of the flow pattern (continuous film or ensemble of rivulets) on the liquid holdup and on the interfacial area is introduced. The predicted flow regime is successfully verified with evidence from the literature, involving a flow down a corrugated sheet. Full article

This study investigates how laser-induced surface modifications influence key properties such as wear resistance, hardness, and friction in dry and lubricated conditions. The research applies nanosecond pulsed laser treatment to create random, quasi-random, quasi-periodic, and periodic surface structures on the steel surface, aiming to enhance the wear resistance and reduce the coefficient of friction (COF). The frictional performance between the carbon steel ball and the texturized surface was evaluated, including an analysis of the initial friction phase contact (single, double, and multi-contact), with the surface topography assessed before and after wear. The results of the pin-on-plate tests indicate that laser texturing improves the hardness by transforming austenite into martensite, modifies the wettability by periodizing the surface, reduces the COF, and enhances the wear resistance. Periodic surface structures allow for better lubricant retention and change in the lubrication regime, contributing to lower friction and a longer surface lifespan. Minimizing ball–surface contact through appropriate surface periodization significantly affects the load transfer. The primary wear phenomena are the adhesive and abrasion wear of a two-body nature, transforming into a three-body one. The study concludes that laser surface texturing is an effective method for enhancing the tribological performance of AISI 321 steel, with potential applications in industries requiring high wear resistance. Full article

The tribological phenomena concerning the lubrication regime change (LRC) during bulk metal forming are comprehensively studied. A multi-step cold forward extrusion process shows the evolution of LRC and reveals the shortcomings of the traditional Coulomb friction law. The previous works of the specific author’s research group on friction are reviewed, focusing on the LRC during bulk metal forming. Various LRC phenomena from various examples are revealed. It has been found that the drawing and forward extrusion processes are vulnerable to LRC because of significant sliding motion at the material–die interface, and that when the strain hardening of the material is slight, the influence of friction increases, and as a result, the influence of LRC increases excessively. The new findings also include the impact of LRC on the macroscopic phenomena of the process and the reason for the sharp increase in friction coefficient via LRC, which is validated by the work of Wilson. This paper aims to make engineers and researchers think much of the tribology with lubricant in bulk metal forming with a focus on the dependence of tribological phenomena on the state of the lubricants and the irrationality of traditional friction law, especially in the forging of materials with a low strain hardening capability. Full article

The antiwear properties of tribofilms formed on steel surfaces lubricated with various multi-component lubricants were investigated at an elevated temperature and under load-speed conditions conducive to sliding in the boundary lubrication regime. The lubricants contained base oil, reduced-level (secondary) zinc dialkyl dithiophosphate (ZDDP), and nitrogenous dispersant. The wear resistance of the tribofilms produced from different oil blends was evaluated in the context of the rate of change in the sliding track volume (wear rate for material loss) and the load-bearing capacity, chemical composition, and thickness of the tribofilms. Surface profilometry and scanning electron microscopy were used to quantify the wear performance and detect the prevailing wear mechanisms, whereas X-ray photoelectron spectroscopy elucidated the chemical composition and thickness of the tribofilms. The oil blends without ZDDP did not produce tribofilms with adequate antiwear properties, whereas the oil blends containing ZDDP and dispersant generated tribofilms with antiwear characteristics comparable to those of tribofilms produced from blends with a higher ZDDP content. Although dispersants can suspend oil contaminants and preserve the cleanness of the sliding surfaces, it was found that they can also reduce the antiwear efficacy of ZDDP. This was attributed to an additive-dispersant antagonistic behavior for surface adsorption sites affecting tribofilm chemistry and mechanical properties. Among the blends containing a mixture of ZDDP and dispersant, the best antiwear properties were demonstrated by the tribofilm produced from the blend consisting of base oil, 0.05 wt% ZDDP, and a bis-succinimide dispersant treated with ethylene carbonate. The findings of this investigation demonstrate the potential of multi-component lubricants with reduced-content ZDDP and nitrogen-based dispersant to form effective antiwear tribofilms. Full article

This work aims to explore the effect of side load and rotational speed on the tribological behavior of a novel ceramic–epoxy composite in Kevlar matrix casing lining that is in contact with a rotating drillpipe tool joint (DP-TJ) coated with the same composite. Three rotational speeds (65, 115, and 154 rpm) and three side loads (500, 700, and 1000 N) were considered under water-based mud (WBM) lubrication. Wear depths, volumes, and specific casing wear rates (K) were determined for each combination of speed and load. The wear depth and K were found to increase with an increasing applied side load. However, the specific casing wear rate at the rotational speed of 115 rpm was found to be the lowest among the three speeds. This is mainly due to a probable lubrication regime change from boundary lubrication at 65 rpm to hydrodynamic lubrication with a thick lubricant film at 115 rpm. The digital microscope images were used to determine the wear mechanism, showing that at low speeds, the main mechanism was abrasive wear, but the increase in the speed brought about more adhesive wear. In contrast, the change in the side load does not affect the wear mechanism of the casing. Scanning electron microscopy and energy-dispersive spectroscopy (EDS) were used to analyze the surface and composition of the novel material before and after the wear tests. Full article

The performance and durability of high-pressure fuel systems in combustion engines are critical for consistent operation under extreme conditions. High-pressure fuel systems are traditionally lubricated with fuel that is compressed and delivered to the combustion chamber. However, lubrication with fuel presents significant challenges in these systems when used with low-viscosity fuels, leading to increased wear rates, especially in reciprocating contacts. This study delved into the tribological performance of steels of varying alloy content (annealed and hardened variants of AISI-52100, CF2, and D2) against alumina and hard 52100 counterbody materials in ethanol and decane environments. Friction and wear behaviors were evaluated, highlighting the influence of material interactions and environmental factors. Elastohydrodynamic lubrication analysis of the tested systems indicated that ethanol and decane form lubricating films of nanometer-scale thickness, confirming the boundary lubrication regimes of the performed tests. In summary, the tribological behavior trends were similar for alumina and 52100 counterbodies. Even though soft 52100 steel demonstrated low friction, its wear was the largest for both tested environments and counterface materials. Among all the tested materials, hard D2 experienced the lowest wear. 52100 and D2 steels showed opposite friction change behavior when comparing hard and soft samples, with lower friction observed for softer 52100 steel and harder D2 steel. Meanwhile, the wear was lower for harder candidates than for softer ones independent of the environment and counterbody material. Raman spectroscopy analysis of the formed wear tracks indicated the formation of carbon films with larger intensities of characteristic carbon peaks observed for more wear-resistant materials. These results suggest the synergistic effect of hardness and tribochemical activity in reducing the wear of materials. Full article

Friction behaviour is an important characteristic of dynamic seals. Surface texturing is an effective method to control the friction level without the need to change materials or lubricants. However, it is difficult to put the manual prediction of optimal friction reducing textures as a function of operating conditions into practice. Therefore, in this paper, we use machine learning techniques for the prediction of optimal texture parameters for friction optimisation. The application of pneumatic piston seals serves as an illustrative example to demonstrate the machine learning method and results. The analyses of this work are based on experimentally determined data of surface texture parameters, defined by the dimple diameter, distance, and depth. Furthermore friction data between the seal and the pneumatic cylinder are measured in different friction regimes from boundary over mixed up to hydrodynamic lubrication. A particular innovation of this work is the definition of a generalised method that guides the entire machine learning process from raw data acquisition to model prediction, without committing to only a few learning algorithms. A large number of 26 regression learning algorithms are used to build machine learning models through supervised learning to evaluate the suitability of different models in the specific application context. In order to select the best model, mathematical metrics and tribological relationships, like Stribeck curves, are applied and compared with each other. The resulting model is utilised in the subsequent friction optimisation step, in which optimal surface texture parameter combinations with the lowest friction coefficients are predicted over a defined interval of relative velocities. Finally, the friction behaviour is evaluated in the context of the model and optimal value combinations of the surface texture parameters are identified for different lubrication conditions. Full article

This paper examines the difference between the effects of anti-wear additives on vegetable and hydrocarbon-based oils. Knowledge of the specific influence of additives on the anti-wear properties of vegetable oils is necessary to increase the efficiency of the development of biodegradable lubricating oils. In addition, this is interesting from the point of view of clarifying the mechanism of action of AW/EP additives. The effect of non-toxic additives—adipic acid monoester and hexadecanol—on hydrocarbon hydrocracking oil and vegetable oil was compared. The comparison was carried out in rolling contact with sliding, sensitive to the separating ability of the oil. It was found that in hydrocarbon oil, the additive affects the parameters of the hydrodynamic friction regime. When adding an additive to vegetable oil, the hydrodynamic parameters do not change. The additive acts in the same way in both oils during mixed and transient modes. The obtained results are compared to available data, and an explanation of the difference is proposed based on the AW/EP mechanism of action. It is concluded that there is little chance of enhancing vegetable oil properties for hydrodynamic bearings. Search criteria for additives that effectively influence the antifriction and anti-wear properties of vegetable oils in mixed and boundary friction modes are proposed. Full article

A mechanical seal is a common type of rotating shaft seal in rotating machinery and plays a key role in the fluid seal of rotating machinery, such as centrifugal pumps and compressors. Given the performance degradation caused by the wear to the face of the contact mechanical seal during operation and the lack of effective predictive maintenance monitoring methods and evaluation indexes, a method for measuring the acceleration of the mechanical seal face’s vibration was pro-posed. The influence of face performance degradation and rotational speed change on the tribo-logical regime of the mechanical seal was investigated. The proposed fault detection model based on support vector data description (SVDD) was constructed. A mechanical seal face degradation test rig verifies the usability of the proposed method. The results show that in the mixed lubrication (ML) regime, the vibration sensitivity of the face increases with the increase in rotational speed. With the decrease in the face performance, the vibration-sensitive characteristic parameters of the face in-crease and change from the ML regime to the boundary lubrication (BL) regime. The incipient fault detection model can warn about incipient faults of mechanical seals. Here, the axial detection result predicted that maintenance would be required 10.5 months earlier than the actual failure time, and the radial and axial detection results predicted required maintenance 12 months earlier than the actual failure. Full article

This work aims to explore the impact of side loads, drill-pipe tool-joint (DP-TJ) speed (rpm), and mud type on the austenitic stainless steel SM2535-110 casing wear characteristics. Actual field drill pipe tool joints, casings, and drilling muds are used in this study. The results of the study show that under both types of lubrication, the wear volume increased with radial load and DP-TJ speed. SM2535-110 casing specimens tested under oil-based mud (OBM) lubrication had higher casing wear volumes than those obtained under water-based mud (WBM) lubrication. This unexpected behavior is mainly due to the increase in the surface hardness of the casing specimens tested under WBM. The results also show that the specific wear rate or wear factor (K) (which is defined as the volume loss per unit load per unit distance sliding) values of specimens tested under WBM are in general two to four times higher than those obtained under OBM. While K values under WBM increase with both the side load and rpm, those under OBM show a sharp decrease with rpm. This behavior under OBM is due to this lubricant’s higher viscosity and the change of lubrication regime from thin film to thick film lubrication at higher rpm. Scanning electron microscopy (SEM) and the digital microscopic imaging (DMI) of SM235-110 casing specimens show that an aggressive combination of adhesive, abrasive, and plastic deformation was observed under WBM, while the dominant wear mechanism under OBM is abrasive wear. Full article

Improving the frictional response of a functional surface interface has been a significant research concern. During the last couple of decades, lubricant oils have been enriched with several additives to obtain formulations that can meet the requirements of different lubricating regimes from boundary to full-film hydrodynamic lubrication. The possibility to improve the tribological performance of lubricating oils using various types of nanoparticles has been investigated. In this study, we proposed a data-driven approach that utilizes machine learning (ML) techniques to optimize the composition of a hybrid oil by adding ceramic and carbon-based nanoparticles in varying concentrations to the base oil. Supervised-learning-based regression methods including support vector machines, random forest trees, and artificial neural network (ANN) models are developed to capture the inherent non-linear behavior of the nano lubricants. The ANN hyperparameters were fine-tuned with Bayesian optimization. The regression performance is evaluated with multiple assessment metrics such as the root mean square error (RMSE), mean squared error (MSE), mean absolute error (MAE), and coefficient of determination (R²). The ANN showed the best prediction performance among all ML models, with 2.22 × 10⁻³ RMSE, 4.92 × 10⁻⁶ MSE, 2.1 × 10⁻³ MAE, and 0.99 R². The computational models’ performance curves for the different nanoparticles and how the composition affects the interface were investigated. The results show that the composition of the optimized hybrid oil was highly dependent on the lubrication regime and that the coefficient of friction was significantly reduced when optimal concentrations of ceramic and carbon-based nanoparticles are added to the base oil. The proposed research work has potential applications in designing hybrid nano lubricants to achieve optimized tribological performance in changing lubrication regimes. Full article

This work develops a numerical methodology for predicting the performance of an automotive piston ring system by considering contact and lubrication mechanics. The rough surface contact mechanics and lubrication occurs on a scale much smaller than the size of the piston rings and therefore the key aspect of the model is an algorithm that simultaneously solves the multiple mechanisms at different scales. The finite element method will be used to model the mechanical deformations of the piston ring surfaces at large scales. The quasi-steady state model includes heat generation due to solid and viscous friction. This heat generation will then be used to predict the temperature rise and thermal effects in the lubricant and component. A statistical rough surface method that renders asperities as elastic–plastic wavy surfaces predicts the solid contact area. The modified Reynolds equation will be solved to consider the effects of mixed hydrodynamic lubrication while using flow factors formulated for actual piston and ring surfaces. The lubricant viscosity depends both on temperature and shear rate. This will allow for the regimes of boundary, mixed, and full-film lubrication to be considered. The model predicts friction for various loads and speeds that are then compared to experimental measurements. Although the contacts operate mostly in the mixed lubrication regime, the model and experiments show changes in friction with load, speed, and temperature. Full article

Research into the effects of different parameters on flow phenomena is necessary due to the wide range of potential applications of non-Newtonian boundary layer nanofluid flow, including but not limited to production industries, polymer processing, compression, power generation, lubrication systems, food manufacturing, and air conditioning. Because of this impetus, we investigated non-Newtonian fluid flow regimes from the perspectives of both heat and mass transfer aspects. In this study, heat transfer of electrical MHD non-Newtonian flow of Casson nanofluid over the flat plate is investigated under the effects of variable thermal conductivity and mass diffusivity. Emerging problems occur as nonlinear partial differential equations (NPDEs) in opposition to the conservation laws of mass, momentum, heat, and species transportation. The shown problem can be recast as a set of ordinary differential equations by making the necessary changes. A modified finite element method is adopted to solve the obtained set of ODEs. The numerical method is based on Galerkin weighted residual approach, and Gauss–Legendre numerical integration is adopted in the modified finite element method application procedure. To clarify the obtained results, another numerical technique is employed to solve the reduced ODEs. With the help of error tables and the flowing behavior of complicated physical parameters on estimated solutions, this study graphically and tabulatively explains the convergence of analytic solutions. Comparing some of the obtained results with those given in past research is also done. From the obtained results, it is observed that the velocity profile escalates by improving the electric parameter. Our intention is for this paper to serve as a guide for academics in the future who will be tasked with addressing pressing issues in the field of industrial and engineering enclosures. Full article

The formation of tribofilms depends on temperature, shear stress, availability of the related chemical components, and characteristics of the near surface region, e.g., roughness and surface chemistry. The purpose of a tribofilm is to separate two sliding surfaces, thus preventing or limiting wear. This research article aims for the first time at a systematic approach to elucidate on a fundamental level the interplay between tribofilm formation in particular thickness and wear behavior in the boundary and mixed lubrication regime. For this, load, temperature and sliding frequency as most relevant parameters are taken into consideration. For that purpose, a piston ring and cylinder liner configuration in an oscillating tribometer was chosen as a model system, with the top dead centre conditions in internal combustion engines of passenger cars as the testing regime. The amount of wear produced during the tribotests is continuously monitored by means of the Radio-Isotope Concentration (RIC) method. The tribofilm is investigated via Atomic Force Microscopy (AFM), Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS) and X-ray Photoelectron Spectroscopy (XPS). The results clearly indicate that the impact of load on the wear rate can be seen in an Archard-like dependency, but changes of temperature and sliding velocity in the boundary to mixed lubrication regime imply a non-linear ratio between wear and tribofilm formation. Full article

This article shows that the change of rough surfaces in the way of their contact interaction can be analyzed using the theory of Markov’s processes. In the framework of existing models, this problem cannot be solved. In this article, the idea of reducing to Markov’s model is shown on a simple discrete scheme, which is then generalized. The approach was applied to the analysis of the friction process, to the fatigue failure mode, in which the surface element changes after multiple contacts, possibly many millions. The Kolmogorov-Feller’s equations for the model of this regime were presented and the model of the influence of lubrication is offered. A calculated example of estimating the evolution of surfaces separated by a lubricant layer is given. Additionally, the technical characteristics as functions of the friction path and the load were evaluated. Full article