Tribological Approach Research Articles

High-silicon spring steel transformation to carbide-free bainitic (CFB) steel: a mechanical and tribological approach under rolling/sliding conditions

The present study concentrates on the development of carbide-free bainite steel and explores its tribological and mechanical characteristics using a newly devised disk-on-disk tribometer. The microstructure of the treated samples was examined through heat treatment at various holding temperatures (300, 350, and 400 °C) and durations (10, 20, and 30 min), along with isothermal transformation. The wear rate demonstrated significant sensitivity to holding duration, transformation temperature, phase fraction, and the stability of retained austenite. The microstructural analysis encompassed atomic force microscopy (AFM), FE-SEM, x-ray diffraction (XRD), and energy-dispersive x-ray spectroscopy (EDS). The study extensively investigated the robust correlation among mechanical properties, microstructure, wear behavior, and the presence of retained austenite (RA) and bainite volume fraction. The findings indicate that carbide-free bainite steel holds promise for replacing conventional railway wheel track steel in the steel industry. The structural property correlations have developed of high silicon steel, hardness reduced with increasing temperature and isothermal preserving time; resulting in a gradual increase in the wear rate of CFB steel. The salt bath soaking temperature of 350 °C with a period of 30 min was found to be the preeminent wear properties condition for CBF steel.

Tribological characterization of the cooling performance when applying cryogenic coolants and minimum quantity lubrication

Cryogenic minimum quantity lubrication (MQL) offers the potential to combine high cooling capacities, advantageous lubrication effects and a significant reduction regarding resource consumption. However, due to the wide range of machining applications and different load cases, an efficient design of the respective supply strategy is comparatively difficult. In this study, a tribological approach is presented that enables a characterization of the cooling and lubrication properties in dependence of the supply strategy and two representative load cases. The results show that the tribological setup is well suited to evaluate the occurring thermomechanical loads in dependence of the cryogenic MQL strategies applied.

Wear Characterization of Cold-Sprayed HEA Coatings by Means of Active–Passive Thermography and Tribometer

The aim of this work is to verify the applicability of thermography as a non-destructive technique to quantify the wear performance of several high-entropy alloy coatings. Thermal profiles obtained from passive and active thermography were analyzed and the results were correlated with the classical tribological approaches defined in standards. HEA coatings made of several chemical compositions (AlxCoCrCuFeNi and MnCoCrCuFeNi) and realized by using different cold spray temperatures (650 °C, 750 °C, and 850 °C) were tested in a pin-on-disk configuration, with a dedicated pin developed for the wear tests. Then, the wear performances of each sample were analyzed with the hardness and wear parameter results. The thermal profiles of passive and active thermography allowed a complete characterization of the wear resistance and performance analysis of the coatings analyzed. The results are also compared with those presented in the literature.

Clothing comfort sensing system based on triboelectric and tribological behavior of fabrics

Static electricity accumulated on fabrics often causes discharged discomfort, fire, explosion, and cardiovascular diseases. Meanwhile, the electricity can be harvested and used for self-powered wearable devices. Therefore, it is essential to regulate fabric triboelectricity through studying the relationship between friction coefficients and triboelectric charges. In this paper, a reciprocating tribometer coupled with triboelectric testing instruments is designed to collect in-situ tribological and triboelectric properties for laterally sliding fabric based triboelectric nanogenerators (F-TENGs). In this case, the regulation factors involve motion conditions (including load, frequency, friction angle, etc.), surface components and environments. The results show that faster sliding speed and lower humidity produce higher triboelectric outputs of F-TENGs. Especially, amino groups modified silk shows an extremely strong electron-donating ability and achieves a high triboelectric current of 382.2 nA when paired with polyimide, which is enhanced by 1.67 times compared with silk. Most importantly, the friction coefficient values of F-TENGs show almost the same trend as the triboelectric outputs. Based on this, a sensing system for monitoring comfort level of fabrics is successfully designed through rubbing tested fabrics and observing indicator lamps. This work proposes a tribological approach with valuable insights of the underlying mechanism of triboelectric charging and extended applications.

Using tribological approach to assess production temperatures of asphalt binders

In this study, ball on three plates (BOTP) experiment has been used to propose an approach for evaluating the mixing and compaction temperatures of asphalt binder. The results are compared and correlated with equi-viscous- and workability- based methods to arrive at the proposed criterion. A viscosity grade binder, VG30, was modified with varying dosages of Sasobit and Rediset, and the study was executed considering two different types of aggregates (Granite and Dolerite). It was found that warm mix asphalt (WMA) binders can reduce the production temperatures of VG30, irrespective of the test methodology. Equi-viscous method was found to be inappropriate in the quantification of the production temperatures of WMA binders. Workability test results indicated that reduction in mixing and compaction temperatures is a function of the type of warm mix additive, dosages used, and aggregate source. Based on the variability of test parameters in BOTP test, a normal load of “1 N” and a sliding speed of “0.3 m/s” were found to give consistent results of coefficient of friction (CoF). The effect of plate type (Granite, Dolerite, and steel) on the values of CoF was found to be insignificant, and the use of steel plates was recommended. The results of BOTP and workability were in good agreement with each other. Temperature ranges corresponding to the CoF of “0.255–0.282” and “0.317–0.350” are proposed for assessing the mixing and compaction temperatures, respectively.

Mechanical cleaning of food soil from a solid surface: A tribological perspective

In this work, a tribological approach was used to distinguish the synergistic effects of mechanical removal and chemical removal (i.e. dissolution) of a layer of representative food soil from a solid surface, using a tribometer, Mini Traction Machine (MTM). Gravimetric and wear measurements of the soil were used to calculate the cleaning rates of burnt tomato puree on a stainless-steel disc, and the corresponding frictional characteristics offers insight of the mechanical removal. The cleaning due to soil dissolution (chemical removal) was quantified by UV–Vis measurements. The overall cleaning rates of food soil featured a linear reduction in mass over time, with a scaled removal rate k = 0.0046 s−1 (5 N applied force and 100 mm s−1 relative velocity), for most cases studied. It was observed that the cleaning rate can be improved with an increasing mechanical load or speed (50% from 1 to 2.5 N and 13% from 50 to 100 mm s−1), but is independent of the initial mass. UV–Vis measurements show that by increasing the load or speed the removal of chunks of burnt tomato puree was enhanced more than removal attributed to dissolution. Similar values of cleaning rates for most experimental parameters were extracted from both the gravimetric and wear measurements. Adhesion and cohesion measurements of the burnt tomato puree were conducted with a micromanipulator. It was found that adhesion forces are higher than cohesion for short soaking times, but for longer times the adhesion forces became weaker and with the additional shear rate in the MTM cleaning experiment, adhesion failure was observed in many cases by the end of the experiment. Indentation measurements showed the change in mechanical properties of the food foulant with a few minutes of soaking in water.

Tribocatalysis Induced Carbon-Based Tribofilms—An Emerging Tribological Approach for Sustainable Lubrications

To comply with the high demand for efficient and sustainable lubrications, carbon-based tribofilms and/or nanomaterials have emerged as a potential solution that can resolve the current major shortcomings of phosphorus- and sulphur-rich tribofilms and protective coatings. Although their employment is still in the early stages of realization and research, these tribofilms receive significant interest due to their capability to continuously and in situ repair/replenish themselves during sliding, which has been an ultimate goal of all moving mechanical systems. Structurally, these tribofilms are complex and predominantly amorphous or disordered with/without graphitic domains (e.g., graphene/graphite, onion-like carbon, etc.). Chemically, the compositions of these tribofilms vary significantly with environments, conditions, and material precursors. Yet, the structural properties of carbon-based tribofilms remain largely ambiguous, which precludes a full understanding of the mechanisms underlying the formation and lubrication performance. This review will summarize the current state-of-art research about the in situ carbon-based tribofilms that have been published since the pioneering works. Particularly, this work will highlight the recent approaches to generate these tribofilms, their associated lubrication performance, current understanding of the formation mechanics, common analytical approaches for these tribofilms, and the compatibility of these tribofilms with other additives. Together, the overall outlooks will be drawn, demonstrating the knowledge gaps and proposing further investigation tactics to tackle these emerging issues.

Introduction With its higher efficiency than solar panels, wind power is a fast-growing worldwide industry, with over 650GW of capacity installed all over the world now. 1.9 GW of freshly installed offshore wind capacity brought the total German fleet to 56.1 GW in 2021. This makes up over 28.000 turbines for now with number rising. Aus Wissenschaft und Forschung 31Tribologie

With the purpose of improving our predesign approach and increasing the end-product sustainability by going from resource wasting field testing to slender tribological model testing, we looked closer to commonly relevant calculation approaches as • Plint’s and Alliston-Greiner’s Energy Pulse (EP) • Matveesky’s friction power intensity (FPI) • Transmitted Energy (TE) to achieve fast and feasible tribo-system ranking for wind turbine bearing cases. With the concept of transmitted friction energy (Ef), satisfactory results were reached. We learned that 2-Disc tribometer may be used to simulate 100 % sliding, making comparison of different slippage rate easier by only using one tribometer, thus reducing measurement inaccuracies caused by different type of machines (e.g., pin on disc) or operator’s influence.

Sustainable tribology for reliability and efficiency

This special issue includes a collection of papers presented at the International Tribology Research Symposium (ITRS) 2021, held from 8th to 10th December 2021 in a virtual mode with the Tribology for Sustainability and Reliability theme. It has been observed that the types of machinery and components are improving daily as per the requirements to fulfill human needs. Due to these requirements in human necessities, new tribological challenges have developed that affect the reliability and efficiency of machinery and engineering components. Furthermore, the governments have also implemented stringent rules and regulations on industries to reduce environmental pollution. Researchers have developed sustainable (green) lubricants, superlubricity concepts in many engineering components, and new methodologies for contact area reduction, such as self-lubricating coatings, surface texturing, and surface modification. Therefore, this editorial has explored tribological advances, and Triboinformatics approaches for achieving sustainability and reliability. The practical, sustainable tribological approaches for the well-being of the society highlighted in this editorial are 1. Sustainable lubrication, 2. Space tribology, 3. Triboinformatics, 4. Biotribology, 5. Additive manufacturing, 6. Light metal matrix composites, 7. Sustainable machining, 8. Electric vehicles. These sustainable tribological approaches deliberated by the plenary, keynote, and invited speakers and participants of ITRS 2021 are guidelines for future research directions of tribology.

Friction and deformation at convergent contacts in geotribological systems

Geotribology reveals the application of a tribological approach to natural, e.g. nonmechanical inorganic tribosystems in the Earth's crust. It aims an integrated view over frictional phenomena in the Earth's crust and tracks the interweaving between the immense seismotectonic energy brought in and generated in the geotribological zones, and the evolution of destructive and constructive contact processes ending with the emergence of new mineral structures preserving system's life. A tribological application concerns the convergent contact deformations in geological objects with different rheology, in the movement of tectonic plates, leading to the emergence of obduction relief structures. Convergent geotribological contacts are places of tectonic collision between large rock plates forming the planetary zones of most active, both seismic and volcanic activity. A typical example is the obduction and subduction zones of two ongoing rock plates, one pushing under the other. Studies of the contact process in geotribozones provide an opportunity for tribology to explain new phenomena in the variety of contact deformations and their full cycle of evolution. Considering the necessity of using a tribological approach to geology when describing friction-induced deformations, the role of rheology, mechanisms of preliminary contact displacement and distribution of energy and energy density in the contact body is shown.

A tribological approach to astringency perception and astringency prevention

Astringency is one of the most complex oral sensations. This dry, puckering mouthfeel occurs when consuming wine, tea, or other foods containing polyphenols. The exact mechanism behind this dry mouthfeel is not completely understood. Here, we describe a systematic tribological approach to measure model and real saliva to understand the specific role of the salivary proteins (mucins and proline-rich proteins (PRPs)) on lubrication-based astringency. Our approach reveals that there are two routes towards lubrication losses, partly involving irreversible molecular mechanisms for which the order of reactivity matters. For human saliva, we find two lubrication mechanisms: (I) Using phenolic compounds, we find aggregation-induced lubrication losses due to hydrogen bond formation, which depend critically on phenol size: large polyphenols allow for aggregation-induced lubrication losses, but small phenols do not. (II) For metal salts combined with saliva, we observe aggregation without lubrication losses as a result of electrostatic interactions. We find that lubrication losses are caused by the specific removal of the salivary PRP layer, whereas mucin aggregation in the presence of PRPs does not lead to lubrication losses. Additionally, we show that the addition of solvents that are able to reduce protein-polyphenol hydrogen bonding (e.g. ethanol) can prevent lubrication losses. Lubrication losses can also be compensated by the addition of highly viscous fluids (glycerol) that can provide viscous lubrication.

Tribological approach for the safety assessment of flooring/walkway surfaces: Application for the prevention of pedestrian fall incidence

This study investigated the role of surface finishes from different material types of floors/walkways on traction properties and identified their effects on slipperiness controls under diverse walking environments to prevent fall incidence. Measurements and analyses of surface textures and traction properties of floors/walkways and interpretations were based on a tribological concept. Dynamic friction tests were conducted amongst nine indoor and outdoor floor specimens and three shoes under four different risk levels of environments. Test results showed that traction performances were considerably influenced by surface finishes of the floor specimens under the moderately (soapy) and highly (oily) risky conditions. This study also uncovered that rough floors did not mechanically ensure higher slip resistance whilst some smooth floors exhibited better slip resistance than the rougher ones. Nevertheless, outcomes from this study provided fundamental, but important information on the walkway traction properties that showed multifaceted features of tribological phenomena. Based on the overall findings, this study proposed an insight to identify the impact of floor/walkway textures on traction performances and consequently exploit sensible design concepts for the floor surfaces to prevent fall incidents.

Valve-seat components in a diesel engine: a tribological approach to limit wear

Within diesel engines, the valve-seat contact is one of the few non-lubricated contacts which is subjected to significant degradation. This degradation is put in evidence by material removal at the intake valve. The material pull out is promoted by the replication of combustion cycles (500 million) and severe operating conditions (pressure 18 MPa). The wear can lead to gas leakage and engine failure. The target of this work was to identify the main parameters affecting this wear. Our approach was based on the tribological triplet and material flows within the contact involving both numerical and experimental approaches. A dynamic model and a valvetrain test bench showed that the wear flows could be activated by the architecture of the valve opening system. Consequently, the limitation of these flows can be obtained by controlling the “global” geometry of the system and therefore without modifying the properties of the materials. In the same way, a finite element model of the local response of the seat-valve contact highlighted the impact of the “local” geometry of the contact. The change of this geometry is a lever to limit the shearing forces which reduces the tearing of the particles and therefore wear. Finally, tests carried out on the engine and on a specifically adapted test bench completed the understanding of degradation mechanisms (source flow, wear flow, etc.). Morphological interpretations of worn surfaces in terms of material flows allowed the understanding of the build-up stages of a protective layer. One solution to promote this internal flow is the use of pollutants from combustion. For example, the burned oil in contact, which isa prioriharmful, becomes an opportunity here. In addition, un-burned hydrocarbons from the combustion of biodiesel help to protect the contact.

Effect of H2O2 Solution’s pH on the Human Enamel Micro and Nanowear

The effect of 30% H2O2 solutions with different pH (2, 4 and 6) on the wear of human dental enamel was studied. Additionally, the whitening efficiency and changes in hardness and morphology were evaluated. The enamel tribological response was accessed through two different approaches: ball-on-plate and atomic force microscopy (AFM), the later following a tribological model based on a single asperity contact. The results showed differences in the specific wear rate and wear mechanisms between the two used approaches. Regardless of the tribological approach used, the wear resistance of enamel was lower for pH = 2. It was observed that pH = 6 leads to a safe and efficient whitening treatment.

Rheological and tribological approaches as a tool for the development of sustainable lubricating greases based on nano-montmorillonite and castor oil

This study investigates the development of novel montmorillonite/castor oil blends to formulate sustainable lubricating greases to promote the replacement of petrochemicals industry-derived materials by substances obtained from renewable sources. Specifically, the effect of the thickener concentration on the rheological, chemical, thermal, tribological properties, and atomic force microscopy (AFM) microstructure of these systems were studied. The results showed that the C20A nanoclay content could be used to modulate the viscosity values, the linear viscoelastic functions, and tribological properties of these montmorillonite dispersions. In general, these gel-like dispersions exhibited remarkable lubricant properties; the samples showed values of the friction coefficient and wear scars similar or lower than those obtained with model bentonite grease.

A novel tribological approach for selection of low friction engine lubricating oil

ABSTRACT A novel tribological rig-based approach is presented for the selection of engine oils with reduced friction characteristics. A combined experimental and numerical investigation has been performed to compare and assess the friction between the piston ring and liner of two different passenger cars lubricated with two different commercial engine oils. The experimental investigations were performed on reciprocating tribo-tester using actual piston ring and liner as the test specimens. The experiments were performed to investigate the influence of contact load and reciprocating frequency on the contact friction. The numerical investigation has been performed with the help of a mathematical model developed using the modified Reynolds equation considering the flow factors for Gaussian surfaces along with Greenwood and Trip’s asperity contact approach. The numerical results have been used to justify and correlate the experimental findings. This paper presents an approach for selection of engine oil for two popular passenger cars in the Indian market.

Tribological Approach and Surface Quality Analysis of Stainless Steel for Cutlery Applications after Surface Grinding

Tribological Approach and Surface Quality Analysis of Stainless Steel for Cutlery Applications after Surface Grinding

Numerical modeling of micro-friction and fiber orientation effects on the machinability of green composites

This paper aims to enhance the predictiveness of a finite element (FE) model for machining of natural fiber composites through a tribological approach based on the micro-friction phenomenon between the cutting tool and the components of the composite structure. A 2D micromechanical model for orthogonal cutting of flax fibers reinforced polylactic-acid (PLA) composites is considered in this study at different orientation of fibers. Results show that the numerical thrust forces are significantly affected by the variation of the micro-friction in the model. An optimized value of the micro-friction coefficient has been found to fit with the experimental results. The FE model provides the ability to calculate with good accuracy the effect of fiber orientation on the machinability of flax/PLA composites.

Reduction of Harmful Emissions from Domestic Power Generator Usage in Nigeria -A Tribological Approach

Worldwide concern for the release of harmful emission from Internal Combustion (IC) engines requires the optimization of the quantity of fuel used, types of fuel blend used and type of lubrication utilized. In Nigeria, the electrical power requirements of many households rely more on alternative sources such as Solar systems and fossil fuel-powered generators. The use of these generators is known to produce exhaust fumes that are harmful to humans and the environment. This study investigated the effect of using two different commercially available lubricating oils for gasoline-fueled power generators for domestic applications in comparison to used oils. These are SAE 40 and SAE 20W50. The effect of Boron additive on the two oil brands and used oils (or aged oils) at different speeds on emission from the exhaust stream from the generator was investigated. This is to provide a better understanding of the behavior of Boron additive with SAE 40, SAE 20W50, and aged oils. The study also compared results of torque and emission measurements from oils containing boron to oils without the Boron additives at different speeds. The instruments used to carry out the measurement are a digital tachometer, torque meter (contact type), and 5-gas exhaust analyzer. Results from this study indicated a general decrease in torque with increased speed for all the lubricating oils. This is in agreement with the results of similar studies on torque outputs from IC engines with increasing speeds. However, oils lubricated with Boron additives minimized this loss at a different speed more in SAE 20W50, SAE 40 than in used oils. Carbon monoxide emission from these results indicated that generators lubricated by aged oils are highest at all speed ranges irrespective of Boron additive inclusion. Cleanliness from a gasoline-powered generator is possible if Boron additive is added to lubricating oils. The concentration of NOx emission was found to rise considerably only when operated at the highest speed for aged oils. The results of this study indicated that tribofilms formed by boron-containing oils played a role in preventing torque reduction or power loss and CO emissions from power generators for domestic use. This behavior was attributed to the friction-reducing boric acid and wear resistance borate glass contained within the trilayer. However, tribofilms formed by used oils on tribological parts of the engine gave poor torque reduction results in comparison to that provided by fresh oils. This indicated that when lubricating oils in power generators used in homes are aged beyond the recommended interval for replacement, substantial power loss and harmful emissions are released to the surroundings.

"Oral" tribology study on saliva-tea compound mixtures: Correlation between sweet aftertaste (Huigan) perception and friction coefficient.

Sweet aftertaste (Huigan) is a sensation perceived after drinking tea, and lasts in the mouth and throat, leading to salivation for an extended period of time. The study aimed to reveal the underpinning mechanisms of Huigan and the its influencing factors. Tribology approach was applied to this study in conjunction with sensory analysis and other physiology assessments. Tea compounds of commercial interest were selected for the study. Preliminary sensory tests of 24 subjects were carried out to evaluate the Huigan intensity of these tea compounds. Based on these tests, 12 subjects were selected and divided into two groups, each with 6 subjects: sensitive subjects and non-sensitive subjects. In vitro tribology measurements were made for samples prepared either prepared as 1:1 mixtures of tea compound solution and human whole saliva or expectorated tea compound solutions along with the saliva which were collected from the subjects after oral processing. The Huigan intensity perceived by the sensitive group was found to be highly correlated with the friction coefficient measured, especially at the sliding speeds lower than 0.5 mm/s.