Elementary, Atomic-Level Friction Processes in Systems with Metallic Inclusions—Systematic Simulations for a Wide Range of Local Pressures

In this work, simulations of friction at the atomic level were performed to evaluate the influence of inclusions coming from metallic nanoadditives in the friction pair. The simple 2D model was applied considering appropriate values of Lennard–Jones potential parameters for given sets of interacting atoms. The real sliding pairs were replaced by effective equivalents consisting of several atoms. The calculations were based on the pseudo-static approximation. The simplicity of the model enabled to repeat the fast calculations in a very wide range of local pressures and for several types of atomic tribopairs. The performed simulations demonstrated a strong dependence of the coefficient of friction (COF) on the atomic environment of the atoms constituting a tribopair. It was confirmed theoretically that the Mo-Fe pair is characterized by lower atomic COF than Fe-Fe, Cu-Fe, and Ag-Fe pairs. This points to the great applicational potential of metallic molybdenum coating applications in tribological systems. Moreover, it was demonstrated that, although Cu-Cu and Ag-Ag pairs are characterized by relatively high COF, they lower the friction as inclusions in Fe surfaces.

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Tribological Aspects, Optimization and Analysis of Cu-B-CrC Composites Fabricated by Powder Metallurgy

Materials ◽

10.3390/ma14154217 ◽

2021 ◽

Vol 14 (15) ◽

pp. 4217

Author(s):

Üsame Ali Usca ◽

Mahir Uzun ◽

Mustafa Kuntoğlu ◽

Serhat Şap ◽

Khaled Giasin ◽

...

Keyword(s):

Weight Loss ◽

Wear Rate ◽

Coefficient Of Friction ◽

Applied Load ◽

Practical Significance ◽

Tribological Characteristics ◽

M 10 ◽

Wide Range ◽

The Coefficient Of Friction ◽

Four Levels

Tribological properties of engineering components are a key issue due to their effect on the operational performance factors such as wear, surface characteristics, service life and in situ behavior. Thus, for better component quality, process parameters have major importance, especially for metal matrix composites (MMCs), which are a special class of materials used in a wide range of engineering applications including but not limited to structural, automotive and aeronautics. This paper deals with the tribological behavior of Cu-B-CrC composites (Cu-main matrix, B-CrC-reinforcement by 0, 2.5, 5 and 7.5 wt.%). The tribological characteristics investigated in this study are the coefficient of friction, wear rate and weight loss. For this purpose, four levels of sliding distance (1000, 1500, 2000 and 2500 m) and four levels of applied load (10, 15, 20 and 25 N) were used. In addition, two levels of sliding velocity (1 and 1.5 m/s), two levels of sintering time (1 and 2 h) and two sintering temperatures (1000 and 1050 °C) were used. Taguchi’s L16 orthogonal array was used to statistically analyze the aforementioned input parameters and to determine their best levels which give the desired values for the analyzed tribological characteristics. The results were analyzed by statistical analysis, optimization and 3D surface plots. Accordingly, it was determined that the most effective factor for wear rate, weight loss and friction coefficients is the contribution rate. According to signal-to-noise ratios, optimum solutions can be sorted as: the highest levels of parameters except for applied load and reinforcement ratio (2500 m, 10 N, 1.5 m/s, 2 h, 1050 °C and 0 wt.%) for wear rate, certain levels of all parameters (1000 m, 10 N, 1.5 m/s, 2 h, 1050 °C and 2.5 wt.%) for weight loss and 1000 m, 15 N, 1 m/s, 1 h, 1000 °C and 0 wt.% for the coefficient of friction. The comprehensive analysis of findings has practical significance and provides valuable information for a composite material from the production phase to the actual working conditions.

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Analysis and Comparative Assessment of Basic Tribological Properties of Selected Polymer Composites

Materials ◽

10.3390/ma13010075 ◽

2019 ◽

Vol 13 (1) ◽

pp. 75 ◽

Cited By ~ 5

Author(s):

Jerzy Jozwik ◽

Krzysztof Dziedzic ◽

Marcin Barszcz ◽

Mykhaylo Pashechko

Keyword(s):

Polymer Composites ◽

Friction Force ◽

Tribological Properties ◽

Friction Pair ◽

Computer Software ◽

Operating Conditions ◽

The Coefficient Of Friction ◽

Cast Polyamide ◽

Friction Path ◽

Materials Used

Phenomena occurring in the contact area between two mating bodies are characterised by high complexity and variability. Comparisons are usually made between parameters such as the coefficient of friction, friction force, wear and temperature in relation to time and friction path. Their correct measurement enables the proper evaluation of tribological properties of materials used in the friction pair. This paper concerns the measurements of basic tribological parameters in the friction of selected polymer composites. Knowing the tribological properties of these composite materials, it will be possible to create proper operating conditions for kinematic friction pairs. This study investigated the coefficients of friction, friction force and temperatures of six polymer composites: cast polyamide PA6 G with oil, PA6 G with MoS2, polyoxymethylene POM with aluminium, polyethylene terephthalate PET with polytetrafluoroethylene PTFE, PTFE with bronze, and PTFE with graphite. The friction surface was also examined using an optical system and computer software for 3D measurements. As a result, PA6-G with oil was found to be the best choice as a composite material for thin sliding coatings.

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Experimental study on the relationship between the friction coefficient and interference in locomotive axle press-fitting

International Journal of Structural Integrity ◽

10.1108/ijsi-01-2021-0007 ◽

2021 ◽

Vol ahead-of-print (ahead-of-print) ◽

Author(s):

Ting Wang ◽

Hanfei Guo ◽

Jianjun Qiao ◽

Xiaoxue Liu ◽

Zhixin Fan

Keyword(s):

Friction Coefficient ◽

Coefficient Of Friction ◽

Friction Pair ◽

Rolling Stock ◽

Content Type ◽

Press Fitting ◽

The Press ◽

The Coefficient Of Friction ◽

The Relationship ◽

Locomotive Wheels

PurposeTo address the lack of data in this field and determine the relationship between the coefficient of friction and the interference between locomotive wheels and axles, this study evaluates the theoretical relationship between the coefficient of friction and the interference under elastic deformation.Design/methodology/approachWhen using numerical analyses to study the mechanical state of the contacting components of the wheels and axle, the interference between the axle parts and the coefficient of friction between the axle parts are two important influencing factors. Currently, as the range of the coefficient of friction between the wheel and axle in interference remains unknown, it is generally considered that the coefficient of friction is only related to the materials of the friction pair; the relationship between the interference and the coefficient of friction is often neglected.FindingsA total of 520 press-fitting experiments were conducted for 130 sets of wheels and axles of the HXD2 locomotive with 4 types of interferences, in order to obtain the relationship between the coefficient of friction between the locomotive wheel and axle and the amount of interference. These results are expected to serve as a reference for selecting the coefficient of friction when designing axle structures with the rolling stock, research on the press-fitting process and evaluations of the fatigue life.Originality/valueThe study provides a basis for the selection of friction coefficient and interference amount in the design of locomotive wheels and axles.

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Angolan vegetable crops have unique genotypes of potential value for future breeding programmes

South African Journal of Science ◽

10.17159/sajs.2016/20150285 ◽

2016 ◽

Vol Volume 112 (Number 3/4) ◽

Author(s):

José P. Domingos ◽

Ana M. Fita ◽

María B. Picó ◽

Alicia Sifres ◽

Isabel H. Daniel ◽

...

Keyword(s):

Strong Dependence ◽

The Other ◽

Vegetable Crops ◽

Cucurbita Maxima ◽

Capsicum Chinense ◽

Local Markets ◽

Potential Value ◽

Wide Range ◽

Different Types ◽

Breeding Programmes

Abstract A survey was carried out in Angola with the aim of collecting vegetable crops. Collecting expeditions were conducted in Kwanza-Sul, Benguela, Huíla and Namibe Provinces and a total of 80 accessions belonging to 22 species was collected from farmers and local markets. Species belonging to the Solanaceae (37 accessions) and Cucurbitaceae (36 accessions) families were the most frequently found with pepper and eggplant being the predominant solanaceous crops collected. Peppers were sold in local markets as a mixture of different types, even different species: Capsicum chinense, C. baccatum, C. frutescens and C. pubescens. Most of the eggplant accessions collected belonged to Solanum aethiopicum L. Gilo Group, the so-called ‘scarlet eggplant’. Cucurbita genus was better represented than the other cucurbit crops. A high morphological variation was present in the Cucurbita maxima and C. moschata accessions. A set of 22 Cucurbita accessions from Angola, along with 32 Cucurbita controls from a wide range of origins, was cultivated in Valencia, Spain and characterised based on morphology and molecularity using a set of 15 microsatellite markers. A strong dependence on latitude was found in most of the accessions and as a result, many accessions did not set fruit. The molecular analysis showed high molecular variability and uniqueness in the collected accessions, as shown by their segregation from the set of global controls. In summary, the material collected is quite valuable because of its uniqueness and the potential of the breeding characteristics it possesses.

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Study on Tribological Properties and Mechanisms of Different Morphology WS2 as Lubricant Additives

Materials ◽

10.3390/ma13071522 ◽

2020 ◽

Vol 13 (7) ◽

pp. 1522 ◽

Cited By ~ 2

Author(s):

Ningning Hu ◽

Xiuheng Zhang ◽

Xianghui Wang ◽

Na Wu ◽

Songquan Wang

Keyword(s):

Wear Resistance ◽

Optimum Condition ◽

Lubricating Oil ◽

Stribeck Curve ◽

Extreme Pressure ◽

Friction Process ◽

Wide Range ◽

The Coefficient Of Friction ◽

The Relationship ◽

Better Than

In the present work, the relationship curve of the coefficient of friction (COF) with varying loads of different morphology WS2 lubricating additives in the friction process at various sliding speeds was studied. On this basis, wear marks and elements on the wear surfaces after friction were analyzed, and then the anti-wear and mechanism effects of WS2 of different forms in the lubrication process were discussed. Meanwhile, the Stribeck curve was used to study the lubrication state of the lubricating oil in the friction process. It was revealed that the COF of lubricating oil containing lamellar WS2 decreased by 29.35% at optimum condition and the minimum COF was concentrated at around 100 N. The COF of lubricating oil containing spherical WS2 decreased by 30.24% and the minimum coefficient was concentrated at 120 N. The extreme pressure property of spherical WS2 was better than that of lamellar WS2, and the wear resistance of spherical WS2 was more stable when the load was over 80 N. The different morphology of WS2 additives can play anti-wear and anti-friction roles within a wide range of sliding speeds.

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Parametric Assessment of Trend Test Power in a Changing Environment

Sustainability ◽

10.3390/su12093889 ◽

2020 ◽

Vol 12 (9) ◽

pp. 3889

Author(s):

Andrea Gioia ◽

Maria Francesca Bruno ◽

Vincenzo Totaro ◽

Vito Iacobellis

Keyword(s):

Statistical Tests ◽

Statistical Significance ◽

Strong Dependence ◽

Generalized Extreme Value Distribution ◽

Monte Carlo Experiment ◽

Data Series ◽

Test Power ◽

Special Cases ◽

Wide Range ◽

Position Parameter

In the context of climate and environmental change assessment, the use of probabilistic models in which the parameters of a given distribution may vary in accordance with time has reinforced the need for appropriate procedures to recognize the “statistical significance” of trends in data series arising from stochastic processes. This paper introduces a parametric methodology, which exploits a measure based on the Akaike Information Criterion (AICΔ), and a Rescaled version of the Generalized Extreme Value distribution, in which a linear deterministic trend in the position parameter is accounted for. A Monte Carlo experiment was set up with the generation of nonstationary synthetic series characterized by different sample lengths and covering a wide range of the shape and scale parameters. The performances of statistical tests based on the parametric AICΔ and the non-parametric Mann-Kendall measures were evaluated and compared with reference to observed ranges of annual maxima of precipitation, peak flow, and wind speed. Results allow for sensitivity analysis of the test power and show a strong dependence on the trend coefficient and the L-Coefficient of Variation of the parent distribution from the upper-bounded to the heavy-tailed special cases. An analysis of the sample variability of the position parameter is also presented, based on the same generation sets.

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Advanced Graphene-Based Transparent Conductive Electrodes for Photovoltaic Applications

Micromachines ◽

10.3390/mi10060402 ◽

2019 ◽

Vol 10 (6) ◽

pp. 402 ◽

Cited By ~ 5

Author(s):

Susana Fernández ◽

Alberto Boscá ◽

Jorge Pedrós ◽

Andrea Inés ◽

Montserrat Fernández ◽

...

Keyword(s):

Thin Films ◽

Strong Dependence ◽

Transparent Conductive Oxide ◽

Electrical Performance ◽

Transparent Electrodes ◽

Surface Reflection ◽

Wide Range ◽

Cell Front ◽

Additional Role ◽

Transparent Conductive Electrodes

New architectures of transparent conductive electrodes (TCEs) incorporating graphene monolayers in different configurations have been explored with the aim to improve the performance of silicon-heterojunction (SHJ) cell front transparent contacts. In SHJ technology, front electrodes play an important additional role as anti-reflectance (AR) coatings. In this work, different transparent-conductive-oxide (TCO) thin films have been combined with graphene monolayers in different configurations, yielding advanced transparent electrodes specifically designed to minimize surface reflection over a wide range of wavelengths and angles of incidence and to improve electrical performance. A preliminary analysis reveals a strong dependence of the optoelectronic properties of the TCEs on (i) the order in which the different thin films are deposited or the graphene is transferred and (ii) the specific TCO material used. The results shows a clear electrical improvement when three graphene monolayers are placed on top on 80-nm-thick ITO thin film. This optimum TCE presents sheet resistances as low as 55 Ω/sq and an average conductance as high as 13.12 mS. In addition, the spectral reflectance of this TCE also shows an important reduction in its weighted reflectance value of 2–3%. Hence, the work undergone so far clearly suggests the possibility to noticeably improve transparent electrodes with this approach and therefore to further enhance silicon-heterojunction cell performance. These results achieved so far clearly open the possibility to noticeably improve TCEs and therefore to further enhance SHJ contact-technology performance.

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Chitosan-ZnO Nanocomposites Assessed by Dielectric, Mechanical, and Piezoelectric Properties

Polymers ◽

10.3390/polym12091991 ◽

2020 ◽

Vol 12 (9) ◽

pp. 1991 ◽

Cited By ~ 1

Author(s):

Evgen Prokhorov ◽

Gabriel Luna-Bárcenas ◽

José Martín Yáñez Limón ◽

Alejandro Gómez Sánchez ◽

Yuriy Kovalenko

Keyword(s):

Dielectric Constant ◽

Flexible Electronics ◽

Piezoelectric Properties ◽

Strong Dependence ◽

Nanocomposite Films ◽

Strong Interactions ◽

Zno Nps ◽

Chitosan Matrix ◽

Three Phase ◽

Wide Range

The aim of this work is to structurally characterize chitosan-zinc oxide nanoparticles (CS-ZnO NPs) films in a wide range of NPs concentration (0–20 wt.%). Dielectric, conductivity, mechanical, and piezoelectric properties are assessed by using thermogravimetry, FTIR, XRD, mechanical, and dielectric spectroscopy measurements. These analyses reveal that the dielectric constant, Young’s modulus, and piezoelectric constant (d33) exhibit a strong dependence on nanoparticle concentration such that maximum values of referred properties are obtained at 15 wt.% of ZnO NPs. The piezoelectric coefficient d33 in CS-ZnO nanocomposite films with 15 wt.% of NPs (d33 = 65.9 pC/N) is higher than most of polymer-ZnO nanocomposites because of the synergistic effect of piezoelectricity of NPs, elastic properties of CS, and optimum NPs concentration. A three-phase model is used to include the chitosan matrix, ZnO NPs, and interfacial layer with dielectric constant higher than that of neat chitosan and ZnO. This layer between nanoparticles and matrix is due to strong interactions between chitosan’s side groups with ZnO NPs. The understanding of nanoscale properties of CS-ZnO nanocomposites is important in the development of biocompatible sensors, actuators, nanogenerators for flexible electronics and biomedical applications.

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Investigation of Friction Over a Wide Range of Normal Forces

ASME/STLE 2007 International Joint Tribology Conference, Parts A and B ◽

10.1115/ijtc2007-44082 ◽

2007 ◽

Author(s):

Dirk Drees ◽

Satish Achanta

Keyword(s):

Surface Roughness ◽

Dual Phase Steel ◽

Normal Force ◽

Diamond Like Carbon ◽

Dual Phase ◽

Normal Forces ◽

Atomic Force ◽

Wide Range ◽

Atomic Interactions ◽

The Coefficient Of Friction

Friction at different force, length, and time scales is of great interest in tribology. The mechanical, chemical, and physical (atomic) interactions, each operating at their own time length and force scale, makes friction complex. This work is an attempt to improve the understanding of friction at normal forces ranging from nN up to N. This investigation was carried out under reciprocating ball-on-flat sliding conditions on engineering surfaces like diamond-like carbon (DLC) and dual phase steel. The test equipments used for this investigation are an atomic force microscope, a microtribometer, and a macrofretting tester. It was observed that for a hard/hard tribocouple like DLC/Si3N4, the variation in the coefficient of friction is negligible whereas the variation is large when the tribocouple is hard / soft like in dual phase steel / Si3N4. By changing the surface roughness of the material, the dependence of friction on normal force could be altered or manipulated.

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Vibratory Feeding

Proceedings of the Institution of Mechanical Engineers ◽

10.1243/pime_proc_1967_182_017_02 ◽

1967 ◽

Vol 182 (1) ◽

pp. 135-152 ◽

Cited By ~ 23

Author(s):

A. H. Redford ◽

G. Boothroyd

Keyword(s):

Phase Difference ◽

Experimental Tests ◽

Harmonic Motion ◽

Fundamental Limitations ◽

Wide Range ◽

Theoretical Predictions ◽

The Coefficient Of Friction ◽

Bowl Feeder ◽

Vibratory Bowl Feeder ◽

Vibratory Feeding

A brief review of previous work on the mechanics of vibratory conveying is presented followed by a new theoretical analysis of vibratory feeding on a track which vibrates with simple harmonic motion and where a phase difference may exist between the parallel and normal components of the track motion. For a wide range of practical conditions, the theoretical predictions are found to agree closely with the results of experimental tests. These show that certain fundamental limitations exist in the performance of conventional feeder drives where the two components of track motion are in-phase. From further theoretical and experimental work, it is shown that under conditions where the appropriate phase difference exists between the two components of track motion, many practical advantages over conventional vibratory feeding are obtained. With a new design of vibratory bowl feeder drive based on the results of the work, significantly higher conveying velocities may be obtained under stable feeding conditions and, further, these high conveying velocities are virtually independent of the coefficient of friction between the component and the track. The results of the present work apply equally to the design of spiral elevators and in-line vibratory feeders.

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