bluuebunny/crossref_metadata_2025_split huggingface dataset:
Queue normalization methods in systems GI/GI/1/m with infinite variance of service time
Authors: Zadorozhnyi V N , Zakharenkova T R , Pagano M 
Published: January 2020

Abstract
Queuing systems with an infinite variance of service time are considered. The average waiting time in such systems is equal to infinity at a stationary regime. We analyze the efficiency of introducing of absolute priorities with infinite number of priority classes determined by the special axis marking on intervals for possible values of service time. It is stated that queues in systems become normalized, i.e. the average queue length become finite, when using regular marking. Furthermore, request loss probabilities radically decrease when buffer size is finite. More efficient marking – exponential marking – is proposed for practical purposes in networks with fractal traffic. The optimization problems of regular and exponential markings are solved.
Oil temperature influence on friction losses in silent chains
Authors: Velicu R 
Published: January 2020

Abstract
Evaluation of friction in chain drives is the first step in the process of reducing the friction. This paper presents the experiments on the analyses of temperature influence on friction in silent chains. A rig dedicated for friction measurements on parallel axes transmissions is used. Friction is measured as friction torque with possibility to control and measure the input rotational speed, chain tensioning, pressure and temperature of the oil for chain lubrication, pressure and temperature of the oil for bearings lubrication. Temperature depending viscosity of chain lubrication oil is measured separately. The functioning conditions of the bearings are maintained constant during the testing and only the temperature of chain oil lubrication is increased and then decreased in the range of functioning temperature of a timing chain. Oil temperature influence on friction from silent chains joints gives an image on the type of lubrication. The reduction of silent chain friction by reducing the functioning temperature may be a very simple solution and this paper shows how much power may be saved. Friction torque is measured for three distinct rotational speeds in the same tensioning parameters. Conclusions on the influence of rotational speed on friction losses with temperature are finally drawn.
On thermal calculation for helical gear transmission system
Authors: Gabroveanu I S , Cananau S , Mirica R F , Ilies A A 
Published: January 2020

Abstract
The purpose of the study in the paper is to evaluate the thermal comportment of the transmission systems with helical gears. Also, the influences of heat on characteristics of gear transmission system, based on the meshing thermal stiffness of gears are analyzed. An experimental testing stand of the system will be used to obtain data. The respond of the transmission under different working conditions is also analyzed. The study concerns the comparison of theoretical results obtained using calculation methods (from literature) and the experimental results, in order to obtain an evaluation of the friction in the meshing gears. The heat (temperature) affects the dynamic characteristics of the system by the meshing stiffness of the gear. The experimental results are used to verify the correctness of the theoretical model.
Eccentric device for varying the gear ratio
Authors: Roth M B , Romanet M , Ripeanu R G 
Published: January 2020

Abstract
In the paper is presented the working principle of the device as well as the constructive-functional scheme for its realization. The use of such a device allows variable gear ratios to be obtained in a very wide range. It has the advantage of a compact construction relative to other mechanisms with varying transmission ratios, such as the crank mechanism. The device contains a worm gear that allows for the eccentricity of a toothed wheel in relation to the cone wheel. The worm gear mechanism also ensures that it is self-locking while it is in operation without the need for other insurance items. The device can be used in the control of actuators in the field of machining or packaging in an automated process.
A bibliometric analysis of scientific research on tribology of composites in Southeastern Europe
Authors: Vencl Aleksandar , Vaxevanidis Nikolaos M , Kandeva Mara 
Published: January 2020

Abstract
In recent years there is a small but increasing number of articles presenting and/or analyzing the scientific production from discrete geographical regions on a certain scientific topic. These articles applied the so-called bibliometric methods in order to evaluate the contribution of different countries in a scientific research field. In the present work, the research output of all countries in Southeastern Europe on the scientific field of composites tribology is presented by using bibliometric indicators such as the total number of publications and citations, the average number of citations per publication, and the h-index. Analysis spans the last ten years and the required scientific data in order to calculate the bibliometric indicators were retrieved using the Scopus® scientific database.
Numerical considerations regarding the occurrence of plastic shearing with implications in scuffing
Authors: Fomin M , Musca I 
Published: January 2020

Abstract
Scuffing occurrence is also correlate with rheological behaviour of the lubricant. Using a viscous-plastic rheological lubricant model and an idealized roughness, as a symmetrical planar pad, a theoretical model of the pad-plane contact behaviour was developed. Based on this theoretical lubricating model, a numerical study was conducted in order to reveal the possibility of plastic shearing occurrence, in a pair formed by a symmetric pad, with dimensions comparable to the real roughness of the specimens previously used in previous experiments and a plane for values of operating parameters comparable to the real ones. The effect of the relative speed in contact, the effect of the minimum film thickness and the effect of the tilt angle of the idealized asperities flanks was analyzed. The numerical results, obtained based on the analytical model developed, correspond as order of magnitude and tendency of the parameters influence with the experimental scuffing results obtained by the authors and those presented in the literature and highlight the possibility of the occurrence of plastic shearing in the vicinity of the peak of the asperity and therefore the possibility of initiating the scuffing phenomena into contact.
Effects of organic compounds and nickel nitrate on friction coefficient of thermosetting
Authors: Păduraru I , Săracu G , Bogdan M , Graur I , Munteniţă C , Cîrciumaru A 
Published: January 2020

Abstract
The principal aim of this study is to point out the effect of organic compounds mixed with nickel nitrate in determined weight ratios on friction coefficient of two distinct types of epoxy systems.The two used organic compounds are starch and agar. Ultrasound exposure is typically used to properly prepare the powder modified composite materials namely to obtain a uniform dispersion of nickel nitrate in to the epoxy. Friction coefficient behaviour of composite materials is essential for successful applications among various modern industries of these challenging materials. Friction coefficient of the modified epoxy matrix was accurately measured using pin-on-disc geometry with TRM 1000 tribometer from Wazau at the Research and Development Center for Thermoset Matrix Composites from Dunărea de Jos University of Galaţi.
Effect of steel fiber addition on the mechanical and tribological behavior of the composite brake pad materials
Authors: Yanar H , Purcek G , Ayar H H 
Published: January 2020

Abstract
Effect of steel fiber addition on the friction and wear characteristics and mechanical properties of non-asbestos composites brake pad material was investigated. For this purpose, the content of steel fiber was added in the range of 0-20 wt.% with changing the rock fiber of the matrix structure. The matrix has also phenolic binder resin, cashew nut shell liquid, aramid pulp, magnetite, rubber and graphite. Friction behavior of the samples prepared from the mixture were tested using a pin-on-disk type test configuration according to the NF F 11-292 French standard. It was observed that coefficient of friction (CoF) of composite samples increased with increasing steel fiber content. After 5wt.% steel fiber addition, the CoF of composite did not significantly change. Although the steel fiber addition caused a significant increase in the CoF of the composite, no significant change can be observed in the specific wear rate with steel fiber addition up to 15wt.%, above which it increased significantly. On the other hand, steel fiber addition to the composite matrix deteriorated the mechanical properties, but improved the fade resistance of the sample.
Ball-on-flat reciprocating test to evaluate dry sliding wear behaviour of reinforced polymer composites
Authors: Iliuta V , Ripa M , Javorova J , Andrei G 
Published: January 2020

Abstract
This paper presents the results of the tribological investigations on polymeric composite materials reinforced with Cu, Zn, Sn, SiO2 and MoS2 microparticles, used for repairing metal parts made of brass and bronze. The tested material were: three composite materials (products of the company Diamant Metallplastic GmbH, Germany): Multimetall Messing (used for repair of brass parts), Multimetall Bronze (used for repair of bronze parts) and Moglice (for brass and bronze parts). The testing was conducted in dry conditions, in ball on flat configuration, by reciprocating method, on the CETR UMT-2 tribometer (Bruker Corporation) at normal loads 20, 30, 40 and 50N, over a sliding distance of 100m. The paper presents studies of the variations of the friction coefficient, linear wear, volumetric wear parameters, profilometric studies with SEM surface morphologies of the wear tracks. The researches allowed the classification of materials according to their tribological behaviour and the results recommend the tested reinforced composite materials as good candidates for repairing metal parts made of brass or bronzes.
Theoretical Analysis of Spherical Bearings Lubricated with Greases
Authors: Radulescu A V , Radulescu I 
Published: January 2020

Abstract
The paper presents theoretical researches concerning the spherical bearings lubricated with greases, in rheostatic conditions: high loads and low velocities. This type of bearing is very appropriate for modelling the human joints (hip, knee), spherical joints from automotive industry (pivots, connecting rods) or special joints from petroleum industry. Spherical bearings may be of the “fitted” type or the “clearance” type. The fitted type of nonflat bearing pad surface is lappedin to fit the runner. When it is operating, the fitted pad will have a varying film thickness across the pad sill, between the pad and the runner. Similarly, in the clearance type the film shape will be non-uniform across the pad sill. The variation in film thickness across the bearing pad, for nonflat pads, influences the resulting pressure distribution in the bearing pad and, hence, its load carrying capacity. In this paper, the pressure distribution and the load capacity are determined for “clearance” type bearings, for two different cases: complete spherical bearings and partial spherical bearings. It has been found that the eccentricity ratio influences the angular position of the maximum pressure, which becomes nearer to the minimum angle of the bearing, once with the increasing of the eccentricity ratio.
Tooth contact analysis of spur and helical gears with crowned profile for pinion
Authors: Cazan S , Dănilă C , Creţu S 
Published: January 2020

Abstract
The paper presents tooth contact analysis (TCA) of modified gears using semi-analytical methods (SAMs). The semi-analytical methods use Love’s analytical formulation for Boussinesq equation of linear half-space theory and Hartnett approach for numerical formulation. The linear contact between two teeth has a finite length and during meshing process the edge effect appears, with a harmful influence on the gear reliability. To eliminate this, some tooth profile modifications are needed. To turn a line contact into a point contact, the crowned lead profile surface is considered. The ways used to obtain the matrices of separation are discussed for both spur and helical cylindrical gears. The large pressures’ systems of equations were solved using the method of conjugate gradients and fast Fourier transform. For validation, in cases of hertzian geometries the SAM results have been compared with results obtained analytically, while for non-hertzian geometries, the SAM results have been compared with FEM results as presented in the specific literature. The developed SAM proved to be an accurate, robust and very fast tool for TCA of spur and helical cylindrical gear.
The influence of operating temperature and bearing steel structure in shakedown of three-dimensional elastic-plastic rolling contacts
Authors: Popescu G 
Published: January 2020

AbstractThis paper describes a model for the prediction of micro-plastic material transformation and associated residual stress field development in through-hardened and case-hardened bearing steels during over-rolling, considering the influence of operating temperature. The main challenge in analysing three-dimensional elastic-plastic rolling contacts is the accurate description of material properties in case of two-phase material, either is a constant amount of retained austenite (through-hardened AISI 52100 bearing steel) or variable amount of retained austenite along depth (case-hardened steel, i. e. 16MnCr5 bearing steel). Material parameters at room temperature, 650and 1000C degrees were obtained by half-compressive cycles tests on an INSTRONTMapparatus with a climate cell and further verified by performing experimental and numerical analyses in case of static indentation between a ceramic ball and a flat steel plate. To check the ability of the proposed models to simulate the elastic-plastic rolling contact in various loading condition, experiments were made on a special designated test rig and recorded values were compared with the numerical simulations obtained by using a semi-analytical solver. Measurements of residual cyclic profiles and residual stresses show a good agreement with theoretical values, leading to a better understanding of the fatigue process in hardened bearing steels.
Microscopic testing and analysis of drinking water filters after the final life cycle, using an experimental stand
Authors: Crişan H G , Crişan O A , Pustan M S , Bîrleanu C J , Merie V V 
Published: January 2020

Abstract
The purpose of this paper was to develop a testing infrastructure, under laboratory conditions, for the drinking water filters used in the household. The mechanical filtration of existing nanoparticles in drinking water distributed to the large public is a very important aspect of ensuring a high level of drinking water quality, at the final consumer-the household user, regardless of the conditions of supply or its distribution. Moreover, the importance of increasing the quality of domestic drinking water is reflected by the need to encourage its consumption, to the detriment of bottled PET packaging (polyethylene terephthalate), which confers a number of disadvantages in relation to environmental protection and consumer’s health. In order to achieve the proposed goal, a computer aided design (CAD) was developed and an experimental stand was designed and built to allow different categories of constructive and structural filters to be tested. The filters were chosen according to well established criteria. Their testing was aimed at identifying the potential and characteristics of mechanical filtration of existing nanoparticles in drinking water. Finally, using the atomic force microscopy technology (AFM), it was possible to microscopically investigate the nanofiltration results performed using the sample of tested filter elements and their classification according to the quality of the filtration obtained.
Influence of lubricant on the friction in an angular contact ball bearing under low load conditions
Authors: Popescu A , Olaru D N 
Published: January 2020

Abstract
The presence of the lubricant in a ball-race contact has two principal effects on friction: reduces the sliding friction, as a result of developing a film thickness between the contact surfaces and increases the rolling friction, as result of developing a hydrodynamic rolling friction. The influence of the hydrodynamic rolling friction on the torque of a modified 7205B angular contact ball bearing has been theoretically and experimentally studied. The experiments demonstrated that, for very low contact loads between balls and races, the effect of the hydrodynamic rolling force is dominant in the total friction torque. The experiments have been validated by using Biboulet’s transition model for hydrodynamic rolling forces developed in ball-race contacts.
Influence of ZnO concentration in rapeseed oil on tribological behavior
Authors: Ionescu T F , Guglea D , Georgescu C , Dima D , Deleanu L 
Published: January 2020

Abstract
This paper presents results of testing the coarse rapeseed oil additivated with different concentrations of ZnO (0.25%wt, 0.50%wt and 1%wt, with 14±5 nm in size), on a four-ball machine. The test parameters were load on main shaft of the machine: 100 N, 200 N and 300 N and the rotational speed 1000 rpm, 1400 rpm and 1800 rpm. For the tested range of ZnO concentration, the value of 1%wt does not improve the friction coefficient, but the wear rate of wear scar diameter was lower than that obtained with the neat rapeseed oil and the values are less sensitive with load and sliding speed for the more severe regimes. The additivation of rapeseed oil with ZnO is still efficient for the tested range of load and speed as compared to neat rapeseed oil. The authors formulated lubricants using as dispersant (2-methoxyphenol) in the ratio 1:1 to the additive. The technology is at scale laboratory and implies mechanical stirring and sonication. The tribological behavior was analysed based on obtained results, by mapping the friction coefficient, the wear rate of the wear scar diameter and the final temperature in the oil bath. For the additivated lubricants the following conclusions could be drawn. Friction coefficient tends to reach 0.1 only for low speed and high load (v = 0.38 m/s and F = 300 N), wear rate of wear scar diameter decreases with the increase of load, for each tested speed, probably because of a full fluid film generation. For F = 250…300 N, the map reveals a poor dependence on the additive concentration. The final temperature in the lubricant bath depends on speed, but for the same speed, it depends less on load, having a maximum value for 0.75% nano additive. These conclusions underlined the necessity of testing the new formulated lubricants because additive concentration and regime parameters could have synergic influences on the tribological parameters.
Study of the effect of duration of non-thermal plasma treatment on the surface properties of polymers
Authors: Tilmatine O , Zeghloul T , Fatu A , Dascalescu L 
Published: January 2020

Abstract
One of the factors affecting the electric charge acquired through friction between the polymers is their surface roughness. The dielectric barrier discharge (DBD) treatment is known to modify the surface characteristics of polymers. The aim of this study is to quantify the effect of atmospheric DBD exposure, in a well-defined configuration on the triboelectric behavior of polymers. Thus, Polytetrafluoroethylene (PTFE) plate samples characterized by different surface roughness were rubbed against bronze plate samples in a triboelectric test bench and then the electric potential at their surface was measured. The results were compared with those obtained for surfaces previously exposed to DBD treatment duration of which did not bring any change in their roughness. It was found that the roughness of the surface of the treated polymers hardly changed for rather short DBD exposure time (a few minutes). Significant changes were noticed for longer treatment duration (30 minutes and more). The samples that had undergone a longer treatment period modification acquired higher levels of electric charge by triboelectric effect.
Effect of deposition oxygen pressure on the properties of cuprous oxide thin films
Authors: Pustan M , Birleanu C , Merie V , Zarbo L , Garabagiu S , Marconi D 
Published: January 2020

Abstract
This study presents the effect of the oxygen pressure during deposition on the properties of cuprous oxide (Cu2O) thin films. The Cu2O is a p-type semiconductor material with a cubic crystallinity structure that has potential applications in solar cells, photo catalysis, gas sensing, superconductor, hydrogen production and thermoelectric generators. Different thicknesses of Cu2O films and different surface parameters are obtained if the oxygen pressure is modified during the depositions process. The samples were characterized by atomic force microscopy technique (AFM) and the results clearly demonstrate that Cu2O thin films properties are improved if the oxygen pressure during deposition decreases. The thickness of films and the surface parameters were measured using the AFM non-contact mode. The thickness and the surfaces roughness increase if the oxygen pressure during deposition decreases. This effect is based on obtaining higher particle sizes at low pressures. The modulus of elasticity and the hardness dependence on the deposition oxygen pressure is monitored by nanoindentation using a diamond Berkovich tip. The materials mechanical properties increase significantly if the oxygen pressure during deposition decreases, respectively. The results are useful to micro and nano-systems designers to fabricate reliable structures based on Cu2O thin films.
Nanoscale friction and wearing of octadecyltrichlorosilane covered silicon surface
Authors: Teodoroff-Onesim S , Besleaga A , Sirghi L 
Published: January 2020

Abstract
Silicon wafers were silanized by plasma hydroxylation and chemical vapour deposition of octadecyltrichlorosilane [OTS, CH3(CH2)17SiCl3]. Then, the OTS covered silicon samples were used in atomic force microscopy (AFM) measurements of wearing and friction at nanoscale. Wearing experiment performed by 1000 cycles of forwards and backwards movements of sharp AFM tip revealed formation of a wearing track with a depth that was much smaller than the thickness of OTS coating, which confirmed a very good wearing property of OTS coating. Friction versus normal loading force experiments performed with the same AFM tip revealed a nonlinear dependence of friction force on the normal loading force in agreement with prediction of Bowden and Tabor’s theory of friction and an increase of friction with the moving speed. Dependence of friction force on the sliding speed is attributed to a transfer of kinetic energy from the moving AFM tip to individual molecules of OTS coating.