TRIBOLOGICAL PROPERTIES OF A NEW KIND OF FRICTION-PROMOTING GREASE IN SLIDING POINT CONTACTS

2015 ◽  
Vol 39 (2) ◽  
pp. 221-237
Author(s):  
Wan Ma ◽  
Zhen C. Zhu ◽  
Yu X. Peng ◽  
Guo A. Chen
Keyword(s):  
Tribological Properties ◽  
Point Contact ◽  
Constant Load ◽  
Normal Operation ◽  
Point Contacts ◽  
Contact Conditions ◽  
Rotating Speed ◽  
Operation Conditions ◽  
Film Forming ◽  
The Coefficient Of Friction

In this paper, the tribological properties and the film-forming properties of the friction-promoting grease (FPG) A under point-contact conditions were investigated by conducting respectively four-ball experiments and FPG A-lubricated ball-and-disc contact experiments. The experimental results indicate that the coefficient of friction (COF) decreases with an increase in the rotating speed at a constant load; FPG A has a good film-forming ability and a good adhesion property; the application of FPG A under hoist’s normal operation conditions could greatly protect the contact surfaces from wear and supply a sufficient COF.

Rheological and Film Forming Behavior of the Developed Nanocomposite Greases Under Elastohydrodynamics Lubrication Regime

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
Jayant Singh ◽  
Deepak Kumar ◽  
N. Tandon
Keyword(s):  
Elastic Recovery ◽  
Point Contact ◽  
Constant Load ◽  
Rheological Parameters ◽  
Shear Stresses ◽  
Al2o3 Nanoparticles ◽  
Film Forming ◽  
Forming Characteristics ◽  
Nano Additives ◽  
Α Al2o3

Performance of grease lubricated point contact under elastohydrodynamics lubrication (EHL) regime is critical in many engineering applications. The present work deals with the evaluation of rheological, film forming characteristics and elastic recovery of newly developed nanocomposite greases. The nanocomposite greases are formulated by dispersing different nano-additives to bare grease (BG). The nano-additives include reduced graphene oxide (rGO) nanosheets, CaCO3 and α-Al2O3 nanoparticles. The microstructure evaluation of the nano-additives and different greases is done using high-resolution transmission electron microscopy (HRTEM). Estimation of the rheological parameters (storage and loss moduli) is done using rotational rheometer. The film forming behavior is recorded using elastohydrodynamic (EHD) rig for range of speed at different temperatures and constant load. The results indicate that change in microstructure due to nano-additive incorporation improves the responses of different greases. Based on rheological response, CaCO3 doped grease seems better but rGO doped grease is able to bear high shear stresses. Further, based on film forming characteristics and reflow or recovery behavior, rGO doped grease is better. The rGO-based grease registers approximately 90% elastic recovery followed by 75% for CaCO3-based grease, 65% for BG and 10% for α-Al2O3-doped grease.

scholarly journals Impact of Operating Time on Selected Tribological Properties of the Friction Material in the Brake Pads of Passenger Cars

Materials ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 884
Author(s):  
Andrzej Borawski
Keyword(s):  
Tribological Properties ◽  
Operating Time ◽  
Friction Material ◽  
Operating Conditions ◽  
Direct Impact ◽  
Passenger Cars ◽  
Wear Factor ◽  
Brake Pads ◽  
Road Users ◽  
The Coefficient Of Friction

Braking systems have a direct impact on the safety of road users. That is why it is crucial that the performance of brakes be dependable and faultless. Unfortunately, the operating conditions of brakes during their operating time are affected by many variables, which results in changes in their tribological properties. This article presents an attempt to develop a methodology for studying how the operating time affects the value of the coefficient of friction and the abrasive wear factor. The Taguchi method of process optimization was used to plan the experiment, which was based on tests using the ball-cratering method. The results clearly show that the degree of wear affects the properties of the friction material used in the production process of brakes.

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

Materials ◽  
2019 ◽  
Vol 13 (1) ◽  
pp. 75 ◽  
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.

scholarly journals Electromigration-induced directional steps towards the formation of single atomic Ag contacts

2020 ◽  
Vol 11 ◽  
pp. 680-687
Author(s):  
Atasi Chatterjee ◽  
Christoph Tegenkamp ◽  
Herbert Pfnür
Keyword(s):  
Fourier Transforms ◽  
Single Point ◽  
Point Contact ◽  
Single Atom ◽  
Point Contacts ◽  
Cross Sectional ◽  
Shell Effects ◽  
Theoretical Approaches ◽  
Average Grain Size ◽  
Thinning Process

Even though there have been many experimental attempts and theoretical approaches to understand the process of electromigration (EM), it has not been quantitatively understood for ultrathin structures and at grain boundaries. Nevertheless, we showed recently that it can be used reliably for the formation of single atomic point contacts after careful pre-structuring of the initial Ag nanostructures. The process of formation of nanocontacts by EM down to a single-atom point contact was investigated for ultrathin (5 nm) Ag structures at 100 K by measuring the conductance as a function of the time during EM. In this paper, we compare the process of thinning by EM of structures with constrictions below the average grain size of Ag layers (15 nm) with that of structures with much larger initial constrictions of around 150 nm having multiple grains at the centre constriction prior to the formation of a point contact. Even though clear morphological differences exist between both types of structures, quantized conductance plateaus showing the formation of single point contacts have been observed for both. Here we put emphasis on the thinning process by EM, just before a point contact is formed. To understand this thinning process, the semi-classical regime before the contact reaches the quantum regime was analyzed in detail. For this purpose, we used experimental conductance histograms in the range between 2G 0 and 15G 0 and their corresponding Fourier transforms (FTs). The FT analysis of the conductance histograms exhibits a clear preference for thinning along the [100] direction. Using well-established models, both atom-by-atom steps and ranges of stability, presumably caused by electronic shell effects, can be discriminated. Although the directional motion of atoms during EM leads to specific properties such as the instabilities mentioned, similarities to mechanically opened contacts with respect to cross-sectional stability were found.

scholarly journals A thermal resistances-based approach for thermal-elastohydrodynamic calculations in point contacts

2017 ◽  
Vol 232 (11) ◽  
pp. 2088-2102 ◽  
Author(s):  
Eduardo de la Guerra Ochoa ◽  
Javier Echávarri Otero ◽  
Enrique Chacón Tanarro ◽  
Benito del Río López
Keyword(s):  
Friction Coefficient ◽  
Film Thickness ◽  
Thermal Effects ◽  
Good Accuracy ◽  
Computational Cost ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Point Contacts ◽  
New Approach ◽  
Ball On Disc

This article presents a thermal resistances-based approach for solving the thermal-elastohydrodynamic lubrication problem in point contact, taking the lubricant rheology into account. The friction coefficient in the contact is estimated, along with the distribution of both film thickness and temperature. A commercial tribometer is used in order to measure the friction coefficient at a ball-on-disc point contact lubricated with a polyalphaolefin base. These data and other experimental results available in the bibliography are compared to those obtained by using the proposed methodology, and thermal effects are analysed. The new approach shows good accuracy for predicting the friction coefficient and requires less computational cost than full thermal-elastohydrodynamic simulations.

scholarly journals Point contact spectroscopy of superconductors via nanometer scale point contacts formed by resistive switching

AIP Advances ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 125217 ◽  
Author(s):  
Mária Dvoranová ◽  
Tomáš Plecenik ◽  
Martin Moško ◽  
Marek Vidiš ◽  
Maroš Gregor ◽  
...  
Keyword(s):  
Resistive Switching ◽  
Point Contact ◽  
Nanometer Scale ◽  
Point Contacts ◽  
Point Contact Spectroscopy ◽  
Scale Point

scholarly journals The Effects of Artificially-Produced Defects on the Film Thickness Distribution in Sliding EHD Point Contacts

1982 ◽  
Vol 104 (3) ◽  
pp. 365-375 ◽  
Author(s):  
C. Cusano ◽  
L. D. Wedeven
Keyword(s):  
Film Thickness ◽  
Contact Region ◽  
Thickness Distribution ◽  
Point Contact ◽  
Optical Interferometry ◽  
Point Contacts ◽  
Thickness Profile ◽  
Inlet Region

The effects of artificially-produced dents and grooves on the elastohydrodynamic (EHD) film thickness profile in a sliding point contact are investigated by means of optical interferometry. The defects, formed on the surface of a highly polished ball, are held stationary at various locations within and in the vicinity of the contact region while the disk is rotating. It is shown that the defects, having a geometry similar to what can be expected in practice, can dramatically change the film thickness which exists when no defects are present in or near the contact. This change in film thickness is mainly a function of the position of the defects in the inlet region, the geometry of the defects, the orientation of the defects in the case of grooves, and the depth of the defect relative to the central film thickness.

Microstructure and Tribological Properties of Cu-Fe Based Braking Materials

2014 ◽  
Vol 941-944 ◽  
pp. 280-283
Author(s):  
Xiao Yang Wang ◽  
Hong Qiang Ru
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Tribological Properties ◽  
X Ray Diffraction ◽  
Pressing Method ◽  
X Ray ◽  
The Coefficient Of Friction ◽  
Worn Surface ◽  
Scanning Electron ◽  
Sic Particle

SiC particle-reinforced Cu-Fe based braking materials were fabricated by the P/M hot pressing method. The phase composition, microstructure and the worn surface of the composite were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD).The tribological properties were evaluated using a disk-on-disk type laboratory scale dynamometer. Results indicate that the friction coefficient is 0.42 in 6800rpm, 0.7MPa. With the increase of rotation speeds the coefficient of friction and stable rate were decreased.

POSITIVE MAGNETO-RESISTANCE IN A POINT CONTACT: POSSIBLE MANIFESTATION OF INTERACTIONS

2007 ◽  
Vol 17 (03) ◽  
pp. 495-499
Author(s):  
V. T. RENARD ◽  
T. OTA ◽  
N. KUMADA ◽  
H. HIRAYAMA
Keyword(s):  
Point Contact ◽  
Quantum Point Contacts ◽  
Point Contacts ◽  
Temperature Dependent ◽  
Quantum Point ◽  
Magneto Resistance ◽  
Unexpected Behavior ◽  
Electron Interactions

We report a non-monotonic and strongly temperature dependent magneto-resistance observed in clean quantum point contacts. At the same time the conductance of the point contact varies linearly with temperature. This unexpected behavior may be related to electron-electron interactions.

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