Experimental and Analytical Investigations on Tribological Properties of PTFE/AP Composites

The tribological properties of polytetrafluoroethylene (PTFE)/AP (poly(para-phenyleneterephthalamide) (PPTA) pulp) composites under different test conditions (load: 2N, 10N; frequency: 1 Hz, 4 Hz; amplitude: 2 mm, 8 mm) were holistically evaluated. PTFE/AP composites with different AP mass ratios of 3%, 6%, and 12% as a skeleton support material were prepared. The coefficient of friction (COF) and wear rate were determined on a ball-on-disk tribometer. Furthermore, the morphology, element composition, and chemical structure of the transfer membrane were analyzed accordingly. The relationships between load, frequency, amplitude, and tribological properties were further investigated. According to the wear mechanism, AP enables effective improvement in the stiffness and wear resistance, which is also conducive to the formation of transfer films.

Approach to Performance Rating of Retroreflective Textile Material Considering Production Technology and Reflector Size

The study investigates retroreflective fabrics’ efficiency from the point of view of the interaction of their visibility, thermo-physiological comfort properties, and durability (represented by physical-mechanical performance). The effect of the combination of two production technologies (reflective transfer films and screen printing method) and two reflector covering sizes (25% and 85%) was examined. Technique for order of preference by similarity to ideal solution (TOPSIS) method was used to determine the best solution considering the abovementioned tested categories of properties. Retroreflective performance was in congruence with the used design coverage factor of the tested pattern. It was found that retroreflection of the tested pattern produced using screen printing technology was significantly lower than retroreflection of an identical pattern made by a transfer film. On the contrary, in terms of thermo-physiological comfort and physical-mechanical performance of the tested samples, screen printing technology shows significantly better results in almost all tested properties, especially in water vapor permeability, moisture management, and physical-mechanical performance. The solution for the abovementioned contradictory results can be achieved by using a combination of the advantages associated with each of these technology methods. Screen printing can be applied to specific regions of clothing that are exposed to extreme loading or sweating, and the transfer of film elements ensures high visibility with respect to the standards and biomotion principles that are deployed as prevalent benchmarks in the industry.

Tribology of High-performance PEEK-, PI-, and ATSP-based Self-lubricating Polymers Up to 300 oC

High-performance polymers (HPPs) with self-lubricating properties are promising materials for bearing and tribological components that demand low friction and low wear in the absence of liquid lubrication. This study reports on the tribological performance of three advanced HPPs, namely ATSP-, PEEK-, and PI-based polymer composites. The experiments were performed using pin-on-disk configuration under dry sliding conditions and different environmental temperatures from 25 (room temperature) to 300 °C. The role of temperature on the formation of polymer transfer films on the steel counterpart was investigated using microscopy and profilometric measurements, and correlations were made to their tribological performance. From the three tested composites, ATSP-based composite exhibited the best overall performance with low friction and low wear.

Rubber Wear and the Role of Transfer Films on Rubber Friction on Hard Rough Substrates

We study the influence of rubber transfer films on the sliding friction between rectangular rubber blocks and a concrete surface. We present experimental results for the friction coefficient for a rubber compound sliding on a concrete surface contaminated by another rubber compound, for two different pairs (A, B) and (C, D) of rubber compounds. For the same rubber compounds, we present theory results which illustrate the relative importance of the viscoelastic and adhesive contribution to the sliding friction. We correlate the calculated rubber friction with the nature of the observed transfer films (or wear processes). Graphical Abstract

Improving the Quality of Running-in of Car Engine Parts During Running-in Using a Complex Action Additive

The purpose of the work is to improve the quality of the process of running-in of car engine parts during running-in using the additive of complex action. The tasks are the theoretical substantiation of the formation of transfer films during engine running-in and the conduct of comparative studies of the developed complex additive to M-8-B motor oil. The paper substantiates that in order to improve the quality and accelerate the running-in of car engine parts during running-in, a complex additive is required, which includes both surfactants and chemically active substances. The preconditions for obtaining transfer films on the friction surfaces of engine connections during running-in are considered. A frictional interaction is described in the case when the soft transfer film is strong and fixed on the main material, and the sliding surface coincides with the boundary between the film and the counter body. The presence in the zone of contact of surfactants with metals leads to the implementation of a special mechanism of frictional interaction, characterized by a colloidal system of particles in the lubricant and structural transformation on the interface. Comparative laboratory studies of the proposed additive were performed. The dependence of the moment of friction force on the time of the tests, the surface roughness of the samples worked in different compositions, as well as the distribution of the microhardness of the samples by depth were investigated. Based on the analysis of additives for running-in of engine parts, the use of complex additives containing surfactants and chemically active substances is determined as promising. Based on these studies, an additive containing ferrite spinel has been proposed. This allows you to control the running-in process through the structurally sensitive properties of the spinel composition. The use of the proposed additive of complex action helps to change the structure of the surface layer of the metal during friction under the action of temperature and load, which leads to improved quality of running-in of car engine parts during running-in.

Effect of Transfer Films on Friction of PTFE/PEEK Composite

This paper investigates the effect of transfer films on friction coefficient of polytetrafluoroethylene (PTFE)/polyetheretherketone (PEEK) composite. Friction experiments were carried out first to investigate transfer-film development during sliding contact of PTFE/PEEK composite with different PTFE volume fractions on a steel counterface. Quantitative relationships between PTFE/PEEK composite friction coefficient and constituent material mechanical properties are then established to facilitate the subsequent investigation of friction mechanisms and influence of transfer films on the composite friction. A micromechanics-based friction theory is developed for predicting PTFE/PEEK composite friction coefficient. The effect of transfer films on composite friction is accounted for based on two distinctly different mechanisms—one with solid-state film lubrication and the other with PTFE as a solid-state lubricant on the top surface of transfer films. The friction theory is first validated through the excellent agreement obtained between the theoretical predictions and the in-house experimental results on PTFE/PEEK composite with up to 20% PTFE (by volume). The validity of the theory is further demonstrated by comparing the theoretical predictions with the test data reported by other researchers in the literature.

Analysis of surface structure of zirconia crystals in case of friction against steel

The article considers the formation of the third body during dry friction of the nanostructured zirconia crystals partially stabilized with yttria against steel. The assumption is substantiated that the tribological properties of the studied friction pair are determined by the properties of the films formed on the surface of the crystals. Friction tests under sliding conditions were performed according to the “disk-finger” scheme. The results of electron microscopic examination of the friction surfaces of crystals are presented. The elemental composition was determined, and the phase composition of the transfer films of various sections of the crystal friction surface was calculated. At high magnifications, it was found that the friction surface of samples with 2-4 mol.% of Y2O3 has the sufficiently homogeneous structure of the films with traces of boundaries of smaller particles of the transferred material. Destruction of the friction surface of a sample with a Y2O3 content of 8 mol.% occurs at a deeper level and affects not only the layer of secondary structures, but also the underlying layers of the base material.