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This paper aims to investigate the temperature dependence of transfer film formation and friction coefficients in NAO friction materials with four different abrasive components, ZrO₂, ZrSiO₄, Al₂O₃ and Fe₃O₄.

8.5% SnS₂ was added as a lubricating component to friction materials. Friction tests comprised 100 times of consecutive braking application for each friction material under constant temperature of 300°C, 400°C, 500°C and 600°C. After the friction tests, the friction surfaces of the counterpart disks were examined by scanning electron microscope to access the formation of transfer film.

Coefficients of friction depended on not only friction temperature but also friction history which is related to development of transfer film. The effect of the transfer film formation was to reduce the friction coefficients for most friction materials. Quantities of the transfer film formation varied with friction materials; at low temperature below 400° the transfer film formation was most active in the Fe₃O₄ materials, while at 600° it was the most active in the Al₂O₃ material. The effect of the lubricating component SnS₂ was to suppress the formation of transfer film, thus enhancing friction coefficients.

The enhancement of friction coefficients with addition of small amount of lubricating components such as SnS₂ is expected to open a new approach in developing high performance-brake pads.

Temperature was the controlling parameter in the present test. Under these test modes, transfer film could be fully developed to access the role of the transfer film.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-10-2019-0427/

This paper aims to reveal the effects of the copper third body on different copper matrix friction materials with a novel experimental way called “exogenous powder.”

An accurate adding device of exogenous copper powder was designed to control the flow rate. The tribological properties with and without exogenous copper powder were investigated by a pin-on-disc tribometer during dry sliding.

Experimental results indicate that the Cu addition tends to increase the friction coefficient. For pure Cu material, the exogenous copper third body exhibits poor fluidity on the friction surface, causing serious adhesive wear on the friction interface. For the Cu 90% + 10% Gr material, the plasticity of exogenous copper powder may intensify the deformation of the third body of the surface, presenting layered accumulation distribution. For the pure Cu and Cu 95% + 5% SiO₂ material, the Cu addition makes the composition and density of the third body uneven in the direction of depth.

The role of the copper component on different materials is revealed from a new perspective, and the relationship between the third body structure and the friction properties is explored.

This study aims to investigate the effect of combined use of granular graphite and petroleum coke on the properties of copper-based friction materials and the friction and wear mechanisms.

Copper-based friction materials with different proportions of petroleum coke and granular graphite were prepared by using powder metallurgy. The friction surfaces were analyzed.

Changing the ratio of petroleum coke/granular graphite affects the formation of oxides and sulfides on the surface of the materials. Increasing the petroleum coke promotes the production of metal sulfide and sulfate in the friction materials and reduces coefficient of friction (COF) and wear. Increasing petroleum coke also increases the amount of carbonic oxide (CO) released during the braking process and promotes the reduction process of iron oxide on the friction surface.

The synergistic effect of carbon materials on copper-based friction materials was studied in terms of the tribological chemical reaction. This research provides useful information for the selection of carbon materials in friction materials.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-02-2020-0075/

The purpose of this paper is to study the influence of friction coefficient of materials with different elastic modulus on the variation of velocity and load under water lubrication and oil lubrication conditions.

Low-viscosity lubricating oil and water were used as lubricants to test the friction performance of the ball-disc contact friction pair in the lubrication state on the universal micro-tribometer multi-functional friction and wear test system.

In the same speed range, the lubrication states from soft to rigid materials are not necessarily similar to each other. Generally, the material with low elastic modulus is suitable in low-viscosity lubricant environments, while the material with high elastic modulus has relatively smaller friction coefficients in oil-lubricated environments compared with water lubrication. However, the coefficients of polyethylene, polytetrafluoroethylen and polyoxymethylene are exceeded by rubber’s coefficients under water lubrication in the same experiment environments, and their lubrication states are not affected by lubricants. The friction coefficient of the friction pair decreases with the increase of loads; however, it does not apply to all materials. The friction coefficients of materials with smaller elastic modulus such as rubber under high loads are rather large. Therefore, the elastic modulus of the material under high loads is a factor to be considered.

The Stribeck curves study of the ball-disk contact friction pair comprising soft and rigid materials, whose elastic modulus is from hundreds of GPa to a few of MPa, was carried out. The influence of different speeds, loads and lubricants on the friction coefficient of the friction pair was revealed, which provided a research basis for the selection and matching of friction pair materials.

Resin-based friction materials are the most widely used key materials in industry for braking and transmission. However, the friction coefficient of resin-based friction materials significantly decreases at temperatures above 300°C, which reduces their friction performance.

This study combines elevated-temperature mechanical experiments with friction and wear experiments to explain the thermal degradation resistance performance and temperature recovery performance of resin-based friction materials. It also investigates the influence of friction material strength and worn morphology on the friction coefficient of materials at elevated temperature.

The experimental results show that the increase in friction coefficient of friction materials below 300°C is mainly due to the increase in worn morphology characterization parameters, and the thermal degradation phenomenon above 300°C is mainly due to the decrease of shear strength of friction film. Basalt fiber can significantly improve the thermal degradation resistance of friction materials. The friction coefficient of basalt fiber-reinforced specimens after thermal degradation reaches 0.421–0.443, which is 19–25% higher than the original. The thermal decay rate is 9.03–11.0%, which is 7.9–9.87% lower than the original. Moreover, the friction coefficient has good cooling recovery performance.

Revealed the thermal degradation mechanism of resin-based friction materials, verified that basalt fibers can improve the thermal degradation resistance of friction materials and provided reference for the development of new friction materials.

The purpose of this paper is to investigate the role of solid lubricants (graphite, coke, ZnS) on brake performance.

In this study, the tribological and surface characteristic of non‐asbestos organic type brake friction materials containing three different solid lubricants (graphite, coke, and ZnS) in different proportions were examined and evaluated experimentally. The coefficient of friction (COF) and wear behavior of the samples were tested on a chase‐type friction tester, and particular emphases were given to the effect of temperature and number of braking cycles on the COF. Each of the lubricants was added to the mixtures in different amounts and seven different brake linings were manufactured, provided that the total amount of solid lubricants and other ingredients were not changed. The worn surfaces of the specimens were analyzed using a scanning electron microscope with energy‐dispersive X‐ray microanalysis.

The experimental results indicate that graphite has a positive effect on the tribological properties of brake linings. However, brake linings containing higher concentrations of ZnS and coke showed an unstable friction coefficient relationship with the temperature and number of braking cycles. The formation of friction layers was detected on the friction surface of these samples, which indicates that an increase in coke and ZnS content increases the discontinuous and unstable friction film areas.

This paper fulfils the effects of solid lubricants (graphite, coke, ZnS) in brake friction materials with detailed tests and analysis.

To determine static friction coefficients between rapid tooled materials and thermoplastic materials to better understand ejection force requirements for the injection molding process using rapid‐tooled mold inserts.

Static coefficients of friction were determined for semi‐crystalline high‐density polyethylene (HDPE) and amorphous high‐impact polystyrene (HIPS) against two rapid tooling materials, sintered steel with bronze (LaserForm ST‐100) and stereolithography resin (SL5170), and against P‐20 mold steel. Friction tests, using the ASTM D 1894 standard, were run for all material pairs at room temperature, at typical part ejection temperatures, and at ejection temperatures preceded by processing temperatures. The tests at high temperature were designed to simulate injection molding process conditions.

The friction coefficients for HDPE were similar on P‐20 Steel, LaserForm ST‐100, and SL5170 Resin at all temperature conditions. The HIPS coefficients, however, varied significantly among tooling materials in heated tests. Both polymers showed highest coefficients on SL5170 Resin at all temperature conditions. Friction coefficients were especially high for HIPS on the SL5170 Resin tooling material.

Applications of these findings must consider that elevated temperature tests more closely simulated the injection‐molding environment, but did not exactly duplicate it.

The data obtained from these tests allow for more accurate determination of friction conditions and ejection forces, which can improve future design of injection molds using rapid tooling technologies.

This work provides previously unavailable friction data for two common thermoplastics against two rapid tooling materials and one steel tooling material, and under conditions that more closely simulate the injection‐molding environment.

The purpose of this paper is to study the influence of braking speed at –20 °C on the wear property of high-speed railway braking materials and the temperature also stress analyses of brake disc friction surface.

Friction brake tester was used to simulate the wear test of high-speed railway braking materials at diverse braking speeds (2,100, 2,400, 2,700 and 3,000 rad/min) at –20 °C and the stress and temperature analyses of brake disc friction surface were carried out by COMSOL.

Compared with 20°C, there is initial stress of brake disc friction surface before brake starting; also, the maximum wear depth is larger at –20°C. Besides, at –20 °C, with the rising of braking speed, the graphite particles on the friction surface of brake pad significantly reduce. And scratches and cracks are formed on brake pad friction surface. Besides, the abrasive wear, adhesive wear and thermal cracks of brake disc friction surface are aggravated. Moreover, the maximal worn depth also increase. Meanwhile, the highest temperature and the maximum thermal stress of brake disc friction surface both raise. Furthermore, the temperature and thermal stress gradients at radial direction of brake disc friction surface aggrandize, which makes the thermal cracks on brake disc friction surface further exacerbated.

In this paper, the wear property of the high-speed railway braking materials is studied by combining experiment and simulation. However, due to the low-speed traveling of high-speed railway was mainly studied in this paper, there may be no comprehensive simulation of the real running condition of high-speed railway. At the same time, the working condition of low-temperature environment cannot be completely simulated and controlled.

The research results of this paper provide a basic instruction for other researchers and also provide an important reference for relevant personnel to choose the braking speed of high-speed railway at –20 °C.

The research of this paper provides a brick for the study of high-speed railway braking materials and also provides some references for the safe service of trains in low-temperature environment.

This paper studied the wear property and carried out the simulation analysis of braking materials at –20 °C at diverse braking speed. The research findings provide an important reference for the selection of braking speed of high-speed railway at –20 °C.

This study aims to determine the braking performance of limestone as a filler in brake friction materials.

Samples containing limestone material (30-35-40%), which can be an alternative to brake friction material filler, were produced. The samples were weighed on precision scales, mixed homogeneously and produced using the hot molding method. The physical and tribological properties of the produced samples were determined, and their microscopic analyzes were made with scanning electron microscopy.

As the amount of limestone increased, the density of the samples decreased. The friction coefficient and wear rates were close to each other and within the optimum limits for all samples. Limestone materials can be used instead of barite materials studied in the literature on brake linings. Microcracks were observed only in samples containing 30% and 35% limestone in microscopic images.

In this study, the wear rate, coefficient of friction and microstructures on the friction surfaces of brake friction materials containing limestone were investigated. The usability of limestone as a filler in brake friction materials provides valuable information to researchers and industrial organizations in the brake friction material field.

The purpose of this paper is to investigate surroundings for transfer film formation and removal, the effect of the transfer film formation on friction coefficients, the effect of four different abrasive components, ZrO₂, ZrSiO₄, Al₂O₃ and Fe₃O₄, on transfer film formation and the effect of lubricating component MoS₂ on transfer film formation and friction coefficients.

Two different MoS₂ contents of 5.5 and 8.5 per cent were added to friction materials with no MoS₂ content, which have four different abrasive components, ZrO₂, ZrSiO₄, Al₂O₃, Fe₃O₄. Friction tests composed of three different stages were conducted for those materials, and the friction surfaces of the counterpart disks were examined by scanning electron microscopy (SEM) to access the formation of transfer film at each stage.

For the transfer film formation, high temperature was a prerequisite, but the magnitude of deceleration rate was not important. The effect of the transfer film formation was to reduce the friction coefficients for most friction materials. Friction coefficients of materials which contain lubricating component MoS₂ were higher than those which contain no MoS₂ for most friction materials. The effect of the lubricating component MoS₂ was to suppress the formation of transfer film, thus resulting in increase in friction coefficients.

The transfer film was rather thin, with thickness of 1-2 µm for most friction materials. That hindered the examination of mechanical properties of the transfer film, such as hardness.

This research explained the surroundings for transfer film formation, and its effect on friction coefficients. The research suggests to suppress the formation of transfer film to make friction materials with high friction coefficient, and the lubricating component MoS₂ can be used for the purpose.

Development of high-friction-brake materials conventionally depends on the use of strong abrasive components, which may induce attacking of counterpart disks. The enhancement of friction coefficients with addition of MoS₂ content is expected to open a new prospect in development of high-performance friction materials, which can be applicable to brake pads for racing cars.

The study is in pursuit of the transfer film formation in successive friction stages, which revealed the conditions for transfer film generation and removal. Specimen preparation for SEM observation of cross section of friction surface was painstaking to not damage the developed friction surface. The study revealed the effect of different abrasive components on transfer film formation and the effect of lubrication contents of MoS₂ on transfer film formation and friction coefficients.