The influence of sample geometry on the friction behaviour of carbon–carbon composites
TL;DR: In this paper, the transition from normal to dusting wear is associated with the attainment of a critical temperature at the interface between the two carbon-carbon composite bodies sliding against each other.
Abstract: Carbon-carbon composites (CC composite for short) are extensively used as aircraft brake pad materials on account of their excellent tribological behaviour at high sliding speeds. It is well known that the tribological behaviour of CC composites is dependent on the nature of the fibre lay up, heat treatment condition employed, etc. More importantly, CC composites also exhibit a transition from a low friction coefficient (μ), normal wear regime, to a high μ, dusting wear regime, when the PV value (P is normal pressure and V is sliding velocity) exceeds a critical value. It is also generally accepted that the above transition is associated with the attainment of a critical temperature at the interface between the two CC composite bodies sliding against each other. The objectives of the present work are two-fold. First, to characterize the transition from normal to dusting wear on the basis of accurate measurement of the interface temperature utilizing an eroding thermocouple and to demonstrate that the attainment of a critical interface temperature is a prerequisite for transition from normal to dusting wear. Second, to study the influence of sample geometry on the critical PV value for transition to dusting wear and to rationalize the above result on the basis of the extent of partitioning of heat generated at the sliding interface into the stationary sample.
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TL;DR: In this article, a study was conducted to study vacuum brazing between carbon-carbon composites (CC) and TiAl alloys with Ag-Cu-Ti filler metal, and a new method of making holes in the CC composite surface was introduced, and the joint was strengthened by the infiltration of filler metals into these holes.
Abstract: The present investigation was conducted to study vacuum brazing between carbon–carbon composites (CC) and TiAl alloys with Ag–Cu–Ti filler metal. The mutual exclusion between the Ag and Ti elements had a significant influence on the joint microstructure. The isothermal solidification of the Ag-based solid solution led to a layered microstructure, which was beneficial to the joining strength. A new method of making holes in the CC composite surface was introduced, and the joint was strengthened by the infiltration of filler metals into these holes.
103 citations
TL;DR: In this article, the combustion synthesis of TiAl intermetallics and their joining to carbon/carbon composites was realized simultaneously, and the successful joint configuration involved putting a carbon and carbon composite ball into the Ti-Al powder mixtures.
Abstract: The combustion synthesis of TiAl intermetallics and their joining to carbon/carbon composites was realized simultaneously. The successful joint configuration involved putting a carbon/carbon composite ball into the Ti–Al powder mixtures. The effect of the residual stresses at the interface on the joining of carbon/carbon composite to TiAl intermetallics was analyzed. Investigation of the reaction products of Ti–45 at.% Al mixtures showed that TiAl and Ti3Al phases were formed by combustion synthesis. The evolution of the interfacial microstructure was investigated.
33 citations
TL;DR: In this paper, a PMC friction material containing phenolic resin, short carbon fiber, graphite, quartz, barite and steel fiber was investigated through using a small-scale friction testing machine.
Abstract: Friction, fade and wear characteristics of a PMC friction material containing phenolic resin, short carbon fiber, graphite, quartz, barite and steel fiber were investigated through using a small-scale friction testing machine. Four different friction materials with different relative amounts of the carbon fiber and steel fiber were manufactured and tested. Comparing with our previous work which contained only steel fiber as reinforcement, friction characteristics such as fade and recovery and wear resistance were improved significantly by adding a small amount of carbon fiber. For the mixing of carbon and steel fiber, the best frictional and wear behavior was observed with sample containing 4 weight percentage carbon fiber. Worn surface of this specimen was observed by optical microscopy. Results showed that carbon fibers played a significant role in the formation of friction film, which was closely related to the friction performance. The brake pad with Steel fibers in our previous work, showed low friction coefficient and high wear rate. In addition, a friction film was formed on the surface with a relatively poor quality. In contrast, the samples with mixing the steel and carbon fiber generated a stable friction film on the pad surface, which provided excellent friction stability with less wear.
30 citations
Cites background from "The influence of sample geometry on..."
...The brake pads as friction material with carbon fiber reinforcement exhibit a high and stable coefficient of friction at high sliding speeds and thus have replaced the conventional metallic brake pads, but their cost is too high[ 7 ]....
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...Fade means friction loss at elevated temperatures [ 7 ]....
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TL;DR: In this paper, a carbon/carbon composite and Ti3Al alloy were brazed using graphene nanoplatelet (GNP) strengthened Ag-Cu-Ti composite filler, and the shear strength of the composite joint first increased and then decreased with the increase of GNP content.
Abstract: Carbon/carbon (C/C) composite and Ti3Al alloy were brazed using graphene nanoplatelet (GNP) strengthened Ag-Cu-Ti composite filler. The brazed joint had the excellent bonding interface, and the microstructure of joint contained TiC, Ti(Cu,Al), GNPs, AlCu2Ti phases. Results showed that the GNPs addition could decrease the thickness of TiC layer. GNPs hindered the atom diffusion and inhibited the growth of TiCu phase on the Ti3Al alloy side. The shear strength of brazed joint first increased and then decreased with the increase of GNPs content, and the brazed joint reached to the highest shear strength 26.7 MPa when GNPs content was 0.1 wt. %. GNPs could reduce the CTE mismatch between C/C composite and Ti3Al alloy, and improve the joint strength due to the relief of residual stress.
27 citations
TL;DR: A facile ammonium-dichromate solution immersion method was introduced to synthesize the copper-wettable Cr3C2 coating on and inside the carbon-carbon (C/C) preform.
Abstract: A facile ammonium-dichromate solution immersion method was introduced to synthesize the copper-wettable Cr3C2 coating on and inside the carbon-carbon (C/C) preform. The formation mechanism and the microstructures of the Cr3C2 coatings were studied. The contact angle between molten copper and the C/C decreased from 140° to 60°, demonstrating the significant improvement in the wettability. The Cr3C2-coated C/C-Cu composite with only 4.2% porosity and 3.69 g cm−3 density was manufactured through copper infiltration. As a result, the thermal and electrical conductivity of the modified C/C-Cu increased significantly due to the infiltrated copper. Also the mechanical properties of the composites including both the flexural and compressive strengths were enhanced by over 100%. The modified C/C-Cu composite exhibited lower friction coefficients and wear rates for different load levels than those of the commercial C/Cu composite. These results demonstrate the potential of the modified C/C-Cu material for use in electrical contacts.
22 citations
References
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Book•
31 Dec 1959
TL;DR: In this paper, a classic account describes the known exact solutions of problems of heat flow, with detailed discussion of all the most important boundary value problems, including boundary value maximization.
Abstract: This classic account describes the known exact solutions of problems of heat flow, with detailed discussion of all the most important boundary value problems.
21,807 citations
Book•
01 Jan 1954
TL;DR: Tabor and Bowden as mentioned in this paper reviewed the many advances made in this field during the past 36 years and outlined the achievements of Frank Philip Bowden, and reviewed the behavior of non-metals, especially elastomers; elastohydrodynamic lubrication; and the wear of sliding surfaces.
Abstract: Originally published in 1950, this classic book was a landmark in the development of the subject of tribology. For this edition, David Tabor has written a new preface, reviewing the many advances made in this field during the past 36 years and outlining the achievements of Frank Philip Bowden. The book covers the behavior of non-metals, especially elastomers; elastohydrodynamic lubrication; and the wear of sliding surfaces, which has gradually replaced the earlier concentration on the mechanism of friction. It remains one of the most interesting and comprehensive works available on a single branch of physics.
5,834 citations
TL;DR: In this article, the authors describe an experimental study on the temperature-dependent tribological behavior and oxidation of a carbon-carbon composite material sliding against itself in ambient air up to 1800°C.
Abstract: This paper describes an experimental study on the temperature-dependent tribological behavior and oxidation of a carbon-carbon (C/C) composite material sliding against itself in ambient air up to 1800°C. Tribological experiments were conducted with a ring-on-ring type of apparatus using a wide range of load and speed conditions. As the specimen temperature gradually increased with frictional heating, the friction of C/C composites experienced two abrupt increases at 150–200°C and 650–700°C. The two transition temperatures divided the friction and wear of C/C composites in ambient air into three temperature-dependent regimes: the normal wear, the water-desorption dusting wear, and the oxygen-desorption dusting wear regimes. The friction and wear also depended on the load and speed conditions. In addition to the wear loss at the rubbing surface, the oxidation loss at the exterior of the specimen also contributed to the weight loss of the specimen, especially at elevated temperatures. The linear wear of C/C specimens amounted to less than 2% of the total weight loss when the maximum specimen temperature exceeded the failure temperature of the oxidation-inhibitor. The effect of specimen geometry on the wear and oxidation at the rubbing surface is also discussed.
61 citations
TL;DR: In this paper, the most important factors influencing the magnitude and stability of the coefficient of friction and rate of wear of graphitic and non-graphitic carbons are investigated and the mechanisms involved are described.
Abstract: Both graphitic and non-graphitic carbons are widely used in a variety of tribological applications. A recent development is the use of carbons for aircraft brake discs and this has prompted an experimental investigation to determine the most important factors influencing the magnitude and stability of the coefficient of friction and rate of wear. Graphitic carbons sliding against themselves, or against metals, sometimes exhibit large and sudden transitions in friction and wear at critical conditions of sliding. These conditions are defined and the mechanisms involved are described. Carbons of low or negligible graphiticity are less prone to transitions than graphitic materials, but their friction and wear properties depend markedly on the way in which the conditions of sliding influence the structure and topography of the surface layers developed during sliding. Examples are given of typical variations of friction and wear with distance of sliding, speed and temperature. Discontinuities in friction and wear can also arise from localised surface misalignments induced either mechanically or thermally. The stability of the coefficient of friction and the rate of wear for both graphitic and non-graphitic carbons can be greatly improved by the incorporation of additives or by the presence of organic vapours in the environment. Examples are described.
49 citations
TL;DR: In this article, the influence of the conditions of sliding on the "dusting" wear of graphitic carbon sliding against non-graphitic carbon was examined and a wear mechanism was proposed in which the adsorption of vapours increases the rate of crack propagation during localised contact by a process analogue to stress-corrosion, and this was supported by an examination of worn surfaces and debris.
Abstract: An examination is made of the influence of the conditions of sliding on the 'dusting' wear of graphitic carbon sliding against non-graphitic carbon. Specific wear rates are essentially independent of load, speed and contact temperature over a wide range, but begin to decrease at speeds above about 10 m s-1. At these high speeds, wear rates increase with increasing environmental pressure and at any one pressure increase with the type of vapour in the order H2, N2, O2, H2O and hydrocarbons. A wear mechanism is proposed in which the adsorption of vapours increases the rate of crack propagation during localised contact by a process analogue to stress-corrosion, and this is supported by an examination of worn surfaces and debris. The existence of a direct relationship between dusting wear rates and the adsorption energies of different gases and vapours on carbons suggests that physical adsorption is primarily involved.
48 citations