Effect of braking pressure and braking speed on the tribological properties of C/SiC aircraft brake materials
Introduction
C/SiC composites are new type of high performance brake materials developed after powder metallurgy (PM) and C/C composites [1]. The advantages of PM brakes are the maturity in material development and low cost, while the application of PM brakes is limited by their major disadvantages such as high weight, poor performance at high temperature, and prone to corrosion [2], [3]. C/C brakes were developed to overcome the disadvantages of the PM brakes, exhibiting excellent thermal and mechanical properties with lower weight. However, the C/C brakes suffer from insufficient stability of friction coefficient caused by humidity [4], [5], [6]. Combining the advantages of PM and C/C brakes, and overcoming most of the disadvantages of PM and C/C brakes, C/SiC composites exhibit some other superior performances such as high and stable friction coefficient, long life, low wear rate, and lower sensibility to surroundings and oxidation [3], [7], [8], [9], [10].
In the early 1990s, Krenkel et al. at the German Aerospace Center (DLR) in Stuttgart started investigations of C/SiC composites for high performance automobile applications [11]. Up to now, the C/SiC brakes have been successfully applied to Porsche, Ferrari and Daimler Chrysler [12], [13]. Investigations by the Ceramic Composite Aircraft Brake Consortium of USA indicated that C/SiC materials may be feasible as a next-generation aircraft brake material [7]. Nowadays, plenty of work have been done for developing C/SiC aircraft brake materials [7], [14], [15], [16], [17], [18], [19]. In 2008, the C/SiC aircraft brakes were installed on a certain airplane for trial flight and achieved success which were prepared by Northwestern Polytechnical University and Xi’an Aviation Braking Science and Technology Co., Ltd. in China [20].
However, the systematical research for the effects of braking parameters on the tribological properties of C/SiC aircraft brake materials has seldom been reported. In the present paper, effects of braking parameters on the tribological properties of C/SiC aircraft brake materials are systematically investigated.
Section snippets
Fabrication
The C/SiC aircraft brake materials were fabricated by chemical vapor infiltration combined with liquid melt infiltration (LMI). The C/SiC were composed of 65 wt.% C, 27 wt.% SiC, and 8 wt.% Si. The density and porosity were 2.1 g cm−3 and 4.4%, respectively [18].
Testing methods
The tribological properties were tested on a disk-on-disk type laboratory scale dynamometer (Fig. 1) by reference to [18]. The kinetic energy absorbed by braking was supplied by the inertia wheels, which were driven by a DC motor. The tested
Effect of braking pressure and braking speed on braking temperature
The effect of braking pressure and braking speed on braking temperature is shown in Fig. 2. It indicated that the braking temperature was increased with the braking speed increasing, and was less influenced by braking pressure.
During braking process, the brake disk translated the kinetic energy into heat energy through friction acting. The total braking energy was increased with the braking speed increasing when the inertia kept constant, and was not related with the braking pressure.
Conclusions
- (1)
The braking temperature increased with increasing braking speed and was less affected by changes in braking pressure.
- (2)
The braking speed and braking pressure significantly affected the friction coefficient. The friction coefficient increased to the maximum value at 10 m/s and then fell afterwards with the increase of braking speed at the same braking pressure. The friction coefficient decreased with the increase of braking pressure at the same braking speed.
- (3)
The wear rate increased with braking
Acknowledgements
The authors acknowledge the financial support of Natural Science Foundation of China (Contract Nos. 90405015 and 50672076), Program for Changjiang Scholars and Innovative Research Team in University, and project supported by the Research Fund of State Key Laboratory of Solidification Processing (NWPU), China (Grant No. 46-QP-2009).
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