Keywords: brake disk, non-linear analysis, cmc composite, contact simulation, FEM analysis.

Composite materials are increasingly being used in the Railway Industry where the resulting performance improvements and achievable cost reductions are significant. Weight savings of up to 50% for structural and 75% for non-structural applications lead to associated benefits of high-speed, reduced power consumption, lower inertia, less track wear and the ability to carry greater pay-loads [1].

In particular, the introduction of lightweight CMC brake disks in the high-speed train sector is important for optimisation of train performance [2]. Low weight and excellent specific heat capacity of CMC materials improve the performance of brake disks. Braking performance of these products is exceptionally good with very low wear rates [3]. By using brake disks, producers are aiming to halve the number of brake disks required per train.

Reducing the number of disks by half can lead to a further reduction of 50% for other heavy brake system components. That would result to a total weight reduction in braking systems of around 65%, and to a capital investment only slightly higher than that of conventional systems. Within this industrial research, numerical contact simulations of a CMC brake disk system have been carried out using LS-DYNA code [4]. The used CMC materials are obtained by applying a hybrid process methodology based on CVI, PIP and RB phases [5,6]. The aim of this paper is the development of an advanced virtual brake testing method in order to numerically evaluate performance and reliability of innovative disk brake prototypes.

A three-dimensional analysis with mechanical loads and friction between the pad and the disk is investigated for effective brake performance. The friction coefficient is defined as a function of relative velocity and pressure. Disk brakes press a set of composite material brake pads against a rotating CMC disk. The pads are made of a composite railway disk brake pad with an organic matrix and the classical UIC shape [7,8]. The "surface-to-surface" contact capability is used for contact modeling, the most powerful and indicate approach to define contact simulations. The part of the brake pad off the disk is restrained in its non-axial degrees of freedom and is loaded with an axial pressure. The disk rotates by prescribing its angular velocity for different emergency braking conditions. Simulations are carried out considering different initial speeds, a deceleration of 0.8 [m/s] and a disk diameter of 580 [mm]. Three working conditions are analysed: a) beginning of braking at a speed of 200 [Km/h], b) beginning of braking at a speed of 300[Km/h], c) pads loaded with different pressures.

The chosen contact numerical algorithm shows a good capability to simulate the complex mechanical interaction between disk and pads (very low values of Hourglass Energy have been found in all the analyses). Moreover, the numerical model shows a very good accordance to the general theory of rotating disks. The analyses confirm that Long-CMC material guarantees a very good mechanical behaviour, even in non-symmetric dynamic load conditions (pads loaded with different pressures). The proposed numerical model shows an interesting flexibility, to be used for different structural materials and various load conditions.

1

MERL "Composite Materials in Transport Friction Applications", Materials Engineering Research Laboratory Ltd. -July, 1999

2

POLI "Informazioni tecnico scientifiche relative a materiali per dischi freno ferroviari", Pubblicazione interna Poli Costruzione Materiali Trazione, 2000.

3

Masahiro SASADA, Kazuya OKUBO, Toru FUJII, Naganao KAMEDA "Effects of hole layout, braking torque and frictional heat on crack from small holes in one-piece brake disks" Doshisha University, Japan.

4

Livermore Software Technology Corporation "LS-DYNA manual" 1999.

5

Deogyu Lee, Anthony M. Waas, "Stability analysis of rotating multiplayer annular plate with a stationary frictional follower load" Composite Structures Laboratory, Department of Aerospace Engineering , The University of Michigan 1996.

6

Azarkhin, A. and Barber, J.R., "Transient thermoelastic contact problem of two sliding half-planes", Wear, Vol. 102, 1985. doi:10.1016/0043-1648(85)90086-9

7

Burton, R.A., Kilaparti, S.R. and Nerlikar, V., "A limiting stationary configuration with partiall contacting surfaces", Wear , Vol. 24, 1973. doi:10.1016/0043-1648(73)90232-9

8

Christie, I., Griffiths, D.F., Mitchell, A.R. and Zienkiewicz, O.C. "Finite element methods for second order differential equations with significant first derivatives", International Journal for Numerical Methods in Engineering, 10, 1976. doi:10.1002/nme.1620100617

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