The geometry and the arrangement of a brake pad for railway vehicles are the important influencing factors for distribution of the temperature and the thermal stress in a brake disc,and closely related to the thermal fatigue damage of the brake disc. The conception of structure function is presented with the view that friction strength on the brake disc is related to the geometry and the arrangement of the pad. Non-uniform heat sources model are suggested based on the structure function, and the temperature and the thermal stress of the brake disc are simulated with FEA software ABAQUS for four difference arrangements brake pads. The results show that changing patterns of the temperature and the thermal stress on brake disc surfaces are coincided with that of structure function. While the peak value of structure function is smaller and the distribution uniformity is better, the temperature and the thermal stress on the corresponding brake disc surface are lower, and distribution is more uniform. Structure function connects the geometry and the arrangement of the brake pad with the friction contact relationship of the brake disc, reflects distribution law of the temperature and the thermal stress and solves the problem of creating a heat source model.
To understand the effects of the third body of copper in the copper-based composite materials on the friction properties, the effect of copper powders on the friction properties of Q235 steel is studied by using the pin-on-disk tester and adding copper powders third body. The results show that when the friction speed at 500-3000 r/min, due to the incremental copper powders, the depth of the furrows on the friction surface was reduced and the adhesion and spalling process of surface third body were intensified, which results that the frictional coefficients of the Q235 steel are increased 0.2-0.35 comparing with that of without adding copper powders. The reason is that incremental copper third body plays the role of increasing the meshing of the asperity and the actual friction area.
The distribution of temperature on the rubbing surface is an important factor influencing the lifetime of a brake disc. With a copper-base sintered brake pad and a forge steel disc, up-to-brake experiments have been conducted on a full-scale test bench at a highest speed of 200 Km/h and a maximum braking force of 22.5 KN. The temperature distributions on brake disc surface have been acquired by an infrared thermal camera, and the contact pressure on the contact surface of the friction pair has been calculated by the finite element software ABAQUS. The results show that the area and thermal gradient of the hot bands increase with the increase of braking speed and braking force. The hot bands occur in priority at the radial location of r=200 mm and r=300 mm, and move radially in the braking process. The finite element modelling calculation indicates that the distribution of the contact pressure on the disc surface in radial direction is in a "U"-shape. The maximum contact pressure occur at the radial locations of r=200 mm and r=300 mm, and the minimum contact pressure occur in the vicinity of the mean radius of the disc. The conformity of contact pressure distributions with the practical temperature evolutions indicates that the non-uniform distribution of the contact pressure is the factor resulting in the appearance of hot bands on the disc surface.
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