Numerical Simulation And Experimental Study Of Temperature And Stress Of The Train Disc Brake Based On The Brake Pads Structure

Disc brake has been widely used in high-speed train brake for its simple structure, high brakeefficiency and large brake power. With the speed of train rising, energy to be consumedincreases during braking, and the brake disc is in state of high and volatility temperature,leading to severe thermal crack damage of brake disc, which has become a major factorrestricting the life of the brake disc. One of the important factors effects distributions of thebrake disc temperature and stress is the structure of brake pads. Therefore, to improve traintraffic safety, it is important to study on distributions of the brake disc temperature and stressand its relation to the brake pads structure under the conditions of high-speed braking.Using friction pair of forged steel brake disc and copper-based powder metallurgy brake padsfor high-speed train, by the numerical simulation method and full scale braking test with topspeed of350km/h, and by infrared thermal imaging technology, the influence of brakingspeed and braking pressure on the disk temperature and stress have been studied, and theinfluence of the brake pads structure on contact pressure and temperature distribution hasbeen discussed on view of the brake pads structure. Conclusions obtained as follows:(1) Based on the view that friction power on the brake disc surface is determined by thegeometry and arrangement of the brake pads, characterization methods of the brake padsstructure have been discussed, concept of brake pads structure function has been proposed,and expressions of brake pads structure function for circular friction pad has been developed.The brake pads structure function describes contact relation between the brake pads and brakedisc which is the basis of the mobile heat source model, and associates mobile heat sourceswith the friction pad geometric features. This parameter objectively describes the structuralcharacteristics of the brake pad, and can be used to evaluate the degree of influence of thebrake pads on uniformity of the brake disc temperature and stress distribution.(2) The values of brake pads structure functions of four brake pads with different arrangementof circular friction pad have been calculated. By simulating the brake disk temperature andstress during the braking process, the variations of the brake pads structure function and thebrake disc surface temperature and stress have been verified, showing a good agreement ofthe two. With increase of the brake pads structure function value, the brake disc temperatureand stress increase. The distribution of the brake disc temperature and stress can be improvedby reducing the changing range of the brake pads structural function value. The brake padsstructural function provides a reference for improving the brake disc temperature and stress,whichis significant for the design of brake pads.(3) The brake disc temperature and stress have been simulated with brake pads of hexagonaland triangular friction pad structure. Under conditions of braking speed of120km/h and braking time of10s, the maximum peak temperature and peak stress of the brake disc, whichcouple with brake pads of hexagonal friction pad structure, are103°C and212MPa,respectively, and those, which couple with brake pads of triangular friction pad structure,206°C and433MPa, respectively. The stress of the latter is double of that of the former, which isdue to that the distribution of structure function value of the hexagonal friction pad has betteruniformity than that of the triangular friction pad.(4) For target of minimum value of the brake pads structure function, the structure of brakepads of circular friction pad has been optimized. When braking with the optimized brake pads,the brake disc peak temperature and peak stress decrease by141°C and383MPa,respectively.(5)The evolutions of the brake disc temperature under the1:1test conditions have been doneby infrared thermal imaging technology. The brake disc temperature increases when brakespeed increases and the temperature exceeds550°C when the braking speed is350km/h. Thedifference of the brake disc temperature increases with increasing of braking speed, and thedifference of temperature under the speed of350km/h is doubled of that under the speed of120km/h. The maximum temperature difference appears in the initial braking stage, andtemperature gradient reduces with the increase of the braking time.(6) The study of variation of the brake disc temperature distribution shows that the brake disctemperature experiences a process of warming-stability-cooling. In the warming stage, thehigh temperature zones appear in priority at both the inner and the outer locations of the brakedisc friction surface, and offset to the middle of the brake disc friction surface with theincrease of the braking time, reaching the highest value of temperature. In the cooling stage,the high temperature zones expanse along the radial direction and reduction in circumferentialdirection, which divides the high temperature zone into discontinuous spots. The evolution ofthe high temperature zone is due to the uneven distribution of friction speed and pressure ofthe brake disc. The rotational motion of the brake disc results in the increasing friction speedwith the enlargement of the friction radius. The structure of brake pads dovetail leads to thatthe inner and the outer locations’ pressure of the brake disc friction surface is higher than thatof other zones’. The combined effects of speed and pressure result in that high temperaturezone with lager friction radius wear in priority. The uneven wear changes the pressuredistribution makes the high temperature zone moving during the braking process.