Thermomechanical Coupling Analysis And Structural Optimization Design Of C/SiC Brake Disc

Braking system is an important guarantee of traffic safety.With the rapid development of economy,the driving speed of vehicles is also increasing,and the requirements of braking system are higher and higher.In the process of braking,the friction between the brake disc and pads leads to a sharp rise of temperature on the surface of the brake disc,which changes the mechanical and physical properties of the brake disc and affects the stability of the brake system.At present,cast iron is a widely used material in automobile's brake disc,but the performance of cast iron material is very sensitive to temperature.With the increase of temperature,cast iron will appear phenomenon of heat recession,and the friction coefficient between the brake pads and disc will decrease,thus affecting the brake effect.carbon-ceramic composite(C/SiC)brake disc has a extensive application prospect in high speed and high braking efficiency fields such as high-end cars,high-speed railway,aircraft and wind turbine due to its advantages of low density,high temperature resistance,high strength and stable friction coefficient.The main way of heat dissipation of the brake disc is heat conduction and heat convection.The main object of this paper is the carbon-ceramic brake disc.The regularities of distribution of the heat transfer coefficient on the surface of the brake disc and the wall of the ventilation hole is obtained through the analysis of the flow field around the brake disc.Under the constant speed,it is found that the heat transfer coefficient of the two surfaces of the brake disc is evenly distributed,which gradually reduces from the outer edge to the inner edge.The maximum value appears near the vent on the outer edge of the brake disc,and the minimum value appears between the two vents on the inner edge.It is shown that the ventilation hole can improve the performance of heat convection on the brake disc surface while accelerating the heat dissipation of the internal structure of the brake disc.The maximum value of heat transfer coefficient of the ventilation appears at the entrance of the windward side and the minimum value at the inner wall of the leeward side.By simulating the flow field at different speeds,the relationship between the heat transfer coefficient of the brake disc and the speed is obtained.With the increase of vehicle's speed,the heat transfer coefficient on the brake disc surface increases obviously,the maximum and average values of the heat transfer coefficient on the inner wall of the ventilation hole increase obviously,while the minimum value increases slightly and not significantly.This is because the maximum value of the heat transfer coefficient of the ventilation hole occurs on the windward side and the windward side is greatly affected by the air's velocity,while the minimum value occurs on the leeward side and the leeward side is less affected.This paper uses ABAQUS software to conduct thermomechanical coupling analysis of the brake disc.In order to compare and analyze the regularities of distribution of temperature and stress of the brake disc which is made using carbon-ceramic material and cast iron material,the braking process of general braking condition is simulated,and some similarities of temperature field and stress field owned by two kinds of brake disc is found.In the process of braking,the temperature and stress increase first and then decrease,and the maximum value appears in the center area of the brake disc surface.The temperature and stress fields on the brake disc surface are distributed in a ring,decreasing from the center to the edge in the radial direction,and symmetrically distributed about the middle plane in the axial direction.The temperature field and stress field of two kinds of brake disc also show many different characteristics.The volumetric specific heat capacity of the carbon-ceramic brake disc is smaller,so the temperature rise in the early stage is relatively faster.The difference between the two temperature peaks is not large,but because the coefficient of thermal expansion of cast iron is much larger than that of carbon-ceramic material,the thermal stress of cast iron brake disc is much larger while the thermal stress of carbon-ceramic brake disc is smaller.In the emergency braking condition,the temperature of carbon-ceramic brake disc rises rapidly,compared with the general braking condition.The temperature and the stress peak are higher,and the stress peak has no delay compared with the temperature peak,while stress peaks of the two kinds of brake disc are delayed under the general braking condition.At last,this paper takes the heat dissipation power of the carbon-ceramic brake disc as the goal,selects 5 design variables,and optimizes the structure and size of the ventilation hole.In the process of establishing the optimization model,the adaptive variable is introduced to simplify the discrete optimization problem with constraints to the unconstrained optimization problem with continuous variables The sample data were collected by orthogonal experimental design method,and the approximate response model was constructed by BP neural network,Then the approximate function relationship between the objective function and the optimization variables was extracted,and the optimal size of the ventilation hole was obtained by genetic algorithm.The heat transfer coefficient of the brake disc before and after optimization was contrastively analyzed and the heat dissipation effect of carbon-ceramic disc is improved obviously after optimization.