Experimental Research And Simulation Analysis On Hot Spot Of Brake Disk Material

Hot spot is a widespread phenomenon on the friction surface of steel brake disc after braking process, the color of hot spot is purplish blue. The existence of hot spot will affect the residual stress distribution state on the friction surface of brake disc, it is the main reason for the formation and extension of fatigue crack, hot spot is very dangerous for the train operation safety, it directly affect the safety of the train and the passengers. There is no systematic research of hot spot in our counties, to solve this problem, this article discusses the formation mechanism of the hot spot and analyses the influence factors of hot spot according to the experimental results and simulation analysis, providing theoretical basis for the brake disc improvement design and accident prevention.In the experimental study, braking test was carried out to create hot spot according to MM 1000 friction test instrument. This article analyzes the compositions,morphology and properties of friction surface layer where hot spot appears under the help of TPF-1 microscope, SEM and Spectrum analyzer. The results show that material metallographic organization where hot spot appears changes from tempered sorbite to martensite, this proves that the temperature where hot spot appears reaches or exceeds 727℃, which is substantially higher than the average temperature of the friction surface. The content of Fe greatly reduced and the content of O increased substantially in the places where hot spot appear. This shows that the temperature rising sharply in this place that the material happens oxidation.In the simulation analysis research, with regard to the elastic-plastic thermal-mechanical coupling simulation, braking simulation of brake disc was carried out. From the result of temperature and thermal stress distribution of the friction surface of the brake disc, there exits obviously local high temperature area, the thermal stress and plastic strain become great in these areas. From the experiment study and simulation analysis, the reason of the hot spot was investigated:there exit obviously local high temperature areas in the braking process, these high temperature areas make the plastic strain become greater, making the pad input more energy in these areas, the energy make the temperature become higher. This vicious circle cyclical repetition happens in the process of disc brake, which creates the hot spot.Simulation of braking process was carried out to analysis the influence factors of hot spot. High specific heat,low expansion coeff alpha and fine conductivity are the reasons why there are less hot spots even no hot spots on the surface of brake disc such as SiCp/A356 brake disc; Ventilation cooling structure such as stiffened plate can greatly reduce the temperature of brake disc, which can reduce the chance of hot spots appear.