Research Of Hot Spot Based On Scaling Test

Currently, a large number of examples which are in domestic and abroad show that the brake discs format the hot spots in the friction surface under the strong thermal load, then lead to crack around the hot spots, result in the growth of micro-crack on the surface followed by long-term thermal fatigue, until the brake discs invalidate because of the overrunning length. This paper reveals the formation mechanism of the hot spots, and put forward practical measures to postpone the emergence of hot spots through the combination of experiments and numerical simulation method, using the analysis of macro and micro.First, design the model with fundamental of geometry similar, kinematics similar and dynamics similar which are based on similar principle to reproduce the hot spots using the MM1000friction test machine, and then correct the parameters for numerical simulation through the experimental results. Through combining the numerical simulation and experimental results, using the analysis of the organization, morphology surface and composition at the hot spots, the paper reveals the hot spot formation mechanism:At each process of braking, the different temperature at the different points of the friction surface lead to the different expansion and different stress of different points also result in the different deformation which makes more severe deformation under the thermal stress and mechanical stress at the frication surface, after that, the original surface contact change into a multi-point contact which makes uneven deformation of the temperature and stress at the friction surface. This phenomenon becomes a vicious circle. With the accumulation of the braking energy the deformation of salience change from the recoverable elastic deformation into unrecoverable plastic deformation, meanwhile, the raised points only allow to release the constraints in normal direction because of the circumferential and radial constraints of the brake disc, after the repeatedly braking, the stress around the salience accumulate to reach the fracture allowed values to produce micro-cracks, then micro-cracks gather to form long cracks, and eventually lead to failure for cracking of the brake disc.After knowing the formation mechanism of hot spots, this paper increase the thickness of the friction surface and the density of cooling ribs which is based on numerical simulation technology to strengthen the heat storage capacity and cooling capacity of the model to postpone the appears hot spots eventually.