Research On Thermal Fatigue Evaluation Method Of SiCp/A356 Composite Brake Disc For High-speed Train

As the most effective brake mode,brake disc has been used in the high speed train.It is important to consider how to avoid early thermal fatigue failure due to strong friction and intense heat flux in brake disc material selecting and structural design.At present,Cast iron and forged steel are normally used for brake discs of high speed strain in our country.Brake disc belongs to unsprung weight,heavier weight of which makes more energy consumption and worse kinetics performance of bogie,so it is a real significant research subject to develop a brake disc with light weight, anti-abrasive and heat resisting material.With the support of National Basic Research and Development program of China (863 program,No.2003AA331190 Research and Application of Metal Matrix Composite Brake Part in High Speed Train),the dissertation studied the thermal cycle performance,fracture mechanism and thermal fatigue character of SiCp/A356 composite latest developed for brake disc of high speed train using experimental method.And thermal fatigue crack initiation and propagation were deeply investigated by Finite element(FE) simulation combined with thermal fatigue test.The main contents are as follows,1.In order to establish thermal elastic plastic constitutive relationship of SiCp/A356 composite,its monotic and cyclic tension performance,physical characters with temperatures were investigated.2.Combining the functional analysis method with the heat conduction differential equations the finite element mathematic model of the period cyclic symmetric structure, ig.brake disc,was constructed for 3D transient temperature field.The cyclic stress strain responses rule of disc under different braking conditions were simulated with the sequence-coupled numerical calculation method.The mechanism of thermal residual stress and its important function at crack initiation and propagation process of disc surface were presented.3.The relationship of crack propagation rate and thermal cycles(a～da/dN) was determined and the influence for crack coming with diameters and thickness of samples were discussed.The thermal elastic plastic constitutive model of micro-unit of metal matrix composite(MMC) reinforced by particle was established by FE simulation technology.The stress strain response of micro-unit was mainly described to open out interface crack mechanism.4.According to the parameters obtained from thermal fatigue test of SiCp/A356 notched sample,quantitative analysis of thermal fatigue crack initiation curve (Δε_T/2～2N_f) and propagation rate curve(da/dN～ΔK) of the material were achieved by finite element method(FEM),which realized forecast of thermal fatigue crack initiation and propagation rule.5.The notched cyclic stress-strain response and crack stress intensity factors are established by thermal elastic plastic FE.The assessment method of thermal crack initiation and propagation law of SiCp/A356 composite brake disc surface was put forward.