【作者】 杨智勇；

【导师】 韩建民；

【作者基本信息】 北京交通大学 ， 车辆工程， 2008， 博士

【摘要】 轻量化是高速列车的关键技术之一。SiC颗粒增强铝基复合材料用于高速列车制动盘可减少簧下重量、实现轻量化。但铝基复合材料的膨胀系数较大、高温强度偏低,复合材料制动盘很容易受到热损伤,这使其使用速度受到限制。本文以有限元模拟计算为基础,通过理论分析和试验研究相结合的方法,开展了高速客车铝基复合材料制动盘的热损伤和结构设计研究。探讨了热损伤的特点和规律,在此基础上开展了制动盘的结构优化设计,提高了其适用的速度上限。本文测试了20wt%颗粒增强铝基复合材料在不同温度下的力学性能及热物理性能,得到了这两种性能随温度变化的曲线。通过有限元计算与试验验证相结合的方法系统研究了复合材料的微观损伤机理,得知室温下复合材料的裂纹萌生以基体撕裂和颗粒断裂为主;高温下其裂纹萌生机制以颗粒脱离和基体撕裂为主。开展了颗粒含量不同、颗粒含量相同但温度不同的铝基复合材料单向拉伸模拟计算,并通过与实测结果相比较,得出结论:颗粒含量不大于20wt%的复合材料的均质假设有限元模拟计算是有效的。这为20wt%颗粒增强铝基复合材料制动盘的均质假设有限元分析有效性奠定了基础。本文建立了三种制动盘制动过程有限元计算模型,并以1∶1制动试验中红外线温度成像系统测试的温度为依据,分析了它们的特点和适用性。在部分盘间接耦合模型的基础上,提出了整盘间接耦合计算模型。进一步研究了弹塑性热-机耦合问题,建立了盘形制动多体接触弹塑性热-机耦合模型。为铝基复合材料制动盘的热损伤和结构设计研究进行了研究方法上准备。本文采用有限元计算、理论分析和试验结果相结合的方法,研究了制动盘热斑、热裂纹和开裂三种热损伤的形成机理、影响因素和预防措施。研究表明,热斑是制动盘摩擦面局部高温区的组织变化和高温氧化的结果;热裂纹是由于制动盘摩擦面高温度区的边缘存在较大的内应力而萌生晶界裂纹,在径向和周向拉应力的作用下,裂纹沿晶界径向扩展而形成的;制动盘中不均匀的温度场分布造成不均匀变形,变形受阻形成热应力,热应力超过材料的高温强度导致制动盘开裂。此外,通过对制动盘热应力的研究,提出了产生制动盘热应力的五种约束。本文以热应力是否导致制动盘开裂为依据,采用有限元计算方法开展了SiC颗粒增强铝基复合材料制动盘结构设计研究。分析了制动盘各组成单元对热应力的影响,提出了制动盘结构单元组合设计方法,归纳了制动盘结构设计的一般原则,设计出了满足280km/h紧急制动条件的铝基复合材料制动盘。更多还原

【Abstract】 Lightweight was one of the key technologies for the high-speed trains. Unsprung weight can be reduced by using SiCp/A356 brake disc, so as to reduce the weight of high-speed trains. Comparing to iron and steels, SiCp/A356 composites has larger linear expansion coefficient and lower strength at high temperature, which increase thermal damage tendency and limit speed range of SiCp/A356 brake discs. Based on finite element simulation, thermal damage and structure design of SiCp/A356 brake disc for high speed train were studied in this paper through theoretical analysis and experimental study. On the basis of the results, the structure optimization design of the brake disc was carried out in order to increase the speed of its application.The mechanical and thermal physical properties of the 20 wt% SiCp/A356 composites at different temperatures were tested in this paper. And the property-temperature curves were obtained. Through the method of the finite element analysis and experiments, micro-damage mechanism of SiCp/A356 composites was investigated systematically. Micro-damage mechanism obtained by the finite element simulation was consistent with the mechanism from the fracture analysis. It can be concluded that the crack initiation mechanism of the composites at room temperature was mainly tear of the matrix and fracture of SiC particles mainly; while the mechanism of the composites at high temperature was SiC particle debonding from the matrix and tear of the matrix. Finite element simulations of the monotonous tensile tests were carried out for different percentage of particle in the composites at room temperatures, and the same percentage of particle in the composites at different temperatures. The simulation results were consistent with the experimental results. It can be concluded that when the content of SiC particles in the composites was no more than 20 wt%, after the uniform assumption for the SiCp/A356 composites was valid during finite element analysis, which established the foundation for the finite element analysis of the SiCp/A356 brake disc.With regard to FEM of disc brake, three typical finite element models for the braking simulation in this paper were established. Based on the temperature data obtained by infra-red temperature test imaging system during 1:1 dynamo test, their characteristics and applicability were studied. On the basis of the part-disc indirect coupling method, the full-disc indirect coupling model was put forward by changing the flux input method. And the multi-contact elastic-plastic thermal-mechanical coupling model of disc brake was established in order to investigate the thermal-mechanical coupling problems. This provides the methods for the research on the thermal damage and structural design of the brake disc.In the aspect of thermal damage mechanism study of SiCp/A356 brake disc, the forming mechanism, influencing factors and preventive measures of three typical thermal damages including hotspots, thermal-cracks and cracking were investigated through the combination of the finite element simulation, the theoretical analysis and the test results in this paper. The results showed that hotspot was caused by the change of structure and the oxidation due to the high temperature caused by surface friction on the brake. Crack firstly initiated at grain boundary due to higher internal stress at the edge of high temperature field caused by surface friction. The cracks propagated along the grain boundary due to the radial and circumferential tensile stress and finally created thermal-cracks. Non-uniform deformation was caused by non-uniform distribution temperature field in the brake disc. When the deformation was constrained by the structure and mechanical constraints of the brake disc, the thermal stress was introduced. If the thermal stress was bigger than the strength of materials at corresponding temperature, it led to the crack of the brake disc. In addition, based on the thermal stress research of brake disk, five kinds of constraints which might lead to thermal stress were summed up.Considering whether the thermal stress led to brake disc cracking, the structure design of the SiCp/A356 brake disc was studied by Finite Element Method (FEM). The effects of the brake disc components on thermal stress were analyzed. A structural components combination method and general principles of structure design of the brake disc were put forward. Based on these researches, a brake disc structure was designed which satisfied the application requirements of emergency braking at 280 km/h.更多还原