Abstract Metastable β-type titanium alloys have garnered significant attention due to their microstructural diversity and excellent mechanical properties. In this study, the metastable β titanium alloy Ti-6Mo-3.5Cr-1Zr was subjected to the optimized heat treatment process. The optimization resulted in simultaneous enhancement of strength and ductility via grain refinement strengthening and transformation induced plasticity during plastic deformation. Furthermore, alloy microstructure analysis was conducted using Scanning Electron Microscope (SEM), Electron Back Scatter Diffraction (EBSD), and Transmission Electron Microscope (TEM) experiments. This work reveals the influence mechanism of solid solution time on the mechanical properties of titanium alloys, which provides theoretical guidance for the subsequent composition design and preparation of high-strength and high-ductility titanium alloys.

The finite element model is established based on the bench test of the landmine blast protection package. The effect of the air gap between the landmine blast protection package and the base plate as well as the stiffness of the package on the deformation of the base plate are investigated. Aluminum sandwich landmine blast protection packages are designed and the effects on the deformation suppression of the base plate are studied using the finite element model. The results show that the air gap is not conducive to the deformation suppression of the base plate. Increasing the stiffness of the package is of benefit to the deformation suppression of the base plate, however, it is necessary to consider the influence of the corresponding increase in thickness of the package on the possible increase in the base plate deformation. The scheme, composed of one piece of 2024-T3 aluminum plate and two pieces of 7mm armored steel, is the best solution among the six aluminum sandwich schemes.

The uncertain ballistic effects and reliability optimization design of the ceramics composite armors are investigated. Considering the material uncertainty, the ballistic penetration process is analyzed through simulation model. The effects interlayer SiC mass fraction and the matrix thickness gradient ratio are discussed. The optimal parameters of both material and structure are obtained through reliability design methods and verified through ballistic experiments. The results show that the standard deviation can be reduced when interlayer SiC mass fraction increases. The ballistic depth can be reduced by increasing the gradient ratio. Through optimization, the ballistic reliability of the ceramic composite armor is improved.

In this paper, in situ scanning electron microscope tensile test was carried out on the Ti-4.5Mo-5.1Al-1.8Zr-1.1Sn-2.5Cr-2.9Zn alloy, and the mechanism of grain rotation, shape change and micro-strain redistribution in macroscopic elastic deformation (stage I), macroscopic elastic-plastic transition (stage II) and macroscopic plastic deformation (stage III) stages were quantitatively investigated by electron backscatter diffraction and digital image correlation. In stage I, it was found that 10.1% of the viewing zone underwent grain rotation or shape change, and the micro-strain was mainly distributed in primary alpha phase (alpha(p)) and their intersection. The result of the separately designed elastic loading-unloading tensile test showed that the rotated alpha(p) no longer returned to the primary orientation. In stage II, the tensile plastic deformation regions reached 52.9%, and grains in beta(T) regions continued to rotate and began to change shape. In stage III, 84.6% of the viewing zone got into the tensile plastic deformation state. Combined with geometrically necessary dislocation density distribution, it was found that some of the regions in low strain state (0 <= epsilon <1%) actually underwent complex tensile plastic deformation. In addition, the maximum micro-strain of the viewing zone was transferred to beta(T) regions.

In the present study, a hierarchical microstructure, which was significantly different from the traditional microstructure of titanium alloys, was prepared by specially designing the solution and aging treatment parameters of a near beta-type hot-rolled Ti-4.5Mo-5.1Al-1.8Zr-1.1Sn-2.5Cr-2.9Zn alloy: (1) Firstly, in the process of solution-treatment (920 degrees C/1 h/WQ), a hierarchical microstructure in equiaxed primary alpha grains (alpha p) composed of nano-scale equiaxed alpha grains (alpha ps) and beta phase embedded between alpha ps was formed by controlling the diffusion rate of beta stable elements in alpha p regions. (2) Then, in the process of aging-treatment (550 degrees C/6 h/AC), a hierarchical microstructure composed of acicular secondary alpha phase (alpha s) with a thickness of dozens of nanometers, smaller acicular alpha phase (alpha ss) with a thickness of 10 nm, distributed in the space of two alpha s, and whisker beta phase (beta whisker), was observed in transformed beta (beta t) regions. Comparing to the solution-treatment of 900 degrees C/1 h/WQ followed by the same aging-treatment, smaller alpha p, a large number of nano-scale equiaxed alpha ps, and denser and finer acicular alpha phases were found in the titanium alloy. Due to the combined strengthening effect of equiaxed alpha p refinement, nano-scale equiaxed alpha ps and acicular alpha phases, the hierarchical microstructure exhibited super-high yield strength of 1255 MPa and ultimate tensile strength of 1420 MPa. Meanwhile, the refined equiaxed alpha p and the nano-scale equiaxed alpha ps could offset the negative effect of acicular alpha phases on plasticity, hence to maintain the plasticity at an acceptable level (elongation: 6%). Such hierarchical microstructure in the titanium alloy overcame the limitation of the strength-ductility trade-off to a certain extent.

针对高速动车组运用中出现制动盘螺栓断裂问题,选取典型断裂螺栓进行失效分析,并在振动和热负荷环境下对制动盘紧固结构受力状态进行试验和分析.研究发现:制动盘螺栓断裂为低应力疲劳断裂,在高于50 g的振动水平下,根据不同的振动频率,摩擦环相对盘毂产生微小相对位移,螺栓承受一定弯曲应力;在长大坡道等极端工况下运行时动车组采用摩擦制动,制动盘各部件由于长时间承受高热负荷及较大的温度梯度,使螺栓承受弯曲应力.针对制动盘螺栓受力情况,提出了变截面螺栓的改进方案,弯曲疲劳试验结果对比表明,新结构螺栓弯曲疲劳性能显著增强,可用于既有动车组轴盘螺栓的替换.

调查分析了高寒动车组制动盘异常磨耗与冰冻寒冷天气及制动盘分布位置的相关性;能谱半定量及金相分析显示闸片上金属熔融物主要来自制动盘摩擦环,且制动盘摩擦面材料没有发生相变,为进一步分析指明了方向.分析表明,制动盘异常磨耗是由极端寒冷的冰雪天气环境、冷焊效应、淬火效应、闸片虚贴、闸片结构因素、夹钳单元制动缓解不彻底以及转向架局部压差和涡流效应等多因素共同耦合作用的结果.提出了具有可操作的改进措施,两年的行车运营结果表明所采取措施取得了良好效果.

从跨坐式单轨车辆转向架特殊布置的结构特点出发,研究分析单轨车辆对基础制动的要求,总结出单轨车辆采用气体转液压的必然性.介绍了气转液制动夹钳单元产品分类,并以带停车制动的制动夹钳单元为例,详尽介绍制动夹钳单元的结构特征和原理设计计算,并结合空气转液压的增压原理以及液压执行机构对车辆的制动机理,深入的分析气转液制动夹钳单元在运营过程中常用制动和停车制动等各项制动功能的实现过程.最后研究总结用于产品检验的关键试验项目,为产品的质量控制提供参考.

动车组高速制动时,由于车辆自身阻力及风阻作用,制动盘承受的热负荷会降低.建立了高速制动时考虑车辆阻力的1∶1制动动力试验模型.利用高速1∶1制动动力试验台,研究了制动初速度350 km/h时车辆阻力对制动盘热负荷的影响,使1∶1制动动力试验工况与现车更接近,得到的试验结果更符合实际.

针对冬季冰雪天气CR H380B型高寒动车组制动盘易发生划伤的实际情况,对制动盘异常划伤原因进行研究,优化闸片结构,设计出适用于冬季的大间隙粉末冶金闸片.干燥及冰雪工况的1∶1制动动力试验结果显示,新研制闸片瞬时摩擦系数平稳、平均摩擦系数符合既有车辆要求,与其对偶的制动盘摩擦面状态良好;装有大间隙粉末冶金闸片的整车紧急制动试验结果显示,制动初速度200 km/h纯空气紧急制动距离为1 525m,小于2 000m评价指标要求,制动初速度300 km/h纯空气紧急制动距离为3711m,小于3 800 m评价指标要求;正线载客运营结果表明,大间隙粉末冶金闸片对改善高寒地区冬季动车组运营中出现的制动盘异常划伤问题有较好的效果.

在跨坐式单轨车辆运用过程中,车辆运营考虑很多重要影响因素,比如安全可靠性、零部件使用寿命、舒适度等,其中车辆运营的经济性指标也是重点考虑的因素.前期重庆2号线延长线使用国产闸片存在磨耗过快的问题,闸片使用寿命为9万km,这不仅增加运营成本,同时还增加了维修和人力成本.针对进口闸片和国产闸片进行磨耗分析,利用1:1制动动力试验和运营制动曲线综合分析,发现国产闸片和国产电制动性能略差,是影响闸片寿命的主要原因.建议改善车辆电制动状况,提升闸片自身性能,降低车辆运营成本.

In this paper, a problem for safety of bogie frame of subway vehicle under overload situation has been discussed.Firstly, the structure of bogie frame and service condition are introduced to explain the reason caused fatigue failure.Then, the testing points are selected in terms of the structure of bogie frame, the characteristics of processing technique, load transfer path and the operation situation of subway vehicle.Based on them, the experiment for acquiring stress data during peak of service is done.After that, the process of fatigue analysis is presented with rainflow cycle counting method using the data above.From the Miner rule, nominal stress method and Goodman relation, the formula for fatigue strength assumed infinite life is obtained.Finally, the results of fatigue analysis according to the approach above is presented in the form of table.The research work provides guidance for maintaining the bogie frame.

The reduction in the friction coefficient for frictional brake disc of high speed EMU applications in a rainy and humidly environment is considered as a serious problem as it affects the safety of the railway vehicle.However,relevant research should be more and more attention through there is a lot of high speed EMU which speed over 300 km/h.The change of friction properties under different work conditions was tested through dynamometer tester,and the similarities and differences between wet and dry friction mode were companied.It is shown that water has a complex effect on the properties of friction materials,as a kind of cooling medium and lubricant.The causes of friction performance change at different conditions and friction layer function and the braking system control strategy were also presented.

In this paper,comprehensively analysis 380 km/h high-speed train brake disc structure,chemical composition and mechanical properties,and obtain low alloy steel to meet the technical requirements of the brake disc material and cyclic symmetry radiating rib structure.Thermal stress calculation results show that the maximum thermal stress during the emergency braking is 448 MPa,which is less than the material yield limit.Fatigue test of a 1000 times of brake disc of train on full scale bench has been Proposed and implemented firstly.Fatigue test results showed that the brake disc friction surface does not appear the hot spots,thermal cracks and other disadvantage conditions.In emergency braking case of 420 km/h of Initial velocity,the thermal imaging testing results show the brake disc surface temperature distribution is uniform,the maximum temperature of the brake disc friction surface is up to 608℃,which is to meet the brake system technology conditions of 380 km /h high-speed train.

The full scale dynamometer brake test bench is introduced,such as work principle,component parts,function,application,and test program,which is the highest speed test bench in China.This paper will help us to more fully utilize the test bench for new products testing and basic research.

In this paper, based the actual application condition of domestic and international brake disc for high-speed train, the low-alloy cast steel of the brake disc for high-speed train is developed. The chemical composition, melting and casting processes as well as heat treatment technology of disc material are studied. The new low-alloy cast steel has the ideal metallographic microstructure, proper physical and mechanical properties. The tensile strength is more than 1100Mpa in 20°C condition, the impact energy value (Aku2) is more than 8J in-60°C condition. The test results show the new low-alloy cast steel developed can meet the brake disc performance requirements for 380km/h high-speed train.

This paper introduces and analyzes China's existing "Hexie" EMU brake system,using the braking technology and the main brake function,especially for CRH3 EMU for a more detailed description and analysis.

Foundation brake rigging is one of the important measures to ensure the safety of urban railway cars running.In the paper the advantages and disadvantages of disc brake and tread brake for the urban railway cars have been analyzed,and the characteristics of urban railway cars have been set forth according to the brake specific types of foundation brake rigging.The result of finite element simulation on the Temperature and thermal stress of the wheel tread shows that it is not appropriate adopting tread brake for the 100 km/h urban railway cars.Finally the disc braking is inevitable trend of development for the urban railway cars which the speed is 100 km/h and even more.

The heat finite element model of wheel mounted disc and pad of high-speed train is set up based on the nonlinear finite element software ABAQUS6.10.According to act information and heat transfer boundary conditions,the temperature field and heat stress field is computed.The results show that the maximum temperature up to 795 C,and high-temperature region concentrated in the central part of the brake disc friction surface area,and the maximum stress up 450MPa,which is less than the Yield strength of the selected steel material,and the simulation result meets the basic technical conditions of high-speed train required.

Test analysis of brake disc of EMU is done in the paper.Some tests have been done such as mechanical properties test,microstructure test,thermal performance test,and full scale dynamometer test,the test result shows that the newly developed brake disc of high-speed EMU with high mechanical properties,dense microstructure,mechanical properties of cold and hot line,and good thermal performance and resistance to fatigue,and that the developed brake discs have reached the international level of same performance brake disc,fully meet the basic brake system performance requirements of high-speed EMU.