Modeling and accurately predicting the fatigue life of a typical stainless steel spot welded rail vehicle, with thousands or even tens of thousands of welded joints, are difficult and time consuming using numerical simulation. Comparison between and optimal selection of existing methods for fatigue life prediction of spot welds are required to evaluate their fatigue life. However, evaluating the merits of the existing prediction methods based on appropriate test methods and evaluation criteria is a key issue to be addressed in spot weld fatigue resistance design research. An optimal selection method for predicting the fatigue life of spot welds was proposed. The existing methods were evaluated using two types of specimen models and test data, including tensile-shear and peel. The power function R~2 was applied to quantify the dispersion of the “calculated stress-fatigue failure number” and the error factor was adopted to measure the simulation prediction accuracy. Furthermore, the mesh insensitivity of each method was tested with different mesh sizes of FEA models, and the construction time of a single weld joint was compared with the modeling efficiency. The nominal stress method, RUPP, umbrella and simplified structural stress method were compared according to the proposed method. The results show that the simplified structural stress method has the lowest dispersion, the highest prediction accuracy, and the most efficient modeling, as well as mesh insensitivity. The effectiveness and practicality of the method were verified by simulating a stainless steel body with nearly 30 000 spot welds.

超声波疲劳试验是获得焊接接头超高周疲劳强度的实用方法.?目前还没有有效方法能够预测和评估任意焊接接头形式的超声超高周疲劳寿命.?文中提出了一种超声简谐共振条件下,评估焊接接头疲劳寿命的瞬态结构应力法,以及超声超高周疲劳主S-N曲线拟合方法.?基于已公开的300个焊接接头试验数据,拟合了铝合金焊接接头20?kHz超高周主S-N曲线.?通过共振模型瞬态仿真分析,后雨流计数获得响应等效结构应力谱,与超高周疲劳主S-N曲线预测焊接结构疲劳寿命.?结果表明,结构应力集中系数不会因焊接接头受到振动或外载大小变化而改变;拟合的超高周疲劳主S-N曲线是一条新的m?=?16.5的窄带,将主S-N曲线法理论的适用范围拓展到了超高周区域,可用于任意接头形式的焊接结构件超声振动超高周疲劳寿命预测.

Welded connections are common in rail vehicle structures and associated equipment. It is well known that fatigue behaviors of welded structure are controlled by fatigue capability of welded joints. Although there exists numerous joint design guidance in Codes and Standards as well as best practices, they are largely empirical and difficult to apply in fatigue assessment of complex joints. In this paper, we adopt a mesh-insensitive structural stress method recently stipulated by ASME Code for fatigue evaluation of pressure vessels and piping components. Starting with stress concentration evaluation of two typical, but complex welded connections of relevance to some rail vehicle structures, we examine how the joint design principle inferred from the two examples can be effectively applied to an actual traction motor frame design and its effective fatigue improvement method. The experimental validation process is also presented for the proposed fatigue improvement technique.

某轨道车辆的一个横向减振器座的焊缝在服役过程中出现了疲劳裂纹.?为了找到疲劳开裂的原因,在获得疲劳载荷谱的情况下,分别采用名义应力法、热点应力法以及结构应力法对开裂焊缝进行了疲劳寿命数值仿真计算.?数值仿真计算的结果表明,与名义应力和热点应力法相比较,结构应力法的计算结果最符合实际情况,且在焊缝应力集中的识别能力上,结构应力法也明显优于其它两种方法.?结合具体的工程实例,进一步讨论了3种方法的本质差异,得出在焊接结构抗疲劳设计的过程中,结构应力法最值得在应用中普遍推广.

瞬态疲劳分析比频域疲劳分析更能反映结构动态特性.该方法因轨道车辆有限元模型太大,仿真时间成本过高而难以被大量、广泛应用.提出基于子结构瞬态结构应力的轨道车辆焊接结构疲劳寿命评估方法.基于Guyan缩减理论,提出子结构模态匹配方法确定动态子结构模型,再对动态子结构模型进行刚柔耦合仿真获得载荷历程.对该模型生成的焊缝子结构模型进行瞬态分析,获得等效结构应力响应时程进行焊缝疲劳寿命评估.以某高速列车焊接车体验证,研究结果表明:所提出方法能考虑轨道车辆刚柔耦合模拟和结构的动态振动特性,与传统方法相比,模态分析时间减少到47％,焊缝疲劳寿命评估结果误差不超过2％,但瞬态仿真时间减少95％.该方法还可以运用于其他焊接结构的瞬态仿真疲劳寿命评估.

为解决焊接结构设计中焊接接头质量等级评定的难题,研究了基于BS EN15085标准和结构应力法的质量等级评定方法.通过疲劳损伤等效原则,研究了获取等效计算疲劳应力的方法,进一步得到应力因数,结合安全等级,实现了等幅和随机载荷作用下焊接接头应力等级的确认和质量等级的评定.为了在实际工程中运用该方法,设计开发了一个可视化焊接接头质量等级评定系统.最后,以某铁路货车车体为评估对象,验证了系统有效性与实用性.

针对虚拟仿真中渲染显示大规模三维模型的计算机资源消耗大、刷新率低的难题,提出基于八叉树的PagedLOD大规模三维模型可视化方法,实现了以零件为单元进行大规模模型数据的动态调度.通过以动车组检修大型模型实例作为验证,结果表明了相比于传统的直接渲染方式,此方法在大规模模型场景中能够在保留原装配树结构的前提下,实现模型数据的动态调度,有效地控制内存的占用,提高场景刷新率.

通过对焊接结构疲劳评估标准分析,归纳了疲劳评估标准对焊接残余应力的考虑,阐明了从计算疲劳寿命角度看,残余应力不需要再另外考虑.设计并制作了一批十字接头试件,采用BS 7608:2014+A1:2015标准对疲劳试验数据进行了分析,结果表明,焊后退火前和不同工艺退火后的十字接头试件疲劳寿命没有显著差异.

Selecting fatigue monitoring points for welding structure in a PHM system or a fatigue bench testing for rail vehicles is a complex and difficult problem. In this paper, a method for selecting fatigue monitoring points for welding structure based on structural stress method is proposed. Firstly, static strength method is selected to obtain the weak points of the welded structure. Secondly, the structural stress method with the standard load spectrum and the actual load spectra is used to achieve more fatigue weak points, and the cumulative damage ratio of various weak points are calculated as well. A selecting procedure is then used to determine the ultimate locations of the fatigue monitoring points based on the fatigue weak points above. Finally, a rail vehicle is taken as an example to verify the method. The result shows that the position of the fatigue monitoring points for the complex welded structure of rail vehicle can be obtained effectively by the method.

为解决目前结构应力法疲劳评估软件不具备三维可视化能力,难以满足大型复杂焊接结构快速抗疲劳设计要求的问题,基于结构应力法和三维可视化方法开发了铁路货车焊缝疲劳寿命评估及可视化系统.提出了重构可视化网格模型装配树、有限元数据绘制单元网格模型等方法构建可视化网格模型,采用结构应力法评估焊缝疲劳寿命,并在可视化网格模型上以彩色云图形式绘制疲劳结果.最后以某铁路货车车体焊缝的疲劳寿命评估作为实例,证明了系统的高效性和实用性.

A finite element model of the double-wall acoustic insulation structure with a air layer and an acoustic absorbent layer made of the poroelastic materials is set up, the responses of this acoustic-vibration system are calculated by using of the direct finite element method when having a diffuse incident acoustic field acting on the incident surface, the radiant acoustic power from the another surface are achieved, then the Transmission Loss(TL) are formulated using the incident acoustic power and the radiant acoustic power. The effects of the thicknesses, elastic modulus, flow resistivity and viscous lengths of the poroelastic materials on TL are analyzed. The results show that the thicknesses and elastic modulus have a significant effects on TL, TL are enhanced with the thicknesses increasing of the poroelastic materials layers, a 4.9dB addition of TL is achieved when thickness is added from 2cm to 3cm; TL are enhanced with the reduction of the elastic modulus in considered frequency range, and TL are reduced with the declining of viscous lengths and with the addition of the flow resistivity when the frequencies are higher than 600Hz.

基于矩形简支薄板模态频率的理论解,推导了模态频率对薄板厚度灵敏度理论解,通过实例计算了矩形简支薄板前10阶模态频率及灵敏度,并计算分析了厚度增加单位值时模态频率灵敏度理论差分解;建立了矩形薄板的有限单元模型,用有限单元法计算了矩形简支薄板的模态频率和振型,分析比较了有限单元数量对模态计算精度的影响;基于有限单元法,用数值微分法计算了薄板模态频率对板厚度的灵敏度,并计算分析了基于有限单元法的模态频率灵敏度差分解.理论推导和计算结果表明,简支矩形薄板模态频率对板厚度灵敏度的理论解与厚度无关,数值微分模态频率灵敏度与理论解的误差最小,其精度高于理论差分解和有限元差分解,证明了数值微分法模态频率灵敏度的准确性和有效性.

Stress distribution characteristics of welded joints of aluminum alloy car body are studied.The finite element model of aluminum alloy EMU body is established,including the structure of welds.Then,the distribu-ted regulation of typical welded joint stress along the length of the weld is analyzed under loads provided by EN 12663-1:2010.The result shows that the stress concentration occurs in lap weld of the floor of under-frame and the side beam of under-frame,which is located near the area of door and cabin.Attention should be paid to these areas when the fatigue strength of car body welded joints is improved by grinding.

Since the stress concentration on the fillet weld of the welded frame for high-speed EMU cannot be identified by nominal stress method,based on structural stress method,the nonlinear stress at weld toe is first decomposed into two parts,including structural stress in external load equilibrium and notch stress in self-equilibrating.Then,according to the equilibrium equation of the force,the corresponding relationships between nodal forces and moments,and line forces and moments are calculated.The calculation formula of structural stress is further derived and the identification process of stress concentration on fillet weld is given.On the basis of the proposed formula and identification process,a special software WSS for stress identification in welded structure is developed with APDL language provided by C/C + + and ANSYS software.The stress concentration on the fillet weld of the welded frame for a high speed EMU is identified.It is verified that the identification method based on structural stress not only can identify the specific position of stress concentration,but also can calculate the specific stress peak and corresponding fatigue life.It can be used to optimize the anti-fatigue design of the welded frame for high speed EMU.

The structure sensitivities of car body can provide the modification information and they are important contents of structure design.This research focus on a car body of double layer EMU,its finite element model is established by using of Hypermesh software,the modal,stress and deformation are calculated by using of the finite element method.Then the plate thicknesses are used as the design variables,the sensitivities of the modal frequencies,stresses and deformations with respect to the design variables are achieved by using of the numerical differential method.The results show that the modal frequency sensitivities with respect to bottom plate,side wall and top plate are relative high positive values,and these with respect to end wall and traction pillow are the negative values;the sensitivities of maximal deformation of bottom plate center with respect to bottom plates,top plate and side wall are relatively large,and these values are all negative;the stress sensitivities of key positions are all negative.Based on this research,the main factors influencing the car body performance are revealed,the improving methods of car body performance are achieved.Based on the structure sensitivities of car body,the car body is modified and a mass reduction of 410 kg is achieved,while the lowest modal frequency is increased and the stress and deformation satisfied the design requirements.

A lightweight optimisation model with static strength and weld fatigue constraints is constructed for the welded frame of a three-axle bogie, and it is solved by an adaptive sequential approximation optimisation (SAO) method based on kriging models. To improve the accuracy of approximate functions on the basis of a small sample set, seven kriging models are used to construct the relationships between weld fatigue damage and plate thickness. The Master S-N Curve Approach is adopted for weld fatigue assessment considering its mesh-insensitivity and reliability. The weight of the bogie frame is reduced by 9.2% after optimisation. The optimisation results give a recommended design for the welded bogie frame and demonstrate the validity of the proposed optimisation method. The robustness analysis results for the recommended engineering design shows that the weld fatigue failure will not happen when the deviations of variables are considered.

With the increasing speed of railway vehicle in China, the problem of fatigue failure in welded structures is becoming more and more serious. Because the frequency range of the external excitation load is wider, the structures are more likely to yield modal vibration, which will accelerates fatigue failure process of welded structures. Therefore, how to make it possible to take the effects of load frequency distribution on fatigue life into consideration when evaluating welded structures is a subject worth studying. Firstly, a new fatigue life prediction method of welded structures is proposed in this paper by the combination of the random vibration theory and the Structural Stress Method in ASME 2007 standard which is the most reliable fatigue life prediction method of welded structures so far. Fatigue life of welded structures can be calculated under frequency domain in this new method which is called Frequency Domain Structural Stress Method. Then, a random vibration fatigue evaluation system of railway vehicle welded structures based on this new method was built through C++ language with the cooperation of commercial software. This system make it possible to predict the fatigue life of welded structures at the product design stage of railway vehicle under random loads from measured or standards(can be force, displacement, velocity and acceleration data). An engineering application case of this system on the random vibration fatigue assessment of a car body lifting structure in an urban railway vehicle was carried out to verify the effectiveness of this system. This system can not only be used in the railway industry, but also in other industries.

Brake squeal is a result of a unstable flutter from brake system, it results to the noise pollution in railway side and excessive wear of wheel tread. A finite element model of brake system for rail freight vehicle is set up, the contact and friction between the brake shoe and wheel tread is considered, the complex modals of brake system are calculated, the possibility of happening chatter and squeal noise are analyzed. The results show that the pressure angle or the brake force direction have a important influence on the unstable chatter and squeal noise, the more greater the pressure angle deviates from the wheel center, the more greater the possibility of happening chatter and squeal noise is, and the possibility of happening chatter and squeal noise is also increased along with the addition of friction factor.

针对改进型660 M W发电机定子机座结构特征,进行了包括承载形式、限界特征和连接工具在内的运输承载结构设计研究.借助于有限元分析,完成了结构优化设计.运输过程实时监控数据表明,改进设计达到预期目标.

In order to solve the problem that the current efficiency of fatigue data management of wagon welded joints is too slow to meet the demand of rapid fatigue design, a 3D visualization system which integrates the virtual model, the fatigue calculation method for weld joints and weld joints fatigue assessment data from virtual and real fatigue test is studied and developed.For the system, an assembly tree structure based on Scene Graph for a CAD/CAE visual model, a weld joint-object-oriented visualization method and a data mutual-mapping technique based on MVC model are proposed.In addition, the equivalent stress amplitude calculation algorithm was integrated to the system and the weld joints fatigue data of master S-N curve method.The IIW nominal stress method and the equivalent stress amplitude method is mapping to the weld joints model with the methods above.Finally, a welded joints fatigue design of the C70E wagon car body is taken as an example was used to prove the validity and usefulness of the software system.