This study investigates the effect of cross braces on the lateral stability and curve passability of heavy haul freight wagons. A vehicle kinetic model of a heavy haul freight wagon was established based on the vehicle-track coupling kinetic theory. The dynamic performance of empty and heavy freight wagons in a straight line section and a curve section with or without cross braces was simulated and analysed. The running stability, acceleration, safety, and wear indexes were analysed. The results demonstrate that the utilisation of cross braces has a considerable impact on enhancing the bogie's stability and the vehicle's critical speed. With cross braces, the vehicle can meet operational requirements at speeds of up to 120 km/h, compared to 70 km/h without them. Nonetheless, it is recommended to install cross braces to minimize wear and tear. The general trend in straight and curved section operation is that the presence or absence of cross braces has a minimal effect on acceleration and stability. Without cross braces, the wheelset lateral force increases, the attack angle of the wheelset decreases, and the wear index increases. Conversely, the use of cross braces can reduce wheel wear.

A dynamic model was developed to assess the impact of cross braces on the lateral stability and curve navigability of heavy haul freight wagons. Simulations evaluated the dynamic performance of empty and loaded wagons under varying cross-brace anti-warp stiffness. The study focused on stability, ride quality during straight-line travel and safety indices across different curve radii. The results show that cross braces significantly enhance vehicle nonlinear critical speed. In straight-line sections, variations in anti-warp stiffness have a minimal impact on vertical ride quality but improve lateral ride quality. In curved sections, stiffness changes have little impact on derailment coefficient, wheel load reduction rate and attack angle but notably affect wheelset lateral force and wear index. Safety and ride quality indices decrease with increasing vehicle speed, while the impact on vertical indices remains minimal. As the curve radius increases, safety indices decrease. Significant changes in attack angle and derailment coefficient are observed when the curve radius shifts from R400 to R600. The study confirms that larger bolt preloads increase anti-warp stiffness while larger mounting angles decrease it. Selecting the appropriate bolt preload and cross-brace angle is crucial for optimising performance and safety in vehicle engineering applications.

This paper presents an innovative method for determining the fatigue life of railway bogie frames with track irregularities and wheel polygonal wear. This method was employed to predict wheel polygon limits to protect against bogie frame fatigue. Firstly, a comprehensive coupled vehicle-track system dynamic model was established. The developed model was validated by comparing the numerical results with field test data. Secondly, the dynamic stress characteristic of the bogie frame with different excitation forms were investigated. A methodology was proposed to compile the stress spectra of bogie frame by considering the influence of the wheel polygonal wear. This approach enabled the construction of comprehensive stress spectra by considering influences arising from both track irregularities and wheel polygonal wear. Subsequently, the stress spectra of the concerned positions on the bogie frame were developed and further used to study the influence of wheel polygonal wear amplitude on the fatigue life of the bogie frame. This facilitated the development of the maintenance limit of wheel polygonal wear from fatigue life perspective. The results suggest that the maintenance limit of wheel polygonal wear should not exceed 0.034 mm in the presence of a 24th-order wheel polygon for a typical high-speed train.

This paper establishes a vehicle-track coupled dynamics model using component force elements (CMP) to analyse the rigid-flexible coupling dynamics of heavy haul freight wagon cross braces, focusing on straight-line running quality, curve negotiation stability, and vibration characteristics. Through systematic simulations of empty and loaded wagon conditions with varying anti-warp stiffness configurations, the research evaluates critical performance metrics, including Sperling ride indices, acceleration profiles, and safety indicators across different curve radii. The analysis at two speeds (60 and 120 km/h) characterises vibration displacement/acceleration patterns at key cross braces locations (endpoints and centre of gravity), with particular emphasis on frequency-domain characteristics and potential resonance phenomena. The results indicate that the flexible cross brace configuration yields nonlinear critical speeds and straight-line stability indices comparable to those of its rigid counterpart. Vibration characteristics demonstrate consistent frequency patterns across different operational conditions. Notably, the dominant lateral Y-direction vibration frequencies approach natural modal frequencies, suggesting potential resonance risks requiring monitoring, though no active resonance was observed. Vertical (Z-direction) vibrations exhibit heightened response amplitudes without triggering modal frequency resonance. The distinct vertical oscillations of the flexible cross braces' centre of gravity are attributed to elastic deformation under dynamic loading.

The bogie frame is a critical load-bearing component, and its failure can significantly impact operational safety. In this paper, a field test was conducted to investigate the primary factors causing the fatigue failure of a metro bogie frame. Subsequently, a random vibration model was developed based on the principle of pseudo excitation, so as to reproduce the high-frequency vibration and dynamic stress of bogie frame considering the service conditions. This model was further employed to assess the effectiveness of rail grinding in extending the fatigue life of the bogie frame and to support the design of an optimized bogie frame with enhanced fatigue resistance in the presence of rail corrugation. The results revealed that rail corrugation is the primary cause of high-frequency vibration in the bogie frame, ultimately leading to fatigue failure. Fatigue damage occurring on small-radius curves (R <= 500 m) accounted for 85 % of the total fatigue damage. Additionally, dynamic analysis results demonstrated that rail grinding effectively reduced vibration levels by 83 % and stress levels by 81 %. Therefore, rail grinding is recommended for small-radius curve sections to mitigate rail corrugation-induced high-frequency vibrations. The newly designed bogie frame exhibited significantly improved fatigue resistance under service conditions, as validated through the proposed random vibration model.

The stress intensity factor is essential to determine the residual fatigue lifetime of cracked components. However, the traditional method used to determine the stress intensity factor is very difficult to characterize the dynamic behaviors of structure arising from the fatigue crack. This paper proposed a methodology to determine the dynamic stress intensity factor (DSIF) of a crack incorporating with the rigid-flexible coupled dynamics. Firstly, a rigid-flexible coupled dynamic model of cantilever beam representing the typical structure of bogie frame with a straight crack was developed based on SIMPACK platform. In the model, the equivalent spring - contact element was employed to model the contact behaviors of crack interface. Subsequently, the DSIF considering the crack closure effect was calculated by the node displacement extrapolation. The validity of proposed method was demonstrated through comparing the DSIF with those obtained by other analytical methods. The results suggest that the proposed methodology can characterize the closure effect of crack, and yield more accurate estimation for the DSIF. This method establishes a link between the multibody system dynamics and the fracture mechanics, which enable us to calculate the DSIF of crack under the operating condition using a rigid-flexible coupled dynamic model.

To study the tread surface hardness difference that caused by wheel diameter difference of wheelsets, an investigation on corresponding factors of wheelset hardness was done. A group of data including wear rate, wheel diameter, wheel rim hardness and tread hardness was collected to serve as the dataset for neural network. Improved extreme learning machine (ELM) based on particle swarm optimization (PSO) algorithm was chosen to be the main method, trained by dataset and used to predict the tread surface hardness difference. The result shows that PSO-ELM is able to describe the changing trend of tread surface hardness difference, and reaches the best correlation level compared to the original ELM and BP network. Finally, the trained network was applied to analyze the relation between tread surface hardness difference, revealing that the rolled steel is a less sensitive material than the casted steel when meeting hardness or diameter difference.

Potential manufacturing defects and dynamic loads in the service could introduce cracks in the bogie frame. These cracks, in turn, can vary the stiffness matrix of system, thereby the variations in dynamic behaviors of bogie frame. This study thus investigated dynamic behaviors of a bogie frame in the presence of fatigue crack through a field test and a numerical model. In the test, the axle box vibrations were measured, which serves as the excitation of the numerical model of bogie frame. Subsequently, a rigid/flexible coupled dynamic model of vehicle was developed, considering the flexibility of bogie frame. A methodology, based on the equivalent spring and contact elements, was developed to model fatigue cracks in the dynamic model. This enables us to simulate coupling behaviors between the vibration and the crack propagation. Upon the proposed model, the evolution of dynamic behaviors of bogie frame considering the crack propagation process was studied under the services loading. The results show that the cracks significantly alter the vibration behavior of the bogie frame, leading to a noticeable response in the high-frequency components. This facilitates further research on crack damage detection and localization. The dynamic stress intensity factor (DSIF) obtained through displacement extrapolation method accurately describes the dynamic propagation behavior of crack tips. This helps us understand the crack propagation models better, thereby the estimation of residual fatigue life of bogie frame.

This study investigates the rare-event system reliability analysis with numerous failure regions. A novel method, based on the parallel tempering (PT) and importance sampling (IS) technique, is proposed. Surrogate models (kriging model) are built for the true performance function and a probabilistic classification function is derived to predict the failure regions. The PT algorithm is used to obtain points populating all of the predicted failure regions. Representative points are identified using the k-weighted-means clustering method. A Gaussian mixture model is formulated by the representative points and importance samples are simulated accordingly. The optimal training points are selected to update all surrogate models. In the framework of IS, the terminating criterion for assessing the estimation error of the system failure probability is devised. The learning process is terminated at the appropriate stage. The method is termed active learning kriging-parallel tempering-importance sampling (ALK-PT-IS). Four numerical examples illustrate the effectiveness and precision of this method.

Operational transfer path analysis (OTPA) is an advanced vibration and noise transfer path identification and contribution evaluation method. However, the application of OTPA to rail transit vehicles considers only the excitation amplitude and ignores the influence of the excitation phase. This study considers the influence of the excitation amplitude and phase, and analyzes the contribution of the secondary suspension path to the floor vibration when the metro vehicle runs at 60 km/h, using an analysis based on the OTPA method. The results show that the vertical direction of the anti-rolling torsion bar area provides the maximum contribution to the floor vibration, with a contribution of 22.1%, followed by the longitudinal vibration of the air spring area, with a contribution of 17.1%. Based on the contribution analysis, a transfer path optimization scheme is proposed, which may provide a reference for the optimization of the transfer path of metro vehicles in the future.

在实际的裂纹扩展仿真分析中需要确定三个主要参数,包括局部裂纹扭转角度、局部裂纹扩展增量以及扩展后裂纹尖端的拟合外伸,而对于裂纹扩展增量往往根据计算结果精度的需求来确定其大小,忽略了裂纹扩展增量对裂纹扩展稳定性的影响.针对这一问题,利用FRANC3D和Abaqus软件联合仿真分析计算了Q235钢CT试样在不同裂纹扩展增量情况下的裂纹扩展特点,并根据裂纹尖端应力强度因子的分布情况得出两点结论:(1)裂纹两端接近结构自由表面,两端趋向于平面应力状态,中间内部裂纹处于平面应变状态,导致应力强度因子SIF呈现中间大、两端小的对称分布,使得在较大裂纹扩展增量的情况下裂纹中部与两端的扩展值差异较大,最终导致裂纹凸凹扩展甚至失稳;(2)在进行裂纹扩展分析时,为保证计算精度和节约计算时间,并且保证裂纹扩展的稳定性,裂纹扩展增量选取为当前裂纹尖端单元特征尺寸的15％～30％比较合适.

针对地铁转向架的焊接构架疲劳强度评估问题,以某城市地铁的转向架构架为原型,对比分析了两种疲劳强度评估方法.采用ERRI B 12/RP 17报告中提出的疲劳强度校核方法计算相关应力,基于DVS 1612标准修正Haigh图中的许用应力幅,再利用修正的Haigh图对构架焊缝进行疲劳强度校核.同时,根据Miner线性累积损伤理论,结合BS 7608标准,对构架焊缝进行线性累积损伤计算.累积损伤值计算结果与疲劳强度校核结果基本一致,均显示在横梁与侧梁连接处疲劳线性累积损伤值最大.对于中、低缺口效应的对接和搭接焊缝,基于无限寿命设计的疲劳强度评估方法偏保守,而对于高缺口效应的角接焊缝,基于BS 7608标准的疲劳强度评估方法偏保守.建议在实践中先对整体焊缝结构进行基于无限寿命设计的疲劳强度评估,再对高缺口效应的焊缝进行基于BS 7608标准的疲劳强度评估.

针对铁道车辆CAE分析中前处理工作量大、软件操作界面不友好以及分析人员存在客观水平差异等问题,设计了适用于铁道车辆排障器的流程化分析系统.首先研究了流程化分析系统所需关键技术,并基于Tcl语言开发出能够识别铁道车辆排障器焊接结构板厚和焊接接头位置的信息模块,最终借助HWTK GUI Toolkit等开发工具基于HyperMesh软件平台设计出CAE流程化分析系统,并通过实例进行验证.结果表明:该系统不仅具有标准化分析流程,且可以大幅度提高工作效率、降低出错概率、缩短排障器研发周期.

为解决气液环簧组合式缓冲器呈现非对称拉压动态特性问题,构建了气液环簧组合式缓冲器动力学模型,基于MATLAB/Simulink软件编制了考虑不同吸能元件特性的车辆冲击动力学模型程序,研究了两辆单车冲击及两列动车组冲击的动态特性.研究结果表明:组合式缓冲器动力学模型既能有效地模拟拉伸状态下环簧缓冲器的线性加载特性,又能较好地模拟压缩状态下气液缓冲器随冲击速度变化的非线性加载动态特性,即组合式缓冲器动力学模型体现了明显的非对称拉压特性;低速与中高速冲击过程中,组合式缓冲器动力学模型及车辆冲击模型可依次完整有效地模拟缓冲器-压溃管-防爬器-车体结构变形产生的缓冲吸能动态过程及磁滞拉压特性曲线;列车冲击速度为5 km·h-1时,最大车钩力及组合式缓冲器最大行程均小于缓冲器阻抗力和行程限值,其压缩加载特性曲线仅呈现出气液缓冲器的加载特性;冲击速度为20 km·h-1时,最大车钩力为2900 kN,最大行程为534 mm,防爬器已经触发,其压缩加载特性曲线呈现出了气液缓冲器-压溃管-防爬器组成的连续力学特性,此时车体结构未发生破坏;冲击速度达到25～30 km·h-1时,列车开始发生结构破坏,车钩力陡升;全自动车钩与半永久车钩参数选型能够满足冲击速度20 km·h-1以内的列车车体结构安全性.

A novel method is proposed, which aims to solve rare‐event hybrid reliability problems with random and interval variables, where the performance function has various failure zones. It combines the active learning Kriging (ALK) model with importance sampling (IS) and evolutionary multimodal‐based multiobjective optimization (EMO‐MMO). The surrogate limit state surfaces (LSS) for the upper and lower failure probability bounds are respectively defined considering the Kriging variance. Failure candidate solutions located in different failure regions are generated by the EMO‐MMO method. Subsequently, all the most probable failure points (MPPs) are identified from those candidate solutions. The IS samples are simulated around the MPPs using the MPP‐based IS method. The IS samples located in unimportant regions are removed in order to improve the efficiency of approximating the surrogate LSSs. The optimal training points are selected from the truncated IS samples to update the Kriging model. After several training iterations, the surrogate LSSs are convergent. Ultimately, a reliable and unbiased estimation of the upper and lower failure probability bounds is provided. The performance of the ALK‐EMO‐IS‐HRA approach is verified through five application examples.

System reliability analysis with small failure probability is investigated in this paper. Because multiple failure modes exist, the system performance function has multiple failure regions and multiple most probable points (MPPs). This paper reports an innovative method combining active learning Kriging (ALK) model with multimodal adaptive important sampling (MAIS). In each iteration of the proposed method, MPPs on a so-called surrogate limit state surface (LSS) of the system are explored, important samples are generated, optimal training points are chosen, the Kriging models are updated, and the surrogate LSS is refined. After several iterations, the surrogate LSS will converge to the true LSS. A recently proposed evolutionary multimodal optimization algorithm is adapted to obtain all the potential MPPs on the surrogate LSS, and a filtering technique is introduced to exclude improper solutions. In this way, the unbiasedness of our method is guaranteed. To avoid approximating the unimportant components, the training points are only chosen from the important samples located in the truncated candidate region (TCR). The proposed method is termed as ALK-MAIS-TCR. The accuracy and efficiency of ALK-MAIS-TCR are demonstrated by four complicated case studies.

Reduction stress concentration effect of structure, changing the structure geometry and reducing the geometry of structure are effective methods to realize the lightweight and improve the endurance strength of welded bogie frame. Taking a bogie frame structure as an example, based on the structural fatigue strength evaluation method of DVS 1612 standard and the specified welding joint quality level, the local welding joint optimization and the local structure shape optimization were carried out in the area of high stress concentration effect of the structure, and the availability of the welded joint located in the area between anti-roll bar mounting block and side frame cover plate had dropped from 1.773 to 0.704/0.871 . At the same time, the thickness of the lower cover plate of the side beam, the inner and outer vertical plates of the auxiliary longitudinal beam and the wall thickness of the steel tube of the transverse beam were reduced. On the premise of meeting the fatigue strength, the goal of lightweight and local structure optimization of the frame was realized.

Based on the structural geometric characteristics of the S-type web wheel of the rail vehicle, two interactive parameterized model dialogs of the S-type web wheel were designed by using AutoLISP and DCL language on the AutoCAD platform under its secondary development environment. The two-dimensional cross-section of the S-type web wheel could be automatically generated in the process of optimizing the geometry of the S-type web wheel. The work of repeatedly drawing the two-dimensional CAD drawing of the cross-section was avoided when the structure of the wheel was changed which improved the efficiency of drawing the S-type web wheel and provided the basic geometric model for the three-dimensional modeling of the wheel structure and the FE stress analysis of the structure.

The existing calculation method is cumbersome for the weight calculation of long-term group of suspended-modular tram. In order to study the new method of weight distribution calculation, the 7-module 100% low floor trams were taken as the research object. Based on the articulated structure between adjacent vehicles of floating type trams and the statically indeterminate theory, the tram body and its installation equipment were simplified as rigid bodies, and by adopting the virtual displacement principle, the static balance equation of the rigid system was derived, and the stress state of different vehicle bodies was analyzed with the deformation coordination principle, and the axle load and wheel weight of the vehicle are calculated. A computer program was written to parameterize the method, and the calculation results were compared with the finite element method. The results showed that the calculation method was reasonable and effective, and could be applied to the weight management of 100% low floor tram design process.

为了研究地铁列车车钩的分级吸能特性,在Matlab 中建立车钩力元的Simulink模型,模拟车钩的分级吸能特性,导入UM多体动力学软件,建立了单自由度六编组车辆冲击动力学模型.参考EN 15227-2011《铁道车辆车体的耐碰撞性要求》标准[1]和相关技术条件要求,在UM中分别模拟8 km/h、15 km/h和25 km/h三种地铁列车连挂碰撞场景.计算结果表明:8 km/h调车冲击工况,碰撞界面处最大冲击力为625.50kN,车钩缓冲器行程为131.52mm;15 km/h轻度冲击工况及25 km/h中度冲击工况,碰撞界面最大冲击力均达到压溃管及剪切装置的标定值,其行程分别为289.21 mm、951.30mm,满足连挂碰撞要求,且最大冲击力及行程都在相应吸能结构的阈值范围内,验证了车钩力元Simulink模型的正确性.