[Objective]Given that trams share rights of road with ground vehicles,the frequent occurrence of collisions be-tween ground passenger vehicles and trams necessitates research into tram collision simulation modeling technology and crash-worthiness.[Method]A specific tram model is selected as the research sample.Using a self-developed pre-processing module for collision simulation analysis,a simulation model for tram collisions is constructed.A detailed study is conducted on sce-narios where a passenger vehicle collides with tram suspension module on the side.[Result & Conclusion]The developed pre-processing module for collision simulation analysis enables efficient and convenient construction of tram collision simula-tion analysis models,significantly improving modeling effi-ciency.As the collision speed of passenger vehicle increases and the impact point location elevates,the lateral intrusion a-mount on tram sidewall exhibits an increasing trend.Particular-ly when the impact angle from passenger vehicle ranges be-tween 90° and 120°,the lateral intrusion amount on tram side-wall reaches its maximum.Finally,through optimized design of the sidewall cross-section,specifically by filling hollow are-as with aluminum foam,the maximum lateral intrusion amount on tram side wall after optimization is reduced by 42％,effec-tively enhancing the tram crashworthiness in side-collision sce-narios.

During the process of plastic deformation, the mechanical response of materials is often influenced by stress states and anisotropic effects, and many existing yield functions are difficult to characterize this phenomenon accurately. This article proposes a yield function based on stress invariants that can encompass a variety of existing relevant models and further expand upon them, conducts parameter sensitivity analysis and concavity convex analysis, and analytically calculates the function parameters under four fundamental stress states. The strain-hardening behavior of four metals, AA7075-T6, QP1180, AA5754-O, and DP980, was described using this function. The advantages and disadvantages of parameter analysis calculation and fitting calculation methods were analyzed. On this basis, the nonlinear dependence of the hydrostatic pressure of the function is expanded and used to describe the yield behavior of three metal foams, namely low-density, high-density, and Duocel, and the failure behavior of rock materials. Extend the function to anisotropy using the Balat'91 linear transformation tensor to describe the anisotropic yield behavior of AA2008-T4, using the interpolation method to describe the anisotropic hardening behavior of zirconium plates. The results show that the yield function proposed in this paper can accurately predict the anisotropic yield and hardening behavior of metal materials, foam metal yield behavior, and geotechnical materials' fracture characteristics.

Honeycomb sandwich structure has been widely used in lightweight and impact protection of rail vehicle structures due to its excellent mechanical properties. In this paper, the plastic deformation, failure response and energy absorption characteristics of honeycomb sandwich panels for rail vehicles under repeated impact loads were studied. The three-point bending tests and low-speed impact tests of honeycomb sandwich panels were carried out, and a three-dimensional numerical model considering the detailed structure of the honeycomb core and the failure of the adhesive layer was established. The model can reasonably simulate honeycomb sandwich panels' stiffness, strength, and structural failure. The effects of impact times and impact angle on the performance indexes of the honeycomb sandwich panel were studied. The results show that when the impact energy is the same, the impact times will affect the energy absorption distribution of honeycomb sandwich panels. With the increase in impact times, the panel's absorption energy decreases, the core's absorption energy increases, and the total absorption energy decreases. For multiple impact conditions, with the increase of impact times, the single energy absorption of the upper panel and core decreases, and the single energy absorption of the lower panel increases. When the impact energy is the same, the rise in impact angle will increase the damage to the honeycomb sandwich panel, and the energy absorption of each part will increase. In addition, the influence of impact times on the energy absorption efficiency of honeycomb sandwich panels is related to the impact angle.

Engineering structures and materials will undergo fatigue, aging, and other degradation behaviors during long-term service under the combined influence of complex boundary conditions. These service damages make the materials and structures no longer meet the initial design requirements and pose a potential risk to the service system. This study proposes a material mesoscopic model to decouple the microstructure into a system composed of matrix and void phases. The matrix phase has an invariant constitutive relationship as an ideally undamaged material, and the different evolutionary behaviors of the void phase are described as damage evolution functions and lead to different stress–strain behaviors of the actual material. First, the damage described by different definitions is proposed, and a nonlinear function of damage evolution consistent with the Weibull distribution characteristic of microstructural continuity is derived. Then, an experimental–numerical method is improved to accurately identify the accelerated damage evolution behavior under various strain rates. Finally, the ideally undamaged constitutive of the matrix phase and the damage evolution function of the void phase are established, which can cover the void nucleation, growth, and aggregation process. Besides, the damage sequence interaction model is established in conjunction with the mesoscopic physical mechanism, and the total damage evolution function for materials containing prior service damage in subsequent ductile deformation is achieved by measuring the apparent elastic modulus of the material only. Finally, the ideally undamaged constitutive and damage evolution function are calibrated for aluminum alloy 6005A-T6, commonly used in the car body structure of rail vehicles, and verified with damaged specimens that experienced certain service loads. The material's damage sequence interaction mode is determined, and the rate-dependent residual strength is predicted.

In recent years, the research and development of high-speed trains has advanced rapidly. The main development trends of high-speed trains are higher speeds, lower energy consumption, higher safety, and better environmental protection. The realization of a lightweight high-speed car body is one of the key features in the development trend of high-speed trains. Firstly, the basic dimensions of the car body’s geometric model are determined according to the external dimensions of the body of a CRH EMU, and the specific topology optimization design domain is selected to establish the finite element analysis model; secondly, the strength and modal analyses of the topology optimization design domain are carried out to check the accuracy of the design domain and provide a comparative analysis for subsequent design. Then, the variables, constraints, and objective functions of the topology optimization design are determined to establish the mathematical model of topology optimization, and the design domain is calculated for topology optimization under single and multiple conditions, respectively. Finally, based on the topology optimization calculation results, truss-type reconstruction modeling is carried out for the car body’s side walls, roof, underframe, end walls, and other parts. Compared with the conventional EMU body structure, the weight of the reconstructed body structure is reduced by about 18%. The results of the finite element analysis of the reconstructed car-body structure prove the reliability and safety of the structure, indicating that the reconstructed car-body scheme meets the corresponding performance indicators.

为研究不同结构参数对质量相同、强度不同的两种铝蜂窝夹芯板低速动态冲击响应的影响,建立了铝蜂窝夹芯板受半球型落锤低速冲击的数值模型,并将有限元计算结果与试验结果进行对比,检验了模型的可靠性.在此基础上,对比研究了不同上下铝板厚度和不同蜂窝芯壁厚对两种铝蜂窝夹芯板在低速冲击下吸能效果的影响.结果表明:在质量相同的情况下,强度小、高度大的夹芯板在低速冲击下力-位移曲线更易出现双峰模式,增加蜂窝芯壁厚或是上下铝板厚度都会使第一次的峰值力增加,第二次峰值力降低;强度小、高度大的夹芯板蜂窝芯在低速冲击中吸能占比更多,强度大、高度小的则是上层铝板吸收的能量更多,前者的质量、体积比吸能更高;铝蜂窝夹芯板质量比吸能和体积比吸能与壁厚边长比、板厚芯高比均呈幂次关系.

This study comprehensively analyzes the failure behavior of metro vehicle end structures (VESs) during collisions, using the common material SUS301L-MT in a stainless steel metro and its VES as the research object. First, constitutive and failure tests are performed on the material, the macro–micro characterization of its mechanical properties is performed, and the failure strains and morphologies under various stress states are obtained and discussed. Subsequently, two failure criteria, Von Mises (VM) and Generalized Incremental Stress State Dependent Damage Model (GISSMO), are calibrated and established. Finally, the crashworthiness evaluation indexes of the VES are defined, and vertical offset collisions of metro VESs for different speed levels are numerically analyzed. The results show that the stress triaxiality significantly affects the failure strain of stainless steel SUS301L-MT, with the maximal difference for different stress states reaching 51.10%. SUS301L-MT stainless steel exhibits strain-rate strengthening and yield hysteresis effects. Overall, the numerical results for the VM criterion are worse than for the GISSMO criterion, which more accurately describes the collision behavior of metro VESs under complex stress states.

为更好地表征轨道列车碰撞过程中不锈钢结构的断裂失效行为,开展了常用SUS301L-MT材料的断裂失效行为研究.首先,进行不同应变率下的单轴拉伸试验和不同应力状态下的准静态断裂试验;然后,通过对断裂试验试件的有限元仿真,利用有限元逆向识别优化法进行了损伤起始与演化的参数识别,得到试件的仿真与试验的力-位移曲线均方差最大值为6.947％,断裂处应变误差最大值为9.551％,仿真与试验的断裂形态基本一致;在此基础上,建立SUS301L-MT不锈钢的损伤起始与演化失效模型(Damage initiation and evolution failure model,DIEM),通过试验和仿真分析,验证了 DIEM失效模型的有效性;最后,为解决该模型的单元尺寸依赖性,通过对不同尺寸单元的有限元模型进行分析,提出DIEM失效模型的单元尺寸修正系数.结果表明,建立的失效模型能够准确表征SUS301L-MT不锈钢的失效行为,修正系数的引入可有效改善该失效模型的单元尺寸依赖性.

In order to accurately describe the fracture behaviour of ductile metals in a wide range of stress states, based on the mechanism of void nucleation, growth, and coalescence during plastic deformation, an uncoupled isotropic ductile fracture model was established, which considered the combination of void shape change and void coalescence through internal necking. Firstly, the effect of the volume and shape changes on the fracture behaviour of the material was summarized and discussed, and the mechanism of interpore dimple shrinkage and consolidation during the void coalescence was studied. Secondly, the parameters of the proposed model are studied in detail to verify the flexibility of the new model. Then, the proposed ductile fracture model was used to construct the 3D fracture locus of AA 2024-T351, AISI 1045, Q460, Mg-Al-Zn-RE, and Ti-6Al-4V materials, and the predicted fracture strain values under corresponding stress states were compared with the experimental results of previous scholars. The effectiveness of the proposed new model is verified. Finally, to demonstrate the superiority of the proposed new model, the predicted results were compared with those of the widely used DF2016, MMC, and Hu models. The prediction results show that the new model has the highest precision compared to the other three. The void shape change and the void coalescence through internal necking play an essential role in the ductile metal fracture process, which should be fully considered.

In this study, the competitive failure mechanism of bolt loosening and fatigue is elucidated via competitive failure tests on bolts under composite excitation. Based on the competitive failure mechanism, the mode prediction model and “load ratio—life prediction curve” ( ξ – N curve) of the bolt competitive failure are established. Given the poor correlation of the ξ – N curve, an evaluation model of the bolt competitive failure life is proposed based on Miner’s linear damage accumulation theory. Based on the force analysis of the thread surface and simulation of the bolt connection under composite excitation, a theoretical equation of the bolt competitive failure life is established to validate the model for evaluating the bolt competitive failure life. The results reveal that the proposed model can accurately predict the competitive failure life of bolts under composite excitation, and thereby, it can provide guidance to engineering applications.

With the development of the rail transit industry, more attention has been paid to the passive safety of rail vehicles. Structural damage is one of the main failure behaviors in a rail vehicle collision, but it has been paid little attention to in past research. In this paper, the quasi-static fracture experiments of SUS301L-MT under different stress states were carried out. The mechanical fracture properties of this material were studied, and the corresponding finite element simulation accuracy was improved to guide the design of vehicle crashworthiness. Through the tests, the fracture behavior of materials with wide stress triaxiality was obtained, and each specimen's fracture locations and fracture strains were determined. Parameters of a generalized incremental stress state dependent damage model (GISSMO) of the material were calibrated, and the model's accuracy was verified with test results from a 45° shear specimen. The GISSMO failure model accurately reflected the fracture characteristics of the material. The mesh dependency of this model was modified and discussed. The results show that the simulation agrees well with experimental data for the force-displacement curve after correction, but the strain distribution needs to be further studied and improved.

目的:不锈钢蜂窝具有较大的额定吸能容量,可以作为车辆端部的吸能材料,现已应用于车辆防爬器的吸能区,因此需研究应变率效应对不锈钢蜂窝动态冲击性能的影响.方法:以304不锈钢为基体材料,建立了不锈钢蜂窝异面压缩数值模型.采用两种不同规格的不锈钢蜂窝进行仿真建模,并结合不锈钢蜂窝的准静态压缩试验,验证模型的有效性.基于不锈钢蜂窝有限元模型,分析应变率效应对不锈钢蜂窝结构压溃应力、吸能和不锈钢蜂窝变形模式的影响.结果 及结论:304不锈钢材料具有明显的应变率强化效应;考虑应变率效应的压溃应力-位移曲线较为光滑,与文献中的试验所得的曲线更接近;考虑应变率效应后,不锈钢蜂窝的峰值压溃应力和平均压溃应力明显增大,最大压缩位移和理想吸能效率有所减少;304不锈钢材料的应变率效应会使蜂窝结构形成塑性铰所需的应变增大,进而影响其变形模式.

为提高电力机车被动安全性,提出回退式车钩剪切螺栓设计方法,并对机车端部结构进行耐撞性设计,提高既有机车的耐撞性.首先,对剪切螺栓开展准静态与动态冲击试验,研究剪切螺栓失效的最大剪切力及失效形式;然后,基于试验数据对剪切螺栓用45号钢J-C本构模型参数进行优化,结合数值仿真讨论最大剪切力的参数依赖性;最后,基于数值仿真,验证回退式车钩的功能可行性,同时,基于多级能量吸收的原则,改进既有机车端部结构并对耐撞性指标进行分析.研究结果表明:剪切螺栓可有效应用于回退式车钩,以保证机车碰撞中车钩回退到恰当的位置;基于试验数据优化后的45号钢J-C本构模型能够准确模拟剪切螺栓剪切力及失效形式,剪切力最大相对误差为4.31％;剪切螺栓的最大剪切力与螺栓自身直径无关,与剪切螺栓凹槽横截面面积成正比;随着螺栓凹槽宽度增大,螺栓的最大剪切力减小,螺栓剪切段的塑性逐渐增强;剪切螺栓的回退式车钩在整车仿真中能够实现回退功能,使吸能装置有效发挥吸能作用;改进后的机车相较于既有机车的纵向最大平均加速度减少了2.49g,峰值界面力减少了472 kN,碰撞前后司机室纵向生存空间增加了12.54％.

Derailment accidents caused by coupler buffer devices should not be underestimated. In this study, a particular type of subway was considered the research object, and a nonlinear finite element model of train collisions with a detailed coupler was established to study the collision characteristics of the coupler under different working conditions. First, the nonlinear mechanical characteristics of the coupler were analyzed. Then, a finite element model, including the energy absorption characteristics of the buffer and the collapse tube, the failure characteristics of the overload protection device, and the motion characteristics of the nodding and shaking head, was established and its reliability was verified. On this basis, a collision finite element model of a subway with four sections was developed. The attitude motion of the couplers and its influence on the derailment behavior of the vehicle was studied under the condition of initial vertical deviation or lateral deviation of the active and passive head couplers during their operation period. The results show that when the collision velocities are equal, the initial state of the head coupler barely affects the axial action characteristics and the pitching deflection angle attitude of the middle couplers; however, it has a certain effect on the yaw deflection angle. Furthermore, the initial state of the head coupler has a significant influence on its motion. The initial vertical deviation of the head coupler increases the derailment risk of the second section of the active subway. Moreover, the initial lateral deviation of the head coupler increases the derailment risk of the active subway and the first section of the passive subway. When the utilization rate of the head coupler is approximately 69%, the derailment risk of the vehicle is reduced.

Small specimen test techniques (SSTTs), developed for scarce materials, industrial products, in-service equipment, etc., could be challenging to obtain sufficient materials for routine testing. This review focuses on the research on millimeter- and micron-scale SSTTs of metallic materials in the past decade. Mainstream small specimens are divided into similarity, penetration, and semi-penetration. Representative tests of the above three categories are analyzed in detail, including the small tensile test, small punch test, and indentation test. The macro- or micro-correlation methods of deformation and failure parameters between the SSTTs and conventional tests are discussed, including Young's modulus, yield strength, ultimate tensile strength, damage evolution, fracture strain, and the stress-strain full-history relationships. Meanwhile, the extensive requirements for material testing are also considered, such as anisotropy and strain rate, temperature, and stress triaxiality sensitivities. The characteristics and modification strategies of the SSTTs are described from the aspects of size effects, inhomogeneous structures, and manufacturing defects. Finally, this paper discusses the application of SSTTs in forging, stamping, welding, and additive manufacturing and highlights the potential development directions of SSTTs. [GRAPHICS] .

在常温下对SUS301L-MT不锈钢进行了应变速率为0.0005 s-1的准静态和0.1～500 s-1的动态拉伸试验,基于经典J-C模型拟合得到其应力-应变曲线,通过最大拟合优度和匹配优度确定应变速率敏感系数,对经典J-C本构模型的模拟准确性进行分析;引入动态放大模量确定马氏体相变强化和绝热温升软化的临界应变,对J-C模型进行修正,并对修正模型的拟合结果进行了验证.结果表明:经典J-C本构模型无法准确描述试验钢在高应变速率塑性变形时的马氏体相变强化效应和绝热温升软化效应;修正后的J-C本构模型可准确描述应变速率在0.0005～500 s-1时试验钢的力学行为,其匹配优度高达0.985,表明该模型合理有效.