Fatigue research of metro car body based on operational loads

Purpose–The principle of infinite life design currently directs fatigue resistance strategies for metro car bodies.However,this principle might not fully account for the dynamic influence of operational loads and the inevitable presence of defects.This study aims to integrate methods of service life estimation and residual life assessment,which are based on operational loads,into the existing infinite life verification framework to further ensure the operational safety of subway trains.Design/methodology/approach–Operational loads and fatigue loading spectra were determined through the field test.The material test was conducted to investigate characteristics of the fracture toughness and the crack growth rate.The fatigue strength of the metro car body was first verified using the finite element method and Moore–Kommers–Japer diagrams.The service life was then estimated by applying the Miner rule and high-cycle fatigue curves in a modified form of the Basquin equation.Finally,the residual life was assessed utilizing a fracture assessment diagram and a fitted curve of crack growth rate adhered to the Paris formula.Findings–Neither the maximum utilization factor nor the cumulative damage exceeds the threshold value of 1.0,the metro car body could meet the design life requirement of 30 years or 6.6 million km.However,three out of five fatigue key points were significantly influenced by the operational loads,which indicates that a single fatigue strength verification cannot achieve the infinite life design objective of the metro car body.For a projected design life of 30 years,the tolerance depth is 12.2 mm,which can underscore a relatively robust damage tolerance capability.Originality/value–The influence of operational loads on fatigue life was presented by the discrepancy analysis between fatigue strength verification results and service life estimation results.The fracture properties of butt-welded joints were tested and used for the damage tolerance assessment.The damage tolerance life can be effectively related by a newly developed equation in this study.It can be a valuable tool to provide the theoretical guidance and technical support for the structural improvements and maintenance decisions of the metro car body.

Estimation of speed-related car body acceleration limits with quantile regression

Purpose–This study aimed to facilitate a rapid evaluation of track service status and vehicle ride comfort based on car body acceleration.Consequently,a low-cost,data-driven approach was proposed for analyzing speed-related acceleration limits in metro systems.Design/methodology/approach–A portable sensing terminal was developed to realize easy and efficient detection of car body acceleration.Further,field measurements were performed on a 51.95-km metro line.Data from 272 metro sections were tested as a case study,and a quantile regression method was proposed to fit the control limits of the car body acceleration at different speeds using the measured data.Findings–First,the frequency statistics of the measured data in the speed-acceleration dimension indicated that the car body acceleration was primarily concentrated within the constant speed stage,particularly at speeds of 15.4,18.3,and 20.9 m/s.Second,resampling was performed according to the probability density distribution of car body acceleration for different speed domains to achieve data balance.Finally,combined with the traditional linear relationship between speed and acceleration,the statistical relationships between the speed and car body acceleration under different quantiles were determined.We concluded the lateral/vertical quantiles of 0.8989/0.9895,0.9942/0.997,and 0.9998/0.993 as being excellent,good,and qualified control limits,respectively,for the lateral and vertical acceleration of the car body.In addition,regression lines for the speedrelated acceleration limits at other quantiles(0.5,0.75,2s,and 3s)were obtained.Originality/value–The proposed method is expected to serve as a reference for further studies on speedrelated acceleration limits in rail transit systems.

A strategy for lightweight designing of a railway vehicle car body including composite material and dynamic structural optimization

Rolling stock manufacturers are finding structural solutions to reduce power required by the vehicles,and the lightweight design of the car body represents a possible solution.Optimization processes and innovative materials can be combined in order to achieve this goal.In this framework,we propose the redesign and optimization process of the car body roof for a light rail vehicle,introducing a sandwich structure.Bonded joint was used as a fastening system.The project was carried out on a single car of a modern tram platform.This preliminary numerical work was developed in two main steps:redesign of the car body structure and optimization of the innovated system.Objective of the process was the mass reduction of the whole metallic structure,while the constraint condition was imposed on the first frequency of vibration of the system.The effect of introducing a sandwich panel within the roof assembly was evaluated,focusing on the mechanical and dynamic performances of the whole car body.A mass saving of 63%on the optimized components was achieved,corresponding to a 7.6%if compared to the complete car body shell.In addition,a positive increasing of 17.7%on the first frequency of vibration was observed.Encouraging results have been achieved in terms of weight reduction and mechanical behaviour of the innovated car body.

Correlation between Tibetan and traditional Chinese medicine body constitutions: A cross-sectional study of Tibetan college students in the Tibet Autonomous Region

Objective:To evaluate the correlation between the body constitution types of Tibetan medicine and traditional Chinese medicine (TCM).Methods:The cluster sampling method was employed to recruit participants from a university in the Tibet Autonomous Region.Tibetan medicine and TCM questionnaires were respectively used to assess the participants' constitution information.Descriptive statistics were applied to analyze the baseline and constitution characteristics of the participants.Two-factor correlation analysis and the paired chi-square test were applied to analyze the correlation between Tibetan and TCM constitution types.Results:Data from 466 Tibetan students were analyzed.The mean scores of the rlung,mkhris pa,and bad kan constitution types in Tibetan medicine were 43.2 (11.1),42.1 (10.1),and 45.0 (8.0),respectively;participants with the three-factor convergence body constitution type accounted for 13.7% of the whole population.Among the TCM constitution types,qi stagnation was the most common (21.5%),followed by the balance type (16.5%);the other constitutions detected were qi deficiency,yin deficiency,and yang deficiency.The rate of consistency for the identification of the three-factor convergence constitution in Tibetan medicine and the balance constitution in TCM was 89.1%,with a Kappa coefficient of 0.57 (P >.05).The rlung constitution in Tibetan medicine was associated with the yin deficiency,yang deficiency,and blood stasis constitutions in TCM.The mkhhris pa constitution in Tibetan medicine was associated with the damp heat and yin deficiency constitutions in TCM.The bad kan constitution in Tibetan medicine was associated with the phlegm dampness,qi deficiency,and yin deficiency constitutions in TCM.Conclusion:There is a correlation between the body constitution types of Tibetan medicine and TCM.The reliability and validity of the Questionnaire for TibetanMedicine Constitution requires improvement,and more studies with larger sample sizes and more varied populations are warranted to verify the correlation between Tibetan medicine and TCM constitutions.

Application of Hot Forming High Strength Steel Parts on Car Body in Side Impact

Lightweight structure is an important method to increase vehicle fuel efficiency. High strength steel is applied for replacing mild steel in automotive structures to decrease thickness of parts for lightweight. However, the lightweight structures must show the improved capability for structural rigidity and crash energy absorption. Advanced high strength steels are attractive materials to achieve higher strength for energy absorption and reduce weight of vehicles. Currently, many research works focus on component level axial crash testing and simulation of high strength steels. However, the effects of high strength steel parts to the impact of auto body are not considered. The goal of this research is to study the application of hot forming high strength steel（HFHSS） in order to evaluate the potential using in vehicle design for lightweight and passive safety. The performance of HFHSS is investigated by using both experimental and analytical techniques. In particular, the focus is on HFHSS which may have potential to enhance the passive safety for lightweight auto body. Automotive components made of HFHSS and general high strength steel（GHSS） are considered in this study. The material characterization of HFHSS is carried out through material experiments. The finite element method, in conjunction with the validated model is used to simulate the side impact of a car with GHSS and HFHSS parts according to China New Car Assessment Programme（C-NCAP） crash test. The deformation and acceleration characteristics of car body are analyzed and the injuries of an occupant are calculated. The results from the simulation analyses of HFHSS are compared with those of GHSS. The comparison indicates that the HFHSS parts on car body enhance the passive safety for the lightweight car body in side impact. Parts of HFHSS reduce weight of vehicle through thinner thickness offering higher strength of parts. Passive safety of lightweight car body is improved through reduction of crash deformation on car body by the application of HFHSS parts. The experiments and simulation are conducted to the HFHSS parts on auto body. The results demonstrate the feasibility of the application of HFHSS materials on automotive components for improved capability of passive safety and lightweight.

Design of lightweight magnesium car body structure under crash and vibration constraints

Car body design in view of structural performance and lightweighting is a challenging task due to all the performance targets that must be satisfied such as vehicle safety and ride quality.In this paper,material replacement along with multidisciplinary design optimization strategy is proposed to develop a lightweight car body structure that satisfies the crash and vibration criteria while minimizing weight.Through finite element simulations,full frontal,offset frontal,and side crashes of a full car model are evaluated for peak acceleration,intrusion distance,and the internal energy absorbed by the structural parts.In addition,the first three fundamental natural frequencies are combined with the crash metrics to form the design constraints.The wall thicknesses of twenty-two parts are considered as the design variables.Latin Hypercube Sampling is used to sample the design space,while Radial Basis Function methodology is used to develop surrogate models for the selected crash responses at multiple sites as well as the first three fundamental natural frequencies.A nonlinear surrogate-based optimization problem is formulated for mass minimization under crash and vibration constraints.Using Sequential Quadratic Programming,the design optimization problem is solved with the results verified by finite element simulations.The performance of the optimum design with magnesium parts shows significant weight reduction and better performance compared to the baseline design.

Reliability and validity of the Tibetan medicine constitution scale: a cross-sectional study of the general population in Beijing, China

Background:The constitutional theory is an important aspect of Tibetan medicine,however a quantitative measurement tool for constitution identification still does not exist.The objective of this study is to evaluate the reliability and validity of a Tibetan medicine constitution scale(TMCS)that consists of three sub-scales and 31 items.Methods:From June to July 2019,622 people from the general population in Beijing,China,aged 18 to 60 were investigated.We employed Cronbach’s alpha(α),split-half reliability,and test-retest reliability to determine the reliability of the scale.The content validity and contract validity of the TMCS were evaluated using factor analysis and correlation analysis based on Tibetan medicine theory.The items were screened according to the reliability test results.Results:After the items were screened,22 items remained in the scale.The Cronbach’s alpha value for the internal consistency reliability of the TMCS was 0.754(95%confidence interval(CI):0.700–0.761).The correlation coefficient for the two-week test-retest of the total score was 0.726(95%CI:0.571–0.834).The split-half coefficient was 0.689(95%CI:0.640–0.734).The scale can be explained by eight potential factors,including morphological structure,physiological function,personality,adaptability,etc.The body mass index was negatively correlated with the score of the sub-rlung scale(r=−0.376),slightly positively correlated with the sub-mkhris pa scale(r=0.099),and positively correlated with the sub-bad kan scale(r=0.362).Conclusion:The TMCS is a reliable and valid instrument that can be used to assess the body constitution of the general population in Beijing,China.Future studies are needed to explore the differences in biological characteristics among the constitutional types and the association between constitution and disease.

基于eM-Carbody平台的轿车白车身工艺规划系统

分析了轿车白车身工艺规划的需求特点,提出了基于eM-Carbody平台的白车身工艺规划系统.系统主要由三大部分构成:工艺数据模型、工艺数据模型信息提取模块以及eM-Carbody平台.依据工艺数据模型,建立零件库、资源库、操作库和工艺知识库等工艺数据库,利用工艺数据模型信息提取模块,实现工艺数据模型与eM-Carbody平台的信息互通.应用该系统成功规划了轿车左前门制造工艺,证明这一系统能很好地满足白车身工艺规划的需求.

Compact Car-Body Surface Design with T-spline Surface

Creating proper B-spline surface models is a very challenging task for designers in car-body surface design.Due to the tensor-product structure of B-spline surface,some undesirable issues of the redundant control points addition,incomplete surface definition and the difficulty of trimming boundary alteration frequently occur,when designing the car-body surface with B-spline surfaces in local-feature-lines construction,full-boundary-merging and visual surface trimming.A more efficient approach is proposed to design the car-body surface by replacing B-spline surface with classical T-spline surface.With the local refinability and multilateral definition offered by Tspline surface,those designing issues related with B-spline surface can be overcomed.Finally,modeling examples of the door,hood and rear-window are given to demonstrate the advantage of T-spline surface over B-spline surface in car-body surface design.

Fatigue test loading methodfor wagon body basedon measured load

Purpose–In this paper,the C80 special coal gondola car was taken as the subject,and the load test data of the car body at the center plate,side bearing and coupler measured on the dedicated line were broken down to generate the random load component spectrums of the car body under five working conditions,namely expansion,bouncing,rolling,torsion and pitching according to the typical motion attitude of the car body.Design/methodology/approach–On the basis of processing the measured load data,the random load component spectrums were equivalently converted into sinusoidal load component spectrums for bench test based on the principle of pseudo-damage equivalence of load.Relying on the fatigue and vibration test bench of the whole railway wagon,by taking each sinusoidal load component spectrum as the simulation target,the time waveform replication(TWR)iteration technology was adopted to create the drive signal of each loading actuator required for the fatigue test of car body on the bench,and the drive signal was corrected based on the equivalence principle of measured stress fatigue damage to obtain the fatigue test loads of car body under various typical working conditions.Findings–The fatigue test results on the test bench were substantially close to the measured test results on the line.According to the results,the relative error between the fatigue damage of the car body on the test bench and the measured damage on the line was within the range of
16.03%–27.14%.Originality/value–The bench test results basically reproduced the fatigue damage of the key parts of the car body on the line.

汽车车身造型设计与气动力分析

为研究车身造型对气动力的影响,根据人机工程相关参数,运用Rhino软件的非统一有理B样条(non-uniform rational B-splines, NURBS)建模技术,构建车身外形,并采用计算流体动力学方法对其外流场进行仿真,得到气动力特性。流场中气流始终附着在车身表面没有出现分离,表明车身造型合理,有利于减小气动阻力。针对尾部结构进行曲线再造,改进后的模型的气动阻力明显减小;附加尾翼和鸭尾造型气动升力减小,侧倾力矩减弱,有利于提高汽车对地面的附着力,提高稳定性,更适合于赛车。文中采用的方法可为设计符合汽车空气动力学特性的车身造型方案及风洞试验提供理论参考。

动车组车体模态频率贡献度和改进方法研究

针对高速列车车体低阶模态频率提升过程中,传统灵敏度分析方法存在的设计变量繁多和难以识别出优先改进部件的难题,提出了一种新颖的车体模态频率贡献度评估与结构改进方法。重点分析了铝合金车体板件厚度与模态频率的灵敏度关系,并在此基础上提出了部件模态贡献度概念,推导和建立了描述部件模态频率灵敏度与贡献度的数学模型。通过对动车组车体中各铝型材的贡献度进行计算,详细分析了车顶、侧墙、底架等六大部件对前3阶模态频率的影响。研究揭示,部件模态贡献度表示了局部部件对整体结构模态影响的大小,呈现了灵敏度无法显示的全局量化指标。车顶部件对车体前3阶模态的贡献度最大,侧墙和底架居中,底架边梁、端墙和牵枕缓最小。车顶与侧墙、侧墙与底架连接处的型材对低阶模态产生了显著影响。通过增加内外板厚度并适度降低内部筋板厚度的策略,可提升1阶垂弯模态频率。应用所提出的方法,基于车体54个部件模态贡献度,成功甄别出车顶和连接处型材等优先优化部件并进行了改进,实现了1阶垂弯模态频率从9.5 Hz提升至10.2 Hz,同时将车体重量增加控制在43 kg以内,验证了方法的有效性和高效性,为车体模态频率的优化提供了清晰的路径。该方法具有广泛的适用性,可推广应用于其他领域的结构模态改进。

基于多目标函数的钢轨打磨廓形优选研究

针对CR400BF和CRH5动车组6~8 Hz主频车体抖动问题,从改善轮轨关系角度出发,分别建立车轮踏面和钢轨廓形样本库,通过确定目标函数和设置边界条件求解得到优选钢轨廓形。建立实参数车辆-轨道刚柔耦合动力学模型和轮轨接触弹塑性有限元模型,通过仿真分析对比优选钢轨廓形和60N廓形的等效锥度、动力学指标和轮轨接触应力。按优选钢轨廓形进行钢轨打磨试验,结果表明:优选钢轨廓形与磨耗车轮踏面匹配时轮轨关系改善,等效锥度小于上限值0.4;与不同磨耗车轮踏面匹配时,优选钢轨廓形动力学指标优于60N,且轮轨接触应力和打磨量均更小;按优选钢轨廓形进行钢轨打磨后,CR400BF、CRH5动车组舒适度、平稳性指标分别减小15.7%、13.1%以上,车体振动加速度主频消除。优选钢轨廓形可有效缓解CR400BF和CRH5动车组车体抖动,优选方法和实施流程可为相关问题研究提供参考。

基于不同标准的煤炭漏斗车车体焊缝疲劳寿命研究

利用接触非线性分析技术,基于AAR标准的名义应力法和ASME标准的结构应力法研究煤炭漏斗车车体焊缝的疲劳问题。首先,建立漏斗车重载车体强度分析模型,利用修正D-P本构模型的实体单元模拟散粒煤、接触单元模拟散粒煤与车体结构的作用,并通过主要载荷作用下车体静强度试验结果验证车体仿真分析结果,应力最大误差小于15%。其次,运用名义应力法,在标准和实测载荷谱下分析车体焊缝疲劳寿命,结果表明:端墙与端漏斗板焊缝寿命最短,为2.72×10^(6)km;基于标准纵向载荷谱的焊缝寿命小于基于实测的计算结果,表明标准的纵向载荷谱相对恶劣。最后,在标准中100t漏斗车重车心盘载荷谱和实测纵向载荷谱下运用结构应力法对车体焊缝进行应力与寿命分析。结果表明:基于结构应力法的焊缝疲劳寿命不及基于名义应力法的疲劳寿命,主要原因是结构应力法的疲劳性能参数适用于各类接头形式,且分析承载复杂焊缝时考虑了面内剪切结构应力的影响。因此,对接头几何形状和应力状态复杂的车体从板座及底架区域的焊缝建议采用结构应力法对其进行疲劳寿命分析。

基于天棚-PID算法的履带车体振动控制研究

随着履带式高炮的快速发展,对行进间车体平稳性提出了更高的要求,因此研究在不同路面下如何减小履带车体振动具有重要意义。在对履带车体进行合理简化的基础,建立拉格朗日运动方程,并引入状态方程进行计算。其次,利用Simulink搭建了履带车体模型,分析了车体在B、D、F级路面下以25 km/h速度行驶时的车体振动情况。然后采用PID控制和天棚-PID控制对模型进行优化。仿真结果表明:从B级、D级到F级路面,传统、PID和天棚-PID控制方式下车体振动的平均增幅分别为5倍、4倍和2倍,天棚-PID控制算法的稳定性较好;在相同等级路面时,采用天棚-PID控制的减振效果明显,车体垂向位移和俯仰角的减缓程度比PID控制提升接近40%,车体横滚角的减缓程度比PID控制提升50%以上。因此,采用天棚-PID控制的履带车体在颠簸路面行驶更加平稳。

基于正交试验法的铝合金车体高压水清洗喷嘴结构优化

抑尘剂等复杂的化合物黏着在铝合金车体上,导致车体污染十分严重,高压水射流清洗方法能够有效去除铝合金车辆车体表面黏着的化合物。通过分析圆柱形、锥形、文丘里形和余弦形喷嘴的射流流场分布、射流出口速度、最大壁面静压、相同清洗宽度下压力值范围,得到余弦形喷嘴的清洗性能最佳,锥形喷嘴次之。基于正交试验法设计五因素、四水平正交试验表,得到常用清洗压力下余弦形喷嘴的最优结构参数:进口直径为40 mm、出口直径为20 mm、过渡段半径为40 mm、出射段长度为25 mm、过渡与余弦部分长度比为4。按照最优喷嘴结构参数进行建模,得到三组压力值下高压水出射速度比未优化前提高了2%,且优化效果随着入口压力值的提高而有所下降。在优化后的喷嘴结构参数下进一步计算得出入口压力为10 MPa时,靶距设置为250 mm能达到较好的清洗效果和节能作用。

车身漆面缺陷的自动检测与定位方法

针对目前国内汽车制造业中面漆后车身表面缺陷难以非接触高精度检测,得不到缺陷确切位置等问题,这里提出了一种结合相位测量偏折术与双目测距原理的车身漆面缺陷检测定位方法。首先采用四步相移法提取车身反射图像相位,运用格雷码进行相位解包裹,再通过判断局部相位突变来提取缺陷;建立缺陷池并通过过滤器去除伪缺陷得到真实缺陷;基于双目测距原理,对检测出的缺陷,取其形状中心再得到具体位置坐标。实验结果表明,该缺陷检测方法能够自动,准确,稳定地检测漆面缺陷;双目测距法能准确地得到缺陷的具体位置,可为后续实现自动打磨提供可靠数据来源。

大头金蝇3龄幼虫细菌多样性分析及其分离菌株分解纤维素的应用研究

Illumina高通量测序平台Novaseq,对大头金蝇(Chrysomya megacephala)3龄幼虫体表与体内细菌进行测序分析。大头金蝇3龄幼虫体表与体内贮存细菌样本中共注释396 OTUs,共注释到13门19纲49目82科137属119种细菌。体内贮存细菌的优势菌属为克雷伯氏菌属(Klebsiella,57.87%),通过纤维素筛选培养基培养,纯化后得到单一菌落,经鉴定为密歇根克雷伯氏菌(Klebsiella michiganensis),制成菌液后进行室内、外模拟秸秆分解试验,室内秸秆平均分解效率为87.31%,室外模拟农田中的秸秆平均分解率为88.52%,进一步对其施用于农业废弃物搭建的人工模拟土壤中,模拟土壤肥力增加,在泥土:麦麸:锯末:豆饼的比例为10:2:2:1和10:2.5:2.5:1时种子发芽指数较高,种子平均发芽指数分别达到80.25%和78.45%。结果表明,大头金蝇3龄幼虫体表携带细菌与体内贮存菌的组成结构及多样性复杂,为其分解纤维素能力及土壤改良等提供理论依据。

基于ADAMS/CAR的麦弗逊悬架优化设计

汽车悬架系统为一多体系统,部件之间的运动关系十分复杂,传统的人工计算很难将悬架的各种特性表述清楚。以国产某轿车为例,应用多体运动学与动力学仿真软件ADAMS中的CAR专业模块建立该车的前后悬架多刚体模型,对其悬架的各种性能进行了仿真分析,研究了悬架几何参数对汽车操纵稳定性的影响,在理论验证的基础上揭示了该悬架的运动规律,在进行优化分析的同时还提出了改进的意见。

车体刚强度结构优化对连发武器射击精度的影响

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