Fatigue damage analysis of epoxy asphalt pavement for steel bridges considering coupled effects of heavy load and temperature variations

To investigate the fatigue damage of epoxy asphalt pavement(EAP)under a heavy load and a d temperature load,the load-figure of the heavy load on the steel bridge deck pavement(SBDP)was simulated first,and the temperature distribution of SBDP during the temperature-fall period in winter was also calculated.Secondly,t e moving heavy load coupled W t the most unfavorable temperatre load was applied to the SBDP,and the tensile stress on the top of SBDP was calculated.Finally,the fatigue damage of EAP was evaluated considering the extreme situation of heavily overloaded and severe environments.The results show that botte heavy load and the temperature load during t e temperature-fall period c n increase the tensile stress on the top of SBDP significantly.In the exteme situation of heavily overloaded and severe environments,a fatigue crack is easily generated,and thus the SBDP should avoid t e coupling effects of the heavy loadand the temperature load in winter.

Influence of Thermal Load on Mechanical Property of Cemented Carbide Material and Heavy Cemented Carbide Inserts Life

A large amount of cutting heat is produced during the heavy cutting process,and insert life is restricted by the effect of thermal load.The thermal load experiment of cemented carbide SCS,WF and YT15 is carried out,and the results show that the bending strength and fracture toughness of cemented carbide material decrease obviously under cyclic thermal load,while in the cooling process,the material mechanical property changes worse suddenly.The high-temperature mechanical property of SCS is the most stable,and that of YT15 is the worst.Further,a relation model among cutting temperature,cutting parameters and insert life is established.Finally,the measures to improve heavy cemented carbide inserts life are summarized from the aspects of cutting parameters selection,insert optimization design and TiCN,Al2O3,TiN complex insert coating.The research results are expected to provide support and reference for heavy cutting technology and insert technology.

Effect of heavy load carriage on cardiorespiratory responses with varying gradients and modes of carriage

Background: The present study was undertaken to determine the effect of different uphill and downhill gradients on cardiorespiratory and metabolic responses of soldiers while carrying heavy military loads in two different modes.Methods: Eight physically fit male soldiers with a mean age 32.0±2.0 years, a mean height of 169.5±4.9 cm, and a mean weight of 63.8±8.4 kg volunteered for this study. Each volunteer completed treadmill walking trials at a speed of 3.5 km/h while carrying no external load, 31.4 kg load in a distributed mode(existing load carriage ensembles) and compact mode(new back pack) over 5 different downhill and uphill gradients(–5%, –10%, 0%, 5%, 10%) for 6 min at each gradient. During the walking trials, heart rate(HR), oxygen uptake(VO_2), respiratory frequency(RF) and energy expenditure(EE) were determined by the process of breath-by-breath gas analysis using a K4 b2 system. The average of the last 2 min data from each 6 min walking trial for each individual was subjected to statistical analysis.Results: All parameters(HR, VO_2, RF, and EE) gradually increased with the change in gradient from downhill to level to uphill. The distributed mode showed higher values compared to compact mode for all gradients, e.g., for VO_2, there was a 10.7, 7.4, 5.1, 28.2 and 18.7% increase in the distributed mode across the 5 different gradients.Conclusions: It can be concluded from the present study that the compact mode of load carriage is more beneficial than the distributed mode in terms of cardiorespiratory responses while walking on downhill and uphill surfaces with a 31.4 kg load.

SYNCHRONOUS EFFECT OF SLIPPING HEAVY LOADS ON RO-RO SHIP ROLLING IN WAVES

Common effect of wave and slip of internal vehicles will make rolling of the roll-on ship serious. This is one of the important reasons for overturn of ro-ro ships. The multibody system with a floating base is composed of ro-ro ship and slipping vehicles. Takes the rolling angle of the ship and the transverse displacements of the slipping vehicles on desk as freedoms. Making use of the analysis of apparent gravitation and apparent buoyancy, the wave rolling moment is derived. By means of dynamic method of multibody system, dynamic equations of the system are established. Taking a certain channel ferry as an example, a set of numerical calculation have been carried out for rolling response of the multibody system with a floating base of a ro-ro ship and displacements response of the slipping vehicles under common effect of free slipping vehicles and wave, and a conclusion has been drawn that the motion of the numerous free slipping heavy loads will trend to be synchronous under restraining of the side-wall bulkhead with time because of repeated collision.

Cost Impact of Increasing Heavy Vehicle Loads on Bridges

This study aimed to investigate the cost impact of meeting the increase in freight demand by doubling the truck weight （AS 1 ）, doubling the traffic volume （AS2）, or legalizing a new-proposed-truck of 97-kip weight instead of the currently legal 80-kip truck （AS3）. The State of Michigan＇s average daily traffic database of year 2001 has been used as a case study. The study was applied only on the very common US Bridge with RC （reinforced concrete） deck over steel girder. Sampling criteria also includes the age of the bridges. The study covered the four-cost-impact categories provided by the NCHRP （National Cooperative Research Program）. The current truck weight and double traffic volume （AS2） show the best scenario to meet the increase in freight demand. However, doubling the truck weight with the current traffic volume （AS 1） was the worst scenario. The use of the proposed 97-kip truck with the current traffic volume （AS3） compromises both, meeting the increase in freight demand and the cost impact.

Critical Loads of Heavy Metals in a Highly Polluted Catchment Area in Egypt

Heavy metals in different environmental compartments can be hazardous to ecosystems. Budgets of Cd, Pb and Zn in small ecosystems of the Shubra El-Kheima area in Egypt are presented. The budgets are not in steady state because they change with time. So the concentrations of the metals are a function of time. The critical loads of heavy metals to soils can be calculated from an inventory of inputs and outputs of the trace components in the catchment area. Critical time is an important parameter for critical load evaluation because it can indicate which of the heavy metals may be the most acute threat to the soils. Egyptian soil in the Shubra El-Kheima area seems to be in danger of heavy metal pollution by Zn, Cd and Pb. The calculated critical loads and their exceedances are approximate indicators of the hazards in the soil system. The critical time is a warning signal to initiate an environmental evaluation of possible pollution hazards.

Study on the Fuzzy Reliability of the Bearing in Planetary Transmission System for Heavy-Loaded Vehicles

Based on the fuzzy mathematics theory and reliability design methods, the fuzzy reliability of the rolling bearing in the planetary transmission system for heavy-loaded vehicles is analysed. The reliability and the fuzzy life expectancy of bearings in a practical planetary gear box are calculated in detail. The results show that the methods give a reference to the correct assessment of such type of bearing. Some measures to improve the reliability are also

THEORETICAL PREDICTION OF SOUND RADIATION FROM A HEAVY FLUID-LOADED CYLINDRICAL COATED SHELL

A theoretical model is developed to predict the sound radiation ability of a cylindrical thin elastic shell of finite length, covered with a damp layer and terminated with infinite cylindrical rigid baffles. This shell is immersed in a heavy fluid extending up to infinity, and excited by a constant point load continuously traveling along the circumferential direction. A frequency-domain representation of the rotating load and three equations of the vibroacoustic coupling problem are given. The equations are solved by means of modal analysis method and asymptotic expansion method. Also, a mathematical expression of modal amplitude of shell radial displacement is obtained. The sound radiation ability of this kind of shell is evaluated and the corresponding numerical results are given.

Performance analysis of air suspension system of heavy truck with semi-active fuzzy control

In order to analyze and evaluate the performance of the air suspension system of heavy trucks with semi-active fuzzy control, a three-dimensional nonlinear dynamical model of a typical heavy truck with 16-DOF（degree of freedom） is established based on Matlab/Simulink software. The weighted root-mean-square（RMS） acceleration responses of the vertical driver ＇s seat, the pitch and roll angle of the cab, and the dynamic load coefficient（DLC） are chosen as objective functions, and the air suspension system is optimized and analyzed by the semi-active fuzzy control algorithm when vehicles operate under different operation conditions. The results show that the influence of the roll angle of the cab on the heavy truck ride comfort is clear when vehicles move on the road surface conditions of the ISO level D and ISO level E at a velocity over 27.5 m/s. The weighted RMS acceleration responses of vertical driver＇ s seat, the pitch and roll angle of the cab are decreased by 24%, 30% and 25%, respectively,when vehicles move on the road surface condition of the ISO level B at a velocity of 20 m/s. The value of the DLC also significantly decreases when vehicles operate under different operation conditions. Particularly, the DLC value of the tractor driver axle is greatly reduced by 27.4% when the vehicle operates under a vehicle fully-loaded condition on the road surface condition of ISO level B at a velocity of 27.5 m/s.

INJECTION MOLDED TUNGSTEN HEAVY ALLOY

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Assessment of Heavy Metal Contamination in Sea Bed Sediment of the Bight of Bonny, Southern Atlantic Coast of Nigeria Using Index Model Analysis

The heavy metal contamination status of Bight of Bonny sea bed sediment was investigated. Sediment samples were collected from eleven locations grouped into three stations. The samples were analyzed to determine the heavy metals (Fe, Pb, Ni, Zn, Mn, Co, Cd, Cu, Cr) concentration using atomic absorption spectrophotometer. Index model analyses, such as geo-accumulation index (I-geo), Enrichment factor (EF), and Pollution load index (PLI) were used for pollution assessment of sea bed sediment. The most predominant heavy metals in the upstream sediment were Fe;13.57 ± 1.838 mg/kg, cobalt;7.987 ± 3.550 mg/kg, and Ni;1.020 ± 0.802 mg/kg, midstream sediment were Fe;8.554 ± 3.010 mg/kg, Co;8.520 ± 4.00 mg/kg, and Ni;1.140 ± 0.879 mg/kg, while the downstream sediment result had Fe;11.12 ± 3.825 mg/kg, Co;7.275 ± 1.700 mg/kg, and Cd;1.025 ± 0.159 /kg. The I-geo results indicate that Cu, Mn, Pb, Cr, Fe, Zn, Ni, and Co were in their background concentrations while Cd had I-geo > 3 which implies a moderately or heavily polluted environment. The EF indicates metal enrichment from anthropogenic sources for Co, Ni, Pb, Cd, Cu, and Cr while Fe and Mn predicate biogenic origin. The PLI of the heavy metals in the three sample stations of sea bed sediment was found to be generally low (<1). The Enrichment Factor and geo-accumulation index strongly suggest the Bight of Bonny sea bed sediment contamination by Cd from anthropogenic sources.

动态空心圆柱扭剪试验的离散元模拟研究

为了揭示应力主轴旋转效应对土体宏细观动力特性的影响,提出土体动态空心圆柱扭剪试验的数值模拟方法,该方法采用FDM-DEM耦合技术模拟物理试验中的完全柔性边界条件,并基于动态伺服原理实现柔性约束下循环动剪应力的精确加载。以重载列车荷载为例,建立“心形”复杂应力路径下重载铁路路基土体动态空心圆柱扭剪的数值试验模型,并通过物理试验验证数值模拟方法的正确性,分析应力主轴旋转效应对土体颗粒的运动状态、局部孔隙率、平均配位数、组构等细观特性的影响。研究结果表明,重载列车荷载引起的应力主轴旋转效应加剧了表征土体细观结构各项参数的变化程度,并加快了重载铁路路基土体竖向塑性累积变形的发展。此研究实现了复杂应力路径下空心圆柱试样的动态加载数值模拟,可为阐明土体在复杂应力路径下的宏细观动力特性演化规律提供参考。

基于参数估计-滑模阻抗控制的SEA性能分析

重载四足机器人的足部与地面接触过程和步态转换过程中会受到不确定的冲击载荷作用,易导致足部机构载荷过大从而造成结构的冲击损坏。因此,针对使用液压串联弹性执行器(series elastic actuators,SEA)作为足部末端在非结构环境下动态性能差的问题,提出了基于环境参数估计的滑模阻抗控制方法(environmental parameter estimation sliding mode,EPESM)。以阀控液压缸的活塞位移传递函数为基础建立了基于位置内环的SEA阻抗控制模型,并以PID作为基础控制器;为改善SEA阻抗控制的动态性能,根据Lyapunov第二法构建稳定的自适应环境参数估计方法对SEA期望位置进行前馈补偿;为提升自适应环境参数估计方法在SEA工作过程中不同阶段的动态性能和环境变化适应性,使用模糊控制方法对自适应环境参数估计方法中的自适应参数进行寻优;以SEA状态方程为基础构建滑模控制器与PID控制器进行动态性能对比分析。仿真结果表明:在变SEA弹簧刚度工况和变环境刚度下,EPESM阻抗控制的响应速度明显更快,可将调节时间从平均5 s缩短到1 s内,能更快地达到预期位移和预期接触力,且能略微降低稳态误差,使接触力误差保持在±6 N内。在动态跟踪工况下,EPESM阻抗控制的动态性能更好,在快速进入跟踪状态后,可以长时间保持0.2 s以内的相位滞后和5.2%的幅值误差。

基于SWOT分析“三从一大”原则在青少年足球训练中的运用

培养青少年足球人才是国家足球人才储备的关键环节,它对于推动我国足球事业向前发展起着至关重要的作用。“三从一大”原则是对足球训练规律进行长期探索后的智慧结晶。在目前我国经济飞速前进和体育事业蓬勃兴起的形势下,青少年足球训练的品质及其成效对未来我国足球的竞技水平具有直接影响。因此,实行“三从一大”的训练法则,即从严、从难、从实战出发、大运动量训练,是提高我国青少年足球技能培养质量的重要策略之一。为了深入掌握并有效运用这一法则,可以运用SWOT分析手段,全方位地审视其在青少年足球训练过程中的优势、不足、机遇和挑战,并根据此分析制订出切实可行的策略。

重型装载机械的液压无级变速器自适应传动控制策略研究

液压无级变速器作为重型装载机械传动系统的核心部件,对提高装载机械的工作效率和性能具有关键作用。然而,由于工况的复杂性,单纯的液压无级变速器已然无法满足工作需求。因此,文章首先对机械液压无级变速器进行了分析,阐述了其速比测算方式。在此基础上,通过构建阻力估算模型提出了一种分工况速比自适应控制策略。实验结果表明,阻力估算模型的误差平均值为4.5%,MAE最低为3.17、MAPE最低为12.93%、RMSE最低为1.02。相较于传统策略,分工况策略能够加快机械液压无级变速器的运行速度、缩短装载机械的作业时间并节省燃油。其速比控制误差最低为3.3%,响应时间最短为5.7 s。

重型拖拉机负载敏感电液提升系统研究现状

主要介绍了负载敏感电液提升系统在农业领域中对于重型拖拉机的重要作用。首先,详细阐述了负载敏感电液比例阀和电液提升系统的原理和功能,然后从电液比例技术、插装阀技术和控制技术等方面对国内外研究现状进行了分析。接着,概述了该领域的主要进展和最新研究成果,并指出了存在的问题。最后,提出了未来重型拖拉机负载敏感系统研究的重点和发展方向,这将有助于学者更好地了解该领域并推动行业技术进步。

基于SRV的重载轴承润滑脂摩擦磨损性能模拟评定方法研究

为提高润滑脂产品配方筛选效率、节约轴承台架试验成本,提出了1种基于SRV摩擦磨损试验机的圆柱滚子-圆盘线接触往复运动模式评定重载轴承润滑脂摩擦磨损性能的试验方法.采用四款重载润滑脂为试验样本,通过Pearson相关性系数法进行了SRV圆柱滚子-圆盘线接触往复摩擦磨损试验结果与FE-8轴承磨损台架试验结果间的相关性探讨,确定了方法最优试验参数,并在最优试验条件温度25℃,载荷1 kN,位移1 mm,往复速率50 Hz下完成了方法重复性考察.结果表明:SRV圆柱滚子-圆盘线接触往复试验方法试验结果重复性良好、可靠性高,与FE8轴承台架结果对应性优于四球机磨斑直径法(SH/T 0204-1992)以及SRV球滚子-圆盘接触试验法(NB/SH/T0721),更适用于重载轴承用润滑脂在摩擦副表界面的抗磨减摩性能的分析评定.

超重型消防车地下室顶板荷载等效取值研究

目前国内各大城市均有采购多辆101 m登高平台消防车(63 t),其重量远远超过了《建筑结构荷载规范》(GB 50009—2012)中原型消防车的重量(30 t),《建筑结构荷载规范》(GB 50009—2012)未对此类消防车给出具体的等效均布荷载取值。以101 m登高平台消防车(63 t)为研究对象,首先通过绘制板的跨中弯矩影响面来确定其最不利位置,然后利用ABAQUS计算出2种荷载工况下板的跨中弯矩值,最后再等效出101 m登高平台消防车(63 t)分别在7 m×7 m、8 m×8 m、9 m×9 m双向板的荷载取值。结果表明:板跨大于6 m的地下室双向板消防车荷载不建议直接取规范值,可按照设计需要采用相应流程进行等效;若对地下室顶板设计精度要求不高,当双向板板跨大于8 m时,63 t级消防车可参照规范要求进行荷载等效。

黄河流域渭河支流泾河(崆峒段)河流表层沉积物重金属溯源解析

河流沉积物重金属污染问题日益突出,严重威胁流域生态系统健康。以黄河流域泾河崆峒段为研究区,采集91个河流表层沉积物样品,测定并分析沉积物As、Cd、Cr、Cu、Hg、Ni、Pb和Zn共8项重金属元素含量及其空间分布特征。采用地累积指数(I_(geo))和污染负荷指数(PLI)系统量化重金属污染特征,并联合应用自组织神经网络(SOM)模型、相关性分析和正定矩阵因子分解(PMF)模型定量解析沉积物重金属污染来源及其贡献率。结果表明:泾河崆峒段河流表层沉积物重金属含量的平均值高低依次为Cr(65.66 mg/kg)>Zn(55.63 mg/kg)>Ni(21.78 mg/kg)>Pb(17.50 mg/kg)>Cu(14.07 mg/kg)>As(10.94 mg/kg)>Cd(0.19 mg/kg)>Hg(0.032 mg/kg)。除Cd和Hg外,As、Cr、Cu、Ni、Pb和Zn含量的均值均低于甘肃省土壤背景值和黄土高原土壤背景值,且As、Cd和Cr含量的均值分别是中国水系沉积物背景值的1.22、1.46和1.22倍。沉积物重金属含量空间分布具有明显的差异性,所有元素高含量和污染相对较重的区域均分布于人类活动强烈和入河口周边流域,且Hg的空间异质性最强。Cd是泾河崆峒段亟需关注的首要污染元素,Hg、Pb、Cr和Zn存在局部污染,Cu、Ni和As为清洁无污染。沉积物重金属的富集可能受污水交通源、农业源、金属冶炼加工源、电镀制造工业源和自然源的共同影响,贡献率依次为33.33%、27.21%、11.02%、15.49%和12.95%。

配电网多端柔性互联协调控制策略

随着社会经济的快速发展和新型电力系统建设的加快推进,柔性互联逐渐成为配电网网架升级和灵活调控能力提升的重要技术手段。针对多端柔性互联系统的功率控制需求,提出了一种面向工程应用的功率协调控制策略,包括在部分馈线重载时合理分配功率的重载限制控制,以及在所有馈线重载时优化潮流分布的功率均衡控制。基于所提策略开发了柔性互联协调控制装置并应用于实际工程。基于电网真实数据的案例分析和工程实测数据验证了所提策略能够应对不同负荷/电源特性的配电网柔性互联场景,有效解决配电网中馈线重载和光伏倒送的问题,提高配电网的供电效率和安全性。