The Influence of Normal Load and Sliding Speed on Frictional Properties of Skin

The study of frictional properties of human skin is important for medical research, skin care products and textile exploi- tation. In order to investigate the influence of normal load and sliding speed on the frictional properties of skin and its possible mechanism, tests were carded out on a multi-specimen friction tester. When the normal load increases from 0.1 N to 0.9 N, normal displacement and the friction coefficient of skin increase. The friction coefficient is dependent on the load, indicating that both adhesion and deformation contribute to the friction behaviour. The deformation friction was interpreted using the plough model of friction. When sliding speed increases from 0.5 mm·s^-1 to 4 mm·s^-1, the friction coefficient increases and ＂stick-slip＂ phenomena increase, indicating that hysteretic friction contributes to the friction. The hysteretic friction was in- terpreted using schematic of energy translation during the rigid spherical probe sliding on the soft skin surface, which provides an explanation for the influence of the sliding speed on the frictional characteristics of the skin.

Experimental study on dynamic load magnification factor for ballastless track-subgrade of high-speed railway

The magnitude of dynamic load produced by high-speed trains depends on many factors,of which train speed is the most critical one.However,it is quite difficult to determine the effect of train speed on dynamic load using the theoretical methods due to the complexity of the interaction between vehicle and track-subgrade.Thus large-scale model test has gradually become an important approach for studying dynamic responses of ballastless track-subgrade of high-speed railway.In this study,a full-scale model of ballastless track-subgrade was constructed in accordance with the design and construction standards for Shanghai-Nanjing intercity high-speed railway line firstly.Then,the dynamic strain of slab and the dynamic earth pressure of subgrade were measured by conducting single wheel axle excitation test.In addition,the relationship between the dynamic load magnification factor（DLF） and the train speed was obtained.Finally,the DLF of track-subgrade under different train speeds was proposed,similar to that given by German Railway Standard.

Model tests on XCC-piled embankment under dynamic train load of high-speed railways

Piled embankments,which offer many advantages,are increasingly popular in construction of high-speed railways in China.Although the performance of piled embankment under static loading is well-known,the behavior under the dynamic train load of a high-speed railway is not yet understood.In light of this,a heavily instrumented piled embankment model was set up,and a model test was carried out,in which a servo-hydraulic actuator outputting M-shaped waves was adopted to simulate the process of a running train.Earth pressure,settlement,strain in the geogrid and pile and excess pore water pressure were measured.The results show that the soil arching height under the dynamic train load of a high-speed railway is shorter than under static loading.The growth trend for accumulated settlement slowed down after long-term vibration although there was still a tendency for it to increase.Accumulated geogrid strain has an increasing tendency after long-term vibration.The closer the embankment edge,the greater the geogrid strain over the subsoil.Strains in the pile were smaller under dynamic train loads,and their distribution was different from that under static loading.At the same elevation,excess pore water pressure under the track slab was greater than that under the embankment shoulder.

Accumulative deformation in railway track induced by high-speed traffic loading of the trains

Prediction and control of the permanent settlement of a track caused by traffic loading from trains is crucial to high-speed railway design and maintenance. In this study, a unified prediction model of accumulative deformation of geomaterials used in railway construction subjected to cyclic loadings is introduced and calibrated using physical model testing. Based on this versatile model, a calculation approach to determine the track structure settlement under repeated loadings caused by the movement of the wheel axle of the train is proposed. Regression analysis on the physical model testing is adopted to determine the parameters involved in the computational approach. Comparison of model test data and computed results shows that the parameters obtained from the back-analysis are consistent throughout the various testing conditions, and the proposed calculation approach is capable of satisfactorily predicting the accumulative settlement of the railway roadbed and subgrade soil for various axle loads and loading cycles. A case study of a high-speed railway is performed to demonstrate the feasibility of the proposed approach in realistic engineering applications. The computation results from the settlement development of a roadbed and subgrade soil are presented and discussed.

Influences of aerodynamic loads on hunting stability of high-speed railway vehicles and parameter studies

The influences of steady aerodynamic loads on hunting stability of high-speed railway vehicles were investigated in this study.A mechanism is suggested to explain the change of hunting behavior due to actions of aerodynamic loads：the aerodynamic loads can change the position of vehicle system（consequently the contact relations）,the wheel/rail normal contact forces,the gravitational restoring forces/moments and the creep forces/moments.A mathematical model for hunting stability incorporating such influences was developed.A computer program capable of incorporating the effects of aerodynamic loads based on the model was written,and the critical speeds were calculated using this program.The dependences of linear and nonlinear critical speeds on suspension parameters considering aerodynamic loads were analyzed by using the orthogonal test method,the results were also compared with the situations without aerodynamic loads.It is shown that the most dominant factors a ff ecting linear and nonlinear critical speeds are different whether the aerodynamic loads considered or not.The damping of yaw damper is the most dominant influencing factor for linear critical speeds,while the damping of lateral damper is most dominant for nonlinear ones.When the influences of aerodynamic loads are considered,the linear critical speeds decrease with the rise of cross wind velocity,whereas it is not the case for the nonlinear critical speeds.The variation trends of critical speeds with suspension parameters can be significantly changed by aerodynamic loads.Combined actions of aerodynamic loads and suspension parameters also a ff ect the critical speeds.The effects of such joint action are more obvious for nonlinear critical speeds.

Theoretical research and experimental validation of quasi-static load spectra on bogie frame structures of high-speed trains

One of the major problems in structural fatigue life analysis is establishing structural load spectra under actual operating conditions.This study conducts theoretical research and experimental validation of quasi-static load spectra on bogie frame structures of high-speed trains.The quasistatic load series that corresponds to quasi-static deformation modes are identified according to the structural form and bearing conditions of high-speed train bogie frames.Moreover,a force-measuring frame is designed and manufactured based on the quasi-static load series.The load decoupling model of the quasi-static load series is then established via calibration tests.Quasi-static load–time histories,together with online tests and decoupling analysis,are obtained for the intermediate range of the Beijing—Shanghai dedicated passenger line.The damage consistency calibration of the quasi-static discrete load spectra is performed according to a damage consistency criterion and a genetic algorithm.The calibrated damage that corresponds with the quasi-static discrete load spectra satisfies the safety requirements of bogie frames.

Study on the subgrade deformation under high-speed train loading and water–soil interaction

It is important to study the subgrade characteristics of high-speed railways in consideration of the water–soil coupling dynamic problem,especially when high-speed trains operate in rainy regions.This study develops a nonlinear water–soil interaction dynamic model of slab track coupling with subgrade under high-speed train loading based on vehicle–track coupling dynamics.By using this model,the basic dynamic characteristics,including water–soil interaction and without water induced by the high-speed train loading,are studied.The main factors-the permeability coefficien and the porosity-influencin the subgrade deformation are investigated.The developed model can characterize the soil dynamic behaviour more realistically,especially when considering the influenc of water-rich soil.

Theoretical Research and Experimental Validation of Elastic Dynamic Load Spectra on Bogie Frame of High-speed Train

When a train runs at high speeds, the external exciting frequencies approach the natural frequencies of bogie critical components, thereby inducing strong elastic vibrations. The present international reliability test evaluation standard and design criteria of bogie frames are all based on the quasi-static deformation hypothesis. Structural fatigue damage generated by structural elastic vibrations has not yet been included. In this paper, theoretical research and experimental validation are done on elastic dynamic load spectra on bogie frame of high-speed train. The construction of the load series that correspond to elastic dynamic deformation modes is studied. The simplified form of the load series is obtained. A theory of simplified dynamic load–time histories is then deduced. Measured data from the Beijing–Shanghai Dedicated Passenger Line are introduced to derive the simplified dynamic load–time histories. The simplified dynamic discrete load spectra of bogie frame are established. Based on the damage consistency criterion and a genetic algorithm, damage consistency calibration of the simplified dynamic load spectra is finally performed. The computed result proves that the simplified load series is reasonable. The calibrated damage that corresponds to the elastic dynamic discrete load spectra can cover the actual damage at the operating conditions. The calibrated damage satisfies the safety requirement of damage consistency criterion for bogie frame. This research is helpful for investigating the standardized load spectra of bogie frame of high-speed train.

Normalization method for asphalt mixture fatigue equation under different loading frequencies

In order to analyze the effect of different loading frequencies on the fatigue performance for asphalt mixture,the changing law of asphalt mixture strengths with loading speed was revealed by strength tests under different loading speeds.Fatigue equations of asphalt mixtures based on the nominal stress ratio and real stress ratio were established using fatigue tests under different loading frequencies.It was revealed that the strength of the asphalt mixture is affected by the loading speed greatly.It was also discovered that the fatigue equation based on the nominal stress ratio will change with the change of the fatigue loading speed.There is no uniqueness.But the fatigue equation based on the real stress ratio doesn't change with the loading frequency.It has the uniqueness.The results indicate the fatigue equation based on the real stress ratio can realize the normalization of the asphalt mixture fatigue equation under different loading frequencies.It can greatly benefit the analysis of the fatigue characteristics under different vehicle speeds for asphalt pavement.

Soldiers' load carriage performance in high mountains: a physiological study

Background: The present study was designed to evaluate load carriage performance at extremely high altitudes with different loads and walking speeds in terms of physiological evaluation. The degree of maximum oxygen consumption changes at high altitudes was also examined.Methods: Twelve Indian Army soldiers were acclimatized at altitudes of 3,505 m and 4,300 m. They walked for 10 minutes on a motorized treadmill at 2.5km/h and 3.5km/h speeds during carrying no loads and three magnitudes of load(10.7kg, 21.4kg, 30kg) at both altitudes. Physiological parameters such as oxygen consumption, energy expenditure, heart rate, and ventilation were recorded for each breath using a gas analyzer. The rating of perceived exertion was also noted after each load carriage session. Maximal oxygen consumption(VO2max) was measured at sea level and the two high altitudes, and respective relative workloads(% of VO2max) were calculated from oxygen consumption. Repeated measure ANOVA was applied to reveal the significant effects of the independent variables.Results: The participants had significant reductions in VO2 max with rising altitude. Marked increases in almost all physiological parameters were observed with increasing load, altitude, and speed. The soldiers expressed heavy perceived exertion levels with higher loads at 3.5km/h at the two high altitudes.Conclusions: Considering the physiological responses, expressions of perceived exertion and changes in relative work load at both of the high altitudes. Indian soldiers are advised to walk slowly with adequate rest in between their schedules and to carry not more than 32% of their body weight.

ANALYSIS OF SALTATION CHARACTERISTICS OF BED-LOAD TRANSPORT IN FLOWING WATER

The study of bed-load transport is of great significance both in theory and in practice.This paper discusses the saltation of bed-load solid grains in flowing water.Experiments and theoretic analysis have been made by means of high-speed photographing and advanced data processing technique with a combined method based on mechanical and statistical theories.It indicates that the saltation is the main form of the bed-load transport under ordinary flowing conditions.In the meantime,taking suecessive saltation as the mod- el of bed-load transport,systematic analysis has been made with regard to the kinematic properties and mechanism of saltation.The statistical analysis shows that the probability density functions of the relative height and length of saltation are in conformity with Γ-type distribution,while the probability density func- tions of the relative velocities of saltation are in conformity with the Gaussian distribution.

Research on dynamic characteristics of high speed milling force based on discontinuous functions

This paper begins with a consideration of the influence of feed per revolution upon the depth of a cut and the impact of the machining method on the direction of tool pressure average and subsequent description of efficient cutting directions and the methods for load cell orientation. The paper goes further into the key conclusions concerning the dependences of the cutting depth at high-speed milling as in the case of discontinuous functions. It ends with recommendations offered for positioning of load cells for cut-up milling and cut-down milling.

15#航空液压油的摩擦磨损性能研究

15#航空液压油是航空领域广泛应用的1种特定型号的液压油.本文中使用MCR302流变仪测量了该液压油的黏温曲线,并选用GCr15钢球通过四球摩擦磨损试验机采用单因素变量法研究了不同载荷、温度和转速对摩擦磨损的影响.同时,使用光学显微镜、白光三维表面形貌仪、扫描电子显微镜和X射线光电子能谱分析仪对钢球表面的磨斑进行微观观察,并分析其磨损机理.试验结果显示,在不同载荷下,摩擦系数相对稳定,但随着载荷的增加,磨斑直径(WSD)逐渐增大,磨损程度变得更严重.随着温度的增加,摩擦系数较为稳定,但液压油的黏度逐渐减小,导致无法形成有效的摩擦反应膜,使磨损现象变得更加显著,尤其在75~100℃范围内,磨斑直径的增长速率最为显著,增加了约60%.随着转速的提高,摩擦系数首先保持不变,然后逐渐减小,而磨损率逐渐降低.润滑状态逐渐从边界润滑过渡到混合润滑和流体动压润滑.

全景影像快速加载与精确量测算法研究

针对全景影像加载速度慢及量测精度低的问题,提出一种全景球金字塔切片模型动态约束加载算法。首先,基于格网球体投影模型构建三维全景场景;其次,对全景影像进行压缩与切片,并设计全景切片金字塔模型;然后,采用逆向墨卡托投影将全景切片作为纹理映射到球体内表面进行渲染,形成全景球金字塔切片模型;最后,按照可视区域约束对金字塔模型切片进行快速加载实现动态可视化,并结合深度图像实现全景影像的精确量测。实验结果表明,选用顶点数量为11904的全景球金字塔切片模型,量测中误差小于3 cm,同时提高了加载速度。

千万吨级主井高速大载重提升技术研究与应用

以千万吨级“双超”矿山——思山岭铁矿主井提升系统建设为背景,从主井提升系统方案、竖井提升运行安全间隙研究、大型化提升技术装备应用、大型主井井塔布置等方面综合论述了主井提升系统参数确定所开展的研究工作以及设计建设采用的新技术、新装备。思山岭铁矿主井提升系统的建设将对我国类似矿山竖井高速大载重提升系统的建设实施具有较强的标杆示范意义。

A Digital Phase Locked Loop Speed Control of Three Phase Induction Motor Drive: Performances Analysis

This paper deals with performance analysis and implementation of a three phase inverter fed induction motor (IM) drive system. The closed loop control scheme of the drive utilizes the Digital Phase Locked Loop (DPLL). The DPLL is safely implemented all around the well known integrated circuit DPLL 4046. An ex-perimental verification is carried out on one kw scalar controlled IM system drives for a wide range of speeds and loads appliance. This presents a simple and high performance solution for industrial applications.

地震和高铁共同作用下桩网复合地基振动特性

为研究地震和高铁列车荷载共同作用下桩网复合地基振动特性,通过建立轨道-路堤-桩网复合地基三维有限元计算模型,分别与实测数据和一维波动理论对比验证模型的正确性。通过对比不同荷载工况下地面位移和加速度时频振动曲线,分析地震和高铁两动载共同作用时不同车速下桩网复合地基时频振动特性,研究桩体模量对桩网复合地基减震效果的影响。研究表明,Hollister地震荷载和高铁荷载共同作用下,距轨道中心1 m处地面振动位移由地震荷载主导,地面振动加速度由列车荷载主导;20 Hz以下地面低频振动由高铁和地震荷载共同控制,地面高频振动主要由列车荷载控制。Lytle Creek地震荷载和高铁荷载共同作用下,桩网复合地基地面振动位移和加速度峰值均大于高铁荷载单独作用下的值;增加桩体模量对高铁荷载单独作用和两动载共同作用下桩网复合地基地面振动均有减振效果,但两动载共同作用下增加桩体模量对地面减振效果比高铁荷载单独作用下弱。

山药综合力学性能测试的研究

为了获得山药在不同加载速度下的力学性能参数,采用微机控制电子式万能试验机(WDW-5E)对“牛腿”山药进行了不同加载速度下的压缩、弯曲、拉伸试验。测得不同加载速度下的轴向抗压强度、轴向弹性模量、径向抗压强度、径向弹性模量、抗弯强度、抗弯弹性模量、抗拉强度、抗拉弹性模量,由此得出山药弯曲断裂载荷在40~140 N之间;轴向和径向的弹性模量随加载速度增大而增大;加载速度对山药其他力学性能参数无显著影响。通过对山药的综合力学性能的研究,能够在收获时调整机具工作参数,降低机械对山药的损伤,为实现山药智能化机械采收提供参考。

Effect of pin rotating speed on lap shear strength of stationary shoulder friction stir lap welded 6005A-T6 aluminum alloy

Stationary shoulder friction stir lap welding （SSFSLW） was successfully used to weld 6005A-T6 aluminum alloy in this paper. Effect of pin rotating speed on cross section morphologies and lap shear strength of the SSFSLW joints were mainly discussed. Results show that joints without flash and shoulder marks can be obtained by the stationary shoulder. Cross section of the SSFSLW joint presents a basin-like morphology and little material loss. By increasing the rotating speed from 1 000 rpm to 1 600 rpm, both effective sheet thickness and lap width increase, while lap shear failure load firstly decreases and then increases. The maximum failure load of 14. 05 kN /s attained when 1 000 rpm is used. All SSFSLW joints present shear fracture mode.