Investigation on mechanism of the improvement in tribological properties of carbon fiber reinforced polytetrafluoroethylene composites by surface treatment

Tribological properties of polytetrafluoroethylene (PTFE) composites filled with differently surface treated carbon fibers (CF), sliding against GCr15 steel under dry sliding conditions, were investigated on a block-on-ring M-2000 tribometer. Experimental results reveal that rare earths (RE) surface treatment reduces the friction and wear of CF-reinforced PTFE (CF/PTFE) composites. Scanning electron microscopy (SEM) investigation of worn surfaces of CF/PTFE composites shows that cracks or pores are visible on the worn surfaces of untreated and air-oxidated composite, while no crack and very few pores present on the worn surface of REtreated composite. The fiber-friction-angling effect makes carbon fibers angled and oriented along the frictional shearing force, and finally parallel to the friction surface, which makes interfacial adhesion become a key factor to tribological properties of CF/PTFE composite. With strong interfacial adhesion between carbon fiber and PTFE after RE surface treatment, carbon fibers are not easily detachable from the PTFE matrix in the process of fiber-friction-angling, which prevents the rubbing-off of PTFE, and accordingly improves the friction and wear properties of the composite.     

密封用填充改性PTFE的研究及应用

PTFE(聚四氟乙烯)的填充改性是近年来研究较多的项目。本文介绍了采用模压烧结工艺制备玻璃纤维和石墨改性的PTFE动态密封材料,并对其拉伸强度、压缩回弹性能和摩擦、磨损性能及耐磨机理做了系统的研究分析,结果表明,该密封材料具备较好的抗拉强度、优异的压缩回弹性能和较好的耐磨损性能,可用于对耐磨耗性、耐温性能要求较高的动态密封场合,具有广阔的应用前景。     

干模式下颗粒粘滑震动试验研究

为了研究浅源地震的诱发机制,基于室内三轴试验,对颗粒材料的粘滑震动特性进行了分析. 采用颗粒直径为0.6～0.8 mm的玻璃珠,在围压为30、60、100、200、400 kPa和600 kPa的条件下,以0.02 mm/min的轴向应变速率,开展干燥、密实玻璃珠的固结不排水三轴压缩试验,结果表明:试样偏应力主震和偏应力应变间距随着围压的增大而增大;除了初始压密阶段外,体变-应变曲线中所有体积的突然收缩均与粘滑震动有关;在30、60、100 kPa围压条件下,围压-应变曲线中出现较多尖而窄的波峰和波谷;在200、400 kPa和600 kPa围压条件下,围压-应变曲线中只有尖而窄的波谷;玻璃珠类颗粒材料发生粘滑震动过程中既有静摩擦也有转动摩擦;颗粒之间应力链的连续变形和破坏是引起颗粒粘滑震动的根本原因.      

高速铁路制动区间钢轨摩擦自激振动研究

为了探究高速铁路制动区间的典型钢轨波磨现象,基于轮轨摩擦自激振动诱导钢轨波磨的观点展开了研究,通过武广高速铁路制动区段的现场调研,掌握该区段的波磨特征并采集相应的轨道不平顺;基于轮轨摩擦自激振动诱导钢轨波磨的观点分别建立制动区段高速列车的动/拖车轮对-轨道-制动系统的有限元模型,并利用复特征值法进行动/拖车轮轨系统的摩擦自激振动分析,比较动/拖车轮轨系统在制动和非制动工况下系统发生摩擦自激振动的可能性,以及在制动工况下动车轮轨和拖车轮轨系统的摩擦自激振动情况;使用控制变量法研究了制动系统摩擦系数和扣件垂向刚度对动/拖车轮轨系统摩擦自激振动的影响规律.研究结果表明：制动工况更容易引起系统的摩擦自激振动;拖车轮轨系统更容易引起系统摩擦自激振动;控制制动装置摩擦系数约为0.30,扣件垂向刚度约为50 MN/m时能一定程度降低轮轨系统发生摩擦自激振动的可能性,进而抑制钢轨波磨的产生.     

一类存在间隙和摩擦的分段光滑振动系统的动力学特性

研究了简谐激励作用下含非光滑力学因素间隙和摩擦的两自由度振动系统的动力学.通过数值仿真揭示了该分段光滑振动系统随激振频率变化呈现的粘滞和非粘滞周期振动及分岔特点,分析了摩擦系数对系统周期冲击振动、分岔及滑移-粘滞状态的影响.     

高速动车组空气弹簧故障模式下转向架动态响应

为了模拟高速动车组空气弹簧发生故障后的工作状态,基于气动力学理论与函数拟合方法,建立了空气弹簧系统的三维耦合动力学模型,并将该模型与高速动车组整车动力学模型进行了联合仿真,研究了空气弹簧故障模式下高速动车组转向架的动力学响应.由空气弹簧泄漏过程分析可知,空气弹簧泄漏导致车辆失稳的可能性较小,但会使平稳性下降;车辆的垂向与横向安全性指标峰值分别出现在泄漏面积约为15 mm2和30 mm2处;差压阀在空气弹簧的泄漏中能够有效保障车辆的动力学性能.由车辆曲线通过性分析可知,车辆通过曲线的方向若与空气弹簧的泄漏在同侧,则轮重减载率高出直线工况约20%;差压阀与高度调整阀的失效均会对车辆的动力学性能造成一定程度的影响,但各项指标仍满足安全性要求.      

兰新客运专线动车组车轮多边形磨耗的机理

由于兰新客运专线的线路复杂环境，动车组车轮多边形磨耗现象严峻，加大了列车运行过程中的轮轨作用力，影响了乘客舒适性，给高速列车的安全运行造成极大威胁. 为解决上述问题，基于长期跟踪客运专线获得的车轮多边形磨耗规律以及摩擦自激理论的观点，建立了轮对-钢轨-轨道板摩擦耦合自激振动模型，通过复特征值分析方法来研究车轮多边形磨耗的形成原因及其发展规律. 研究结果表明，在直线线路上，轮轨间蠕滑力饱和引起的摩擦自激振动易导致车轮第15～16阶多边形磨耗；在制动系统和轮轨系统耦合的情况下，动力轮对和非动力轮对对应的不稳定振动频率分别容易引起第23～24阶和第22～23阶车轮多边形磨耗；轮轨之间的黏着系数变大可能是导致冬春季车轮多边形发展速度较夏季快的重要原因.      

Experimental Analysis and Optimization of Timing Belt Guide Plate Material on Engine Operational Friction Loss

We focus on the friction loss measurement and reduction of the timing belt guide plates of a fourcylinder gasoline engine. To minimize the friction loss caused by the dynamic friction of the guide plates during timing belt motion and improve the efficiency of the internal combustion engine(ICE), we adopt four different plastic materials in fabricating the guide plates. With controlled engine boundary conditions and operational modes, an AVL electric dynamometer is used to measure the output of the engine. The results indicate that selecting polytetrafluoroethylene(PTFE) as the additive in fabricating the guide plates can effectively reduce the friction loss, so that the output torque and output power of the engine can be improved, thus reducing fuel consumptions. This work also has positive impact on the efficiency optimization of similar ICEs.     

弹性支承块式无砟轨道冲击振动传递衰减特性试验

针对重载铁路弹性支承块式无砟轨道(LVT)在实际应用中出现的弹性部件变形过大、易损坏等问题, 优化设计了既有弹性支承块, 将支承块短侧边坡度由1∶17.00调整为1∶4.85, 取消了块下垫板, 并采用一体化弹性套靴; 为验证设计成果, 建立了传统型LVT和改进型LVT足尺模型, 采用质量为1 120 kg的重载货车轮对, 以20 mm的落高进行落轴冲击试验, 分别从时域和频域角度对比分析了冲击作用下竖向振动在钢轨、支承块、道床板、底座板及地面等结构部件沿线路纵、竖、横向的传递衰减特性。研究结果表明: 轮轨产生的高频振动能量沿钢轨纵向传递, 低频振动能量传递给下部其他轨道结构; 竖向冲击振动在纵、竖向传递的过程中不断衰减且衰减速率逐渐降低, 在支承块和道床板表面横向传递过程中, 向外侧边缘传递振动增大; 相比传统型LVT, 改进型LVT整体弹性系数减小21.1%, 而阻尼系数增大5.4%, 其振动周期、衰减时长、振动峰值分别比传统型LVT小37.0%、21.3%和3.4%, 各结构部位功率谱密度峰值比传统型LVT小30%以上; 改进型LVT轨道结构各部位Z振级比传统型LVT小, 在地面处减小了3.65 dB, 能更有效、迅速地衰减轮轨冲击力和轨道结构振动, 振动水平更低, 降低了冲击作用对环境的影响。研究结果对于开展LVT减振性能试验验证、优化与工程应用有参考价值。      

风积沙的工程力学性质试验研究

结合毛乌素沙漠沙样,对风积沙的工程力学性质进行了系统的试验研究。试验结果表明:风积沙的压实可采用常规的击实试验方法和振动密实法,压实效果受颗粒级配、含水量、荷载大小、振动频率及振幅等多种因素影响;风积沙的内摩擦角与压实度之间呈线性变化规律,颗粒级配是主要影响因素,含水量影响较小;风积沙的室内回弹模量和加州承载比与压实度之间大致呈非线性增大规律,在某一压实度区间增大的幅度非常小。     

一类摩擦碰撞振动系统的周期振动特性研究

建立了一类两自由度摩擦碰撞振动系统的力学模型,确定Poincare截面,通过数值仿真,分析了系统在简谐激振力作用下的周期碰撞振动特性,并讨论了传动带运动速度、传动带与质量块间的摩擦系数对系统周期碰撞振动特性的影响.研究结果表明系统的周期碰撞运动的形式呈现多样化,且在一定的系统参数下,传动带运行速度和摩擦系数的变化对系统的冲击速度影响不大,但对系统的动力学特性有较大的影响.     

An experimental study on flowrate and stability for 600MW supercritical steamturbine control valve

An experimental study on flowrate and stability of a type of control valve of 600MW supercritical steamturbine was presented by measuring instruments of static, dynamic pressure and vibration in self-designed test rig. The investigation shows that flow coefficient is 30% up more than that of the control valve of GX-1 type used widely in domestic power plants now, as small-medium lifts. If the relative lift （h/D） is less than 20%, the valve can always work steadily in all the pressure ratios. When the h/D is between 20% to 24%, big vibration of valve stem occurs if the pressure ratio is between 0.7 to 0.8. When h/D is more than 25%, relatively great vibration happens in a wide range of pressure ratios of 0.4 to 0.85.     

基于有限元功率流的桥梁-承轨台轨道结构振动特性研究

用功率流理论从能量的角度研究轨道结构的振动特性,它兼顾了力和速度的相位关系,比传统的以力、位移、加速度和速度等单个指标来衡量振动特性更具有综合性。建立了桥梁一承轨台轨道有限元模型,对其进行谐响应分析,从而得到输入钢轨和承轨台的总功率流,进而评价其振动特性。改变扣件的刚度和阻尼,研究扣件参数的改变对于钢轨和承轨台输入总功率流的影响。     

Field Tests for Investigating the Extraction Rate of Piles Using a Vibratory Technique

Factors directly affecting the extraction rate of the piles pulled out by a vibratory pulling system are summarized and classified into five categories (excitation force, resistance, vibration amplitude, pile plumbness keeping, and slowing down at the later stage) from the mechanics and engineering practice. Field tests on steel sheet piles extracted by vibratory technique in different soil conditions are conducted to ascertain how these factors affect the extraction rate of a pile with regard to three major actors of vibratory pile pulling: the pile to be extracted, the selected pulling system, and the imposed soil conditions. The extraction rates of three different sheet pile types (having up to four different lengths) pulled out by two different vibratory pulling systems are documented. The piles with different lengths and types, pulled out with or without a clutch, have different extraction rates. The working parameters governing the vibratory hammer, such as excitation force and vibration amplitude, exert significant influences on the rate of pile extraction, especially in the early stages of up-lift process. The extraction rate of the piles driven in different soil conditions is uniform because different extraction resistances mainly refer to shaft friction. The properties of the pile-soil interface influence the extraction rate of the piles, and the extraction rate decreases with the time for which the piles have been buried in the earth.     

SoC的可靠性和低功耗协同优化

针对SoC的高可靠性和低功耗的设计要求,分析了动态电压与频率调节技术对系统功耗、温度和软错误率的影响,构建了SoC的可靠性和功耗的协同优化设计模型,提出了可靠性和低功耗协同设计的新方法,并通过考虑可靠性的动态电压与频率调节调度算法进行了仿真,验证了算法的有效性和可行性.结果表明,在可靠性降低5%的情况下,可节省约15.99%的功耗.     

液压控制技术在筑路机械中的应用

近年来,国内外筑路机械控制技术的主要发展方向是低能耗、高精度,能适应各种复杂作业并且操作简便舒适。液压技术由于其传动功率大,容易实现手动与电动控制,对筑路机械性能的提高起到了积极的保障作用。     

基于KDE及Markov的高速列车传动系振动评价及可靠性分析

为研究高速列车运行过程中传动系的振动情况及可靠性，对CRH3型高速列车传动系关键部件的振动加速度数据进行实车采集，采用核密度估计（KDE）法对采集数据统计处理，得出各关键部件在各方向上振动响应的概率密度函数近似曲线，据此对传动系的关键部件进行振动评价；通过MATLAB计算各关键部件振动加速度的最优置信区间；对传动系及传动系的关键部件定义“安全”和“故障”两种状态，建立关键部件的威布尔比例失效率模型及传动系的Markov状态转移模型，以传动系当前状态为初始状态，基于实时故障率及维修率分析传动系可靠性的变化. 研究结果表明:传动系中轴箱轴承、齿轮箱以及电机轴承的垂向振动最强，振动加速度集中分布在25倍、20倍、10倍重力加速度范围内，概率99.75%的均方差值分别在20.5026倍、17.6712倍、11.4693倍重力加速度内；计算得到各关键部件振动加速度概率为99.75%的最优置信区间，为系统的振动监测阈值优化及故障评估提供参考；故障率及维修率是影响传动系统状态概率的关键因素，当故障率增加30%时，系统的状态概率约下降10%，当维修率由0.05提升至0.10时，可使系统的可靠性提高20%.      

A standard cell-based leakage power analysis attack countermeasure using symmetric dual-rail logic

Leakage power analysis （LPA） attacks aim at finding the secret key of a cryptographic device from measurements of its static （leakage） power. This novel power analysis attacks take advantage of the dependence of the leakage power of complementary metal oxide semiconductor （CMOS） integrated circuits on the data they process. This paper proposes symmetric dual-rail logic （SDRL）, a standard cell LPA attack countermeasure that theoretically resists the LPA attacks. The technique combines standard building blocks to make new compound standard cells, which are close to constant leakage power consumption. Experiment results show SDRL is a promising approach to implelnent an LPA-resistant crypto processor.     

Approach for Reliability Evaluation of Cross-Linked Polyethylene Under Combined Thermal and Vibration Stresses

Based on Wiener process model, a new approach for reliability evaluation of cross-linked polyethylene(XLPE) is proposed to improve the lifetime evaluation reliability of XLPE under multi-stressing conditions and study the failure probability distribution. In this paper, two accelerated aging tests are carried out under combined thermal and vibration conditions. The volume resistance degradation data of XLPE samples are tested with a24 h interval under the accelerated stressing conditions at(130℃, 12 m/s~2) and(150℃, 8.5 m/s~2), respectively.Nonlinear degradation data obtained from the experiment are transformed to linear intermediate-variable values using time scaling function, and then linearized degradation data are calculated and evaluated on the basis of linear Wiener process model. Considering traditional Arrhenius equation and inverse power criterion, parameters of the linear Wiener model are estimated according to the maximum likelihood function. The relationship curves on probability density and reliability are given, and the lifetime distribution of XLPE under different stressing conditions is also obtained for evaluating the reliability of XLPE insulation. Finally, the life expectancy of XLPE is 17.9 a under an allowance temperature of 90℃ and an actual vibration acceleration of 0.5 m/s~2. The approach and results in this paper may be used for reliability assessment of high-voltage multiple samples or apparatuses.     

Hilbert-Huang变换在声振信号检测钢管混凝土脱空中的应用

提出了基于Hilbert-Huang变换的钢管混凝土脱空检测方法,通过对瞬态冲击下脱空钢管的声振信号进行分析,提取出了瞬时幅值特征样本,采用改进的K均值聚类法对特征样本进行二类模式识别,从而对钢管混凝土的脱空进行判定,试验研究表明本方法的可行性。