An experimental check of the resolving power of an instrument for determining dynamic coefficients of friction

An experimental confirmation of the theoretical conclusions regarding the possibility of increasing the accuracy with which dynamic coefficients of friction can be determined using an instrument with an inclined plane is presented. Translated from Izmeritel’naya Tekhnika, No. 3, pp. 48–49, March, 2009.     

机场跑道摩擦系数测试车标定装置研究

根据摩擦车力传感器标定需要,提出一种机场跑道摩擦车标定方法.分析了摩擦车和标定系统的标定原理和标定方法,选用PC104模块作为控制核心,设计控制系统完成标定实验,针对标定装置中测力传感器的非线性问题,应用基于分段最小二乘法拟合的数据处理方法.实验结果验证了算法的有效性.     

固化压力对一种纸基摩擦材料摩擦性能的影响

基于本实验室制备的一种炭纤维增强纸基摩擦材料, 研究了固化压力对材料孔隙率, 动摩擦系数, 静动摩擦系数之比, 摩擦力矩曲线的影响。研究结果表明: 孔隙率随固化压力增加而下降; 动摩擦系数随制动压力的增加均呈下降趋势; 静动摩擦系数比值随制动压力的增加分布趋势较为复杂: 较低的固化压力条件下, 静动摩擦系数之比略有上升, 而较高的固化压力条件下静动摩擦系数之比则略有下降趋势; 摩擦力矩曲线随固化压力升高有轻微翘曲出现。综合考虑固化压力对动摩擦系数、 静动摩擦系数比值以及摩擦力矩曲线的影响, 在这种纸基摩擦材料成分不变的条件下, 其对应较为合适的固化压力约为3.4MPa。      

微分和表观静摩擦系数的表式

当前,工程师和科学家都对微牛和纳牛量级载荷静摩擦系数（以下简称微牛纳牛静摩擦系数）很感兴趣。但文献中至今没有详细讨论过微牛纳牛静摩擦系数与载荷的关系,而且发表的实验结果都不相互讨论。从微分静摩擦系数的定义出发,导出几种典型模型下微分静摩擦系数和表观静摩擦系数的表式,并据此广泛讨论这些文献中的实验结果。     

A fractal model for the static coefficient of friction at the fiber-matrix interface

The physical, geometrical, and mechanical properties at the fiber/matrix interface of a fiber-reinforced composite material have a dominant effect on the overall mechanical behavior of these materials. Specifically, the toughening of these materials is largely attributed to the energy dissipation due to the frictional sliding of fibers at their interface with the matrix material. The micromechanisms involved with interfacial failure and sliding are currently not entirely understood, and the failure threshold is generally predicted using macro-scale friction laws which neglect the micromechanical aspects. The objective of this study is to explore the derivation of a macro-scale static coefficient of friction at the interface of a previously debonded fiber based on the micro-scale properties of the contacting surfaces. Presented results illustrate that the macro-scale static coefficient of friction obtained from the proposed micro-scale model is independent of the normal load and is therefore consistent with the classical Amontons-Coulomb phenomenological laws of friction.     

金属橡胶非线性干摩擦副的接触作用机理及其仿真结果分析

从金属橡胶材料的干摩擦阻尼产生的机理入手,提出了一种全新的金属橡胶非线性干摩擦结构单元力学模型, 该结构单元由一对带有轴向和径向两个方向的弹性元件构成,它们既表示了金属丝之间的摩擦特性,同时也表示了螺线卷线匝在受力变形时的弹性特征。以建立的金属橡胶材料力学模型为基础, 采用多个摩擦副单元串联组成的结构,深入研究了线匝的摩擦接触, 通过对结构单元组成系统的计算机模拟仿真,对金属橡胶元件在不同载荷作用下的滞迟回线进行了深入地分析和研究,在静态载荷作用下,研究了结构单元的摩擦系数、结构单元的摩擦角对金属橡胶结构摩擦耗能的影响,在动态载荷作用下,研究了载荷的幅值、载荷的频率、载荷的初始相位对摩擦耗能的影响, 此项研究工作大大减少了静态和动态试验方面的工作。     

结合面静摩擦系数的统计模型

基于粗糙表面形貌的统计参数,综合考虑微凸体的完全弹性、弹-塑性和完全塑性三种变形机制,建立了结合面静摩擦系数的统计模型。该模型反映了静摩擦系数是由接触材料性能参数、表面形貌统计参数以及法向载荷共同决定的。通过仿真研究了微凸体高度的随机分布、塑性指数以及法向载荷等因素对静摩擦系数的影响规律。结果表明,修正的指数分布相比简单的指数分布对高斯分布有着较好的近似,且预测值近似等于高斯分布预测结果的均值;静摩擦系数随着塑性指数的增大而减小且变化趋缓;法向载荷增大时,静摩擦系数呈现减小的趋势,但在双对数坐标系下最大静摩擦力仍与法向载荷呈线性正比的关系。     

负刚度摩擦阻尼装置的开发及应用研究

消能减震技术通常需要在多个楼层布置减震装置才能有效降低结构的地震响应,占用了较多的结构空间。针对此种问题提出在底部楼层布置负刚度阻尼装置的减震方案,形成力学上的隔震层,用减震实现类似隔震的效果,以减少阻尼器的布置数量。为实现该减震方案,研发了一种基于氮气弹簧的负刚度摩擦阻尼装置,该装置具有行程大,力学性能稳定等优点。性能试验验证了负刚度摩擦阻尼装置可以实现具有负刚度特征的滞回模型,对负刚度摩擦阻尼装置布置于底部楼层的减震方案进行了模拟分析,结果表明仅在底层布置负刚度阻尼装置可以获得理想的减震效果。     

Calculation of friction coefficient of a solid-liquid interface via a non-equilibrium molecular dynamics simulation

The problem of characterizing a fluid flow near a solid surface is considered. The interface parameters are the friction coefficient and the hydrodynamic location of the interface. A method to obtain quantitatively these parameters from a non equilibrium molecular dynamics (NEMD) simulation is presented. Results for the flow of a soft sphere fluid confined between two corrugated surfaces are presented.     

摆杆式重型车轮拆装装置的设计与动态仿真

针对重型车轮拆装困难和现有拆装机械复杂的现状,设计了一种摆杆式重型车轮拆装装置.介绍了其结构方案和工作原理;利用几何分析法,确定了车轮中心的4个极限位置;利用Pro/E软件进行了运动学仿真,得到了车轮中心的轨迹区域,并分别分析了装置的摆杆长和侧支架间距对轨迹区域的影响,确定了装置在最佳调整范围时,轨迹区域左右跨度和上下跨度的比值.通过现场应用,表明装置具有对中率高、拆装方便、稳定性强、安全可靠、便于车载和野外使用的特点.     

带式输送机用直线电机静动态特性试验与分析

多机驱动在输送装备实现高速、长距离、大运量等方面起着至关重要的作用。直线电机因其具有不存在摩擦、无旋转传动部件、能够沿输送机长度方向任意布置和降低输送带张力等特点而成为特殊高性能带式输送机较理想的中间驱动方式。通过分析直线电机的工作原理,对直线电机与旋转电机的优缺点进行了比较;针对带式输送机用直线电机,对比确定了其次级型式,并进行了次级输送带结构设计;基于封闭式散料储运物料试验系统建立了静动态特性试验台,并运用欧拉公式及逐点张力法求得直线电机推力(输送带张力差),进而分别对电压、气隙与推力之间的比例关系进行了试验验证,并间接进行了动态试验(机械特性试验),得到了推力关于输送带速度的数学表达式;基于Belt Analyst带式输送机计算分析软件,对输送带稳定运行及启动过程的张力进行了仿真分析,并与试验张力进行了对比分析。试验结果表明:推力分别与电压平方、气隙倒数的平方成正比;电压、气隙与推力之间的理论曲线与试验值相符;直线电机的推力与输入功率的比值较大,并随着气隙的减小,比值越来越大;与旋转电机相比,此直线电机无临界转速,并显示出很软的机械特性;稳定运行时张力的仿真值与试验值基本吻合,其相对误差均小于2%,但启动过程中张力试验值与仿真值误差较大,间接表明保证启动过程气隙均匀的重要性。研究结果可适用于多机配合驱动超长距离带式输送机的改进与实际应用中。     

刚性包带式星箭连接装置解锁分离过程动力学分析

刚性包带式星箭连接装置能够为重型运载火箭提供更高的星箭连接承载能力,但对其分离释放过程的动力学研究尚未深入。该研究建立刚性包带式星箭连接装置非线性动力学分析模型,采用显式动力学仿真法分析了包带接头分离速度、分离冲击响应和捕获运动规律,研究解锁时间和预紧力等因素对分离与捕获过程的影响规律。结果表明:延长解锁时间和减小预紧力会导致包带接头分离速度降低,卫星冲击载荷减小,与捕获器接触时长增加,与脱离端框时间延后,甚至可以改变包带分离运动规律,引起卫星倾斜分离,在工程应用中应综合考虑。     

Pad flattening ratio, coefficient of friction and removal rate analysis during silicon dioxide chemical mechanical planarization

Pad flattening ratio (PFR) was investigated as a non-destructive pad surface analysis method on the IC1000 K-groove pad during silicon dioxide chemical mechanical planarization. The PFR defines as the ratio of the bright area to the total image area. A series of marathon polishing runs were performed under ex-situ diamond disc pad conditioning, ex-situ high-pressure micro jet (HPMJ) pad conditioning and no pad conditioning methods where PFR analysis was performed to estimate the amount of pad surface flattening or glazing under these conditions. With no conditioning, PFR increased rapidly to 40% indicating severe glazing. With ex-situ diamond disc pad conditioning, PFR remained relatively constant below 12%, suggesting a rough and stable pad surface for polishing, while with ex-situ HPMJ conditioning it increased gradually and stabilized at the value of about 23%. Real-time analysis of friction force and silicon dioxide removal rate showed a clear correlation among the PFR, the coefficient of friction and the removal rate during the silicon dioxide chemical mechanical planarization.     

The influence of coefficient of friction in thermal prediction of refill friction stir spot welding process of AA7075-T6

Numerical modelling of refill friction stir spot welding helps in the deep investigation of physics involved in the joining process. The current study investigates four variants of contact models and their influence on thermal prediction in the process. The contact models with constant shear and coulomb friction coefficients and temperature-dependent shear and coulomb friction coefficients were used in the numerical models to investigate the influence of friction coefficients in the prediction of thermal cycles in refill friction stir spot welding. The results from the numerical model are compared and validated with the experimental results from a previous study. The contact model with temperature-dependent coulomb friction coefficient was concluded to be more reliable when compared to the other three contact models. The temperature for this contact model at the centre of the weld is 505 °C, which differs from the temperature recorded in the experiment by 2 %. The peak temperatures of numerical models with constant coulomb and shear friction coefficients differ from the experimental temperature at the weld centre by 5.17 % and 16.8 % respectively.     

三维网络SiC对铝合金干摩擦磨损性能的影响

用销-盘式高温摩擦磨损实验机研究了LF3铝合金及三维网络SiC(体积分数分别为10％、20％、30％)增强LF3铝基复合材料的干摩擦磨损性能，测量了复合材料及基体合金在室温和高温(25-300℃)条件下的摩擦系数和磨损率，用扫描电镜(SEM)观察其磨损表面，研究了三维网络SiC对铝合金磨损机制的影响．结果表明：复合材料的干摩擦磨损性能远优于基体合金(LF3)，而且随着温度的升高，复合材料的抗磨损性能明显提高．三维网络SiC在磨损表面形成硬的微凸体起承载作用，同时其独特的结构制约基体合金的塑性变形和高温软化，并保护在磨损表面形成的氧化膜．在相同实验条件下，复合材料的摩擦系数、磨损率随着增强体的体积分数的增加而降低．复合材料的摩擦系数在滑行过程中的稳定性明显高于基体合金．     

基于LuGre摩擦模型的叶片碰撞摩擦特性研究

建立了基于LuGre摩擦模型的叶片冠间碰撞摩擦模型,研究了叶片冠间接触碰撞和摩擦的动力学特性和减振机理。并研究了冠间间隙、动静摩擦系数对成组自带冠叶片碰撞摩擦减振效果的影响。通过分析摩擦过程中鬃毛的变形,对LuGre模型进行有条件的简化,研究了带冠叶片接触碰撞运动和摩擦运动的分岔特性。研究结果表明,LuGre摩擦模型可以更加完善的描述预滑动阶段叶片冠间的摩擦特性。     

Increasing the precision of measurements of the characteristics of internal combustion engines

Questions related to techniques of increasing the precision with which the global extrema of time, phase, and frequency characteristics of the functioning processes of the internal combustion engine are measured are considered. These techniques are realized by means of an expert measurement system with digitization of the signals. __________ Translated from Izmeritel’naya Tekhnika, No. 2, pp. 48–51, February, 2007.     

基于非线性静、动力方法的RC简支梁桥连梁装置参数优化研究

连梁拉杆装置是防止强震下RC梁式桥纵向落梁的有效措施,需要对其合理刚度取值进行研究。以典型的铁路RC简支梁桥为对象,采用基于FEMA440性能点轨迹法的能力谱分析方法,以现行《铁路工程抗震设计规范》设计谱及汶川地震动为需求,讨论了不同的场地类型和设防烈度下连梁拉杆的最优刚度分布。研究表明,场地类型对连梁装置刚度取值无显著影响,在8度罕遇烈度设防的四种场地下,连梁装置的刚度均可在0.05~0.15倍的梁体线刚度范围内取值,可有效抑制墩、梁相对位移及桥梁整体地震响应。设防烈度对刚度取值有显著影响,当PGA不超过0.2g时,可不予设置;当PGA为0.4g和0.6g时,连梁拉杆的合理刚度可分别取为0.1倍和0.2倍的梁体线刚度。采用非线性动力时程方法验证了上述结论的合理可靠性,可供桥梁抗震设计及规范修编参考     

一维动静组合加载下深部石英片岩破坏研究

为研究锡铁山铅锌矿深部石英片岩的力学特性,利用分离式霍普金森杆(SHPB)对埋深863¹ 264m的试样进行25、30、35MPa轴压下的一维动静加载实验,和采用LS-DYNA软件模拟了25、30、35、40、45、50 MPa轴压情况下的冲击实验。研究结果表明:在冲击作用下,试样的一维动态抗压强度和破坏所需的入射能随着埋深的增加而增加,并呈现出常见的压剪破坏模式;当轴压40MPa左右,埋深1 428m的岩石动态抗压值达到最大;当轴压低于40 MPa时,轴压的增大能加强试样的抗压能力;当轴压大于40MPa时,轴压的增加反而减弱了试样的抗压能力。     

Increasing the performance characteristics of a cutter used to saw diamond crystals

We show that the application of two-sided ultrasound charging to disks used to cut natural diamond crystals and further hardening of surfaces by depositing diamond-like film on them considerably raise the performance characteristics of a cutting instrument. A. N. Sevchenko Scientific-Research Institute of Applied Physical Problems at the Belarusian State University, Minsk, Belarus. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 72, No. 5, pp. 1004–1007, September–October, 1999.