A numerical flat plate friction line and its application

This paper studies the regression of a numerical two-dimensional flat plate friction line using the RANS method with the SST k - co turbulence model. Numerical simulations with different inlet turbulence kinetic energies are first conducted. Comparing with the experimental data, the finest grid and the appropriate inlet turbulence kinetic energy are selected to compute the fiat plate friction resistance at 14 Reynolds numbers. Two numerical friction lines are obtained by the least squares root fitting method and one similar to that of the ITTC-1957 line and the cubic polynomials in logarithmic scales, and the results are compared to the friction line proposals available in the open literature. Finally, the full scale viscous resistance predictions of DTMB5415, KVLCC2, SUBOFF are compared between the numerical friction line and the friction line proposals available in the open literature based on the form factor approach. It is shown that the form factor keeps relatively constant via the numerical friction line for the bare hull, but the form factor concept in extrapolating the model test results is not appropriate for appended hulls. It is suggested that for computing a form factor numerically, it is best to use a numerical friction line.

Research on design system of band conveyer driven by linear friction

The band conveyer driven by linear friction is a new device. It can reduce drivesize and conveyor belt tensity, and increase delivery capacity. It has feasibility and usability particularly in altering the original conveyer and solving the problems of capacity insufficiency. The technology has brought certain difficulty for engineers, because it has certaindifficulty both in theory and in calculation. Therefore, Visual Basic 6.0 programming technology was used to develop a set of 'the design system of the band conveyer driven bylinear friction.' After being proved in the field, it can completely meet the demands of thedesign. This paper introduced its main theory or basis in design, so as to provide relatedtechnical support to this kind of project.

Study of the Judder Characteristics of Friction Material for an Automobile Clutch and Test Verification

The friction judder characteristics during clutch engagement have a significant influence on the NVH of a driveline.In this research,the judder characteristics of automobile clutch friction materials and experimental verification are studied.First,considering the stick-slip phenomenon in the clutch engagement process,a detailed 9-degrees-of-freedom(DOF)model including the body,each cylinder of the engine,clutch and friction lining,torsional damper,transmission and other driveline parts is established,and the calculation formula of friction torque in the clutch engagement process is determined.Second,the influence of the friction gradient characteristics on the amplification or attenuation of the automobile friction judder is analyzed,and the corresponding stability analysis and the numerical simulation of different friction gradient values are carried out with MATLAB/Simulink software.Finally,judder bench test equipment and a corresponding damping test program are developed,and the relationship between the friction coefficient gradient characteristics and the system damping is analyzed.After a large number of tests,the evaluation basis of the test is determined.The research results show that the friction lining with negative gradient characteristics of the friction coefficient will have a judder signal.When the friction gradient value is less than-0.005 s/m,the judder signal of the measured clutch cannot be completely attenuated,and the judder phenomenon occurs.When the friction gradient is greater than-0.005 s/m,the judder signal can be significantly suppressed and the system connection tends to be stable.

Measurement of the friction coefficient of a fluctuating contact line using an AFM-based dual-mode mechanical resonator

A dual-mode mechanical resonator using an atomic force microscope （AFM） as a force sensor is developed. The resonator consists of a long vertical glass fiber with one end glued onto a rectangular cantilever beam and the other end immersed through a liquid-air interface. By measuring the resonant spectrum of the modified AFM cantilever, one is able to accurately determine the longitudinal friction coefficient ξv along the fiber axis associated with the vertical oscillation of the hanging fiber and the traversal friction coefficient ξh perpendicular to the fiber axis associated with the horizontal swing of the fiber around its joint with the cantilever. The technique is tested by measurement of the friction coefficient of a fluctuating （and slipping） contact line between the glass fiber and the liquid interface. The experiment verifies the theory and demonstrates its applications. The dual-mode mechanical resonator provides a powerful tool for the study of the contact line dynamics and the rheological property of anisotropic fluids.

线接触弹流润滑摩擦副刚度阻尼拟合公式

弹流润滑油膜具有显著的弹簧阻尼作用,对齿轮、滚动轴承、凸轮等高副接触零件的动力学性能具有重要影响,然而目前关于弹流摩擦副刚度阻尼的认识还不统一。运用数值方法求解线接触弹流润滑摩擦副的摩擦学-动力学耦合模型,获得线接触弹流润滑摩擦副在简谐激励下的阻尼环,通过阻尼环识别出线接触弹流润滑摩擦副的刚度和阻尼;用变量控制的方法研究载荷、卷吸速度、材料参数等对线接触弹流润滑摩擦副刚度和阻尼的影响,并分析载荷、卷吸速度影响线接触弹流润滑摩擦副刚度阻尼的机制。结果表明,线接触弹流润滑摩擦副刚度阻尼随载荷增加而变大,随速度增加而减小。在数值解的基础上,拟合出线接触弹流润滑摩擦副刚度和阻尼公式,结果显示,载荷对弹流润滑摩擦副的刚度和阻尼影响最显著,而且弹流润滑摩擦副的刚度随载荷、速度和材料参数的变化幅度比阻尼的大。对拟合公式精度的检验表明,在很宽的参数范围内,拟合公式计算结果与数值解的相对误差小于10%,所提出的刚度和阻尼拟合公式具有很高的精确性。

特高压输电线路磁场对电力金具材料摩擦磨损的影响

目的通过分析特高压直流线路工频磁场环境对电力金具材料磨损行为的影响,探究其磨损机理,为联接金具的磨损失效预测提供理论依据。方法分析线路实际运行参数,计算工频磁场强度,采用自制电磁线圈与M-2000型磨损试验机相结合,通过分组控制变量法研究额定工况下金具材料的磨损过程,以及不同磁场强度下材料的磨损行为。结果在磁场环境中材料的磨损程度远小于无磁场情况下。在0~800 A/m范围内,随着磁场强度的增加,摩擦因数稍降低,质量损失量和磨损率呈下降趋势。在不同磁场强度下磨损试样均呈现越贴近摩擦接触表面区域其显微硬度越高,且随着纵深向后呈递减趋势。在无磁场情况下,磨损接触表面的犁沟较深,遍布锯齿型边缘的凹坑和山脊型微凸峰。在磁场环境中试样的接触表面和磨屑表面更加光滑平整,且氧含量明显升高。结论在无磁场情况下,接触表面为严重的磨粒磨损和黏着磨损。在磁场环境中,磨损试样在短时间内经历了初期磨合阶段和磨损加剧阶段,从而加速过渡到稳定磨损阶段,由严重的磨粒磨损和黏着磨损加速向轻微磨损转变。稳定阶段的主要磨损机制为氧化磨损,并伴随着轻微的磨粒磨损、黏着磨损,以及两摩擦副与磨屑“阻隔层”之间的三体磨损。工频磁场环境对试样磨损起到了一定的减摩作用,磨损程度减轻。

进口汽车用制动器衬片摩擦性能检测与产品不合格原因分析

随着国家经济的快速发展和人民对高质量、安全性的生活方向发展,而进口汽车在这一需求下逐年呈上升趋势,其中进口汽车用制动器衬片是汽车制动系统中最关键的安全零件,对制动效果起关键性作用,本文采用取样法对汽车盘式制动器衬片的摩擦性能进行测定和分析,并针对进口汽车用制动器衬片摩擦性能检测不合格原因分析。

煤矿长距离带式输送机线摩擦驱动增压装置设计与应用

针对线摩擦带式输送机运行过程中,空载、少载时承载带与传动带间摩擦产生的驱动力不足,导致主机系统能耗增加,以及满载时承载带与传动带间摩擦力激增造成的皮带过度磨损问题,设计了带式输送机线摩擦驱动增压装置,并通过模拟软件对其进行仿真分析.结果表明,摩擦驱动增压装置可按照预先设定的压力大小,自动调节皮带的法向力,能够改善驱动力不足的现象,有利于输送机长距离、大运量运输.同时为类似工况下线摩擦带式输送机的大规模投产使用提供借鉴.

钢架桥施工对下穿隧道的影响

鉴于钢架桥的施工往往会对其下穿隧道产生一定的影响,文章运用有限元软件Midas GTS NX建立三维模型,研究钢架桥施工对下穿隧道的影响。研究结果发现:使用摩擦型桩基的钢架桥,在施工过程中引起的隧道变形以竖向沉降为主,且桩基距隧道的距离越近,隧道结构的变形越明显;钢架桥桩基及上部结构施工过程中,会引起衬砌水平向和竖向的收敛,且有衬砌的竖向的收敛值大于水平向的收敛值;钢架桥施工过程中,桩基轴力表现出由上至下逐渐减小的特点,侧摩阻力表现为由上至下逐渐增大的特点,这与实际工程中摩擦型桩的工作机理相一致。

桩摩阻力计算方法比选评估

通过收集上海地区典型工程试桩资料,统计应用黄强法及延伸线法计算的桩基桩侧摩阻、桩端阻力,与桩侧摩阻、桩端阻力的实测值进行对比分析。研究发现两种方法计算得到的端阻比大于实测值,且延伸线法结果离散性更大。故采用黄强方法打五折确定桩端阻力和桩侧摩阻力。

Theoretical analysis of thermoviscoelastic contact between friction lining and wire rope in mine friction hoists

Serious accidents of mine hoists caused by high-speed sliding between friction lining and wire rope are often seen in coal mines.In order to solve this problem,we analyzed the contact characteristics between friction lining and wire rope.Then we carried out a dynamic mechanical analysis(DMA) to explain the change in mechanical properties of the friction lining as function of temperature and load frequency and found that temperature has a stronger effect on the mechanical properties than the frequency.We used multiple regression analysis to obtain the thermoviscoelastic constitutive relations of the friction lining.As well we derived the analytic solution for the thermoviscoelastic contact radius and pressure by combining the theory of viscoelastic contact mechanics with thermoviscoelastic constitutive relations.

平整机组暗纹缺陷形成机理

针对国内某双机架平整机组生产过程中带钢出现的暗纹缺陷,分析了暗纹缺陷的宏观形貌,推断出暗纹形成的原因为平整轧制过程中金属流动受阻,并对比机组在湿平整改造之后的暗纹缺陷消失情况,进一步证实了推断的准确性。首先,通过平整过程中带钢的整体受力情况分析,确定了影响暗纹生成的主要作用力为平整轧制力和带钢与工作辊的摩擦力。针对平整过程中辊系和带钢的受力与变形情况,分别建立了辊系弹性变形模型、带钢出口厚度模型和金属塑性变形模型,进一步确定了通过联立模型求解轧制力沿带钢横向分布的计算方法,根据平整过程中轧制力计算模型给出了摩擦系数的反算方法。在此基础上,采取半无限平面假设分析带钢暗纹的受力模型,并考虑带钢平整过程中受到的垂直集中力和水平集中力,给出了暗纹判定标准并命名为暗纹指数。最后,选取典型规格生产带钢的生产工艺进行计算,确定了不同取样厚度下的暗纹指数,分析了取样厚度与暗纹缺陷发生的关系。

周期性载荷作用下的滚珠丝杠相邻滚珠间热弹流数值计算

滚珠丝杠相邻滚珠之间存在零卷吸速度接触,与常见的纯滚动或滚滑接触相比工况更恶劣,周期性载荷作用下相邻滚珠之间的接触则更为复杂。建立零卷吸工况下正弦波载荷作用的滚珠丝杠相邻滚珠间热弹流数值计算模型,采用多重网格法求解压力,多重网格积分法求解弹性变形,逐列扫描技术求解温度场,实现对线接触热弹流润滑的数值模拟。并以R100-25Y2型滚珠丝杠为研究对象,分析其油膜特性以及载荷幅值和表面波纹度对油膜特性的影响,结果表明:在加载过程中,由于挤压效应增强,“温度-黏度楔”效应增强,油膜凹陷深度及中心膜厚增大,最小膜厚减小,接触区最大温升增大,摩擦系数减小,卸载过程则相反;由于载荷变化的时变效应,油膜变化相比载荷变化存在一定的滞后性,而载荷波动幅值的增大进一步增强了该滞后性;表面波纹度的存在造成油膜压力和膜厚曲线的波动,特定的波纹度长度可导致中心膜厚和最大温升增大,而最小膜厚和摩擦系数减小。

Effect of ZrSiO_4 on the Friction Performance of Automotive Brake Friction Materials

Friction-wear properties of the ZrSiO4 reinforced samples were measured and compared with those of plain bronze based ones. For this purpose, density, hardness, friction coefficient wear behaviour of the samples were tested. Microstructures of samples before and after sintering and worn surfaces were also investigated by scanning electron microscopy （SEM）, and the wear types were determined. The optimum friction-wear behaviour was obtained in the sample compacted at 500 MPa and sintered at 820℃. Density of the final samples decreased with increasing the amount of reinforcing elements （ZrSiO4） before pre-sintering. However after sintering, there is no change in density of the samples including reinforcing elements （ZrSiO4）. With increasing friction surface temperature, a reduction in the friction coefficient of the samples was observed. However, the highest reductions in the friction coefficients were observed in the as-received samples containing 0. 5% reinforced ZrSiO4. The SEM images of the sample indicated that while bronze-based break lining material without ZrSiO4 showed abrasive wear behaviour, increasing the amount of ZrSiO4 resulted a change in abrasive to adhesive wear mechanism. All samples exhibited friction-wear values, which were within the values shown in SAE-J661 standard. With increasing the amount of reinforcing ZrSiO4, wear resistance of the samples was increased. However samples reinforced with 5% and 6% ZrSiO4 showed the best results.

Roughness evaluation in shotcrete-lined water tunnels with invert concrete based on cases from Nepal

Most of the existing roughness estimation methods for water tunnels are related to either unlined or concrete/steel-lined tunnels. With the improvement in shotcrete technology, advancement in tunneling equipment and cost and time effectiveness, future water tunnels built for hydropower projects will consist of rock support with the extensive use of shotcrete lining in combination with systematic bolting and concrete lining in the tunnel invert. However, very little research has been performed to find out tunnel surface roughness for shotcrete-lined tunnels with invert concrete, which is important in calculating overall head loss along the waterway system to achieve an optimum and economic hydropower plant design. Hence, the main aim of this article is to review prevailing methods available to calculate tunnel wall roughness, and to use existing methods of head loss calculation to back-calculate roughness of the shotcrete-lined tunnels with invert concrete by exploiting measured head loss and actual cross-sectional profiles of two headrace tunnels from Nepal. Furthermore, the article aims to establish a link between the Manning coefficient and the physical roughness of the shotcrete-lined tunnel with invert concrete and to establish a link between over-break thickness and physical roughness. Attempts are also made to find a correlation between over-break thickness and rock mass quality described by Q-system and discussions are conducted on the potential cost savings that can be made if concrete lining is replaced by shotcrete lining with invert concrete.

刮板输送机中部槽的磨损特性及其耐磨优化研究现状

为了降低刮板输送机中部槽磨损失效而产生的影响和提高耐磨性能,综述中部槽磨损特性和耐磨优化研究的发展历程,包括磨损形式、磨损原因、磨损形貌和磨损区域等理论研究,输运条件、煤岩散料特性等试验研究,离散元法及与多体动力学耦合的仿真分析等。概括耐磨材料、表面强化技术、结构改进、仿生设计等4种提高中部槽耐磨性能的方法。提出磨损特性研究的下一步方向为磨损内在本质的研究、磨损定量的研究,提出用非线性理论方法进行中部槽磨损量拟合、磨损预测等新的研究思路;耐磨优化研究重点应在节约成本,并将耐磨技术尽快应用于刮板输送机生产实际;用非线性理论方法进行中部槽磨损量拟合预测,并从中部槽摩擦副之间的相互作用为出发点进行磨损特性和耐磨优化的研究。

基于滑模变结构的虚拟总轴控制策略研究

印刷过程中高精度的套印取决于预套准阶段对调节辊的精准定位。针对摩擦对套印精度的影响,以及扰动对同步精度的影响,提出了基于滑模变结构的虚拟总轴控制策略,并利用李亚普诺夫函数证明了该控制算法的稳定性。实验结果表明所提出的控制策略不但能够有效地扰动及预套准阶段摩擦对系统跟随性能的影响,而且能提高无轴传动印刷机的同步控制精度。

一种摩擦线机运小车在线自动加油方法的应用

摩擦线机运小车在线自动加油装置可实现机运小车在线自动加油工作,此种方法无需将机运小车下线到维修站,也无需人工进行加油,解决机运小车加油工作量大、效率低的问题。

薄板铝合金搅拌摩擦焊的组织与力学性能

采用单、双面焊方法对2 mm厚5052铝合金进行了搅拌摩擦焊试验,研究了接头的微观组织形貌、显微硬度、拉伸性能和断口形貌。结果表明:单、双面焊接头内部均存在“S”线,双面焊能够有效改善“S”线的分布情况,避免单面焊底部弱连接;单、双面焊焊缝截面横向硬度均呈“W”型,硬度沿厚度方向总体逐渐降低,单、双面焊沿厚度方向硬度最高分别为68.4 HV、84.2 HV,双面焊焊缝晶粒更加细化;单、双面焊平均抗拉强度分别为198、210 MPa,双面焊接头力学性能优于单面焊;通过接头断口形貌分析,单、双面焊接头断裂方式均为韧性断裂与撕裂韧性断裂混合形式。

基于ANSYS的汽车盘式制动器的结构优化设计

汽车在制动时,动能瞬间转换成大量热能,这些热量来不及散发,使制动盘和摩擦衬片的温度瞬间上升,材料的热衰退直接影响到制动的可靠性,所以制动器的瞬态热-固耦合分析在制动器设计过程中有着举足轻重的作用。本文在SolidWorks软件中建立了某轿车盘式制动器的简化三维模型,并通过ANSYS Workbench软件对某轿车紧急制动时的制动器进行了瞬态热-固耦合仿真分析,分析了制动盘和摩擦衬片的可靠性,得到刹车后制动器、制动盘和摩擦衬片温度随时间的变化云图。热-固耦合分析结果表明,制动器的温度变化及分布规律是合理的,所以此设计的制动器散热性能良好,符合预期目标。同时本文在满足安全系数要求的情况下,对制动盘进行打孔和开槽,既增强了制动盘的散热性能,又提高了制动盘结构强度和安全系数,进一步实现了结构轻量化,为以后制动器的优化设计提供了参考。