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.

Effect of thickness of friction material on contact state of ultrasonic motor

Performances of ultrasonic motor (USM) considerably depend on contact state between stator and rotor.Based on an electric contact method,the effects of thickness of single homogeneous friction material and gradient friction material on contact state between stator and rotor were studied.The relative contact length was employed to describe the contact characteristics of stator and rotor.With the decrease of thickness of friction material,the contact characteristic of stator and rotor were analyzed and compared when single homogeneous friction material and gradient friction material were used.The experimental results showed that the effect of gradient friction material on contact characteristic is smaller than that of single homogeneous friction material when the thickness of friction material decreases.The result can provide experimental guidance for design and choosing of friction material for USM.

Numerical Analysis of Thermo-Elastic Contact Problem of Disc Brakes for Vehicle on Gradient Surfaces

In this study, the thermo-elastic effects of frictional heat generation in a disc brake system due to braking actions were simulated. The mathematical model that defined the problem was developed from the kinetic and potential energies of moving vehicles on the gradient surfaces. This problem was solved for the selected geometry of disc brake and pad with their material properties selected from existing literatures using the finite element method and the computational results were obtained. The thermal deformation obtained was in good agreement with similar literature results. Also, for the same braking period and conditions, the results showed that a vehicle ascending a hill gave a higher temperature rise, Von Mises stress and thermal deformation on brake contact surfaces than when descending hill. Therefore, the braking period required to bring a moving vehicle in ascendent motion to a lower speed is expected to be shorter because of the gravity effect than horizontal motion, while descendent motion requires longer braking period.

Pressure Gradient, Power, and Energy of Vortices

We consider small vortices, such as tornadoes, dust devils, whirlpools, and small hurricanes at low latitudes, for which the Coriolis force can be neglected. Such vortices are (at least approximately) cylindrically symmetrical about a vertical axis through the center of a calm central region or eye of radius . In the region fluid (gas or liquid) circulates about the eye with speed . We take to be the outer periphery of the vortex, where the fluid speed is reduced to that of the surrounding wind field (in the cases of tornadoes, dust devils, and small hurricanes at low latitudes) or deemed negligible (in the case of whirlpools). If , angular momentum is conserved within the fluid itself;if , angular momentum must be exchanged with Earth to ensure conservation of total angular momentum. We derive the steepness and upper limit of the pressure gradients in vortices. We then discuss the power and energy of vortices. We compare the kinetic energy of atmospheric vortices and the power required to maintain them against frictional dissipation with the same quantities for Earth’s atmosphere as a whole. We explain why the kinetic energy of atmospheric vortices must be replaced on much shorter timescales than is the case for Earth’s atmosphere as a whole. Brief comparisons of cyclostrophic flow with geostrophic and friction-balanced flows are then provided. We then consider an analogy that might be drawn, at least to some extent, with gravitational systems, considering mainly spherically-symmetrical and cylindrically-symmetrical ones. Generation of kinetic energy at the expense of potential energy in fluid vortices, in geostrophic and friction-balanced flows, and in gravitational systems is then briefly discussed. We explain the variations of pressure and gravitational gradients corresponding to generation of kinetic energy exceeding, equaling, and falling short of frictional dissipation. In the Appendix, we describe a simple method for maximizing power extraction from environmental fluid (air or water) flows. In summary, we provide an overview of features and energetics of Earth’s environmental fluid flows and of gravitational analogies thereto that, even though mostly semiquantitative, hopefully may be helpful.

大屯锡矿尾砂膏体环管管输数值模拟研究

膏体管输沿程阻力是影响管道设计与采场充填质量的关键因素之一,采用Fluent建立与实际环管实验系统一样的管道输送的几何模型,分析得到不同管线沿程阻力损失之间的关系以及膏体配比参数对沿程阻力损失的影响规律。研究表明:膏体在管道中弯管处的速度和压力都发生急剧的变化,弯管外侧压力和速度明显大于弯管内侧,有着明显的梯度。在水平管段速度和压力在管道径向上存在明显的梯度,呈结构流的特点,分为柱塞流动区和边界层区域。在膏体管道输送中管道内膏体的速度和压力均存在着边界效应,随着流速的增大,管输阻力增大;随着膏体质量浓度增加,沿程管道阻力损失变大;随着屈服应力与塑性黏度的增加,沿程阻力损失也增大,获得了不同物料组成、管道内径、管流流速下水平段膏体压力损失,为大屯锡矿最终输送泵、充填管道选型提供了依据。

考虑相含量的TC17钛合金线性摩擦焊中的残余应力

为了获得准确的TC17钛合金线性摩擦焊中的残余应力,建立TC17钛合金弹性常数与相分数之间的数值关系。结合焊接区域的相分数,获得呈梯度分布的弹性常数,并将其引入轮廓法进行计算。结果表明,TC17钛合金的弹性常数与α相分数呈正相关,在宽度约4 mm的焊接区域呈现明显的梯度分布特征;若忽略相分数的梯度分布,计算残余应力时相对误差可达36.06%;修正后的残余应力呈双峰分布,在热影响区边缘处达到峰值,约为442 MPa。这说明考虑相分数的梯度分布是必要的。

微织构排布方式对水润滑轴承启停过程摩擦学性能的影响

梯度排布微织构在提升水润滑轴承摩擦学性能方面具有显著效果,然而梯度排布微织构在水润滑轴承中的应用仍缺乏系统性研究。为了探究梯度排布微织构对水润滑轴承启停过程摩擦学性能的影响,基于Greenwood-Tripp微凸体接触模型、Archard磨损模型求解轴瓦表面的磨损量。通过CFT-I材料表面性能综合测试仪对CNC雕刻机加工的织构化表面进行水润滑条件下的摩擦学试验研究。针对光滑、单一圆形织构、圆形与三角形以轴向交错平行■和周向交错平行分布(1212)方式梯度排布的表面,测量各个表面的磨损量和摩擦因数。通过立体显微镜、扫描电子显微镜对摩擦磨损试验前后的表面形貌和摩擦因数进行分析。数值模拟和试验结果显示,与光滑表面和单一织构化表面相比,梯度排布微织构化表面磨损量和摩擦因数显著降低;圆形与三角形以■方式的梯度排布微织构化表面摩擦学性能最佳,接触表面磨损量最小、表面摩擦因数最低。梯度排布微织构在流体润滑过程中相互影响,可以起到提高轴承表面举升力,减少表面接触,降低表面磨损和摩擦因数的作用。研究不同形状、排布方式下梯度排布微织构化表面的磨损量和摩擦因数的变化规律,可为舰船装备水润滑轴承研制阶段主动设计提供理论基础。

水下平板通气减阻特性研究

为了研究通气射流对水下平板阻力特性的影响,本文采用Mixture多相流模型和Realizable k-ε湍流模型研究了三维水下平板通气射流的流动结构特征,得到了水下平板表面气液流场结构和减阻特性。数值结果表明:气体注入后,受来流影响而紧贴壁面向下游发展。当气体稳定覆盖在平板壁面后,平板阻力系数较不通气情况降低了16.73%。另外,因气体注入壁面边界层后,提升了壁面上的速度梯度,降低了壁面流体粘性系数;在气膜覆盖区(α_(l)>80%),因流体粘性系数的下降量远大于速度梯度的上升量,使流体粘性系数对气膜核心区内的减阻率起决定性作用;对于远离气膜核心区外的壁面,切向速度梯度对摩擦阻力系数的贡献增强。

基于激光熔覆的缸套表面梯度材料制备及其摩擦学性能研究

目的研究功能梯度材料对缸套表面的抗磨减摩作用,提升缸套-活塞环配副的摩擦学性能。方法通过激光打标机在缸套表面制备具有30°角规则纹理排布的凹槽,在凹槽内采用同轴送粉的方式熔覆镍含量不同的铁基粉末,分析熔覆合金层的金相组织,并利用往复式摩擦磨损试验机研究在一定载荷压力下功能梯度材料缸套的摩擦学性能。结果熔覆层金相组织呈现梯度排布,熔覆层与基体材料分子原子交互扩散形成良好的冶金结合。牌号为350、镍质量分数为4.2%、铁质量分数80%的粉末所制备的功能梯度材料,减摩效果最为明显,相比未经处理的对照组,平均摩擦因数降幅为25.4%,且该组在试验中接触电阻的平均值最大,相比对照组提升了63.45%。牌号为330、镍质量分数为9%、铁质量分数为70%的粉末制备的缸套,表面支撑指数最高为0.78,相比于未处理的对照组,增幅达到35%,且试验组活塞环经摩擦后,磨损量均小于对照组。结论制备了30°角分布的功能梯度材料,能使得缸套-活塞环摩擦学系统在工作过程中摩擦副的润滑油膜厚度更厚,且在运行过程中更稳定,以减少摩擦力和降低摩擦因数。同时,增强其支撑能力和储存润滑油的能力,使所制备的缸套摩擦因数显著降低。牌号为350的材料,改善摩擦学性能的效果最优。

温度梯度下SAMs膜对油滴迁移行为控制及减摩效果试验研究

采用自组装单分子膜技术以及局部紫外光刻技术相结合的方法,制备了条形润湿性表面,用于解决由温度梯度作用造成的油滴热毛细迁移而导致的接触区域乏油问题.使用高速摄像机以及接触角测量仪,对温度梯度下,液体石蜡在所制备表面与原始不锈钢表面上的迁移速度、迁移距离及接触角进行了对比.结果表明:在不锈钢表面设计的条形图案能够有效地抑制油滴的热毛细迁移现象.将制备表面进一步应用于摩擦磨损试验中,发现所制备表面能使液体石蜡在摩擦的过程中始终汇聚在摩擦接触区,减缓了接触区乏油,能够明显减少摩擦磨损.此研究为解决由油滴热毛细迁移而引起的接触区乏油问题提供了新思路和新方法.

基于梯度依赖的非局部摩擦模型的土坡稳定性分析

研究了基于梯度依赖的非局部摩擦模型下圆弧滑裂面土坡的稳定性,并对梯度依赖的非局部材料参数进行讨论与分析,研究了此参数对土坡安全系数的影响,从微观的角度分析宏观工程问题发挥机理的本质,发现带微观性质的非局部材料参数变化时,土坡安全系数变化虽然不大,但变化趋势很明显.当讨论土体相关参数对安全系数的影响时,根据梯度依赖的非局部摩擦模型与局部摩擦模型的对比,发现安全系数对内摩擦角的变化比较敏感,可为工程中土坡治理提供参考依据.

医用炭/炭复合材料表面梯度CVD热解炭涂层的摩擦性能研究

采用医用炭/炭复合材料并通过梯度化学气相沉积法(CVD)在其表面制备热解炭涂层,研究分析了涂层的显微结构、摩擦系数、磨损情况.结果发现,该热解炭涂层表面被直径约20μm热解炭球致密覆盖,在断口处呈现紧密、多层的热解炭.与用沥青浸渍/炭化法制备的炭/炭复合材料相比,在干摩擦时,热解炭涂层样品的摩擦系数更大;在模拟人体关节的湿摩擦时,它的摩擦系数低;在干摩擦和湿摩擦的情况下,它的磨损要小很多.这些结果表明利用梯度的化学气相沉积法(CVD)制备医用炭/炭复合材料的涂层可以提高其表面的耐磨性.

超声马达梯度涂层摩擦材料研究

超声马达摩擦材料应同时具有良好的摩擦学特性和一定的接触变形要求,目前所用单一均质结构摩擦材料较难满足这一要求,需要研制新型摩擦材料.本文从摩擦学的减摩结构模型反推出一种增摩结构模型,针对超声马达对摩擦材料的要求,提出梯度涂层摩擦材料的设计思想,采用表面黏涂法研制了一种具有梯度结构的涂层摩擦材料.利用超声马达模拟试验装置考察了涂层厚度对超声马达性能的影响,初步验证了模型的正确性.在本文的试验条件下,当涂层材料表层厚度为1mm,底层厚度为0.7mm左右时,超声马达具有较好的性能.与其它种类的摩擦材料相比较,梯度涂层摩擦材料可以满足超声马达的使用要求,可望提升超声马达的性能,具有良好的发展前景.

测试压裂分析诊断技术在海拉尔油田的应用

介绍了测试压裂分析解释技术在海拉尔油田复杂岩性储层压裂中的应用成果。阐述了导致近井高摩阻、高停泵压力梯度和高滤失等疑难问题的机理和原因;讨论了应用测试压裂诊断分析技术确定压裂目的层存在难点的方法及相应的处理措施;详细总结分析了针对海拉尔复杂岩性储层压裂,形成的近井高摩阻、高停泵压力梯度及天然裂缝发育程度的诊断评价标准和相应处理技术的应用效果;提出了需要进一步研究解决的具体问题和技术难点。

摩擦因素对微压痕实验的影响

材料在发生微米亚微米尺度不均匀变形时表现出尺度效应,微压痕问题是典型代表。目前的微压痕研究中普遍采用无摩擦假设,而相对缺少对摩擦因素的深入研究。基于CMSG低阶应变梯度塑性理论,通过有限元分析研究了摩擦因素对微压痕实验的影响。结果表明对于目前普遍采用的较钝的Berkovich压头(简化为圆锥后顶角为140.6?),摩擦的影响并不重要,可以简化为无摩擦情况。

压差密度仪在海上油田应用中的适应性探讨

受海上油田高产、井斜大、油管生产等影响,传统放射性流体密度仪的替代仪器压差密度仪应用初期测量效果较差。为此,在深入研究压差密度仪测井原理的基础上,探讨了影响压差密度仪测量效果的各类因素,并进行了实际测井资料分析研究。结果表明,摩阻、加速度、井斜及硅油等因素对测量值均有影响,其中摩阻是影响测量效果的最主要因素。结合海上油田生产状况,总结提出了考虑摩阻影响的仪器适用性图版,该图版对作业前压差密度仪的适用性分析有较好的指导意义。

一种新的长输管道泄漏点定位方法

将压力梯度法与逆瞬态法结合,提出了适合长输管道的泄漏点定位方法.该方法将泄漏点前后的摩阻系数以及泄漏流量系数看作优化控制变量、水击方程的数值计算结果与测量值之差的绝对值作为控制目标,利用遗传算法优选泄漏点前后的摩阻系数,与压力梯度法结合不断迭代求解泄漏点的位置.通过输水管道的泄漏实验得到该方法漏点定位的平均误差为4%左右.

高温流变应力曲线修正方法

通过Cr9Mo钢在摩擦和温度梯度共同作用下的热压缩实验来模拟材料的压缩过程,将实验得到的流变应力曲线直接作为材料的真实流变应力曲线输入模拟程序材料库中,将模拟和实验所得载荷与位移的变化关系曲线进行对比,并利用迭代法消除两者误差,从而获得材料修正后的流变应力曲线.结果表明,所提出的修正方法可以降低摩擦和温度梯度所造成的流变应力误差,可以获得精确的材料流变应力曲线,简单、实用并具有普适性.

三种压裂液体系在苏里格气田现场施工应用中的比较

通过对羟丙基胍胶压裂液体系、羧甲基胍胶压裂液体系、清洁压裂液体系从压裂液配方、压裂施工机理、压裂施工加砂量、压裂施工摩阻、压裂后产量五方面在苏里格气田施工现场数据分析,确定了其摩阻梯度、伤害气层的大小顺序,找到了其优缺点及其适用范围。

硅含量对喷射沉积SiC_p/Al-Si功能梯度复合材料摩擦磨损性能的影响

对喷射沉积技术制备的不同硅含量铝基功能梯度复合材料进行室温摩擦学性能研究。结果表明：当硅含量分别为7%、17%和20%时,SiCp/Al-Si功能梯度复合材料的摩擦因数随载荷或滑动速度（转速）的增加而减小;随着SiC颗粒含量的增加,摩擦因数呈增大趋势;随基体硅含量增加,摩擦因数越稳定。在转速300~500 r/min、700~900 r/min和载荷10~30 N、40~50 N时,磨损率随转速、载荷的增加而升高,随SiC颗粒含量的增加而降低,梯度变化明显;在转速500~700 r/min和载荷30~40 N时,随转速、载荷的增加,磨损率反而减小;随基体硅含量的增加,磨损率呈降低趋势,材料在摩擦过程中生成的机械混合层（MML）厚度呈减小趋势。