预压力对弯纵振子微驱动的瞬态摩擦和磨损影响研究

利用自行研发的试验系统研究2种不同摩擦配副间瞬态摩擦和磨损,自动记录了预压力条件下摩擦配副正压力与驱动力的动态曲线,给出了摩擦副磨损表面光学照片.对2种不同配副动态正压力和驱动力峰值随预压力变化进行数据处理,得到其变化规律曲线,并对微驱动摩擦和磨损机制进行分析.结果表明:对于不同的摩擦副材料,随着预压力增大,弹性模量大的动态正压力大,而弹性模量小的驱动力效果好;超声波微驱动过程中,纵向振动造成下试样表面的微凸峰塑性破坏,而由弯曲引起的横向摆动造成下试样表面擦伤.     

纤维织物型摩擦材料弹性模量的实验研究

介绍了织物衬垫型摩擦材料压缩弹性模量的实验测试研究工作,在液压压机上应用差分位移测试装置精确测试了不同压力下的衬垫变形量,从而获得衬垫弹性模量。对不同工艺固化压力下的衬垫材料弹性模量进行了实验研究,测试了固化压力对自润滑衬垫材料力学性能的影响。准确的衬垫摩擦材料弹性模量数据对应用自润滑衬垫材料的轴承设计计算具有非常重要的意义。     

基于摩擦正交实验的连续回转电液伺服马达定子材料的选择

为了降低摩擦对连续回转电液伺服马达低速性能的影响,根据马达定子及叶片的耐磨性要求,从多种常用于马达定子的材料中筛选出3种材料,采用正交实验设计思想,在不同硬度、表面粗糙度及不同压力的情况下,利用MPX200型盘销式摩擦试验机进行摩擦磨损实验,通过极差分析方法得到对摩擦系数影响最大的因素为定子内表面粗糙度;并利用Dimension 3100型原子力显微镜(AFM)观察分析了3种材料的磨损表面.结果表明,定子材料为Cr12MoV,叶片材料为W18Cr4V时,其摩擦系数及磨损量最小,Cr12MoV磨损表面呈轻微的犁沟现象,符合马达定子工况要求,为大排量超低速连续回转电液伺服马达的设计及加工提供了参考依据.     

弹性模量对水润滑轴承的性能影响

从材料的角度,研究弹性模量对水润滑塑料合金轴承的性能影响,包括轴承承载能力、水膜形状曲线、压力曲线和最小水膜厚度等。研究表明:在选择水润滑轴承材料时应根据其承载能力来确定轴承材料的弹性模量范围;在承载能力范围内,从弹性模量这个角度来说,应当尽可能选择弹性模量低并具有良好摩擦磨损性能的材料,因为选择较小弹性模量的材料有利于提高最小水膜厚度,从而改善水润滑轴承摩擦副的摩擦磨损性能。     

SiO2颗粒增强酚醛树脂基摩擦材料力学性能研究

为探讨陶瓷颗粒对树脂基摩擦材料力学性能的影响,以SiO_2颗粒增强酚醛树脂基摩擦材料为例,利用三点弯曲实验研究颗粒特征对弯曲强度的影响,建立材料内部弹性应力场分布模型,并从细观力学角度进行分析。实验结果表明:添加二氧化硅陶瓷颗粒后,复合材料的弯曲强度降低、弹性模量升高;复合材料弯曲断裂截面显示脆性断裂特征,断裂过程中裂纹遇到颗粒贯穿通过;复合材料弯曲强度随颗粒含量增加而降低,随颗粒弹性模量增加先减小后增大。理论分析表明:陶瓷复合树脂基摩擦材料内部最大应力值位于颗粒边缘处;最大应力值随颗粒与基体弹性模量比值增大而增大;复合材料的平均应力与颗粒的含量成正相关。实验和理论研究表明,陶瓷颗粒添加引起材料内部应力集中,且与颗粒弹性模量和颗粒含量成正相关。     

磁流变弹性体的磁致摩擦性能研究

为探究磁流变弹性体的磁致摩擦性能,通过试验制备了不同质量分数的各向同性和各向异性的磁流变弹性体,搭建了摩擦试验台架并进行摩擦试验,试验结果表明:各向同性的磁流变弹性体在磁场作用下,摩擦因数随磁场增加而降低,并随着羰基铁粉质量分数增加呈非线性变化,当质量分数大约在1:1.5时,摩擦因数变化最大,减小了约25%,但对于各向异性的磁流变弹性体,磁场的施加对摩擦因数的影响具有不确定性,试验还发现这种磁流变弹性体的摩擦因数在轻载条件下随着负载的增大而减小。随后从材料表面的粗糙度、弹性模量以及正压力角度对试验现象进行解析,构建磁流变弹性体摩擦因数与弹性模量关系模型,并选取质量分数为1:3的样本试验进行验证,当磁场强度约为500 m T时,磁流变弹性体表面粗糙度减小约20.7%,磁场强度约为250 m T时,弹性模量增大约22%,与理论预测相符。     

丁腈橡胶对腰果壳油改性酚醛树脂基摩擦材料性能的影响

为使腰果壳油-酚醛树脂基摩擦材料满足重型机械和设备的使用要求,基于干法工艺,采用丁腈橡胶对腰果壳油-酚醛树脂进行共混二次改性,研究不同含量丁腈橡胶对摩擦材料力学性能、耐热性能、摩擦磨损性能的影响。结果表明:丁腈橡胶的加入能够提高摩擦材料的冲击强度,同时降低材料的弹性模量和剪切模量,但随着橡胶含量的增加,摩擦材料的耐热性逐渐下降;丁腈橡胶含量的增加会提升摩擦材料的摩擦因数稳定性并能够保证较高的低温摩擦因数,当橡胶质量分数5%时,摩擦材料表现出最好的抗磨损性能。     

电液伺服摆动马达的密封泄漏与摩擦特性

为了提高电液伺服摆动马达的密封效果,借助于有限元软件ADINA对采用聚四氟乙烯密封件和O形圈的组合密封在不同密封结构、预压缩量和介质压力下进行接触应力分析;由缝隙流动原理推导泄漏量和摩擦力之间的关系;综合考虑密封泄漏量和摩擦力,确定适合于摆动马达的密封结构形式及预压缩量;利用摩擦磨损试验机测试聚四氟乙烯在相同介质压力、不同频率下的摩擦因数,分析其摩擦情况。结果表明,O形圈预压缩量为20%时具有较好的密封效果;星形密封件具有更高的耐压能力,更适合于摆动马达的应用场合;聚四氟乙烯的摩擦因数随着工作频率的增加而减小,说明其适合在高频率的条件下工作。研究表明,该组合密封符合电液伺服摆动马达的动态性能要求。     

低速大扭矩液压马达摩擦副磨损机制研究

针对油缸和曲轴构成的摩擦副磨损严重,影响低速大扭矩液压马达性能和寿命的问题,根据摩擦副油膜理论对该类液压马达在高速低载的工况下摩擦副易产生磨损的原因进行理论分析,找出影响摩擦副油膜承载能力和稳定性的因素。结果表明:适当地增加摩擦副张角的范围有利于提高油膜的承载能力;液压马达在低速工况下运行稳定,当转速较高时,由于剪切流作用明显,导致摩擦副一侧的油膜承载能力有所降低,不利于摩擦副的稳定运行;在一定范围内,油液压力越大,油膜系统的响应灵敏度越高,马达运转速度较高时,有利于摩擦副系统的正常运行。     

超声波电动机定子和转子接触状态的数值分析

提出了一个描述行波超声波电动机定子和转子接触的简化模型，用有限元法计算了摩擦材料的弹性模量和动摩擦因数对定子和转子接触状态的影响。建立了在一定接触条件下与定子接触的摩擦材料的变形和其弹性模量的关系。测试了摩擦材料性能对超声电动机堵转力矩的影响。根据数值计算结果和试验确定的摩擦材料性能，得到了更精确的摩擦材料的接触变形范围，为摩擦材料的选择提供了依据。     

履带车辆硬地面转向阻力矩算法的研究

提出履带车辆一边履带驱动、另一边履带制动实现转向时地面产生的阻力矩的计算方法。通过建立相对车辆静止的动坐标系,推导出履带板上任意点的运动速度方程。地面对履带板上接触点的摩擦力方向与该点的运动速度方向相反,从而确定出产生转向阻力矩的摩擦力的大小和方向,对转向中心取矩得到转向阻力矩。通过求解运动学方程组,得出转向阻力矩。研究表明,履带与地面问摩擦力沿履带方向的分力提供转向驱动力,垂直履带方向的分力产生转向阻力。该转向阻力矩计算方法比传统计算方法更加精确。     

Investigation of the overall friction coefficient in single-pass scratch test

Single-pass scratch test on bilinear elastic–plastic materials with a conical indenter was simulated using a three-dimensional finite element model. The influence of the interfacial friction coefficient μ_s and the apical angle α of the indenter on the induced maximum tangential force F_T, normal force F_N, and the overall friction coefficient μ=F_T/F_N, were systematically studied. It was found that the induced tangential force is greater than the normal force when the apex is small and vice versa when the apex is large. The tangential force increases with μ_s, but the normal force decreases with μ_s. The overall friction coefficient μ was found to increase linearly with μ_s and tangent of the attack angle of the indenter. The relationship between the adhesion frictional component (μ_a), the plowing frictional component (μ_p), and the interfacial friction coefficient μ_s was analyzed. An analytical model for the overall friction coefficient μ was also developed based on the interaction between the indenter and the specimen and compared to the numerical results. The model was found to yield a good agreement with the finite element simulation results.     

Mechanical anisotropy of the human knee articular cartilage in compression

Articular cartilage exhibits anisotropic mechanical properties when subjected to tension. However, mechanical anisotropy of mature cartilage in compression is poorly known. In this study, both confined and unconfined compression tests of cylindrical cartilage discs, taken from the adult human patello-femoral groove and cut either perpendicular (normal disc) or parallel (tangential disc) to the articular surface, were utilized to determine possible anisotropy in Young's modulus, E, aggregate modulus, Ha, Poisson's ratio, v and hydraulic permeability, k, of articular cartilage. The results indicated that Ha was significantly higher in the direction parallel to the articular surface as compared with the direction perpendicular to the surface (Ha = 1.237 +/- 0.486 MPa versus Ha = 0.845 +/- 0.383 MPa, p = 0.017, n = 10). The values of Poisson's ratio were similar, 0.158 +/- 0.148 for normal discs compared with 0.180 +/- 0.046 for tangential discs. Analysis using the linear biphasic model revealed that the decrease of permeability during the offset compression of 0-20 per cent was higher (p = 0.015, n = 10) in normal (from 25.5 x 10(-15) to 1.8 x 10(-15) m4/N s) than in tangential (from 12.3 x 10(-15) to 1.3 x 10(-15) m4/N s) discs. Based on the results, it is concluded that the mechanical characteristics of adult femoral groove articular cartilage are anisotropic also during compression. Anisotropy during compression may be essential for normal cartilage function. This property has to be considered when developing advanced theoretical models for cartilage biomechanics.     

Experimental investigation on the effect of tangential force on wear and rolling contact fatigue behaviors of wheel material

The study aims to explore the effect of tangential force on wear and rolling contact fatigue (RCF) behaviors of wheel material using a JD-1 wheel/rail simulation facility. The normal, tangential and lateral forces between the wheel/rail rollers are controlled, and the magnetic power brake was used to generate the tangential forces (16–330 N). The results indicate that the surface hardness and wear loss of wheel rollers increase with the tangential force increasing. The surface cracks mouths are perpendicular to the resultant directions of the frictional forces. There are visible secondary cracks and multilayer cracks and the interlayer material of multilayer cracks are easy to break. The compositions of wear debris consist of Fe₂O₃, Fe₃O₄ and iron.     

纤维方向对单向C/SiC复合材料磨削加工性能的影响

为了研究碳纤维编织复合材料的去除机理,探明纤维编织方向对磨削加工性能的影响,设计并制备了单向复合材料C/SiC,并沿纤维典型方向进行了磨削实验。结果表明,单向复合材料磨削时,切向磨削力和法向磨削力均呈如下规律：法向磨削＞纵向磨削＞横向磨削;磨削加工过程中表面粗糙度值呈如下规律：纵向磨削＞法向磨削＞横向磨削。对加工表面显微形貌的分析,揭示了陶瓷基复合材料微观多向去除机理。     

Seizure of elastic material sliding through a rigid die

Mechanisms causing frictional locking due to the interaction between normal load and frictional force are described. The particular type of jamming produced when an elastic material is pushed between fixed rigid plates is discussed in detail. Experiments, using rubber as the elastic material and aluminum for the rigid plates, support a theoretical analysis of this effect.     

切向力对高温发汗润滑胞体结构的接触稳定性影响

基于高温发汗润滑材料厚壁胞体的接触力学模型,利用ANSYS有限元软件分析了切向力与法向力耦合作用下厚壁胞体孔口应力的分布情况,从而探讨了切向力对厚壁胞体接触稳定性的影响。结果表明：切向力的存在对单孔厚壁胞体的接触强度及其断裂失效行为影响不大,但是会导致双孔及四孔厚壁胞体的接触强度下降,而三孔厚壁胞体的接触强度及断裂失效行为不但与切向力的大小有关,而且与切向力的方向密切相关。因此,在胞体材料结构设计与制备中,控制其胞体结构形态非常重要。     

Numerical and theoretical study of friction between atomically clean surfaces and effects of impurities

Sliding friction between atomically clean surfaces with and without impurities is studied numerically and theoretically. We show that the maximum static frictional force shows complicated behavior as a function of the elastic constant of the material, which results from various discommensurate structures. We also show that impurities can diminish the maximum static frictional force. Velocity dependences of the kinetic frictional force in the absence and presence of impurities are calculated. Transverse pinning, which yields static frictional force along the transverse direction to the sliding direction, shows peculiar behavior. It is also shown that the direction of the sliding motion can deviate from that of the external force.     

离心泵后泵腔内液体压力数值分析与验证

离心泵轴向力的大小与泵腔内压力分布密切相关,而试验测量轴向力成本较高,因此采用数值模拟展开泵腔内压力分布规律研究,并提出简便的试验测量轴向力方法显得格外必要。利用数值模拟计算,在0.6 Q_(sp)~1.2Q_(sp)工况下,研究离心泵后泵腔压力沿轴向、径向、切向分布规律,绘制后泵腔压力在0°、90°、180°、270°及压力均值沿径向分布曲线,得出后泵腔轴向力大小,推导两种近似计算泵腔轴向力公式,提出简便的试验测量泵腔轴向力方法,并将后泵腔压力模拟结果与试验结果对比,验证模拟结果的真实可靠性。结果表明:同一流量工况点,后泵腔压力沿轴向保持不变,沿径向随半径增大而增大。流量越大,后泵腔压力沿切向分布越具有轴对称性,沿径向增大越均匀。后泵腔轴向力两种公式计算结果与数值计算结果相对误差极小,后泵腔区域压力均值与其径向几何中心处压力均值大小相等。在试验测量离心泵泵腔轴向力时,只需要测量泵腔沿180°径向中心处压力值,便可近似求得泵腔区域轴向力大小。