钢-钢摩擦副在不同润滑和接触形式下的高温减摩性能的研究

用多功能SRV试验机评价了在干摩擦和油润滑条件下,试验参数对钢-钢摩擦副在点接触和线接触形式下的高温减摩性能的影响。结果表明,在试验范围内,随着试验负荷的增大,钢-钢摩擦副在干摩擦条件下线接触摩擦因数和点接触摩擦因数呈逐渐下降的趋势,这种下降趋势在线接触时尤为明显;但在油润滑条件下,试验负荷的增大对钢-钢摩擦副之间的线接触和点接触摩擦因数的影响不显著。在干摩擦条件下,不论是在点接触还是线接触形式下,试验速度对钢-钢摩擦副之间的高温点接触和线接触摩擦因数的影响并不显著;但在油润滑条件下,试验速度对钢-钢摩擦副的高温线接触和点接触摩擦因数的影响都比较显著,特别是在较高的试验速度时影响更为明显。     

粗糙表面微凸体对液黏传动的影响

为研究液黏传动过程中粗糙表面的承载特性,将分形理论引入到两粗糙表面摩擦过程之中,分析传动过程中混合摩擦和边界摩擦两阶段的微凸体承载过程,考虑微凸体弹塑性变形,对M-B模型进行修正,建立修正的微凸体承载模型。建立基于修正M-B模型的微凸体承载模型。通过数值仿真得到有效面积系数、分形参数对液黏调速离合器传动过程的影响规律;对修正的微凸体承载模型的计算结果与M-B模型的计算结果进行对比分析。结果表明:微凸体接触载荷和传递转矩随着面积比的增大而增大,当有效面积系数与尺度系数增大时,接触载荷与传递转矩均有所增大;分形维数为1.5时,微凸体接触载荷与传递转矩最小且随面积比的变化最为缓慢;在整个接触区域内,弹性变形区域的面积、接触载荷以及传递转矩最大,其次是弹塑性变形区域,塑性变形区域最小;考虑弹塑性变形时,微凸体接触载荷与传递转矩均有所下降;修正M-B模型和M-B模型间的修正系数范围在25%以内,修正系数随着有效面积系数、尺度系数的增大而增大,随着分形维数的增大而减小。     

Frictional properties of branched polyethylene I. The true area of contact

Using a specially designed apparatus the friction and apparent area of contact between a hemispherical polymeric specimen and a glass flat were measured under various loads. The results show that the decrease in the coefficient of friction with increase of normal load cannot be explained by the use of the Hertz equation to describe the variation of the contact area with load even when the equation is modified to allow for the non-linearities of polymer mechanical behaviour. Factors which make the prediction of contact area as a function of load more complex are discussed.     

超音速火焰喷涂WC-Co涂层耐磨性研究

利用超音速火焰喷涂（HVOF）工艺制备了WC-Co涂层，测定了涂层孔隙率、显微硬度及干摩擦磨损过程中涂层材料失重，得出涂层干摩擦因数随时间的变化关系，分析了涂层摩擦磨损机制。结果表明，WC-Co涂层致密，平均孔隙率为1．29％，显微硬度达1140HV（测试载荷2．94N），干摩擦条件下材料失重低于电镀Cr镀层2个数量级；摩擦初期，干摩擦因数迅速增加，主要磨损特征是粘结相富Co区的犁沟切削，摩擦中后期，摩擦副间实际接触面积增大，摩擦因数变化较小，磨损趋于稳定。WC-Co涂层的主要磨损机制是疲劳磨损和犁沟切削。     

Elastic–plastic spherical contact under combined normal and tangential loading in full stick

The behavior of an elastic–plastic contact between a deformable sphere and a rigid flat under combined normal and tangential loading with full stick contact condition is investigated theoretically. Sliding inception is treated as a plastic yield failure mechanism, which allows static friction modeling under highly adhesive conditions. Several contact parameters such as: junction tangential stiffness, static friction force and static friction coefficient are extensively investigated. The phenomenon of junction growth and the evolution of the plastic zone in the contact region are briefly described. It is found that at low normal dimensionless loads the static friction coefficient decreases sharply with increasing normal load, in breach with the classical laws of friction. As the normal load further increases the static friction coefficient approaches a constant value that is about 0.3 for many material properties combinations.     

Friction and Wear Behavior of Steels under Different Reciprocating Sliding Conditions

The friction and wear behavior of ISO 100Cr6 steel ball sliding against conventionally hardened carbon and low-alloy steels was studied. The effect of hardness, hardening capacity, normal load, and sliding speed on the coefficient of friction and friction energy was investigated. Friction tests were carried out, without lubrication and under ambient conditions, on a reciprocating friction tester in which a ball-on-flat contact configuration was adopted. The results showed that there is a relative tendency for the friction properties to decrease with increased hardening capacity and decreased hardness. The results showed that increasing normal load decreases the coefficient of friction for the two steel nuances. However, increasing sliding speed increases the coefficient of friction of low-alloy steel and decreases the coefficient of friction of carbon steel. The oxidation of wear debris influences the wear mechanisms and friction behavior.     

Sliding wear behavior of planar random zinc-alloy matrix composites

The friction and wear behavior of planar random zinc-alloy matrix composites reinforced by discontinuous carbon fibres under dry sliding and lubricated sliding conditions has been investigated using a block-on-ring apparatus. The effects of fibre volume fractions and loads on the sliding wear resistance of the zinc-alloy matrix composites were studied. Experiments were performed within a load range of 50–300 N at a constant sliding velocity of 0.8 m s⁻¹. The composites with different volume fractions of carbon fibres (0–30%) were used as the block specimens, and a medium-carbon steel used as the ring specimen. Increasing the carbon fibre volume fraction significantly decreased the coefficient of friction and wear rates of both the composites and the medium-carbon steel under dry sliding conditions. Under lubricated sliding conditions, however, increasing the carbon fibre volume fraction substantially increased the coefficient of friction, and slightly increased the wear of the medium-carbon steel, while reducing the wear of the composite.Under dry sliding conditions, an increasing load increased not only the wear rates of both the composite and the unreinforced zinc alloy, but also those of their corresponding steel rings. However, the rate of increase of wear with increasing load for both the composite and its corresponding steel ring was much smaller than for the unreinforced zinc alloy and its corresponding steel ring. The coefficient of friction under dry sliding conditions appeared to be constant as load increased within a load range of 50–150 N for both the composite and the unreinforced zinc alloy, but increased at the higher loads. Under any load the coefficient of friction of the composite was lower than half that of the unreinforced zinc alloy under dry sliding conditions.     

A Numerical Model for the Dry Sliding Contact of Layered Elastic Bodies with Rough Surfaces

A numerical model for the two-dimensional dry sliding contact of two elastic bodies with real rough surfaces has been developed, where an elastic body contacts with a multi-layer surface under both normal and tangential forces. The model uses surface profile data directly recorded with a stylus measuring instrument and it is suitable for use on a microcomputer. Green's function for a unit normal load and a unit tangential load for the generalized plane strain problem are derived. Verification of the accuracy of the model by reproduction of test case results is presented. Contact pressure distribution for layers of varying coefficient of friction, thickness and elastic modulus is analyzed.     

Experimental and numerical investigation of the sliding behaviour in a fretting contact between poly (methylmethacrylate) and a glass counterface

The fretting conditions in a contact between poly (methylmethacrylate) and a rigid counterface have been investigated using both experiments and finite elements computations. The computation of the microdisplacements in the contact area during a tangential loading allowed the determination of the critical displacement for transition from partial sliding to gross sliding conditions. These conditions were mapped in friction maps as a function of the contact loading parameters (i.e., normal load and displacement amplitude) and the friction coefficient. This analysis was performed assuming that the polymer behaved elastically and that the friction obeyed Coulomb's law. Experimental results were found to be in accordance with the numerical predictions, despite the fact that some plastic deformation of the polymer surface occurred during tangential loading.     

Effects of Normal Load,Sliding Speed,and Surface Roughness on Tribological Properties of Niobium under Dry and Wet Conditions

The effects of normal load, sliding speed, and surface roughness on the friction and wear of high-purity niobium (Nb) during sliding without and with an introduction of water were systematically investigated. Increasing the normal load or sliding speed decreased the friction of the Nb under the both dry and wet conditions because the increased wear of the Nb decreased the interfacial shear strength between the steel ball and Nb by promoting the surface roughening and the production of wear debris. However, the Nb tested at the lowest sliding speed under the lowest normal load with water exhibited the lowest friction and wear due to the formation of oxide layer on the wear track. The friction and wear of the Nb tested under the dry condition decreased with increased surface roughness because the higher interfacial shear strength between the steel ball and smoother Nb resulted in the earlier breakdown of the native oxide layer and direct contact between the steel ball and Nb. However, increasing the surface roughness of the Nb increased its friction and wear under wet conditions, probably due to the easier breakdown of the oxide layer that formed on the rougher surface during sliding. The tribological results clearly showed that the introduction of water during sliding had a significant influence on the tribological properties of the Nb.     

弹性金属塑料复合材料的摩擦磨损特性研究

在MPX-2000摩擦磨损试验机上，用环盘摩擦副，结合扫描电镜分别评价了弹性金属塑料（EMP）复合材料与钢在油润滑和干摩擦条件下的摩擦磨损特性。结果表明：两种试验条件下，相同滑动速度的摩擦系数随载荷的升高而减小，当载荷为2000N，滑动速度小于3.52m/s时，摩擦系数基于趋于稳定，EMP磨损率随滑动速度和载荷的升高耐增加，但不同试验条件的增幅不高，油润滑下滑动速度小于3.52m/s和干摩擦条件下滑动速度小于1.96m/s时，EMP以微切削，塑性变形和梨沟磨损为主，并在摩擦副两表面形成转移物。     

Effect of contact stress on friction and wear of ultra-high molecular weight polyethylene in total hip replacement

This paper studies the effect of contact stress on friction and wear of ultra-high molecular weight polyethylene (UHMWPE) acetabular cups by means of friction and wear joint simulator testing under serum lubrication. For a given applied load, increasing the contact stress by increasing the ball/socket radial clearance decreased both the coefficient of friction and the wear rate. Friction and wear were highly correlated. The dependence of friction on contact stress for the UHMWPE socket under serum lubrication was similar to that of semi-crystalline polymers under dry sliding. This finding indicates the occurrence of partial dry contact at asperity levels for the metal-polyethylene ball-in-socket joint under serum lubrication.     

半金属基粉末摩擦片摩擦磨损性能研究

在不同工况下研究半金属基粉末摩擦片与淬火45#钢配副时,载荷和转速对其摩擦磨损性能的影响,并分析其磨损机制。结果表明,在油润滑和水润滑下,半金属基摩擦片高速下的磨损量要明显低于低速下的磨损量,而干摩擦下其高载高速下的磨损要高于高载低速时的磨损量。油润滑下随载荷的增大,半金属基摩擦片的摩擦因数逐渐升高;水润滑下随载荷的增大,高速时摩擦因数先增大后减小,低速时则逐渐降低;干摩擦下随载荷的增大,高速时摩擦因数呈现出先升高后降低再升高的趋势,低速时则先升高后降低。干摩擦时摩擦面十分粗糙,有比较明显的沟状磨痕和硬质颗粒脱落后残留的凹坑;而水润滑和油润滑时摩擦面较为光滑。     

烟炱对电接触磨损的影响

选用常见的铜作为电接触材料,将烟炱溶液喷洒于试样表面,进行不同载荷下的电接触微动试验,用3D形貌仪和SEM对磨痕形貌进行分析。结果表明:载荷对材料的电接触性能影响显著,接触电阻与法向载荷成反比,即增加载荷可改善摩擦副的电接触性能;接触区域的有效导电面积是有限的,故载荷达到某一值后,随着载荷的增加,接触电阻不再有明显的下降趋势;小载荷下,烟炱的加入恶化了摩擦副的电接触性能,随着载荷的增加,这种恶化作用逐渐减小;摩擦因数随着载荷的增加而降低,载荷较低时(2～6 N),摩擦因数曲线可见明显的上升期、跑合期、下降期、稳定期;而载荷较高时(8～10 N),只有上升期和稳定期;大载荷下,触头接触区域匹配良好,摩擦副表面迅速达到了平衡点,摩擦因数较稳定。在电化学的作用下烟炱颗粒在摩擦副表面形成固体膜,起到减摩抗磨的作用。     

Fretting wear behavior of AZ91D and AM60B magnesium alloys

The fretting wear behavior of the AZ91D and AM60B magnesium alloys are investigated using a reciprocating fretting wear machine under dry conditions with different numbers of cycles, different normal loads, slip amplitudes and frequencies. The worn surfaces and wear debris were examined using scanning electron microscopy and optical microscopy in order to understand the predominant wear mechanisms of two magnesium alloys. The results indicate that the AZ91D alloy displays a lower friction coefficient and lower wear quantity than the AM60B alloy. The AZ91D shows a higher capability than AM60B in resisting crack nucleation and propagation. Both AZ91D and AM60B show similar friction and wear characteristics. The wear quantity increases with increasing normal load, but decreases with increasing frequency. The friction coefficient also decreases as the normal load is increased. Fretting frequency had little effect on the friction coefficient. In a long term, the fatigue wear and abrasive wear were the predominant wear mechanisms for AM60B and delamination wear, adhesive wear and abrasive wear for AZ91D.     

Contact problem for elastic layer and rigid cylinder with friction forces

The contact problem for the elastic layer of an arbitrary thickness and the rigid cylinder with friction forces acting in the contact area is solved and the solution is analyzed. Domains of applicability of the widely used solutions, i.e. the solution for a rigid cylinder and elastic half-space and the solution for a thin elastic layer, are determined for the contact under consideration. It is shown that for coatings from composite materials with a low elastic modulus both solutions can result in a significant error. Typical modes of the elastic displacement of the layer surface are given for different contact area width, Poisson’s ratio, and friction coefficient. The example of the calculation of the particular contact for the layer of the polymer composite with a low elastic modulus is presented.     

Influence of particle content and porosity on the wear behaviour of cast in situ Al(Mn)–Al2O3(MnO2) composite

Aluminium-based tribological materials may reduce the weight of components, leading to significant fuel economy. The aim of the present study is to investigate the wear and friction in cast in situ Al(Mn)–Al₂O₃(MnO₂) composites synthesized by dispersing MnO₂ particles in molten aluminium, which get reduced to form Al₂O₃ particles. Wear tests have been conducted at four normal loads of 9.8, 19.6, 29.4 and 39.2 N and at a constant sliding speed of 1.05 m/s using a pin-on-disc wear testing machine, under dry sliding conditions. The results of the investigation indicate that the cumulative volume loss and wear rate of in situ composites are significantly lower than those observed in either the commercial aluminium or Al–Mn base alloy, under similar loading and sliding conditions. The influences of both reinforcing particle and porosity contents on the tribological behaviour of in situ composites were evaluated. It has been found that at a given particle content, the wear rate increases with increasing porosity content due to its combined effect on real area of contact and subsurface cracking. The wear rate of in situ composites with relatively lower porosity decreases with increasing particle content, but does not appear to change significantly or even increases a little with increasing particle content when the composites have relatively higher porosity. In view of large fluctuations in coefficient of friction during sliding, no effect of particle or porosity contents on the coefficient of friction could be determined unambiguously for different in situ composites.     

The frictional pattern of tactile sensations in anthropomorphic fingertip

In this report, to consider the technology of frictional tactile sensations (FTS) for a prosthetic fingertip, the anthropomorphic fingertip (silicone) was compared with the human fingertip in terms of sliding friction (reciprocating sliding on an acrylic plate under a load force of ∼2.5 N max.) and the prototype of a FTS was demonstrated. In the results, the friction coefficient of the human fingertip changed according to the contact location more than the anthropomorphic fingertip. In the demonstration, the prototype FTS that faked the human fingertip could generate a high friction coefficient and the peculiar signal pattern at each contact location. Moreover, the prototype FTS recognized a slight difference in the surface roughness of the copier paper. In conclusion, the friction coefficient in the human fingertip increases when increasing the contact area under the same load force. Increasing the contact area induces stiction and stick-slip phenomena, generating a high friction coefficient and vibrations. Moreover, the high friction coefficient amplifies slight contact signals and supports FTS in a prosthetic fingertip.     

浸渍磷酸盐石墨与9Cr18Mo不锈钢配副的摩擦磨损性能研究

针对航空发动机石墨密封常用的摩擦副浸渍磷酸盐石墨(M234Ao)和9Cr18Mo不锈钢材料,在UMT-TriboLab试验机上进行球-盘、销-盘接触摩擦试验,研究其低速轻载、高速重载工况以及干摩擦、油润滑下的摩擦磨损性能,利用接触式形貌仪、金相显微镜等对摩擦副表面进行观察分析,并分析其磨损机制。结果表明：在油润滑及面-面接触下的摩擦因数和磨损率明显低于干摩擦和点-面接触下;添加油介质可以降低界面摩擦剧烈程度,抑制金属氧化以及降低摩擦因数,特别是在高速重载工况下;M234Ao和9Cr18Mo配副间的磨损机制以磨粒磨损和黏着磨损为主,伴随有犁沟、微裂纹及擦伤现象。     

SLM成形表面织构对TC4钛合金干摩擦磨损性能的影响

基于一步法思路,采用金属3D打印机基于激光选区熔化（SLM）技术制备表面带有凹坑织构的TC4钛合金试样,采用光学相机、超景深显微镜和扫描电镜观察织构成形情况,利用激光共聚焦位移测试仪和显微维氏硬度计分别测试表面粗糙度和表面硬度,在干摩擦条件下采用摩擦磨损试验仪考察不同载荷下织构密度对TC4钛合金试样摩擦学性能的影响,并使用扫描电镜对摩擦实验前后的表面形貌进行分析。研究结果表明：一步法SLM成形能够在TC4钛合金表面获得成形良好的直径500 μm的织构;随着织构密度的提高,钛合金试样表面粗糙度增大,表面硬度有所降低;干摩擦条件下,提高TC4钛合金试样织构密度有利于磨屑的收集从而减少试样的三体磨损,提高载荷有利于改善摩擦副接触状态;5 N载荷下40%织构密度试样的平均摩擦因数和磨痕宽度均最小,与无织构试样相比,平均摩擦因数和磨痕宽度分别降低12%和16%;40%织构密度下,载荷提高会引起摩擦因数的降低和磨损量增大,磨损表面犁沟和片状剥落增多。在干摩擦条件下,3D打印一步法制备的表面织构可以显著改善TC4钛合金的磨粒磨损和黏着磨损。