低速冲击下的界面响应和磨损行为*

为探究低速冲击下界面响应与磨损行为之间的联系，开展多周次的低速冲击磨损实验；通过分析冲击过程中的接触力峰值、接触时长、接触力冲量、动能耗散等，研究冲击速度对接触界面的力学响应的影响；通过对冲击磨痕的磨损轮廓和形貌、磨损体积的检测分析，以及对磨痕区域元素组分变化的测试，研究冲击速度对接触界面磨损损伤行为的影响。结果表明：冲击速度的增加会导致接触界面在更短的时间内受到更强烈的力学作用；能量吸收率对冲击速度的变化不敏感，但冲击速度的提高会导致单位能量造成的磨损损伤逐渐降低；冲击磨痕可分为以塑性变形和以剥层磨损为主要损伤形式的2种区域；磨损区内经历了严重的摩擦氧化，并随着冲击速度的增加发生冲击副材料转移。因此，冲击速度越高，接触界面间的摩擦越剧烈，形成的表面氧化层避免了冲击副与基底材料的直接接触，延缓了磨损损伤的进一步发展。     

Nanoscale Tribology,Energy Dissipation and Failure Mechanisms of Nano- and Micro-silica Particle-filled Polymer Composites

Nanoscale energy dissipation and failure mechanics of silica nano- and micro-particle-filled polymer composite have been evaluated using advanced electron microscopy, scanning probe microscopy and nanoindentation techniques. Objective of this study is to understand the role of nano-microstructure and strength of particle–matrix interface and effects of geometrical gradient (spatial variation of surface height) and mechanical gradient (spatial variation of effective modulus) on energy dissipation process and subsequent failure mechanisms. In order to understand the role of geometrical gradient and mechanical gradient during the energy dissipation process, we carried out amplitude modulation simulation of soft–hard–soft surfaces with zero initial height and with 10 nm initial height of the hard material. Nanoindentation results show hardness and reduced modulus of the nanocomposite are homogeneous; however, the hardness and reduced modulus of the microcomposite were found to be heterogeneous. In the microcomposite, the sharp edges of particles increase friction, and heterogeneous mechanical properties result in high-energy dissipation. Large particles with weak interfacial bonding were easily removed, it resulting in defects on the sliding surface that acted as failure “hot-spots”. These characteristics result in relatively high friction and wear of the microcomposite. The nanocomposite showed better tribo-mechanical performance compared with that of the micro-particle-filled composite.     

钢纤维和莫来石纤维增强陶瓷基摩擦材料的性能研究

采用热压烧结法制备出钢纤维和莫来石纤维增强陶瓷基摩擦材料,对比分析钢纤维、钢纤维和莫来石纤维的混杂纤维以及莫来石纤维增强陶瓷基摩擦材料的机械性能和摩擦磨损特性。利用扫描电子显微镜(SEM)观察不同温度下的磨损表面和磨屑形貌,并研究其磨损机制。研究结果表明,钢纤维和莫来石陶瓷混杂纤维增强的陶瓷基摩擦材料具有较高的机械强度以及良好的摩擦稳定性和耐磨性能,以莫来石纤维增强的陶瓷基摩擦材料,摩擦因数表现出严重的热衰退,且具有低的耐磨损性能。SEM分析表明,在从低温到高温的摩擦过程中,钢纤维和莫来石陶瓷混杂纤维增强的陶瓷基摩擦材料的磨损形式主要由黏着磨损转化为黏着磨损与磨粒磨损的复合磨损形式,而以莫来石纤维增强的陶瓷基摩擦材料,其磨损形式以磨粒磨损为主。     

On the interdependence between kinetics of friction-released thermal energy and the transition in wear mechanisms during sliding of metallic pairs

Sliding of complying solids is often associated with the release of thermal energy. This energy accumulates within the mechanically affected zone (MAZ) of the rubbing pair. The accumulation of thermal energy within the MAZ tends to maximize the potential energy at the interface. Now, since a maximized potential energy renders the sliding system unstable, one (or both) materials will respond in a manner that consumes (dissipates) part or all of the accumulated energy in order to re-establish system stability or at least equilibrium. The material response may be in many forms: oxidation, crack initiation, wear debris generation, transition in wear mechanism, etc. As such, one may consider that these processes are intrinsic responses by the material to dissipate energy. Moreover, many of these responses are triggered at different stages of rubbing according to the balance between the rate of external thermal energy release (which is a factor of the nominal operation parameters) and the rate of thermal energy accumulation—RTEA (which is mainly a function of thermal transport properties of the rubbing pair). An interesting feature of this view is that the later quantity—RTEA—is directly related to the ability of the particular solid to dissipate thermal loads. This quantity, which is termed here as the heat dissipation capacity (HDC), is directly related to the state of blockage of energy dissipation paths within the rubbing solid. The objective of this paper is therefore to study the relation between the change in the HDC of a sliding solid and the transition in the mechanism of wear. It is shown that there exists an inverse correlation between the change in the HDC and the transition in the mechanism of wear. Moreover, it is also shown that a so-called ratio of residual heat (RRH, representing the ratio between the actual thermal load and the part of that load that is not dissipated by the solid) is a significant parameter that influences the magnitude and mechanism of wear. The findings are applied to explain the wear behavior of two tribo systems: a titanium (Ti-6Al-4V) sliding on itself and sliding on a steel (AISI M2) counterpart.     

煤基浸锑石墨密封材料性能研究

为提升石墨材料在高强度机械密封工况下的机械性能和密封性能,以煤炭加工的附加值产品（煤焦和沥青）为原料制备多孔石墨材料,然后通过高压浸锑制备煤基浸锑石墨密封材料;比较浸渍前后石墨材料的机械性能、微观结构差异、元素组成变化、摩擦磨损性能,分析浸渍锑后石墨材料性能的增强机制。结果表明：高压浸锑后石墨材料的机械强度和耐磨性能得到明显提升,其中密度增加了26.6%,抗压强度增加了114.3%,硬度增加了63.3%,气孔率下降了94%,绝对磨损量减少89.3%,平均摩擦因数降低了46.4%。高压浸锑后石墨材料中的孔隙被金属锑填充,并连接在一起形成条状,在摩擦磨损过程中充当骨架作用,从而提高石墨材料的抗磨性能;在浸锑石墨密封材料,微细网状的金属充填物可以减少材料的磨粒磨损,从而维持润滑膜的稳定,因而其可以作为高温等恶劣工况下的密封材料使用。     

Morphologies of the wear debris of polyetheretherketone produced under dry sliding conditions: Correlation with wear mechanisms

Wear debris contains extensive information on the tribological behaviours of materials [M.Q. Zhang, Z.P. Lu, K. Friedrich, On the wear debris of polyetheretherketone: fractal dimensions in relation to wear mechanisms, Tribol. Int. 30 (1997) 87–102]. Investigations on wear debris morphology will be helpful for understanding materials’ friction and wear processes. In this work, the wear debris obtained from block-on-ring (BOR) tests of three polyetheretherketones (PEEKs) with different molecular weights was studied. The mechanical properties of the three PEEKs were characterized in a previous work [G. Zhang, A.K. Schlarb, Correlation of the tribological behaviors with the mechanical properties of poly-ether-ether-ketones (PEEKs) with different molecular weights and their fiber filled composites, Wear, 2008, in press]. In this work, the influences of the mechanical properties of PEEKs and apparent pressure on wear debris morphology were studied. Based on analyzing wear debris morphologies, possibly involved tribological mechanisms were discussed. The results indicate that the tribological mechanisms have a close relationship with the morphology of the wear debris. Under low pressures, particle-like wear debris suggests that the micro-cutting effect exerted by the protruding regions of the counterpart dominates the tribological behaviour. Under high pressures, rod-like, bamboo-raft-like and film-like debris were noticed. This fact suggests that the transferring of PEEK to the counterpart and the plastic flow occurring in the PEEK surface layer play important roles on material loss.     

Tribological properties of epoxy nanocomposites: III. Characteristics of transfer films

The multiple parts of this study are intended to experimentally and analytically elaborate the tribological properties of epoxy nanocomposites, reinforced by short carbon fibres (SCF), nano-TiO₂ particles, polytetrafluorethylen (PTFE) powders and graphite flakes, in order to understand the role of fillers in modifying the wear behaviour of the materials. In this part, the influences of two solid lubricants, PTFE and graphite, were studied and compared. The transfer films established with two lubricants in sliding wear of epoxy nanocomposites against metallic counterparts were characterised under different sliding conditions. The morphology of transfer films was examined using scanning electronic microscopy (SEM), while their mechanical properties were investigated using micro-hardness tests. A method was proposed to determine the thickness of transfer films based on micro-indentation. The role of transfer films in dissipation of frictional heating was also studied. Epoxy nanocomposites containing both PTFE powders and graphite flakes showed a synergised effect in wear performance, especially under very severe wear conditions.     

The effect of molecular orientation through uniaxial prestraining in poly(vinyl chloride) and polycarbonate on their friction and wear characteristics

The mechanical and tribological properties of polymers generally depend on the exact details of their molecular arrangements, i.e. both their crystalline morphology and their molecular orientation, these being intimately related. The objective of this paper is to investigate experimentally the effect of uniaxial prestraining of specimens of poly(vinyl chloride) (PVC) and polycarbonate (PC) on their friction and wear characteristics.For this purpose tensile sheet specimens of PVC and PC were uniaxially stretched to varying final extensions, thus obtaining various degrees of molecular orientation and mechanical anisotropy. Short pins were subsequently cut from these deformed sheets and tested at a sliding speed of 27.5 cm s⁻¹ and a moderate normal load of 49 N in an instrumented pin-on-disc friction and wear testing machine with stainless steel as the rotating disc material. Results obtained on the friction coefficient and wear rates for various samples are presented and correlations are made with uniaxial prestrain, mechanical energy to fracture and loss modulus.     

An energy-based model for the wear of UHMWPE

An energetic approach to model the wear of tribological systems in which one of the components of the pair is polymeric is presented in this work. Experimental data, obtained in ultra-high molecular weight polyethylene (UHMWPE) pin-on-disk tribological tests, showed that a linear correlation between the wear rate of the polymer and the dissipated energy exists, independently of the lubricant, of the material used as counterbody and of the surface finishing of both polymer and counterbody. This fact strongly suggests that, in UHMWPE-based tribological systems, energy dissipation is mainly caused by the elasto-plastic deformation and wear of the polymer. Based on this assumption, it is developed a mathematical model that yields for a physical interpretation of the parameters of the experimental wear vs. energy correlation. These parameters are intrinsic wear properties of the polymer and can be used for the optimization of polymer-based tribological systems.     

几种人字门底枢材料的摩擦磨损性能研究

通过摩擦磨损试验和摆动试验对比考察了几种人字门底枢材料在水润滑和脂润滑条件下摩擦磨损性能，并进行摩擦磨损机制分析，选出一种综合性能较好的材料，进行一些机械性能的测试，为下一步台架模拟试验作准备。研究表明：一种新材料FZ5（3）在摩擦磨损试验和摆动试验中都表现出优异的性能，通过硬度测量、拉伸性能等试验表明其具有优良的机械性能。     

Contact fatigue and wear behaviour of bismaleimide polymer subjected to fretting loading under various temperature conditions

Cracking and wear induced by fretting is a critical problem for industrial composite structures. Thermosetting bismaleimide resin is a promising material due to its good mechanical and thermal properties. The effect of temperature regarding fretting cracking and fretting wear is presently investigated. The temperature effect on crack initiation and propagation is quantified combining experiments and modelling. The fretting wear is explained using a friction energy wear approach. A bilinear evolution of wear volume versus the dissipated energy is identified and related to a protective third body layer. These various damage evolutions are compared to the viscoelastic properties of the polymer.     

不同铜含量浸金属碳滑板的载流摩擦磨损性能*

为研究不同铜含量的浸金属碳滑块的载流摩擦磨损性能,在环-块试验机上研究3种不同铜含量(铜质量分数分别为1.17%、27.8%、50.45%)浸金属碳滑板与铜银合金接触线在载流条件下的摩擦磨损性能,并比较不同电流情况下的材料磨损表面形貌的变化。结果表明:铜含量对浸金属碳碳滑板的摩擦磨损性能有不同的影响。其中铜质量分数为1.17%的材料在200 A小电流情况下整体磨耗量较小,但是在400 A大电流情况下,电弧热、焦耳热产生的500℃左右高温会导致材料气化、掉块,严重加剧材料的损耗;铜质量分数为50.45%的材料在小电流情况下磨耗最大,但材料的运行温度整体较低,即材料的散热性能较好;铜质量分数为27.8%的材料在小电流与大电流情况下综合磨损性能最好。与铜银合金线对磨时,铜含量较高的材料出现了较为明显的黏着磨损,铜含量越高的材料其黏着磨损现象越明显。     

Tribological Enhancement of Aluminum by Porous Anodic Films Containing Solid Lubricants of MoS2 Precursors©

Porous anodic films containing molybdenum disulfide precursors were developed for self-lubricating purposes on aluminum by an initial anodizing and a subsequent re-anodizing process. The self-lubricating films were then examined with respect to the morphology, microstructure, and composition of the anodic film material and the lubricant, using X-ray diffraction, electron microscopy, energy dispersive X-ray analysis and X-ray photo-electron spectroscopy. The dry sliding wear of aluminum supporting such self-lubricating films was significantly reduced, as a result of greatly reduced coefficients of friction. The enhanced lubricity, due to the MoS₂ precursors contained within the porous anodic film, leads to wear mode changes from severe abrasive and adhesive wear for uncoated aluminum, to a mild film fatigue wear, for aluminum supporting the self-lubricating anodic films. The wear mechanism change is suggested by the wear and friction curves, as well as confirmed by wear track morphology.     

Expressing wear rate in sliding contacts based on dissipated energy

The wear of materials in sliding contacts is considered as resulting from an energy dissipation due to friction between the contacting first bodies. Up to now, no standard procedure in tribology is available to relate that dissipated energy with wear losses for different sliding wear tests and conditions. In this paper, a procedure is proposed to correlate the volumetric wear loss of one first body with the dissipated energy for unidirectional and bidirectional ball-on-flat tests. The model can be useful to predict the service lifetime of components from a limited number of laboratory tests. The validity and limitation of the wear loss versus dissipated energy model is illustrated for hard coatings like TiN and (Ti, Al)N, and multilayered (Ti, Al)N/TiN coatings. The effect of the applied normal load and the relative humidity (RH) of the ambient air on the wear rate for these different coatings are shown as well. A mild oxidational wear model is used to describe the material loss on these coatings in sliding contacts.     

Fretting Wear Behavior of Laser Peened Ti-6Al-4V

This work deals with the influence of laser peening on the fretting wear behavior of Ti-6Al-4V. Laser peening was carried out on Ti-6Al-4V. The laser-peened surface was characterized by transmission electron microscopy. Surface roughness, nanoindentation hardness, residual stress, and tensile properties of the material in both laser-peened and unpeened conditions were determined. Fretting wear tests were conducted at different normal loads using a ball-on-flat contact geometry. Laser peening resulted in the formation of nanocrystallites on the surface and near-surface regions, increased hardness, and compressive residual stress. Laser peening did not affect the tensile properties and surface roughness significantly. There was no considerable difference between the values of the tangential force coefficient of laser-peened and unpeened samples. The fretting scar size, wear volume, and wear rate of laser-peened specimens were lower than those of unpeened samples. This may be attributed to an increase in surface hardness due to strain hardening and grain refinement at the surface and near-surface regions, higher compressive residual stress, and higher resistance to plastic deformation of laser-peened samples.     

Mechanical Properties and Three-Dimensional Topological Characterisation of Micron, Submicron and Nanoparticles from Artificial Joints

Study of the geometry, nanomechanical properties and three-dimensional topographic characteristics of ultra-high-molecular-weight polyethylene (UHMWPE) wear particles provides an insight into understanding the wear mechanisms in artificial joints, which have not been fully explored. In this study, UHMWPE particles were generated, collected and then separated into three groups based on their size: micrometre, submicrometre and nanometre. Particle size distribution and shape features were investigated using scanning electron microscopy. Atomic force microscopy was used to quantify wear particle topographic features and nanomechanical properties. From the wear particle geometry analysis, it was found that nano- and submicron-sized particles had a granular shape while micrometre-sized particles had a flake-like morphology. Moreover, the mechanical properties and topographic characterisation of the UHMWPE material indicated that the nano- and submicron-sized particles had a much greater modulus and smoother surface than that of the micron-sized particles and bulk polymer sample. These differences in the geometric, topographic and mechanical properties between the nanoparticles, submicron particles and the micron particles revealed that the micron particles were most likely to be produced under macroscopic polymer asperity wear, while the nano- and submicron-sized particles were generated under microscopic polymer asperity wear. These findings provide a deeper understanding of the wear mechanism and processes of wear particle generation. Furthermore, the information may be useful to develop strategies for controlling and minimising the production of wear particles with particular features.     

栓接结合部在动载荷下的能量耗散特性

研究栓接结合部在动载荷下的能量耗散特性,对描述机械系统复杂力学行为具有重要的理论和实际意义。利用Bouc-Wen模型模拟栓接结合部的迟滞非线性特性,提出在动载荷下系统能量耗散计算方法和参数辨识方法。为验证所提方法的正确性,利用Mindlin模型所仿真出的非线性迟滞曲线作为栓接结合部所获得的试验数据,对Bouc-Wen模型进行参数辨识,并采用力控制方式分析Bouc-Wen模型中各个参数对系统能量耗散特性的影响规律。结果表明:随着量纲一切向力的增加量纲一能量耗散随之非线性递增;参数A、δ、γ和n对能量耗散的影响与其灵敏度相关,灵敏度越大则能量耗散的递增速率也越大;能量耗散随着参数A、γ和n的增加而增加,但参数δ则反之;栓接结合部能量耗散不仅与Bouc-Wen模型中的参数相关,而且与系统激励频率和振幅非线性相关;量纲一切向力与量纲一能量耗散之间关系可表示为η=aΓb的函数形式。     

Wear processes in sliding systems

A sequence of events involved in sliding wear is outlined. Local contacts cause large plastic strains in either or both solid components. The plastic deformation changes the near-surface microstructure in ways which make the material unstable to local shear. This in turn produces transfer of pieces of deformed material which are further deformed and mixed with counterface material and/or environmental components to produce ultrafine-grained material. The very fine microstructure in this transfer material is stabilized by the mixing in (mechanical alloying) of a second phase. The relative hardness of the transfer material and the adjacent substrate material affects the surface topography, the smoothness of sliding and the nature of the wear debris. Loose debris is commonly derived from the transfer material. This picture has been developed with the aid of analysis of experiments on unlubricated systems, but it is expected to be at least partly relevant to many “lubricated” systems as well.     

材料磨损与微电子机械系统中的磨损现象

磨损是材料和机械失效的主要原因之一。本文介绍了近年来材料磨损性能材料的进展,磨损的几种破坏机制以及相应的磨损理论模型,并介绍了MEMS中磨损研究的现状。     

多因素影响的格莱圈材料摩擦磨损试验研究*

格莱圈由聚四氟乙烯(PTFE)矩形滑环和丁腈橡胶(NBR)O形圈组成。为了研究不同因素对于格莱圈密封材料摩擦磨损性能的影响,利用UMT-3多功能摩擦磨损试验机,通过改变往复频率、粗糙度、润滑状态研究格莱圈材料与45钢配副时的摩擦磨损性能,利用SEM对试块试验前后表面形貌进行观测,并对摩擦磨损机制进行分析。试验结果表明:在干摩擦和滴油润滑条件下PTFE材料相比NBR材料具有更为优异的摩擦磨损性能;NBR材料表面粗糙度过高或过低都会导致摩擦因数升高,表面粗糙度对具有自润滑性能的PTFE材料的摩擦因数影响不大;高往复频率会使NBR材料摩擦因数降低,过高或过低的往复频率都会使PTFE材料摩擦因数降低;NBR材料的磨损形式以磨粒磨损和黏着磨损为主,PTFE材料以黏着磨损和疲劳磨损为主。