An engineering theory and an experimental method for contaminant wear testing

An engineering theory and experimental method for contaminant wear are proposed. By analysing the wear characteristics of hydraulic components, the contaminants' wear strength σ_m, wear factor ƒ_m, lubrication parameter λ_l, flexibility parameter λ_a, and material parameter λ_m, etc., can be defined. In addition, a new test apparatus, ‘MMU-5’, that can be used for studying wear properties under lubrication conditions, is reported. The friction pair of the tester is composed of two ring specimens. The most important aspect of this tester is that the gap between the two specimens can be adjusted from 0 to 100 microns. Using the tester, parameters such as λ_l, λ_a, λ_m, and ƒ_m, are investigated experimentally. Finally, the application of the corresponding engineering theory is assessed.     

Improvement of ductile iron wear resistance through local surface reinforcement

Ductile iron (DI) or spheroidal graphite cast iron is an attractive ferrous material being widely used due to its combination of low cost and good combination of strength, toughness and fatigue endurance. However, under severe service conditions, experienced in seashore, earth-moving and mining applications the performance and reliability of DI are limited due to its poor wear resistance. Wear resistance of DI can be improved through different heat treatment and surface engineering techniques, each having some limitations and drawbacks. Recently, a new method called OPTICA has been introduced, which through local reinforcement with inserts improves wear resistance of ductile iron without compromising other properties.Results of the present investigation show that tribological properties of ductile iron can be greatly improved by local surface reinforcement. Through the formation of carbides a hard transition or functional gradient zone is formed around the inserts, which then carries the load and improves wear resistance of ductile iron, at the same time maintaining low friction. However, wear resistance of reinforced ductile iron can be improved even further, using proper austempering process. If austempered at 350 °C, wear resistance of ductile iron will become comparable or even better than reference Hadfield grade steel. In this paper reinforced or reinforcement refers to locally alloyed material in preselected zones of the casted object if not specified otherwise.     

Reduction in wear of metakaolinite-based geopolymer composite through filling of PTFE

Metakaolinite-based geopolymer composite containing 5-30% (volume fraction) polytetra-fluoroethylene (PTFE) was synthesized using compound activator composed of aqueous NaOH and sodium silicate at room temperature. Flexural strength, compressive strength and elastic modulus of the composite were measured. Tribological behaviour of the composite sliding against AISI-1045 steel was investigated on an MM-200 friction and wear tester. SEM, EDS and XPS analysis were conducted on worn surfaces and wear debris. The results show that mechanical strength of the composite was lower than corresponding geopolymer while the wear model became mild. The friction process was stable and the wear rate was dramatically reducted by 86-99.4%. The improvement of tribological properties of the composite was attributed to form a brown soft thin layer on the worn surface of the composite containing Fe₂O₃ came from tribochemical reaction. EDS analysis on the worn surfaces indicate the content of Fe increase along with the increase of volume content of PTFE in the composite. Furthermore, the counterpart, the steel ring was also protected from terrible wear as occurred when friction with geopolymer without any filling of solid lubricant. There is a brown thin layer mainly composed of Fe₂O₃ on the steel ring.     

Simulation of the development of a railway wheel profile through wear

In this paper a method of calculation is presented for determination of the evolution by wear of railway wheels. The results are compared with the development of the profile of the wheels in the Amsterdam Metro, and satisfactory agreement is achieved. For ordinary railway lines the agreement is worse, since we did not take into account wear due to flanging.     

Study of solid contamination in ball bearings through vibration and wear analyses

In rolling bearings, contamination of lubricant oil by solid particles is one of the main reasons for early bearing failure. In order to deal with this problem, it is fundamental not only the use of reliable techniques concerning detection of solid contamination but also the investigation of the effects of certain contaminant characteristics on bearing performance. Nowadays, non-invasive techniques, such as vibration measurements, are being increasingly used for on-time monitoring of machinery performance. In this context, the present work investigates the effect of lubricant contamination by solid particles on the dynamical behavior of rolling bearings, in order to determine the trends in the amounts of vibration affected by contamination in the oil and by the bearing wear itself. Experimental tests were performed with radial ball bearings lubricated by oil bath. Quartz powder in three concentration levels and different particle sizes was used to contaminate the oil. Vibration signals were analyzed in terms of the root mean square (rms) values. The results show that changes in the rms values of vibration in the high-frequency band, from 600 to 10,000 Hz, were associated to the changes in oil lubrication in the bearing contacts, caused by oil contamination and wear damage on the bearing surfaces.     

Friction and wear response of nitride coating deposited through PVD magnetron sputtering

Surface engineering with applied coating plays a vital role in any industrial application. These coatings are meant for better mechanical and tribological characteristics when applied on to the materials. The major challenge in selecting a suitable coating strategy is their input process parameters. There are several parameters which influences the coating properties, but it is hard to choose one of them and ignoring others. Multilayers of tungsten nitride are attracting great interest to modulate their tribological and mechanical properties through physical vapour deposition process due to their wide application range. These multilayer nitride films were deposited through unbalanced reactive magnetron sputtering technique. The tribological tests were performed on a pin-on-disc tribometer at room temperature and it has been observed that friction and wear values reduce drastically while applying multilayer coatings. Later, artificial neural network (ANN) is employed to optimize the tribological properties of sputtered coatings.     

Controlling nested wrinkle morphology through the boundary effect on narrow-band thin films

Frontiers of Mechanical Engineering - We describe the formation of nested wrinkles created by the thermal mismatch between a narrow-band thin film and a compliant substrate. When a film is...     

An analysis of the in vivo deterioration of Co-Cr-Mo implants through wear and corrosion

The degradation of Co-Cr-Mo ASTM F75-92 hip implants after a harvesting period of 81 months in sheep was investigated. Hip prostheses and tissue samples were obtained from a medical study involving total hip arthroplasty of the cemented type in 12 sheep. Upon euthanasia, the explants were retrieved for analyses of the surfaces and evidence of degradation, while tissue samples from the interface regions were harvested for chemical analysis and evidence of Co, Cr, and Mo contents. Clear evidence of wear and corrosion was detected. Results also indicated that the modes of metal transport through the poly(methyl methacrylate) bone cement play an important role as the surface degradation mechanisms of the metal. The results are being discussed in terms of electrochemical and triboelectrochemical behaviour of the Co-Cr-Mo alloy.     

Two-Dimensional filtration

An algorithm for solving a filtration problem is described. A method for the linearization of the problem in small elements and the subsequent joining of solutions without violating the flow character and the law defining the process is shown. Examples of jet streams are presented.     

Fretting wear

This review covers developments in fretting wear over the past three years. The threshold amplitude of slip at which fretting damage becomes apparent is found to be in the region of 0.5 μm. Very low amplitudes of slip and low frequencies (0.001 Hz) are particularly damaging in electrical contacts, leading to high resistances resulting from oxide build-up. In high temperature fretting, oxide formation can give protection. In titanium alloys this can be improved by ion implantation, particularly with bismuth. In aqueous solutions, such as sea water, fretting stimulates the chemical dissolution of material, which accounts by far for the major part of the wear.     

基于磨耗稳定态的高性能摩擦磨损实验机研制

电气化铁路中电力机车靠受电弓滑板与接触网导线的滑动接触来获取动力,它们之间的摩擦接触状态直接影响到机车的运行速度和牵引力,同时其摩擦磨损性能决定了机车连续运行的时间和接触网导线的使用寿命.实际应用中二者构成了一对机械与电气耦合的特殊摩擦副,它们之间的磨耗过程是1个非常复杂的物理化学过程.通过研究发现,机车在正常运行过程中,滑板与接触网导线在运行一段时间以后会出现1个磨耗量较低、磨耗率相对稳定的阶段,在该阶段中摩擦副表面有一层光亮的膜层,称此时为磨耗稳定态,磨耗稳定态对磨擦副的性能及运行寿命具有重要的影响.为了对受电弓滑板与接触导线的载流磨耗特性进行实验研究,分析磨耗稳定态出现的规律,制作了1台高性能摩擦磨损实验机.实验机实验参数调节范围宽,测量精度高,功能强,也可用于电刷和电机滑环等滑动电接触实验.     

Effect of wear debris on wear in rolling-sliding motion

The effect of wear particles on wear was investigated using a four-ball extreme pressure lubricant test apparatus. The wear particles present in both filtered and unfiltered oil samples were examined using a duplex Ferrograph analyser and a bichromatic microscope. The wear track widths were measured for various wear modes and were found to increase if the wear debris was recirculated. The size of the wear particles increased with test duration.     

Sliding wear rig

As a preliminary to studies on cam and follower systems, a rotating cylinder on reciprocating flat wear rig has been developed. This has turned out to possess a number of useful characteristics not available in more conventional rigs. The rig has been particularly useful in that it has produced wear areas large enough for detailed comparison of a range of quantitative surface analysis methods. Esca, sem/empa, sem/edax have been compared for the quantification of antiwear surface elements.     

Wheel-rail wear simulation

This paper declares the method for the computation of the wheel-rail surface degradation in a curve where the major surface degradation phenomenon is a combination of wear and plastic deformation. Simulating the form change of the wheel-rail contacts help to identify the risk of severe or catastrophic wear resulting from increased train speeds and axle loads and can help in determining more efficient maintenance schedules for track and rolling stock. The method was previously used to simulate the form change in a two-roller contact. The progress is made in the terms of general geometry modelling, which makes differences in the various contact configurations. The normal contact problem is analysed using the modified Winkler method and calibrated using the results from FEM modelling of the wheel-rail contact with elastic-plastic material model. A piecewise approach and stick-slip analysis of the rolling-sliding contact solves the tangential problem. A linear wear law is used in the wear computation. The form change for a typical two-point contact in a low radius curve was analysed and discussed.