查看更多>>摘要：Nitrile butadiene rubber (NBR) is a water-lubricated bearing material that demonstrates excellent vibrational absorption and impact resistance; however, rapid wear under abnormal conditions is still a serious problem. Graphene (Gra) and carbon nanotubes (CNTs) are two types of carbon nanomaterials with different dimensions and excellent mechanical and friction properties. In this work, Gra and CNTs were used to fill the NBR, and a multifunctional friction and wear testing machine was used to study their impacts on the friction between NBR and ZCuSn10Zn2 under water lubrication conditions. The results indicate that both Gra and CNTs can effectively reduce the adhesion and the friction coefficient of NBR during the friction process. The two-dimensional lamellar structure of Gra is more likely to precipitate from the NBR matrix to generate a surface lubrication film, which can effectively reduce the friction coefficient. Both Gra and CNTs can prevent crack initiation and propagation in NBR during the wear process, thereby effectively reducing the wear of NBR. Compared with the two-dimensional structure of Gra, the one-dimensional linear structure of carbon nanotubes can "trap" the NBR molecular chains more effectively during the friction process, thus reducing the initiation and propagation of wear cracks and further improving the wear performance of NBR.
查看更多>>摘要：Industrial upscaling frequently results in a different coating microstructure than the laboratory prototypes presented in the literature. Here, we investigate the wear behavior of physical vapor deposited (PVD) MoS_2 coatings: A dense, nanocrystalline MoS_2 coating, and a porous, prismatic-textured MoS_2 coating. Transmission electron microscopy (TEM) investigations before and after wear testing evidence a crystallographic reorientation towards a basal texture in both samples. A basal texture is usually desirable due to its low-friction properties. This favorable reorientation is associated to a tribological compaction of the porous specimens. Following running-in, sliding under high contact pressure ultimately leads to a wear rate as small as for an ideal grown bulk MoS_2 single crystal grown by chemical vapor deposition (CVD). This suggests that the imperfections of industrial grade MoS_2 coatings can be remediated by a suitable pretreatment.
查看更多>>摘要：Transfer films are known to be important determinants of friction and wear, specifically in dry sliding of polymers on metals. Still, the kinetics of transfer film formation, the stability of transfer films, the in-situ correlation of friction and the extent of transfer film formation, are not yet fully understood. The main reason for this is the lack of time-resolved quantitative data on transfer film formation. Therefore, Transfer Film Luminance Analysis (TLA) was applied to block-on-ring sliding wear tests of polyphenylene sulfide (PPS) and selected PPS composites containing graphite, polytetrafluoroethylene (PTFE) and short carbon fibers (SCF) against steel. Though fundamental in nature, the tests' parameters were chosen to closely match the operating conditions of dry-running bushings. While PPS filled with graphite or PTFE formed laterally homogeneous and temporally stable transfer films, SCF-containing composites exhibited recurrent spontaneous partial degradation of the transfer film. Significant fluctuations of the coefficient of friction (COF) were found to be the result these. Notably, when the extent of transfer film formation is reduced by such degradations, friction increased. Regarding material composition, mixed fiber/solid lubricant grades still exhibited transfer film instabilities and COF fluctuations, albeit at a much lower level. At the same time, no impact of partial transfer film degradation on wear was found.
查看更多>>摘要：The paper attempts to determine the influence of boron in the presence of chromium, vanadium and titanium on abrasion resistance and wear mechanisms using low-alloy steels as an example. The obtained tribological properties were correlated with the hardness, carbon content and prior austenite grain size. Tribological tests - the dry sand-rubber wheel test - were conducted in the presence of loose abradant, and the major wear mechanisms were then determined using scanning electron microscopy. The results indicate that the improvement of resistance to abrasion may be supported by the combined addition of chromium, boron and vanadium. For unalloyed or chromium steels, a micro-addition of boron provides no benefits in terms of improving tribological properties.
Mohammad Jahedol IslamYan ZhangLiang ZhaoWentao Yang...
13页
查看更多>>摘要：Due to its ability to machine both conductive and non-conductive materials, electrochemical discharge machining (ECDM), a non-traditional micromachining method, is widely used. It has high accuracy in metal processing, a high material removal rate (MRR), and a low tool wear rate (TWR). However, there has been little research on the situation that occurs when the TWR becomes higher than the MRR. Moreover, the wear mechanism is not clearly understood because of the complexity of ECDM. In this study, the mechanism by which the TWR becomes higher than the MRR is investigated from three important aspects: (i) type and concentration of the salt solution, (ii) pulse interval, and (iii) energy. Moreover, three processes were observed in the machining area based when electrical discharge machining and electrochemical machining occur together: (i) spark discharge, (ii) ionic bombardment, and (iii) expansion of the plasma channel. These processes are investigated in this paper using experimental data and images. The results show that expansion of the plasma channel in the machining area is the key to the switch in the wear mechanism where the ratio of the TWR and MRR is higher than 1. The surface characteristics of the brass tool electrode and the SUS304 workpiece electrode were analyzed using scanning electron microscopy (SEM) and energy dispersive spectrography (EDS). No signs of chemical etching were found on the tool electrode tip in the SEM images. Moreover, EDS identified tool electrode materials, such as copper and zinc, on the workpiece surface when the wear mechanism changes.
查看更多>>摘要：Inconel 690 alloy is widely used in nuclear steam generator tubes, which always suffer from various complex fretting wear behaviors during their service period. This study aims to investigate the effect of the ultrasonic surface rolling process (USRP) at different static pressures on the sliding fretting wear behavior of Inconel 690 alloy at room and 300℃ air temperature environments. Results indicate that the grains in the alloy surface layer are refined after treatment through the USRP, improving some of its surface mechanical properties. The fretting wear resistance of Inconel 690 alloy is also enhanced, and the higher static pressure is, the more obviously the strength effect would be. In addition, the extent of the fretting wear at 300℃ is less than that at room temperature. Furthermore, the abrasive, delamination, and wear oxidation mechanisms can be observed in all test samples during the entire fretting wear process.
查看更多>>摘要：Polygonal wear is a common defect that appears along the railway wheel circumference, and a rapid propagation of which can come into being a considerable harm to the train operation quality, fatigue lifetime of components and environmental noise. On-board anti-slip controllers are commonly applied in electric locomotives aiming to avoiding the obvious slipping appearance of the powered wheelsets. This paper purposes to investigate the influence of anti-slip control threshold on wheel/rail interactions and polygonal wear evolution of locomotive wheels based on the train-track interaction and long-term polygonal wear evolution simulations. The simulation results indicate that the anti-slip control threshold and wheel/rail adhesion status greatly affect the wheel/rail tangential interactions. The dominating wheel polygonal wear with the 17-18 harmonic order propagates principally with an initial wheel defect. The anti-slip control threshold has an evident effect on the development of wheel polygonal wear. It further indicates that adopting the anti-slip controller with a lower threshold can availably restrain the propagation of polygonal wear of locomotive wheels, which is also confirmed by the practical applications.
查看更多>>摘要：Although the railways in windblown sand areas has been continuously developed in recent years, the effect of dynamic windblown sand environment on the wear and damage of wheel-rail under different slip ratios is still unclear. This work focused on the effect of Gobi and desert dynamic windblown sand environments on the wear and damage behaviors of wheel-rail under different slip ratios using a twin-disc rolling contact fatigue machine. The corresponding experiments in dry condition (without wind and sand) were also performed for comparison. The results indicated that in these three conditions (Gobi, desert and dry), their trends of adhesion coefficient with slip ratio were not exactly the same. The wear rate of wheel and rail in these three conditions could be ranked as: dry > desert > Gobi. As the slip ratio increased, the fatigue wear of wheel and rail gradually aggravated. Furthermore, the oxidative wear of wheel also gradually exacerbated, especially in Gobi dynamic windblown sand environment. Based on the results of experiments and finite element simulations, the interaction mechanism between sand and wheel-rail interface was proposed and the reasons for wear reduction in dynamic windblown sand environments were summarized.
查看更多>>摘要：Low lambda applications, such as gears and bearings in off-road vehicle drivetrains, are an area of interest regarding tribological performance and failure mode investigations. In previous work [1], tests were conducted with variable rolling/sliding contact conditions under low lambda (λ < 0.5), demonstrating that a transition point exists where the primary failure mode changes from pitting/abrasive wear to micropitting, driven primarily by the lambda ratio. That work has been extended here to λ ≈ 1.2, showing another transition in the failure mode from micropitting to mild abrasive wear/no failure. These transitions tend to occur rather abruptly, suggesting that the amount of asperity contact (lambda ratio) alone doesn't explain them. The goal of the present work is to investigate the reason these failure modes transition with respect to increasing lambda ratio by evaluating the tribofilm, residual stress, and retained austenite at three different lambda ratios (0.05, 0.4, and 1.2) that represent the conditions under which the different failure modes occur. These investigations reveal that there are differences in the tribofilm composition and coverage, while the thickness is similar for all conditions. The presence of ZDDP elements in the tribofilm promotes micropitting, and increased tribofilm coverage results in longer life. Additionally, it is demonstrated that higher levels of retained austenite and compressive residual stress contribute to longer life.
查看更多>>摘要：Bolt connection plays an important role in assembly structures. Under long-term vibrations, bolted joint interface will change due to fretting-induced friction and wear behavior. This leads to changes in the dynamic characteristics of assembly structures, which increases the difficulty of control of the structure. In this paper, a new random fretting test method was developed to reproduce realistic vibration situations as much as possible and to study the evolution of contact parameters (friction coefficient and contact stiffness) of bolted joint interfaces with increasing wear. A recently developed test rig was used to perform the fretting wear tests under random oscillation. During the tests, interface hysteresis response and bolt preload were recorded. A model-based parameter estimation method was developed to estimate the friction coefficient and tangential contact stiffness. The evolution curves of contact parameters were obtained, and the effects of initial bolt preload, excitation level, and surface roughness were discussed. To the authors' knowledge, no studies on the fretting behavior of bolted joint interfaces under random vibration have been published. This research can promote a better understanding of the fretting wear behavior of bolted joints and provide a basis for the dynamic analysis of joint-dominated structures.
NSTL
Elsevier