查看更多>>摘要：? 2021Radial fretting is defined as the damage caused by the relative motion of a ball under a variable normal load. The conducted experimental tests proved the existence of this damage even in contacting bodies with similar materials and elastic properties; however, the reviewed analytical methods do not predict damage under these conditions, and the numerical methods are time-consuming, especially when the investigation requires the analysis of several loading cases or during large number of cycles. The main objective of this work was to develop a fast analytical method to analyse radial fretting wear. For this purpose, a novel formulation for contact displacements under a normal variable load was built and merged to different contact mechanic formulas. For validation purposes, false brinelling in thrust bearings was used as a representative industrial example. The results were compared with a FEM model showing a relative difference under 9% and a massive reduction of the calculation time of more than 30 000 times, moreover experimental tests were carried out, showing a good agreement between the density of friction energy and the obtained fretting damage what endorse the use of this formulation for the analysis of a large number of cycles and loading cases.
查看更多>>摘要：? 2021 Elsevier B.V.In-situ composites with clear advantages of a clean interface, adequate particle size, and good interfacial bonding between the reinforcement and matrix play a lead role in choosing materials with superior tribological properties. In this study, in situ TiC reinforced Zinc Aluminum alloy composites were prepared, and the effect of applied load and abrading distance on the high-stress abrasive wear response of these composites was investigated. Matrix alloy and conventionally used Gunmetal were also tested for high-stress abrasive wear properties. It was observed that increasing the TiC reinforcement content from 5 wt % to 10 wt % results in improved wear resistance in the Zinc aluminum-based composite. The 10 wt % TiC reinforced composite shows superior wear behaviour among all samples and proves to be a suitable replacement of gunmetal in bearing applications.
查看更多>>摘要：? 2021 The AuthorWear is the most serious problem in service of moving steel parts. To mitigate it, we have studied phase transformations in the surface layer of Vanadis 6 tool steel obtained after several treatment routes. Changes in wear resistance were examined in particular. There are various ways to improve the quality of surfaces of tool steels for cold working - including mechanical, chemical or physical vapour deposition (PVD) coatings. Several multistage processes of surface layer modification were applied: turning-burnishing, turning-burnishing-PVD, grinding-nitriding, turning-burnishing-nitriding, turning-nitriding-polishing, turning-burnishing-nitriding-polishing, and turning only used as a reference. To provide comparability, samples were subjected to heat treatments in vacuum furnaces with gas quenching until a hardness of ≈62 ± 1 HRC was achieved. Scanning electron microscopy observations, X-ray diffraction analysis, and finally ball-on-disc tribological tests against Al2O3 balls as counterparts provide information about wear and friction values. The best wear resistance – more than ten times higher than after turning only - was achieved for a sample following the turning-burnishing-PVD sequence. The turning-burnishing (130 N)-nitriding sequence may act as an alternative to the grinding-nitriding treatment. Wear rate values for the two latter variants are almost the same.
查看更多>>摘要：? 2021 Elsevier B.V.The cavitation erosion of materials in sandy water is a very important topic in water conservancy and industrial production. In this paper, an ultrasonic vibration cavitation apparatus and underwater low-voltage electric discharge device are applied to investigate the erosion characteristics of 6063 aluminium specimens in sandy water with different sediment sizes and concentrations and the underlying mesoscale damage mechanism. The results show that the specimen damage gradually increases as the mean sand particle size increases. When the mean sand particle size is less than 0.120 mm, the resulting damage is lower than that in pure water. When the sand concentration is less than 10 kg/m3, the resulting damage is not very different from that in pure water. As the sediment concentration in the sand-water mixture increases, the influence of the sand particles on cavitation gradually increases. The bubble-particle interaction experiments reveal that the cavitation bubbles that interact with multiple small spherical particles show obvious non-spherical morphology and prolong the collapse time during the first collapse phase and reduce the collapse strength. The results of the bubble-particle interaction experiments verify the erosion characteristics obtained from the ultrasonic vibration cavitation test, which is significant for elucidating the damage mechanics of specimens in sandy water.
查看更多>>摘要：? 2021 Elsevier B.V.Nano-finishing of miniature gear is a tough job since its geometry is complex. Traditional gear finishing methods can cause burns, micro-cracks, scratch marks, burrs, pits and thermal distortion in gear teeth profiles. Because of the limited spacing between the gear teeth, miniature gears can only be finished with a few processes. This article reports on the new uniform flow restrictor used in the rotational magnetorheological fluid-based finishing (R-MRFF) method to ensure a consistent and precise polishing of gear profiles. The uniform flow restrictor is analyzed using a commercial software program (COMSOL? Multiphysics) focused on finite element analysis (FEA). The surface roughness simulation is also performed using the results of the FEA and force analysis on active abrasives. The simulated roughness values are consistent with experimental values. Later, the experiments are performed without and with a novel uniform flow restrictor on the SS316L spur gear teeth pro?le to examine and compare the ?nishing performance. After finishing the gear, the minimum surface roughness of Ra = 23.9 nm at the tooth profile is achieved, and further, all manufacturing defects are entirely removed. Concurrently, the teeth geometry profiles are not affected. The uniform finishing of miniature gear with a continuous smooth surface may improve its work performance, transmitting power ability, reliability, fatigue life and form accuracy.
查看更多>>摘要：? 2021 The AuthorsHard chromium plate (HCP) has been the wear resistant coating of choice in the nuclear industry for decades, but new protective coatings are required as a result of the hazardous nature of Cr(VI) compounds used in electroplating. This study compares the wear performance of candidate replacements materials, Cr2O3 and Cr3C2–NiCr. These two coatings are also compared with HCP and a WC-(W,Cr)2C–Ni coating assessed in an earlier publication. The Cr2O3 and Cr3C2–NiCr coatings were supplied having been applied to Inconel 625 substrates using high velocity oxy fuel (HVOF) and thermal detonation gun spray techniques, respectively. A ball-on-flat sliding wear configuration was used with three environments: dry, deionised water, and borated water to partially simulate nuclear reactor water chemistry. Wear rates were measured using both volume and mass standard metrics. The wear surface samples were characterised using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) in order to establish the operative wear mechanisms. All three candidate coating materials exhibited similar wear performance to HCP in the three test environments. There was, however, enough of a difference between performance in deionised and borated water, to merit the use of borated water in future testing. The data gathered using SEM and XPS provided insight into the wear mechanisms. These include both particle pull-out and tribolayer formation. The XPS data revealed that Cr3C2 is preferentially removed from the Cr3C2–NiCr coating during wear testing in a borated water environment.
查看更多>>摘要：? 2021 Elsevier B.V.This article presents the development of a slurry-jet erosion test rig and characterisation procedure for slurry erosive wear behaviour of elastomeric materials. Key parameters such as the mass of impacting particles, particle concentrations, impact angles, and slurry velocities can be set and controlled accurately by following an established measurement protocol. The results for slurry velocity, concentration, and temperature showed an excellent control using the test rig. The test rig was designed to maintain the slurry temperature change within ±2 °C as required by BS/ISO 23529 and no additional cooling system is needed. Characteristics of silica sand particles in the slurry experienced very little change after several test batches in terms of average particle size, particle distribution, and angularity. Commissioning of the rig was carried out by evaluating erosion behaviour of polychloroprene rubber with the variation of mass of erodent particles and impact angles. The results showed that the developed erosion test rig and testing procedure were reliable for investigating slurry erosive wear processes of elastomers. Erosive wear resistance of different elastomers to slurry-jet erosion can be investigated under varied test parameters. The experimental erosion wear results were compared with calculated values using the theoretical models of cutting and deformation wear.
查看更多>>摘要：? 2021 Elsevier B.V.Severe deformation of Hadfield steel occurs via different deformation mechanisms (slip or twinning) depending on the crystallographic orientation and direction of the applied load. The development of these mechanisms under dry sliding friction was investigated by comparing the calculated values of slip stresses for <001> and <111> single crystals. Shear stress calculations with allowance for the friction force showed that twinning is not the predominant deformation mechanism for the considered orientations. TEM studies of the dislocation structure, repolished and etched surface revealed agreement between the experimental and numerical data. According to EBSD analysis, reorientation on the worn surface and in the subsurface region changes depending on the combination of principal stresses in different areas of the worn surface. These results confirmed that conditions for the deformation mechanisms (slip and twinning) are determined by the local conditions in the sample mesovolume. The wear curves demonstrate two stages of even and uneven wear. The uneven wear mechanism is substantiated by the analysis of the structure in the subsurface region, wear debris, and the worn surface. An empirical scheme of the wear and damage accumulation mechanisms is proposed.
查看更多>>摘要：? 2021 Elsevier B.V.Traffic-induced wear of road pavements is known to possess directional characteristics. Quantitative characterization of wear directionality in terms of surface texture properties has practical significance in the study of wear mechanisms and driving safety analysis. However, the pavement texture parameters and indices in use today are unable to reveal the directional characteristics of pavement wear. This study proposed a texture statistic, the Directional Wear Index (DWI), to measure pavement wear directionality based on a laser scanned image of a pavement surface. First, macrotexture peaks that were likely to be subjected to traffic abrasive actions were identified as primary peaks using the concept of topographic prominence. Next, a slope ratio was calculated to characterize the shape of a primary peak. DWI was determined as a function of the prominence-weighted sum of the shape codes of all the primary peaks of the surface analyzed. The calculated value of DWI defines both the direction and the magnitude of directional wear of the pavement wear. The proposed concept and DWI calculation procedure were validated using field measured data of actual in-service pavement segments with known directional wear characteristics.
查看更多>>摘要：? 2021 The AuthorsMicropitting is a type of surface fatigue damage that occurs in rolling-sliding contacts operating under thin oil film conditions. It is caused by stress fluctuations, brought about by surface asperity interactions, which lead to initiation and propagation of numerous surface fatigue cracks and subsequent loss of material. Despite its increasing importance to gear and bearing reliability, the mechanisms of micropitting are poorly understood. This is particularly the case concerning the effects of friction on micropitting which are difficult to study under controlled conditions. This is because it is difficult to isolate the friction effects from other influential factors, in particular from the build-up of any anti-wear tribofilm and its subsequent effect on the running-in of counterface roughness that is known to strongly affect micropitting through its influence on severity of asperity stresses. This paper presents new data on the impact of friction on micropitting obtained using a new test methodology. Micropitting tests were conducted using a ball-on-disc MTM rig with the additional functionality to continuously monitor the growth of tribofilm during the test. Friction was varied by using custom-made oils containing different concentrations of MoDTC. Crucially, the effect of friction was isolated from the effect of counterface roughness running-in by introducing the MoDTC blend only after the running-in period was completed with a ZDDP solution alone. This approach eliminates the influence of MoDTC on ZDDP anti-wear tribofilm growth in early stages and hence ensures the same running-in takes place in each test. This gives similar asperity pressure history, regardless of the amount of MoDTC present. Results show that friction has a very significant impact on micropitting; for example, the extent of micropitting was reduced by a factor of 10 when friction coefficient was reduced from about 0.1 to 0.04. Lower friction results in fewer surface cracks which grow at a shallower angle to the surface than those at higher friction. Numerical analysis of contact stresses present under tested conditions indicates that the primary mechanism by which friction affects micropitting is through its effects on near surface stress fields: reducing friction reduces the local tensile and shear stresses in the near surface, asperity-influenced region, which may in turn be expected to mitigate crack initiation and propagation. The results presented may help in designing oil formulations that can extend component lifetimes with respect to both wear and micropitting damage through controlling tribofilm growth and friction.
NSTL
Elsevier