Demirer, E.Pourasiabi, HamidMcInnes, L. J.Knibbe, R....
16页
查看更多>>摘要：Although the trends of abrasion performance versus carbide volume fraction (CVF) of white cast irons (WCIs) have been studied to some extent, there remain gaps in understanding of the factors controlling performance. This study addresses three knowledge gaps. Firstly, the influence of testing conditions, more closely reproducing ore chute service, has been determined using the inner circumference abrasion test (ICAT), which included different natural rock types. The benefit of WCI compared to steels was much greater in basalt than in granite or greywacke. Secondly, the current work shows monotonic behavior for granite and greywacke but performance reversal in basalt, demonstrating that the reversal is not due to "more severe" or "high stress" conditions. The literature variously shows monotonic, plateauing, or reversing CVF dependence but has not convincingly explained these behaviors. Thirdly, the Cr/C ratio (previously neglected) shows no effect in granite, but lower Cr/C gives poorer performance in basalt. The trends are explained by relative responses of the microconstituents to different minerals. Basalt abrades both steel and the WCI matrix but not M7C3, thus maximizing the benefit of WCI but creating roughened surfaces with protruding carbides. This promotes carbide fracture in hypereutectic alloys and, hence, the reversal. Harder minerals create less differential and hence less protrusion and no plateau.
查看更多>>摘要：Tilting pad journal bearings (TPJBs) often use externally pressurized oil to lift off journals for safe start and stop procedures and enhanced load capacity under heavy loads. This article presents an in-depth analysis of TPJBs with the jacking oil mechanism. The finite element method is used to solve the pressure distribution, and the Newton-Raphson technique is used to solve the resulting pad forces, pad moments, and oil flow rates in the pad's recess region. Excellent correlations with the archival test data validate the numerical model. Two sets of comprehensive parametric analyses are conducted to study the effects of jacking oil flow rate and recess geometry on the bearing's static and dynamic characteristics. It is found that the bearing performance improves with increasing jacking oil flow rate and decreasing recess area but at the expense of increased breakaway pressure. Thus, the selection of jacking oil flow rate and recess geometry must consider the bearing performance and breakaway pressure simultaneously.
查看更多>>摘要：This study predicts the squeal instability of a rotary compressor using a full-size finite element model. A complex eigenvalue extraction method was used to study the tendency toward squeal of the rotary compressor during working. The numerical results showed that the unstable vibration frequency of the rotary compressor was 6,908 Hz, which corresponded to the frequency of the rotary compressor squeal. The squealing vibration of the rotary compressor was also measured, with results showing that the measured squeal frequency was in good agreement with that predicted by the finite element model. Transient dynamic analysis results showed that when squeal occurred, the main frequency of the normal acceleration of the upper flange was the same as that of the tangential acceleration. This phenomenon showed that the coupling of the normal vibration and tangential vibration of the upper flange was a main reason for the compressor squeal. Also, the greater the friction coefficient, the higher the likelihood of a squeal occurrence.
查看更多>>摘要：CaWO4 and WO3 nanoparticles were prepared by the sol-gel method and Pechini method. The morphology and structure of nano-CaWO4 and nano-WO3 were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Tribological, hot forming, and hot rolling lubrication properties of nano-CaWO4, nano-WO3, and mixed nano-CaWO4-WO3 as antiwear additives in water-based fluid were investigated using a four-ball friction and wear testing machine, Gleeble tester, and two-high rolling mill, respectively. Results showed that 0.3 wt% mixed nano-CaWO4-WO3 has excellent tribological properties in water-based fluid. The average wear scar diameter values decreased from 0.62 to 0.37 mm (mixed WO3-CaWO4) and the coefficient of friction value reduced from 0.080 to 0.064. This was due to the formation of a tribofilm (similar to 30 nm) on the worn surface during the forming process, avoiding direct contact between the metals. During Gleeble hot forming, the lubrication effect of the mixed nano-CaWO4-WO3 was the best. The nano-WO3-CaWO4 particles were relatively dispersed and dis not bond together under high temperature and pressure conditions, which played a role in reducing friction resistance between friction pairs. With the addition of 0.3 wt% mixed WO3-CaWO4 nanofluid, the surface quality was improved and it had the lowest surface roughness in the hot rolling process.
查看更多>>摘要：Inspired by the surface texture of bivalve shell, bionic wavy grooves were designed and prepared on the bionic coating of TC4 using laser marking technology. A response surface method was used to optimize the parameters of bionic texture structure for improving the tribological behavior. The influence of coupling mechanisms of bionic coating and texture on the tribological performance of TC4 alloy was investigated. The results show that the bionic wavy grooves reduce the fluctuation of loading force. The coupling of bionic texture and coating breaks the continuity of coating interface, and the peeling wear debris is easily captured by the bionic wavy grooves. The repairing effect of solid lubricant is increased, so the complete lubrication film can be formed more easily on the worn surface during the sliding process.
查看更多>>摘要：This article describes the finite element modeling of a spherical hybrid thrust bearing (SHTB), taking into account the influence of three-dimensional surface irregularities and magnetorheological (MR) lubricant behavior. The rheological behavior of MR lubricant was described using the Herschel-Bulkley model, and the yield shear stress relationship of MR fluid was expressed using the asymmetrical sigmoidal function. The finite-element method (FEM) is used to solve the governing Reynolds equation for an irregular surfaced SHTB configuration along with the orifice restrictor equation. The findings of the study indicate that the performance of the SHTB is improved by considering the three-dimensional (3-D) surface irregularities and operating with MR fluid at the expense of power loss due viscous friction. The percentage increase in the value of dynamic coefficients ((S) over bar) and ((C) over bar) due to the coupled effect of MR fluid and three-dimensional surface irregularity ((h) over bar (a) = 0.125) on the spherical hybrid thrust bearing is of the order of 52.37% and 71.22%, respectively, at epsilon(y) = 0 and I = 2A.
查看更多>>摘要：Herein, the analytic hierarchy process (AHP) and central composite experimental design in response surface methodology (CCD-RSM) are used to evaluate and optimize the tribological parameters of bionic textured AISI 4140-SnAgCu self-lubricating composite under the conditions of load (L: 20-40 N), velocity (V: 16-32 mm/s), and distance (D: 40-80 m). AISI 4140 biomimetic composites exhibit excellent tribological properties under the conditions of L-27.15/V-16.43/D-40, L-27.05/V-17.08/D-60, and L-27.42/V-17.85/D-80, respectively. The sensitivities of influence factors on the tribological overall score are load, velocity, and distance, in order from high to low. The good antifriction properties of self-lubricating composites under conditions with the optimized tribological parameters benefit from the fact that the solid lubricants are uniformly spread at the contact interface.
查看更多>>摘要：WC-12Co-reinforced Ni-based coatings were fabricated on Inconel 718 substrates using a high-velocity air-fuel (HVAF) technique. The as-fabricated coatings were heat-treated at a temperature of 970 degrees C, 1000 degrees C, 1030 degrees C, or 1070 degrees C. The microstructure, mechanical properties, and tribological behaviors of the heat-treated coatings were investigated systematically. The results showed that the heat treatment could reduce the porosity of the coating and promote the metallurgical bonding of the interface between the coating and the substrate. As the heat treatment temperature increased from 970 degrees C to 1000 degrees C, the hardness and toughness of the coating increased gradually. After being heat-treated at 1000 degrees C, the coating possessed the best comprehensive mechanical properties and the best tribological properties at both room temperature and 580 degrees C. The wear rates of the as-fabricated coatings were 2.63 x 10(6) mm(3) N-1 m(-1) at room temperature and 3.96 x 10(-5) mm(3) N-1 m(-1) at 580 degrees C, respectively. Also, the wear mechanisms were fatigue wear as well as abrasive wear accompanied by mild adhesive wear, respectively. However, the wear rates of the coating heat-treated at 1000 degrees C were 1.04 x 10(-6) mm(3) N-1 m(-1) at room temperature and 3.87 x 10(-)(5) mm(3) N-1 m(-1) at 580 degrees C, respectively. The wear mechanisms of the heat-treated coatings at room temperature were mainly fatigue wear and abrasive wear, while the wear mechanisms at 580 degrees C were mainly abrasive wear accompanied by mild adhesive wear. With the increase of heat treatment temperature above 1000 degrees C, the mechanical properties and tribological properties of the coating deteriorated gradually.
查看更多>>摘要：Due to the diversity of debris morphologies and their states in the images, automatic wear debris analysis is still a challenge. Instance segmentation is an advanced technique of deep learning used for computer vision tasks. It can detect and delineate each distinct object of interest appearing in an image. An instance segmentation model using a modified mask branch with larger feature map and dilated convolution is proposed and applied to the ferrography images, so that five typical types of wear debris corresponding to different wear conditions can be located, segmented, and recognized, even if they are small, blurred, or overlapped. The mean average accuracy on the test set is about 88% when the intersection over union threshold is 0.5. This method realizes an end-to-end process of wear debris identification that can eliminate the error caused by the intermediate steps. In addition, it obtains accurate quantitative debris information-that is, the type, quantity, and size of debris-which provides a solution for intelligent wear debris analysis and automatic wear detection.
查看更多>>摘要：Hot stamping is an effective method to improve both the elongation and plasticity of ultra-high-strength steels and thus a higher specific strength can be achieved, making weight reduction in motor vehicles possible. However, due to the die temperature rise and the cooling liquid within hot stamping applications, the friction in its forming stage is always a nonisothermal mode. Therefore, a high-temperature slider-on-sheet strip (SOSS) tribotester to simulate sliding friction in hot stamping of 22MnB5 hot stamping steel sheet was designed and custom-made. Then, it was employed to exploit the high-temperature friction behavior and mechanism of bare 22MnB5 hot-stamped boron steel sheets under different die temperatures and extra cooling conditions. Results show that the friction coefficient obtained under the pure die cooling conditions is lower than that obtained under extra cooling conditions, which is attributed to the formation of thicker oxide layers on the surface of specimen during the cooling process. In addition, the friction coefficient is obviously decreased when the die temperature is increased to 200 degrees C, which is ascribed to the co-action of the destruction of the oxide layers and the formation of bainite.
NSTL
Taylor & Francis