Theoretical life prediction of tribo-pairs such as seals, bearings and gears with the failure form of wear under mixed lubrication depends on quantitative analysis of wear. Correspondingly, the wear life test depends on an accelerated wear test method to save the time and financial costs. Therefore, the theoretical basis of accelerated test design is a wear model providing a quantitative relationship between equivalents and accelerated test duration. In this paper, an accelerated wear test design method based on dissipation wear model entropy analysis under mixed lubrication is proposed. Firstly, the dissipation wear model under mixed lubrication is verified by standard experiments as a theoretical basis. Then, an accelerated wear test design method is proposed, taking the entropy increase in the dissipation wear model as an equivalent. The verification test shows that 20 times acceleration could be reached by adjustment of the entropy increase rate. The effect of entropy increase rate gradient of duty parameters is also discussed, revealing the fastest acceleration direction. Finally, the advantages and disadvantages of the proposed method are discussed. The results in this paper are expected to contribute to long life predictions of tribo-pairs.
The gas–liquid miscible backflow pumping seal (G-LMBPHS) is a non-contact mechanical seal that is suitable for high-speed bearing chambers. However, the tribological properties and wear mechanisms of the frictional pair of G-LMBPHS in an oil–air environment have not yet been comprehensively studied. In this study, the tribological properties of six frictional pairs, consisting of three hard materials (18Cr2Ni4WA, Al2O3 coating, and Cr2O3 coating) and two soft materials (metal-impregnated graphite [Metal-IG] and resin-impregnated graphite [Resin-IG]), were analyzed using a disc-on-disc tribometer. An oil–air environment was created using a minimal quantity lubrication (MQL) system and a closed chamber. The results show that the COF of the four frictional pairs consisting of two coatings and two graphites decreases gradually with increasing rotational speed, and the frictional pairs composed of Al2O3 coating and Resin-IG and Cr2O3 coating and Resin-IG have the lowest COF between 0.022 and 0.03. Therefore, the frictional pairs of G-LMBPHS are in a mixed lubrication condition. The lubricant in the oil–air environment is adsorbed and stored in pits on the surface of graphite and coatings, enhancing the hydrodynamic effect of the spiral grooves and reducing the COF by up to 45%. Metal-IG has better wear resistance than Resin-IG, and the frictional pair consisting of Cr2O3 coating and Metal-IG has the lightest wear. This study provides an important basis for the selection of G-LMBPHS frictional pairs in oil–air environments.
A surface topography characterization parameter system based on fractal parameters has been established, and several estimation methods for these fractal parameters have been suggested accordingly. Since scale dependence exists in these conventional methods, it is necessary to find an estimation method for characterization parameters with uniqueness. An estimation method for ideal fractal parameters for multi-scale measurement of polished surface topography is proposed in this study. Polished surfaces of two materials, WC-Ni and 9Cr18Mo, are measured under multi-scale for frequency component analysis. This study proposes an estimation method for ideal fractal parameters based on a modified determination method for the scale-free region and the decomposition of frequency components into three classifications. The reasonable results verify the existence of ideal fractal parameters: for the WC-Ni surface, ideal fractal dimension D = 1.3 and scale coefficient G = ; for the 9Cr18Mo surface, ideal fractal dimension D = 1.2 and scale coefficient G = . Additionally, it is revealed that the scale-dependent components conform to the same regulation on the same instrument by comparing the results of two materials. The conclusions of this study are expected to support tribology research and mechanical engineering related to surface topography.
Scale-free region is a specific frequency region only in which the fractal characteristics for surface topography exists. The uniqueness in fractal characterization exists in theory; however, by incorporating the conventional methods, various scale-free regions can be obtained for the same surface profile, resulting in the non-uniqueness of fractal characterization and reconstruction. Therefore, this paper aims to solve the non-uniqueness problem of the scale-free region. Firstly, the origins of such non-uniqueness are revealed, including random components introduced by manual selection under single-scale and information distortion affected by measuring frequency under multi-scales. Then, a filtering method based on an equal PSD amplitude Weierstrass-Mandelbrot function is proposed to extract the length and particular fractal components of the scale-free region. The proposed method is verified by acquiring the unique scale-free region length l_0 and calculating the unique fractal dimension D with the extracted fractal components. Additionally, measurement influences are discussed, including measuring frequency and length. Further application on surfaces with different grinding processes and roughness levels is also conducted to test the practicability of the method. In summary, the necessary conditions for measuring the scale-free region are revealed. On this basis, obtaining method for the scale-free region is proposed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.