| With advantages of environment-protection, cheap, efficient shock-damping and noise-reducing, compact structure, and easy to maintenance, the water-lubricated bearing has huge prospect of wide applications.The friction performance of bearing depends on the water lubricated conditions, hardness, dynamic viscoelasticity, surface morphology, structure of rubber liner, and so forth. Working condition or lubrication state being changed to take up enough water-film forming may be beneficial to reduce wet friction coefficient of the bearing.Due to low vaporization pressure of water, cavitation wear caused by vaporization of lubricated water is likely to occur. Furthermore, the water flow is inevitably mixed with tiny solid sand particles in actual running condition. In addition, subjected to complex forces from itself and outside, the bearing is likely to be impacted momentarily by concentrated load, and generate shock vibration. That requires the bearing has excellent wet-sliding property and perfect wear-resistance, erosion-resistance as well. But it is impossible for bearing to have both low friction-coefficient and large carrying-capacity at the same time under its normal working conditions.Moreover, owing to the low elasticity coefficient of rubber liner, it is getting to appear elastic deformation obviously even applied light load(relatively lower water-film pressure), to change the thickness and shape of water-film, further to affect the pressure distribution of water-film, which makes the water-lubricating mechanism more complex. Therefore, the study on water-lubricated bearing should consider not only geometry shape and structure of grooves and surfaces, but also material properties of rubber liner.At present, there are no mathematical and physical models yet for general use to calculate the characteristics of fluid flow distribution in bearing clearance cavity with different types. Most numerical studies have only gotten thickness of lubricating water-film or charts of pressure distribution. Many more researches need to be systematically analyzed. Such as, the whole velocity and pressure distribution of flow field along longitudinal axis and circumference of the clearance cavity in the bearing with multiple grooves according to different eccentricity values and clearance values of the bearing, various shapes of the groove; the two-way fluid structure interaction between changing of flow field pressure and deformation of rubber liner; cavitation effect of the bearing; and numerical simulating on turbulent lubrication in flow field of the bearing as well.Hence, taking cavitation effect into consideration, the dissertation numerically computed the flow field characteristics of hydrodynamic lubrication in turbulent state of the grooved bearing in different water lubricants(clear water and water content with sand), and simulated the two-way fluid structure interaction between changing of flow field pressure and deformation of rubber liner in clear water. Combine with friction wear bench-test of the bearing under different working conditions, investigate causes, mechanisms and critical influence factors of wear in the bearing using SEM to observe the micro-morphology on its worn surface and analyze. Then try to reveal wear mechanisms of the bearing under various working conditions. Furthermore, propose a simple and efficient method to increase operational performance of the bearing through improving the processing property of rubber liner composites.The main contents and contributions of this dissertation are as follows:1. Under actual working conditions, the lubricating water is likely to appear cavitation phenomenon and the flow field is inevitably contaminated with solid sediment particles. The dissertation described the clear water flow-field as gas-liquid two-phase flow field, and described the water content with sand flow-field as gas-liquid-solid three-phase flow field. According to the theory of erosion wear in multi-phase flow field, cavitation wear, erosive wear caused by sediment particles, cavitation-erosion interactive wear of rubber liner are simulated respectively and analyzed contrastively. Induced by fluid pressure, indentations appear on working surface of the bearing. It is available to form lubricating water-film. Because the pressure of flow field produces deformation of rubber liner, meanwhile the deformation makes fluid distribution changed, thus accelerates the formation of hydrodynamic lubricating water-film, which further causes pressure of flow fluid varied. So the calculation model of flow field in the bearing lubricated by clear water is introduced to simulate the deformation of rubber liner under dynamic pressure of flow field, considering two-way fluid-structure interaction between changing of flow field pressure and deformation of rubber liner. Numerical simulation of lubricating model for the grooved bearing is carried on and elastic deformation of rubber liner affected by dynamic pressure is qualitatively analyzed. Based on it, enrich the elasto-hydrodynamic lubrication theory of water-lubricated bearings.2. With taking cavitation effect into consideration, the numerical computing model of water-lubricated bearing in turbulent state lubrication is established. Pressure distribution of water-film and deformation distribution of rubber liner are respectively investigated under conditions of different eccentricity values. And calculating expression of correspondent load-bearing capacity and friction coefficient are achieved as well. In order to prove the possibility of fatigue wear in water-lubricated rubber bearing theoretically, the value and distribution of shear stress, normal stress and deformation on working surface of bearing liner are obtained by using Computational Fluid Dynamics(CFD) methods and ANSYS MFX, under two-way fluid structure interaction between changing of lubricating water-film and elastic deformation of bearing rubber liner. Combined with friction wear test of bearing, through SEM observing the micro-morphology on worn surface and analyzing, confirm the existence of(sliding contact) fatigue wear on bearing experimentally. Then find out its critical influence factors, investigate the cause and mechanism of bearing fatigue wear, and provide properly evaluating criterion for performance improvement of rubber bearings.3. The friction performance of water-lubricated bearing depends on the lubricated conditions, hardness, dynamic viscoelasticity of rubber, and so forth. After surface modified by silane coupling agent KH-550, palygorskite(AT) nano-powder was added in NBR rubber mixed, compression molded and vulcanized to prepare AT/NBR rubber-liner vulcanizate sample and AT/NBR water-lubricated bearing sample. Proved by testing results, comprehensive mechanical properties, hardness and reinforcement of AT/NBR rubber-liner vulcanizate sample were enhanced. Detected by dynamic mechanical analyzer(DMA), initial storage modulus value of AT/NBR rubber-liner vulcanizate sample was higher than initial storage modulus value of NBR rubber-liner vulcanizate sample. That meant the filler particles of AT/NBR rubber-liner vulcanizate was more compatible with rubber matrix and had more uniform and refined dispersion in it. That is to say, the processing property of AT/NBR rubber-liner vulcanizate was improved. Also detected by DMA, the loss factor values(at 0℃, under 1Hz) of NBR and AT/NBR rubber-liner vulcanizate samples were approximately the same, the wet sliding properties were almost unchanged. Tested by friction wear-test machine of bearing, water-lubricated friction coefficient of AT/NBR bearing sample decreased. Those experiments show that performance index of AT/NBR bearing sample made better than NBR bearing sample’s and met the requirements of MIL-DTL-17901C(SH) specification. |
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