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351.
352.
Electro-hydrostatic actuator (EHA) pumps are usually characterized as high speed and small displacement. The tilting inertia moment on the cylinder block produced by the inertia forces of piston/slipper assemblies cannot be ignored when analyzing the cylinder block balance. A large tilting inertia moment will make the cylinder block tilt away from the valve plate, resulting in severe wear and significantly increased leakage. This paper presents an analytical expression for the tilting inertia moment on the cylinder block by means of vector analysis. In addition, a high-speed test rig was built up, and experiments on an EHA pump prototype were carried out at high speeds of up to 10,000 r/min. The predicted nature of the cylinder block tilt at high speeds corresponds closely to the witness marks on the dismantled EHA pump prototype. It is suggested that more attention should be given to the tilting inertia moment acting on the cylinder block of an EHA pump since both wear and leakage flow between the cylinder block and the valve plate are very much dependent on this tilting moment. 相似文献
353.
354.
《中国航空学报》2016,(2):554-559
In order to satisfy the drastic temperature change and high chemical activity in directional solidification of Nb–Si based alloys, Y_2O_3 crucible is demanded to possess high thermal shock resistance and erosion resistance. This paper improved the sintering degree and density of Y_2O_3 crucible by optimizing the sintering temperature and time, and its practical application performance was investigated. Y_2O_3 grains gathered with the increase of sintering temperature and time, and the contact area enlarged, resulting in the open pores being changed into closed pores.The higher density caused the improvement of erosion resistance of Y_2O_3 crucibles. However, excessive density weakened the thermal shock resistance. Considering high-temperature strength, erosion resistance, thermal shock resistance and costs, optimum sintering temperature and time of Y_2O_3 directional solidification crucible were 1800 °C and 120 min, respectively, and the porosity was20%. Improved Y_2O_3 crucible has been successfully applied to directional solidification of Nb–Si based alloys, and significantly reduced the oxygen contamination. Slight interaction occurred between Hf and Y_2O_3, but no obvious dissolution, penetration or erosion was found, showing good erosion resistance and thermal shock resistance. 相似文献
355.
A Cr-Si co-alloyed layer was successfully deposited on TA15 alloy by the double glow plasma surface technology to improve its poor wear resistance at elevated temperature.The microstructure,composition,and phase structure of the layer were investigated by SEM,EDS,and XRD.The tribological behaviors of the Cr-Si co-alloyed layer at 20 ℃ and 500 ℃ were analyzed in details.The results indicated that the friction coefficient and wear rate of the Cr-Si coalloyed layer at 20 ℃ and 500 ℃ were much lower than those of the substrate,which was due to higher hardness and superior elastic modulus.This layer may become an approach to effectively improving the wear resistance of TA15 alloy at elevated temperature. 相似文献
356.
总结了波音737NG飞机自动油门电门组件的故障现象,在数据分析的基础上,确认了电门组件失效的原因,探讨了航线排故方法,并给出测量微动电门电阻的施工参考标准。 相似文献
357.
Aiming at the requirements of installation and work environment of metal-based fiber Bragg grating(FBG)sensor,a resistance spot welding method is presented.Firstly,the effect of welding parameters on welding quality is discussed theoretically,and a suitable resistance spot welding method for the metal-based FBG sensor is proposed for the first time.Then through serial resistance spot welding tests,the feasibility and practicability of the method are verified,and optimal welding parameters for two different tested metals are obtained.Fatigue performance test validates FBG sensors installed by the proposed method with good fatigue properties and long-term stable measurement performance.The research results can provide technical guidance for engineering structure long-term safety monitoring. 相似文献
358.
从经济学视角出发,发现企业变革中存在阻力问题的原因主要表现在以下三个方面:一是路径依赖使企业变革受到惯性阻力;二是信息不对称使得员工恐惧产生变革阻力;三是变革的风险成本大于收益,困扰企业变革前进的脚步。基于此,要消除企业变革的阻力问题可以从加强对员工的培训力度、让员工参与变革、塑造共同愿景、建立强有力的领导团队以及提高员工对变革的适应性等几个方面着手。 相似文献
359.
Abradable seal rubber has been widely used in aero-engine fans to improve their efficiency by reducing the clearance between rotating and stationary components. To investigate the high-speed scraping behavior between a vulcanized silicone rubber and a Ti-6Al-4V fan blade and evaluate the abradable performance of seal rubber, abrasion tests were conducted at a blade tip velocity of 50–300 m/s with an incursion rate of 100 lm/s. The influences of the blade tip velocity on the wear mechanism and interaction forces were specially analyzed. It is shown that abrasive wear and pattern wear are the predominant wear mechanisms, and pattern wear can be seen as the emergence and propagation of cracks. With an increase of the blade tip velocity, both of the final incursion depth and wear mass loss of seal rubber exhibit growth trends. The gradual changes of rubbing forces with an increase of rubbing time are the characteristic of abrasive wear, and force curves with unstable mutations are a reflection of pattern wear. At a constant incursion rate of 100 lm/s, the maximum values of interaction forces decrease first and then grow with an increase of the blade tip velocity, and the blade tip velocity of 150 m/s becomes the cut-off point between abrasive wear and pattern wear. 相似文献
360.
The H13 hot-working tool steel is widely used as die material in the warm forming of Ti–6Al–4V titanium alloy sheet. However, under the heating condition, severe friction and lubricating conditions between the H13 tools and Ti–6Al–4V titanium alloy sheet would cause difficulty in guaranteeing forming quality. Surface modification may be used to control the level of friction force, reduce the friction wear and extend the service life of dies. In this paper, four surface modification methods(chromium plating, TiAlN coating, surface polishing and nitriding treatment)were applied to the H13 surfaces. Taking the coefficient of friction(CoF) and the wear degree as evaluation indicators, the high-temperature tribological behavior of the surface modified H13 steel was experimentally investigated under different tribological conditions. The results of this study indicate that the tribological properties of the TiAlN coating under dry friction condition are better than the others for a wide range of temperature(from room temperature to 500 C), while there is little difference of tribological properties between different surface modifications under graphite lubricated condition, and the variation law of CoF with temperature under graphite lubricated is opposite to that under the dry friction. 相似文献