Papers by Author: Le Gu

Abstract: In this work, carbon films were deposited by magnetron sputtering on silicon substrate. The effect of sputtering time on the surface wettability and mechanical properties of carbon films was investigated. Contact angle measurement was used to analyse surface wettability, and the nanomechanical properties were characterized by nanoindentation. In experiments, the sputtering time was 45 min, 60 min, 75 min and 90 min. The measurement results show that the maximum film hardness was achieved for sputtering time 90 min, with a value of 2.34 GPa. Longer sputtering time resulted in preferable mechanical properties. It was analyzed that the size of the crystal grains on the substrate surface and thickness of the films were increased with the increment of sputtering time. The surface roughness decreased with the increase of sputtering time. Moreover, Youngs modulus increased with sputtering time and the maximum value was 16.94 GPa. The contact angle measurement results show that the prepared films take on the hydrophilicity. The minimum contact angle was achieved for sputtering time 45 min with a value of 54o.

Abstract: Radial lip seals made from PTFE composites are used more frequently for sealing of crank shafts in automotive and aerospace industries. Due to the seal loses materials and finally fails. Through experiment on a test rig, the tribology performance of seal can be predicted. Because of the non-linear elasto-viscoplastc material properties of PTFE composites, the finite element analysis (FEA) is adopted. A modified iterative remeshing method is adopted in wear process. The lip wears out according to the contact pressure of the node on the contact surface. Comparisons between numerical simulation and short-term service are made. The results show that the maximum of contact pressure decreased and width increased with wear time added, and the maximum of contact pressure moves toward the lip tip. Finally, it reaches lip tip, the phenomenon of uneven contact pressure was disappeared.

Abstract: Semi-dynamic method is employed to calculate the local stiffness of angular contact ball bearing, accounting for the influence of geometrical deflects caused by shaft coaxiality in the process of bearing assemble. The effect of coaxiality on the bearing deflect is computed, and the relationship of local bearing stiffness to coaxiality is analyzed.

Abstract: The tribological performances of mixed PTFE-based composites were evaluated on the MM-200 block-on-ring test rig under dry friction condition. The following filler contents: carbon fiber (CF), flake graphite (FG) and spherical graphite (SG) were adopted to investigate their effects on the tribological performances of the composites. The experiments were carried out by a four levels orthogonal table-L₁₆（4³）, and the experiment data were deal with the methods of range and variance analysis. The results shown that all the filler contents could reduce wear, and the wear rate was stable when the content of fillers were more than 10 wt.%. The degrees of three fillers affecting the wear of composites were CF>FG>SG, and that affecting the friction coefficient were SG>CF>FG. The friction coefficient decreased with increasing the contents of SG, increased with that of CF, first decreased and then increased with that of FG. When the contents of FG is 15 wt.%, the friction coefficient is the lowest. The main worn form was adhesion wear.

Abstract: A two-disk test rig researching surface damage and ultimate performance of rolling-sliding tribo-parts in extreme conditions is designed. Variable speed (rolling speed up to 83.6m/s, sliding speed up to 16.4m/s) of the rolling/sliding contact are input by motor spindle and regulated with gear. Variable load (Hertzian contact up to 4GPa) is applied with hydraulic cylinder. High temperature (~+300°C) and cryogenic environment(liquid nitrogen) is implemented by changing the lubricant condition. Thermal-stress analysis with ANSYS shows that the temperature and stress of the tester body is reasonable. As the signals judging failure, such parameters as temperature and vibration of the supporting bearing, power consumption of the main spindle, temperature of the tribo-parts surface are monitored in real time. Kingview, PLC, VB and MATLAB software are employed in the online monitoring system to collect data automatically. Types of tribo-parts were tested in the test rig, getting their ultimate performance and the effect of each parameter on surface damage.

Abstract: According to roller profile modification method, several commonly used modified rollers were selected into the bearing dynamic analysis combined with dynamic model of bearing. As the three types of modified roller an example, simulation program was established to analyze the load distribution of loaded roller under the working conditions of upright loading and offset loading of bearing, respectively. The effects of modified roller on bearing dynamic parameters were discussed. The results provided optimal direction for bearing selection and design under different working conditions.

Abstract: The friction and wear behavior of Si₃N₄, SiC and ZrO₂ sliding against M50 bearing steel under vacuum condition at various applied load were investigated. The results showed that the properties of different ceramic materials cause the difference in wear behaviors. The coefficient of friction was lowest in SiC and M50 bearing steel couple than other cases for graphitic carbon replaced carbidic carbon at the worn layer of SiC. The specific wear rate of ZrO₂ was highest and the lowest was Si₃N₄. The ceramic ball materials have transferred on M50 bearing steel surfaces and tribofilm consistently formed on the ceramic balls wearing surfaces. Dominant wear behaviors for three structural ceramics were adhesion abrasion, plastic deformation and brittle fracture. The couple with Si₃N₄ and M50 showed the best operating conditions for friction and wear resistance under higher applied load.

Abstract: The tribologcial performance of PTFE composites filled with different contents of spherical-graphite and Flake-graphite were comparatively evaluated on MM-200 test rig in block-on-ring configuration under dry condition. The microstructures of worn surfaces of PTFE composites were examined with SEM, and wear mechanisms was also analyzed. The changes of notched impact strength with the content changed were also considered. The results show that the tribological performance of spherical-graphite was better than flake-graphite with same weight filled: The friction coefficient of spherical-graphite, about 0.10~0.15, was under flake-graphite, about 0.12~0.18; the wear rate of spherical-graphite was lower than flake-graphite at each content. Notched impact strength of spherical-graphite was from 7.0kJ/m² to 8.7 kJ/m² with the content increased, while flake-graphite was fall rapidly from 8.5kJ/m² to 3.0kJ/m² with the content added more than 5wt. %.

Abstract: In this work, the feasibility of using planetary ball milling for coating bearing balls with a self-lubricating film was investigated. Bearing balls with appropriate amount of MoS2 powder were put into vacuumed stainless steel vials and ball milled. With proceeding of ball milling, thickness of the self-lubricating film increased at first and then decreased. X-ray diffraction (XRD) and X-ray photoelectron spectrum (XPS) results revealed that the surface of the self-lubricating film was MoS2 and the inner region was a mixture of iron molybdenum alloys (Fe3Mo, FexMoy), MoS2 and FeS. Friction coefficient between the self-lubricating film and bear steel was 0.06~0.1.

Abstract: The friction and wear performances of Si3N4 ceramics sliding against bearing steel and to find optimal operating condition against M50 bearing steel couples under high vacuum surroundings were investigated. The tests were studied on the ball-disk machine under different loads and steady sliding velocity. The worn surfaces of tested samples were examined using optical microscope，SEM and XPS. The results showed that the friction coefficient of Si3N4 was decided by the applied load, the critical load of Si3N4’ friction coefficient was 10N applied load; The critical load of Si3N4’ specific wear rate was 5N applied load, the specific wear rate of Si3N4 drop rapidly as the applied load exceeded the critical load; The dominant wear mechanisms of Si3N4 ceramics were adhesion wear, brittle facture and furrow wear in vacuum.