Le Gu

Tribological Performance of M50 Steel Tribo-Parts

The tribological performance of M50 bearing steel under extreme conditions such as those experienced by aircraft bearings was investigated to ascertain the ultimate capacity and failure regularity of the contact surfaces. Experiments were carried out on a two-disc test rig using synthetic aircraft engine oil No. 4050 at approximately 80°C. The testing proceeded until surface failure was detected via a sharp rise in the temperature of the tested disc and the power consumption of the motor. Heat treatment and surface finishing were applied to the tested discs in the same way as for aircraft engine ball bearings. The topography of the worn areas was observed both on the surface and in cross sections using optical microscopy and scanning electron microscopy (SEM). The maximum total contact temperature, that is, the sum of the monitored bulk temperature and the calculated flash temperature, was analyzed. The Vickers hardness and residual stress of the worn areas as a function of depth were measured. The results show that the damage was mainly spalling on the slow disc surface and was primarily adhesive welding and tearing on the fast disc surface. At a slide–roll ratio of 0.12, a cross section of the contact surfaces can be divided into three layers: a white layer that includes material damage, a grain refinement layer, and a layer without obvious changes. At slide–roll ratios of 0.12 and 0.15, the typical depth within which the hardness and residual stress of M50 steel was significantly affected was less than 50 μm.

The Effect of Roller Profile Modification on Roller Bearing Performance

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.

Image Acquisition and Segmentation for Ceramic Bearing Ball Surface Inspection System

Surface and subsurface defects in ceramic bearing balls significantly affect ball strength and lifetime. A brief review of nondestructive evaluation technologies on hybrid bearing balls was presented. An automatic ceramic bearing ball surface inspection system based on computer image technology was developed. Various surface defects were imaged by microscope and image digitizer on a novel ball surface unfolding mechanism. Top-hat and logarithm transformations were applied to eliminate uneven lighting disturbance. An automatic seeded region growing algorithm based on histogram concavity analyses and Otsus method was developed for defects segmentation. The results show that the experimental system is effective for ceramic ball surface and subsurface defects detection

Fatigue Behavior of Hybrid Ceramic Ball Bearings in Liquid Nitrogen

Hybrid ceramic ball bearings, which are composed of silicon nitride (Si3N4) balls, ANSI 440C stainless steel rings and PTFE based composite retainers, are tested at high speed and heavy loading in cryogenic conditions. The rolling contact fatigue behavior of steel rings and ceramic balls in liquid nitrogen is analyzed. In addition, four-ball fatigue testing was done at room temperature with oil lubrication. The crush load of ball against ball in liquid nitrogen, which directly relates to the inner quality of the balls, is also evaluated. The results show that the spalling of silicon nitride balls, rather than micro pitting on the steel raceways, is the main cause for the failure of the hybrid ball bearings in liquid nitrogen. The fatigue mechanism of the ceramic balls is similar to that of ceramic balls at room temperature, but the characteristics of crack propagation are different because of differences between the cryogenic liquid medium and oil. Although most of the fatigue cracks originated from internal defects within the ceramic balls, the silicon nitride balls exhibit a high load capacity. When silicon nitride balls are loaded against steel balls, the steel balls are crushed while the silicon nitride balls do not exhibit plastic deformation. When ceramic balls with a 11.113 mm diameter are loaded against each other, crushing takes place at a nominal contact stress of 27∼29 GPa. Presented a the 58th Annual Meeting in New York City April 28–May 1, 2003

Boundary Tribological Behaviors of Untreated and Surface-Modified M50 Steel Lubricated by Fuel JP-10

ABSTRACT To explore the possibility of using advanced surface engineering techniques (ASETs) to solve the wear problems caused by the poor lubricity of pure, low-viscosity aviation fuel JP-10, polished M50 bearing steel sample surfaces were treated with nitrogen ion implantation, TiAlN coating deposition, and Ta coating deposition followed by high current pulsed electron beam (HCPEB) irradiation, respectively. Boundary tribological behaviors of these ASET-treated and untreated steel samples sliding in pure JP-10 against a Si3N4 ball (ball-on-disc model) were investigated under 2.0 GPa in the atmosphere and the friction tests indicated that significant, reductions, although to different extents, in friction and wear were achieved by these modified surfaces. Simultaneously considering the tribological performance and potential pollution caused by wear debris to JP-10, HCPEB-treated Ta coating with a lowest average friction coefficient of 0.11 and a specific wear rate of around zero was the fittest to offset the inadequate lubricity of JP-10 itself under the laboratory condition.

Analysis and Evaluation of Interface Mechanics for Thin Films using the Method of Image

The evaluation of interface mechanics was very useful for the design of thin solid film. According to the method of image, interface stresses and deformations of coating-substrate system were gained. Using this mathematical calculation model, the indentation test data was carried out and the results were analysed. Based on the mechanical model and test, the critical state of interface stresses from elastic deformation to plastic yield was evaluated. From experimental and calculating results, interface shear stress and normal stress had different affecting level for the coating failure under the same surface load. And a fitting relationship equation for the two stresses was also gained to determining the failure value in designing. The method of this paper could be used for thin film interface mechanics design and evaluation.

Effect of Implantation Sequence on Tribological Behavior of GCr15 Steel by PBII

In the present work, the effect of implantation sequence on tribological behavior of GCr15 steel treated by plasma-based ion implantation of carbon and nitrogen has been investigated. The treated GCr15 steels were characterized for microstructure and abrasive wear performance through combination of Raman spectroscopy, nano-indentation, and wear tests. Raman spectroscopy indicated that diamond-like carbon (DLC) films were formed after implantation of carbon with or without implantation of nitrogen, and the implantation of nitrogen after the implantation of carbon destroyed the graphite structure of the DLC films. The nano-indentation and wear tests showed that nanohardness as well as wear resistance of the GCr15 steel treated with the implantation sequence of nitrogen-carbon was better than those with the implantation sequence of carbon-nitrogen. Meanwhile, the properties were improved with increasing of carbon ion fluence.

Nanomechanical Properties and Surface Wettability of Carbon Films Prepared by Magnetron Sputtering

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.

Analysis on Dynamic Contact Force in High Power Density Gear Transmission Based on Flexible Model

Recently, most of researchers pay more attention to the flexible model for solving dynamic contact force in high power density gear transmission. But, the detailed formula of the contact force parameters is not given. Therefore, in this paper the detailed calculation of coefficient of restitution (COR) is proposed, which can solve the elastoplastic contact deformation problems compared with other method. To improve the simulation efficiency, a flexible model based on ADAMS and Hertzian theory is presented. According to the simulation results, the normal contact force of the flexible model is much higher than that of the rigid model in plastic contact deformation. Meanwhile, the normal contact force delay exists in flexible model compared with rigid model. At last, the flexible model simulation results are close to the theoretical result in steady state. Consequently, the flexible model can be applied to analyze dynamic characteristic in reasonable time and many revolutions of the high power density gear transmission.

Modeling and Simulation of Wear in PTFE Lip Seals

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.