Yukio Fujii

Flaking failure in rolling contact fatigue caused by indentations on mating surface (I): Reproduction of flaking failure accompanied by cracks extending bi-directionally relative to the load-movement

The crack growth in rolling contact fatigue has been investigated with a newly devised testing rig. A surface crack normally extends in the direction of the load-movement, and flaking failures accompanied by cracks extending in the direction opposite to the load-movement are rarely observed. However, in some situations, cracks extending in the opposite direction appear with an as not as yet clarified mechanism. In this study, a double-roller type rolling contact fatigue testing rig has been devised to reproduce the opposite-direction crack growth. Equally spaced artificial indentations are marked on the surface of one roller, while the other roller surface is defect-free. In that set-up, a flaking accompanied by cracks extending bi-directionally to the load-movement almost always occurs on the defect-free roller surface. The appearance of the flaking is consistent throughout the tests, but the cycles to failure vary according to test conditions such as (1) contact load, (2) additional tangential force between the rollers, (3) the number of artificial indentations, (4) whether the defect-free roller is operated as the driver or the follower, (5) rotational speed, and (6) size of artificial indentations.

Flaking failure in rolling contact fatigue caused by indentations on mating surface (III): Mechanism of crack growth in the direction opposite to the load-movement

In rolling contact fatigue, we have discovered that a flaking failure accompanied by cracks extending bi-directionally relative to the load-movement occurs on a defect-free surface due to the influence of indentations on a mating surface. We have also demonstrated, using stress analysis, the initiation of incipient cracks in the subsurface region resulting from indentations on the mating surface. In the present study, we focus on the stage of crack extension in the direction opposite to the load-movement. Firstly, mode II fatigue crack growth properties are investigated by conducting mode II fatigue testing, which has been previously presented. Subsequently, stress intensity factors at a subsurface crack are calculated by using a finite element method for the case of an indentation on the mating surface moving through the contact area. In this calculation, the configuration of the modeled crack is very similar to cracks actually observed. Based on the results of both the stress analysis and the cracking seen in actual tests, the mechanism for the development of opposite-directional cracking is proposed to be a mode II extension of an incipient subsurface crack.

New retainer material for high speed and high temperature cylindrical roller bearing

Cylindrical roller bearings are being developed which can operate over 300°C and greater than three million DN for innovative gas-generators. Under such severe conditions, it is necessary for retainers to be frictionless, lightweight and strong. After preliminary testing, SiC particle reinforced aluminum alloy composite appeared to have good friction and wear properties. Its specific gravity is about one-third of the present material in use, silver-coated SAE4340. In the course of the study, two different friction and wear tests were conducted to investigate the optimum volume fraction of SiC. The results indicated that the most efficient volume fraction was 20vol%. The tensile strength of Al-20vol%SiC was about 140MPa at 300°C. Based on the results of FEM analysis, 140MPa is considered sufficient to endure any stress concentration caused by tensile hoop stresses up to four million DN. Presented at the 54th Annual Meeting Las Vegas, Nevada May 23–27, 1999