New Test Method for High cycle fatigue resistance under rolling motion and high Hertzian contact stresses
1. Scope
Test procedures used by the state-of-the-art for evaluating the frictional properties as well as resistances against fatigue, wear and scuffing are FZG gear tests, FE8 (DIN 51819, ISO 23608) or FE9 (DIN 51821) test machines, 2-/-4-roller machines and WAM&MTM machines. This tribometric test methodology enables to determine the resistance against fatigue under high Hertzian contact stresses and rolling motion in a geometry with narrow/tight radii between the three test specimen (racetrack #1, ball, racetrack #2). The geometry consists of three specimen (racetrack #1, ball, racetrack #2) illustrated in Figure 1. The concave raceways are crossed at 90° to each other and the oscillation movement is tilted by 45° to these raceways so that the raceways guide the single ball by themselves. The type of motion is oscillatory (reversed) rolling. This test geometry is tribologically sollicited in a translatory oscillation apparatus with electromagnetic linear drive having an integrated stroke/position sensor. Hertzian contact stresses P0max can be high as 3.000 MPa. AS test results, the cycles until fatigue and the associated evolution of coefficient of friction as well as the wear volumes can be determined.
Keywords
fatigue, rolling, reciprocating, friction, wear
Rationale
Even deposition processes exists to coat any surface geometry, it is in the development not feasible to coat inner or outer surfaces for screening testing, like circumferical surfaces of disks or gears (FZG) or inner /outer rings of ball bearings. Another aspect is the simple manufacturing and the easy coating of The viewing/visible surface of the raceways of the test pieces can be easily coated with thin films and the test pieces are simple to produce.
This tribometric test methodology will be used for screening the fatigue resistance under rolling motion of monolithic materials and/or thin film coatings. Further, the impact of additives or its limiting concentration and formulated lubricants under the severeness of the regime of mixed/boundary lubrication on
a. White etching cracks,
b. fatigue/delamination/spalling
can be assessed.
