PSI - Issue 7

Hisao Matsunaga et al. / Procedia Structural Integrity 7 (2017) 460–467 Hisao Matsunaga / Structural Integrity Procedia 00 (2017) 000–000

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and dimensions of the rolling bearings were subsequently adjusted by grinding, with the track surfaces processed by super-finishing. The average Vickers hardness, HV , measured with a load of 9.8 N, was 751 for JIS-6206 and 754 for JIS-51305, respectively. A drilled hole was introduced at the bottom of the grooved track as a crack-starter. The hole diameter, d, ranged from 0.05 to 0.1 mm, and the depth of the hole-edge, h', ranged from 0.05 to 0.175 mm. 2.2. Experimental method Figure 1 displays a schematic of the rolling bearing and test rigs. During the RCF test, steel balls (JIS-SUJ2) measuring 9.525 mm in diameter were rolled between the inner and outer rings under a contact load. Eleven balls were used as the thrust balls. The lubricant used was ISO-VG68. The maximum contact pressure, q max , ranged from 2.5 to 3.4 GPa, with a rate of rotation of 3900 min − 1 for JIS-6206 and 1000 min − 1 for JIS-51305. Figure 2 presents an example of the observation of a cross-section after an RCF test. The fatigue life, N f , was defined as the number of cycles, N, at which a sub-surface crack reached the surface. When fatigue failure did not occur at N = 1.0 × 10 8 cycles, the fatigue test was terminated. After the fatigue test, the cross-section of the hole was observed by optical microscopy.

Table 1: Chemical composition of the tested bearings (mass %).

Element

C

Si

Mn

Cr

P

S

Ni

Cu

Mo

6206

0.98 1.03

0.23 0.26

0.36 0.33

1.43 1.33

0.014 0.010

0.004 0.004

0.02 0.02

0.004 0.002

0.01 0.01

51305

Outer ring

Inner ring

Rolling element (Ball)

Inner ring

Rolling element (Ball)

Outer ring

(a-1) Deep-groove ball bearing.

(a-2) Thrust ball bearing.

Filter

Radial load

Axial load

Thrust bearing

Test bearing

Lubrication oil

Cage

Pump Radiator

Balls

Housing

Housing

Thrust bearing

Lubrication oil

(b-1) Rigs for the fatigue test of deep-groove ball bearing.

(b-2) Rigs for the fatigue test of thrust ball bearing.

Fig. 1: Schematic of the rolling bearings and rigs for the fatigue test.