Discussion
For a ball bearing, the fatigue life in millions of revolutions is given by \(L = \left(\dfrac{C}{P}\right)^{n}\), where \(P\) is the constant applied load and \(C\) is the basic dynamic load rating. Which one of the following statements is TRUE?
Answer: C
The true statement is n = 3, assuming that the outer racing is fixed and inner racing is revolving.
The load-life relation for rolling bearings is \(L_{10} = (C/P)^{n}\) with \(n = 3\) for ball bearings (and 10/3 for roller bearings). The basic dynamic load rating C is defined for the standard condition in which the inner ring rotates and the outer ring is stationary, the usual arrangement on a rotating shaft.
An exponent of 1/3 inverts the relation and would make life increase with load, which is absurd. A rotating outer race with a fixed inner race is a different condition, for which catalogues apply a rotation factor, so the rating with n = 3 is stated for the inner-race-rotating case.
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