Fatigue life ~ 1/load^3 - theoretical basis?
Fatigue life ~ 1/load^3 - theoretical basis?
(OP)
I was just thinking about the life equation.
L10 = 1E6 * (C/P)^3 revolutions.
Did it come from empirical data?
If the mechanism is fatigue, doesn't fatigue S*N accumulate proportional to load which would suggest a relationship (C/P)^1 instead of (C/P)^3 ?
It would seem maybe the explanation is the bearing is operating outside the linear range for fatigue.
Does a bearing typically operate with stresses above the elastic range? Down near the endurance range?
L10 = 1E6 * (C/P)^3 revolutions.
Did it come from empirical data?
If the mechanism is fatigue, doesn't fatigue S*N accumulate proportional to load which would suggest a relationship (C/P)^1 instead of (C/P)^3 ?
It would seem maybe the explanation is the bearing is operating outside the linear range for fatigue.
Does a bearing typically operate with stresses above the elastic range? Down near the endurance range?
=====================================
Eng-tips forums: The best place on the web for engineering discussions.





RE: Fatigue life ~ 1/load^3 - theoretical basis?
FAG has been saying that if the the equivalent stress is less than ~1/8 the basic dynamic stress rating then life can be infinite.
SKF lists the endurance or fatigue limit right along side the other load ratings. Usually less than the 1/8 thumb rule.
RE: Fatigue life ~ 1/load^3 - theoretical basis?
at the low end of loading, fatigue cycle accumulation rate is proportional to P^0 (life proportional to P^(-0) )
at the high end of loading, fatigue cycle accumulation rate is proportionalt to P^0 (life proportional to P^(-1) )
So for a range including both high and low loading we might fit a life curve something between P^(0) and ^(-1).
I would pick P^(k) where -1 < k < 0.
But the standard relation is P^(-3)... how is that consistent? Did Lungren whatshisname make it up?
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Fatigue life ~ 1/load^3 - theoretical basis?
varies by the cube of the load.
So if your load is 1/2 the rated
load you life would increase by
the 2 cubed or by 8 times.
I think it was by 3 for ball bearings
and 3.333 for roller bearings.
RE: Fatigue life ~ 1/load^3 - theoretical basis?
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Fatigue life ~ 1/load^3 - theoretical basis?
the raceways being approx .0001 times
the roller diameter which is not really
the same phenomenom. This is only at
the surface and not at the core of the
material. The surface material might be
in the range of 63Rc and the core may be
only in the 24 Rc range. Really not
certain what endurance limit is imposed
on an non isomorphic product.