fatigue life
fatigue life
(OP)
I'd like to find out more about the fatigue-strain relationship of mechanical component.
Is it a linear relationship?
For example, if I increase the width of gear or chain, did I just doubled its fatigue life?
I remember faintly that it's not a linear relationship, but more of a curve.
Anyone know?
Thanks
Is it a linear relationship?
For example, if I increase the width of gear or chain, did I just doubled its fatigue life?
I remember faintly that it's not a linear relationship, but more of a curve.
Anyone know?
Thanks





RE: fatigue life
Approximately.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: fatigue life
That means it's theoretically possible to make mechanical components with infinite fatigue life.
Is it often done in real life?
Thanks
RE: fatigue life
However, yes, in the past many people have designed to the endurance limit.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: fatigue life
One would hope they are designed to infinite fatigue life.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: fatigue life
RE: fatigue life
an infinite fatigue life is not really an infinite life in most cases anyway, due to corrosion, wear, and other factors which will change the strength and/or usefulness of the part as time goes on. ex: A piston ring may not snap in half, but if the face is worn off it's not much good anymore, is it?
RE: fatigue life
IIRC, Markl's fatigue testing involving piping tees and reversed bending also resulted in an inverse 5th power relation between alternating (bending) stress and fatigue life in cycles.
Norm
RE: fatigue life
The number of cycles for postulated events in power plants only range up into the ten thousand-ish range, hence there's no worry about hundreds of thousands or millions of cycles of some predictable event happening vs the 1E6 cycle 'limit'.
Norm
RE: fatigue life
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: fatigue life
RE: fatigue life
Current ball and roller bearing design encourages abandoning the infamous L10 life when the contact stresses are below some nominal value. But the fine print sets stringent requirements on cleanliness and the absolute attainment of EHD lubrication.
No comment on the relationship of endurance limit to stress levels. Especially when "good" stress inducing processes like shot-peening, nitiriding and prestrain can have such a remarkable effect on actual fatigue life.