S-N curve for etd-150
S-N curve for etd-150
(OP)
Does anyone have or know how to get a S-N curve for etd-150?
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RE: S-N curve for etd-150
RE: S-N curve for etd-150
RE: S-N curve for etd-150
RE: S-N curve for etd-150
Reference: Shigley, Joseph Edward, and Mischke, Charles R., Mechanical Engineering Design, Fifth Edition, McGraw-Hill Book Co., Inc., 1989, Section 7.
A reasonably accurate approximate S – N curve for any steel can be constructed using the following equations given in this reference.
Log Sf = Log a + b Log N = Log (1.62 Sut) + Log N-0.0851
a = (0.9 Sut)2 / Se = 1.62 Sut
b = -(Log (0.9 Sut / Se)) / 3 (= -0.0851 when Se = .5 Sut)
Se = 0.5 Ftu = Endurance Limit = Stress corresponding to “infinite” life of 1,000,000 or more cycles.
Sf = Stress corresponding to a fatigue life, N, of 1000 to 1,000,000 cycles inclusive.
These equations are based on rotating beam test data, and must be adjusted for stress ratios other than R = -1.
Hope this helps.
RE: S-N curve for etd-150
If your application does not see a lot of variable amplitude loading, then perhaps you can use the equation, but substitute a more conservative number for the endurance limit-- maybe 0.35*Ftu or 0.4*Ftu instead of 0.5*Ftu.
RE: S-N curve for etd-150
Interesting caveat. Thank you for the additional information on this material.
I would normally use Goodman diagrams, cumulative damage methods, etc., to account for variable amplitude alternating stresses. The stresses of varying amplitude, varying stress ratio, etc, can be converted to equivalent constant amplitude stresses—always, of course, with the understanding that these methods are not precise, and must be used with care and judgement.
It sounds as if this material is not a typical steel, and should be derated as you suggest; but if that is the case, it seems to me that it should be derated for any fatigue analysis. Why are variable amplitude stresses relevant?
Regards
Lcubed
RE: S-N curve for etd-150
You are correct in your assumption that this material should be "derated" for any fatigue analysis-- constant amplitude or variable amplitude. I was trying to explain that the equation you provided is suitable for constant amplitude loading, not for variable amplitude. Obviously you understand cumulative damage, so as long as those methods are employed, conversion to an equivalent constant amplitude stress can be done.
RE: S-N curve for etd-150
I see. I misunderstood. Thanks for the clarification. I think I should have expanded slightly on my statement about rotating beam data and adjustments for stress ratios not equal to 1.0. There is probably not enough emphasis on that, and a little guidance might also have been in order.
From your knowledge of this material, would you suggest that the 1,000 cycle point be lowered, i. e., slip the entire curve down by 20 - 30 percent, or leave the 1,000 cycle point at 0.9 x Su and steepen the slope between 1,000 and 1,000,000 cycles? That is, do you know if this material is more or less susceptible to HCF than to LCF?
Thanks again for your input.
RE: S-N curve for etd-150
RE: S-N curve for etd-150
Can you provide additional details on what stress ratio was used? Stress amplitude? Notch geometry/stress concentration? What is the source of this data?
RE: S-N curve for etd-150
My reference is a photocopy from La Salle Steel's "Engineering Data Book". I've been searching for the original with no success, and unfortunately my photocopy cuts off all test specifics except for:
"Rotating-Bending Test method for notched and unnotched".
I am sure that a more complete data sheet is availble from one's local steel distributor.
RE: S-N curve for etd-150
RE: S-N curve for etd-150
Thank lcubed for your valuable post.
I wonder if you have equations of bending fatigue for predicting S-N Curve for any steel. I don't know if we can use these equations to draw S-N curve of any kind of steel for design use.Thank you!
RE: S-N curve for etd-150
Mr.LCUBED has supplied the S-N equations for rotating beam test, I doubt very much if anyone can supply S-N curve equations based on bending fatigue data for any steel or alloy.I can't find the Reference: Shigley, Joseph Edward, and Mischke, Charles R., Mechanical Engineering Design, Fifth Edition, McGraw-Hill Book Co., Inc., 1989, Section 7.
Thanks million