Who can help me with S-N Curve equations for bending fatigue?
Who can help me with S-N Curve equations for bending fatigue?
(OP)
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
Thanks million





RE: Who can help me with S-N Curve equations for bending fatigue?
http://www.amazon.com/exec/obidos/tg/detail/-/0070568995/104-2528612-0223159?v=glance
or your local university library.
you might also contact the Linda Hall Lib. as they have a good information retrieval service
RE: Who can help me with S-N Curve equations for bending fatigue?
stress amplitude = fatigue strength coefficient* (2 N(f))^b
N(f) is the cycles to failure
2N(f) is the number of load reversals to failure
b is the fatigue strength exponent
For an AISI Type 1015 steel
b= -0.11
fatigue strength coefficient where 2N(f) =1, 120 Ksi
For an AISI Type 1045 carbon steel (quenched and tempered-225 BHN)
b= -0.095
fatigue stregnth coefficient, 178 Ksi
RE: Who can help me with S-N Curve equations for bending fatigue?
Thank you for your rapid reply,and I really appreciate your valuable information.
Lcubed's post is as follows:
"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."
I mean I want to predict bending S-N curves of some steel for design use,just like the formula given above by Lcubed.That is,We give a series of bending cycles,and get a series of bending fatigue strengths,with the alreday known static strngth as ultimate tensile srength or hardness.based on these data,we can draw a S-N curve for any steel.
In your supplied formula,I wonder the difference between N(f) and 2N(f).and do you mean I can write the formular as follows:
For 1015: Sf=a*1120^b
where b=-0.11
If I give a N(f)=10000 cycles, How can I calculate the Bending strength Sf?
Thanks again.
RE: Who can help me with S-N Curve equations for bending fatigue?
The stress amplitude, which is stress range/2, is plotted versus 2N(f) or load reversals, where R=-1. This is common for S/N fatigue data curves.
Thus, if you have N(f) = 10,000 cycles, the 2N(f) = 20,000 reversals
Therefore using Basquins Rule;
stress amplitude = 120 Ksi * (20,000)^-0.11
stress amplitude = ~ 40.4 Ksi where R=-1
RE: Who can help me with S-N Curve equations for bending fatigue?
Thanks again for your valuable post!
Can I use this equation for predicting bending fatigue S-N curve of any steel? for example, low alloy carburizing steels(8620),quench and tempered steels(4140),nitriding steels,low carbon steel sheets or bars? What fatigue stregnth coefficient should I use?
I want to predict bending S-N curves of any steel for design use with no test data avilable.
Can I use the present known static strngth as ultimate tensile srength or hardness to predict S-N curve for any steel?
Forgive me for so much questions.
Best regards
RE: Who can help me with S-N Curve equations for bending fatigue?
The equation can be used for most carbon and low alloy steels. You will need to determine two important parameters; the fatigue strength coefficient and the fatigue strength exponent. I believe that the reference book which I cited earlier ("Fracture Mechanics of Engineering Materials" Hertzberg) contains these parameters for many steels and other materials, as well. I would recommend you obtain a copy of this reference book.
RE: Who can help me with S-N Curve equations for bending fatigue?
Thanks a lot!
In China,I can't get the information of this book.I have contacted the Author Dr.Hertzberg,He said He Had retired and no longer worked in this field. He can't give me any help. Just as you said,Can you recommend me where I can get this book,or if you don't mind,send me the equations for any metal material.Thanks again.
Henryzhang
RE: Who can help me with S-N Curve equations for bending fatigue?
www.newtonlibrary.com/si/A001710.html
www.brook-tech.fsnet.co.uk/stress_books/0471012149.htm