Stress and metal fatigue
Stress and metal fatigue
(OP)
When talking about metal fatigue, we know that number of loading cycles to failure is related to stress. But the stress we talk about here refers to max. stress or stress range?
I'd expect both max stress and stress range affect the number of cycles. Yet in a typical S-N curve I see only the max stress. Information regarding stress range is missing? Then how is that S-N curve useful to us?
Anybody help me clear my doubt?
I'd expect both max stress and stress range affect the number of cycles. Yet in a typical S-N curve I see only the max stress. Information regarding stress range is missing? Then how is that S-N curve useful to us?
Anybody help me clear my doubt?





RE: Stress and metal fatigue
RE: Stress and metal fatigue
Here is a web site that you will find useful regarding a tutorial on fatigue.
https://www.efatigue.com/fatiguecalc.html
RE: Stress and metal fatigue
stress range, but for low cycle fatigue, the test data used to generate the fatigue curve is usually strain range data , multiplied by a constant youngs modulus, to generate an apparent stress range. Since the alternating range in low cycle fatigue is often in excess of yield, one would need to adjust the stress value to account for plastic yielding.
swall:
I hear that the latest theories ( from people that work with aluminum) are that there is no such thing as a fatigue limit , that the values often used for steel are a result of an inaccurate test protocol or limited instrument accuracy.
RE: Stress and metal fatigue
There has been a great deal of research, both academic and industrial, in the very high cycle range (also called ultra high cycle and gigacycle) that shows even steels do not necessarily possess an endurance limit. Here are some previous threads with links to references on the subject:
http://www.eng-tips.com/viewthread.cfm?qid=242798
http://www.eng-tips.com/viewthread.cfm?qid=270181
RE: Stress and metal fatigue
RE: Stress and metal fatigue
Now I come across DNV-RP-C203 and BS 7608B "curves", what are these two standards all about, and any copies available on-line?
RE: Stress and metal fatigue
DNV-RP-C203
http://www
BS 7608 is a standard published by the British Standards Institute (BSI), and is not frely available. You can pay to download a copy from the following website:
ht
RE: Stress and metal fatigue
Thanks for the links.
Btw, I found the 2010 edition of DNV-RP-C203:
http://
RE: Stress and metal fatigue
http://www
good luck!
www.priamengineering.co.uk