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I removed the last paragraph. It was a rather poor general description of fatigue. If the reader wants to know what fatigue is they need to simply follow the included link to a very good article on the subject. That being said, when I wrote this page I could find no information on the subject. I am happy to say that has changed. Portions of this article were included verbatum in Fatigue_(material) where it should be. Unless someone complains or does it first, I am going to drop this page and forward it to Fatigue_(material) some time after the January 1, 2007. -- Commdweeb 13:16, 7 November 2006 (UTC)
Fatigue Limit and Endurance Limit have subtly different meanings. Fatigue limit does indeed mean the asymtotic stress amplitude value on an S/N curve below which the metal will not theoretically fail by fatigue. Of the common metals, only steels and titanium alloys show this characteristic. Other metals and alloys display an S/N curve which becomes asymtotic to the "x" axis i.e. there is no stress amplitude below which the metal will not fail given a sufficient number of oscillations. In the absence of a "Fatigue Limit" some assessment of a metal's fatigue capability must be made. Conventionally, a value of "N" equal to 107 is used and the corresponding value of "S" gives a design figure. This is the "Endurance Limit". Other values of "N" are sometimes used so the Endurance Limit must be quoted as a value of stress amplitude at a particular number of cycles.
Roger Tyler MSc
The meanings of Fatigue Limit and Endurance Limit are not only subtly different, they also appear to be a little fuzzy.
Could the distinction between these two terms be just a cultural thing, or is the distinction between these terms just not that well defined? - AndrewDressel ( talk) 02:38, 18 April 2008 (UTC)
The concept of fatigue limit (as a strength below which a material does not crack irrespective of the number of cycles) has been challenged, see for example the article "There is no infinite fatigue life in metallic materials" by Bathias (in Fatigue & Fracture of Engineering Materials & Structures, Volume 22, Number 7, July 1999 , pp. 559-565). Many authors still haven't included this in their books, so there are lots of places that state the existence of the fatigue limit. From what I've seen in recent articles, "fatigue limit" is used in the traditional meaning, whereas "endurance limit" is more used for a specific number of cycles. I'll see if I can find references on this =) Kashieda ( talk) 09:35, 15 September 2008 (UTC)
The article seems undecided whether copper / aluminium have a nonzero Se or not. Is it zero, or is it 0.4? Bernd Jendrissek ( talk) 03:01, 1 June 2011 (UTC)
I question the 'typical values' quoted in the article, which are in terms of UTS - and quite high. For steel, values of the order of 10 to 35 MPa seem to be common in the literature. i.e. only a few % of UTS. This is because the practical application of the limit introduces real-world derating factors that are not present in laboratory test environments, such as surface condition. Aero.355 ( talk) 08:58, 22 July 2011 (UTC)
There is a growing body of evidence which suggests that " most materials do not have a fatigue limit at 107 cycles but instead their fatigue strength gradually decreases as fatigue life reaches 108 – 1010 load cycles." [1] The question is how best to reflect this in the lede. For example:
Does anyone with a materials sciences background want to take a crack at it? - AndrewDressel ( talk) 16:15, 5 August 2013 (UTC)
What theories are there for some materials having a limit and others not, or for predicting the limit if any ? Some says it's related to crystal structure FCC/BCC/HCP. Could it depend on temperature relative to creep point ? - Rod57 ( talk) 16:07, 30 July 2020 (UTC)
Graph seems to show an unspecified steel and pure aluminium ? Any data on different steels, eg various stainless steels, inconel, and various aluminium alloys ? - Rod57 ( talk) 16:07, 30 July 2020 (UTC)
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I removed the last paragraph. It was a rather poor general description of fatigue. If the reader wants to know what fatigue is they need to simply follow the included link to a very good article on the subject. That being said, when I wrote this page I could find no information on the subject. I am happy to say that has changed. Portions of this article were included verbatum in Fatigue_(material) where it should be. Unless someone complains or does it first, I am going to drop this page and forward it to Fatigue_(material) some time after the January 1, 2007. -- Commdweeb 13:16, 7 November 2006 (UTC)
Fatigue Limit and Endurance Limit have subtly different meanings. Fatigue limit does indeed mean the asymtotic stress amplitude value on an S/N curve below which the metal will not theoretically fail by fatigue. Of the common metals, only steels and titanium alloys show this characteristic. Other metals and alloys display an S/N curve which becomes asymtotic to the "x" axis i.e. there is no stress amplitude below which the metal will not fail given a sufficient number of oscillations. In the absence of a "Fatigue Limit" some assessment of a metal's fatigue capability must be made. Conventionally, a value of "N" equal to 107 is used and the corresponding value of "S" gives a design figure. This is the "Endurance Limit". Other values of "N" are sometimes used so the Endurance Limit must be quoted as a value of stress amplitude at a particular number of cycles.
Roger Tyler MSc
The meanings of Fatigue Limit and Endurance Limit are not only subtly different, they also appear to be a little fuzzy.
Could the distinction between these two terms be just a cultural thing, or is the distinction between these terms just not that well defined? - AndrewDressel ( talk) 02:38, 18 April 2008 (UTC)
The concept of fatigue limit (as a strength below which a material does not crack irrespective of the number of cycles) has been challenged, see for example the article "There is no infinite fatigue life in metallic materials" by Bathias (in Fatigue & Fracture of Engineering Materials & Structures, Volume 22, Number 7, July 1999 , pp. 559-565). Many authors still haven't included this in their books, so there are lots of places that state the existence of the fatigue limit. From what I've seen in recent articles, "fatigue limit" is used in the traditional meaning, whereas "endurance limit" is more used for a specific number of cycles. I'll see if I can find references on this =) Kashieda ( talk) 09:35, 15 September 2008 (UTC)
The article seems undecided whether copper / aluminium have a nonzero Se or not. Is it zero, or is it 0.4? Bernd Jendrissek ( talk) 03:01, 1 June 2011 (UTC)
I question the 'typical values' quoted in the article, which are in terms of UTS - and quite high. For steel, values of the order of 10 to 35 MPa seem to be common in the literature. i.e. only a few % of UTS. This is because the practical application of the limit introduces real-world derating factors that are not present in laboratory test environments, such as surface condition. Aero.355 ( talk) 08:58, 22 July 2011 (UTC)
There is a growing body of evidence which suggests that " most materials do not have a fatigue limit at 107 cycles but instead their fatigue strength gradually decreases as fatigue life reaches 108 – 1010 load cycles." [1] The question is how best to reflect this in the lede. For example:
Does anyone with a materials sciences background want to take a crack at it? - AndrewDressel ( talk) 16:15, 5 August 2013 (UTC)
What theories are there for some materials having a limit and others not, or for predicting the limit if any ? Some says it's related to crystal structure FCC/BCC/HCP. Could it depend on temperature relative to creep point ? - Rod57 ( talk) 16:07, 30 July 2020 (UTC)
Graph seems to show an unspecified steel and pure aluminium ? Any data on different steels, eg various stainless steels, inconel, and various aluminium alloys ? - Rod57 ( talk) 16:07, 30 July 2020 (UTC)