Talk:Fatigue (material)

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[edit] Good Job

This article is very well done. Its is much better than most materials science articles on Wikipedia. Good Job! Perhaps this will be up to featured article caliber soon. Iepeulas 13:12, 12 June 2006 (UTC)

[edit] Bending but not breaking

Hey does anyone know how you can bend metal without breaking it? —68.17.132.200

If you heat the metal up sufficiently while forming, it will become more ductile and so shouldn't break. If you want to bend it while it is cold, you may be able to anneal it to remove any work hardening effects. —BenFrantzDale 14:47, 18 January 2006 (UTC)
Metal is routinely bent without breaking it. That is part of the usefulness of metals. It is repeated or excessive bending that causes problems. —Preceding unsigned comment added by 82.36.90.96 (talk • contribs)
Additionally one can change the stress state that the material undergoes. For example rolling and extrusion are both used to form metal through the modification of the stress state.—Preceding unsigned comment added by 129.22.154.194 (talk • contribs)

[edit] Stress frequency influence in fatigue

The "S-N" curve for a material represents its life, in terms of cycles, for a determined applied stress. My question is: How does the fatigue life vary to the applied load frequency? Is this life unchanged for different frequencies? Pedro.makiyama 12:33, 30 January 2007 (UTC)

Frequency appears not to have much effect on fatigue life, unless time is also important through environmental effects or static fracture processes are also involved.—Preceding unsigned comment added by 82.36.90.96 (talk • contribs)

Frequency dependence depends on the material and environment. In many metals, frequency may become important at high temperatures and/or when combined with corrosive environments. The theory is that lower frequency (such as when you apply the load and hold it awhile before releasing it) allows more time for detrimental chemical reactions to attack the material. For those scenarios, the fatigue life for a given stress generally decreases at lower frequencies. Jagad5 22:13, 27 April 2007 (UTC)

[edit] Phenomenology

Shouldn't this article contain some reference to the phenomenology of fatigue, like Persistant Slip Bands (PSB), dislocation cell structures etc? There don't seem to be any references to these phenomena in any other article. Mike 09:37, 14 May 2007 (UTC)

Yes. —Ben FrantzDale 10:50, 14 May 2007 (UTC)

[edit] Ultrasonic Impact Treatment - biased promotional material?

"The most recent development in the field of surface treatments utilizes ultrasonic energy to create residual compressive stresses that surpass those achieved by shot peening, laser peening, and other legacy methods."

Sounds to me like a non-neutral advertisement that somebody is trying to slip in for their technique. If you can show a peer-reviewed citation for these highly unlikely statements, feel free to put them back in. Tarchon 21:11, 17 May 2007 (UTC)

It's just peening using ultrasonic frequencies. "Ultrasonic energy" and "surpass" is BS IMO. Sigmund 21:22, 2 June 2007 (UTC)

[edit] Cyclic overload and LCF

i also agree that bending a paperclip is not a good example for fatigue, but rather for work hardening. on the other hand, the paragraph of LCF says, that LCF is usually measured in the plastic regime. so what is now the exact difference between LCF and cyclic overload?

schwobator, german wikipedia
Bending a paperclip is LCF. Work hardening or softening doesn't change that. Cyclic overload is a term used in fatigue whenever large plastic strain amplitudes are applied in an otherwise small amplitude/elastic strain history. This would be covered when discussing variable amplitude fatigue. Sigmund 21:16, 2 June 2007 (UTC)

This answer is confusing. Best surely to say that bending a paperclip is not fatigue as known normally. Low cycle fatigue is normally associated with strain within the elastic range. I have thus reverted the edit. Peterlewis 10:26, 3 June 2007 (UTC)

Low cycle fatigue is associated with cyclic plasticity. Just look up the Coffin-Manson relation further down the page. An example of cyclic overload is: 1) bend the paperclip back and forth with a certain amplitude. 2) apply one larger amplitude. 3) continue cycling as in 1). This is often done to study the effect of hardening and residual stresses on fatigue life. Sigmund 09:25, 4 June 2007 (UTC)
No. Low cycle fatigue is brittle crack growth over a few cycles, and plasticity is irrelevant. These variables are quite distinct and separate. Peterlewis 10:10, 4 June 2007 (UTC)
Please consult any textbook on the subject before you make any assertions. Fatigue of metallic materials by Klesnil and Lukas is an excellent read. Sigmund 10:13, 4 June 2007 (UTC)
I would recommend Dowling as well.—Preceding unsigned comment added by 129.22.154.194 (talk • contribs)
Textbooks are always out of date unfortunately! I don't recall any sign of plasticity in the low cycle fatigue cracks which brought the Comets down. You should not try to confuse the issue of what is and what is not fatigue. I have published several papers on low cycle fatigue (4 to be exact) in the failure of a large storage tank, with no trace of plasticity whatsoever. Peterlewis 18:04, 4 June 2007 (UTC)
I really hope you had nothing to do with de Havilland. Here's the most recent article I could find on the topic: http://dx.doi.org/10.1016/j.ijfatigue.2007.04.014 This one may also be of interest: http://dx.doi.org/10.1016/j.ijfatigue.2006.09.004 Note that subscript p denotes plastic. If you've found something wrong or outdated in the book of Klesnil and Lukas, I'd be very interested. So would the fatigue community, so please, go ahead and publish that as well.

[edit] Simple Illustration of da/dN vs dK plot needed

It would be helpful to include a simple plot of da/dN vs dK when making reference of the Paris slope.—Preceding unsigned comment added by 129.22.154.194 (talk • contribs)

[edit] Separation and clarification of stress and strain controlled fatigue crack growth

Equations for both stress and strain controlled fatigue crack growth are presented but no discussion of their differences is included.—Preceding unsigned comment added by 129.22.154.194 (talk • contribs)

[edit] Paris Slope Clarification

Under the Paris Slope paragraph of the article it states, "and m is typically in the range 3 to 5.". This is correct for metals, but not other materials such as ceramics which have a much higher Paris slope(m). Additionally the value needs to be cited. —Preceding unsigned comment added by 129.22.154.194 (talk • contribs)

[edit] Mechanical failure mode?

why is sex listed as a mechanical failure mode? —Preceding unsigned comment added by 24.2.56.141 (talk) 19:14, 29 September 2007 (UTC)

  • It was vandalism to the Mechanical failure modes template. -Fnlayson 19:21, 29 September 2007 (UTC)

[edit] Fair use rationale for Image:Ewing and Humfrey fatigue cracks.JPG

Image:Ewing and Humfrey fatigue cracks.JPG is being used on this article. I notice the image page specifies that the image is being used under fair use but there is no explanation or rationale as to why its use in this Wikipedia article constitutes fair use. In addition to the boilerplate fair use template, you must also write out on the image description page a specific explanation or rationale for why using this image in each article is consistent with fair use.

Please go to the image description page and edit it to include a fair use rationale. Using one of the templates at Wikipedia:Fair use rationale guideline is an easy way to ensure that your image is in compliance with Wikipedia policy, but remember that you must complete the template. Do not simply insert a blank template on an image page.

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BetacommandBot (talk) 14:00, 25 February 2008 (UTC)

[edit] Intrinsic and Extrinsic Toughening mechanisms

A section on the intrinsic and extrinsic fatigue toughening mechanisms might be helpful as well. R.O. RITCHIE's paper Mechanisms of fatigue-crack propagation in ductile and brittle solids does a nice job of covering the various fatigue toughening mechanisms and could be used as a guide for inclusion in the article. —Preceding unsigned comment added by 129.22.154.234 (talk) 19:12, 15 April 2008 (UTC)

[edit] Fatigue limit vs endurance limit

I've copied this here from the Fatigue limit discussion page in case that's a backwater that no one watches.

The article currently defines fatigue limit as the constant amplitude (or range) of cyclic stress that can be applied to a material without causing fatigue failure, and endurance limit as the stress amplitude for a chosen number of cycles (usually 107) for structural metals such as aluminium, that do not have a distinct fatigue limit and will eventually fail even from small stress amplitudes.

However:

  • Beer and Johnston, in Mechanics of Materials (ISBN: 0-07-837340-9), state "The endurance limit is the stress for which failure does not occur, even for an indefinitely large number of loading cycles." "For nonferrous metals, such as aluminum and copper...one defines the fatigue limit as the stress corresponding to failure after a specified number of loading cycles, such as 500 million." This sounds like the exact opposite of Roger Tyler MSc's comments above and the current article.
  • R.C. Hibbeler, in Mechanics of Materials (ISBN: 0-13-008181-7), states "this limiting stress is called the endurance or fatigue limit." Although he points out the difference between the "well definined" limit for steel and the "not well defined" limit for aluminum, he makes no further distinction between the two expressions.
  • N.E.Dowling, in Mechanical Behavior of Materials (ISBN: 0-13-905720-X), states "such lower limiting stress amplitudes are called fatigue limits or endurance limits.
  • Bannantine, Comer, and Handrock, in Fundamentals of Metal Fatigue Analysis (ISBN: 0-13-340191-X), state "certain materials, primarily body-centered cubic (BCC) steels, have an endurance or fatigue limit, Se, which is a stress level below which the material has an "infinite" life." "Most nonferrous alloys have no endurance limit..." "A pseudo-endurance limit or fatigue strength for these materials is taken as the stress value corresponding to a life of 5 x 108 cycles."
  • The currectly cited reference says "The Fatigue limit is the maximum completely reversed stress for which it is assumed that the material will never fail regardless of the number of cycles." It uses but does not define endurance limit. It does, however use the expression "endurance/fatigue limit" twice, suggesting that they may be interchangable.

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) 14:08, 18 April 2008 (UTC)

They are basically the same thing. For ferrous metals they are. For non-ferrous metals and materials without a infinite life strength (or a very low one), a stress level at a set number of cycles is often used and called fatigue limit. The fatigue limit article seems to have it backwards. -Fnlayson (talk) 14:47, 18 April 2008 (UTC)
Cool. Is there an absolute authority that I should cite, or are Beer and Johnston good enough? -AndrewDressel (talk) 15:08, 18 April 2008 (UTC)
  • That should be fine. Some of my books say endurance limit is the stress for an infinite life and say fatigue limit is synonymous or state it is the fatigue strength for ~108 cycles. In any event the defination for endurance limit seems clear. -Fnlayson (talk) 15:31, 18 April 2008 (UTC)


[edit] Are 'tired' clock mainsprings caused by fatigue?

Was wondering if the well known phenomonon of clock and watch mainsprings losing some of their torque and becoming 'tired' or 'set' after decades of use is caused by metal fatigue? Talk:Creep (deformation) says it's not creep. I'm editing Mainspring and can't find any information on this failure mode. Thanks --ChetvornoTALK 21:33, 15 May 2008 (UTC)

  • More related to fatigue. The spring is yielding under repeated loading. Has to be a low cycle fatigue problem. The yield strength can change under cyclic loading. In any event it is deformating under the repeated loads. -Fnlayson (talk) 21:59, 15 May 2008 (UTC)

[edit] Basquin's Law

A good job. Nice explanation.

I miss some elaboration on the Basquin's Law and especially its relation to material properties. Basquin’s law of fatigue states that the lifetime of the system has a power-law dependence on the external load amplitude :

N * sk = C

where: N is fatigue life, s is remote stress (maximum stress?), k is metarial dependent factor.

Camille T (talk) 17:26, 22 May 2008 (UTC)