Talk:Young's modulus

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[edit] Symbol

Do people find Y the symbol used for the modulus in literature? Its used here as well as E (in the table).

This should be standardized. All texts I've refered to use E. --Eat411 08:58, 23 March 2006 (UTC)
Indeed, I have always seen E used to represent Young's Modulus. I am changing the article now. It can be reverted if there is good reason to use Y. Going through a few books here really quick, the following use E for the modulus of elasticity:
  • Mechanics of Materials be Beer et. al.
  • Theory of Elasticity by Timoshenko and Godbeer
  • Advanced Mechanics of Materials by Boresi and Schmidt
  • The AISC Steel Construction Manual
  • The ACI committee 318 Building Code
I could name quite a few more if necessary. I've never seen Y. --Notthe9 15:30, 10 November 2006 (UTC)
Y is used quite regularly in journal articles (e.g. Physical Review Letters 95 195501), it should at least be mentioned in the article, though Ashby, "Engineering Materials 1" uses E 129.78.64.106 08:14, 23 November 2006 (UTC)

[edit] Table section should be checked thoroughly

I think the table is inaccurate to say the least. For some of the materials the unit is GPa and some it is MPa according to my textbook. On some materials it isn't even the correct table column the data is from. Let's take aluminum as the example. According to this wikipedia article, young's modulus is 69 GPa, but this is a wrong lookup. My textbook says that its space-expanding-coefficient is 69 * 10^(-6) K^(-1), and the correct value in Pa is in another column(!). The correct value being 13 * 10^(-12) Pa^(-1) (That's 13 MPa). My point is that the table should be removed until it has been thoroughly checked and corrected, and the data should come from a place where we can be sure that there are no legal issues. Last but not least, this discussion is very messy and should be organized a bit. I have a report due in 4 hours, so i might come back and fix it later.—The preceding unsigned comment was added by 80.62.69.154 (talk • contribs) 02:19, 3 May 2006.

Um... what's a space-expanding-coefficient, and what's it got to do with this article? The Young's modulus of Aluminium is generally agreed to be about 69-70 GPa (see, for example, Aluminium or this course slide from a Cornell university course, or numerous other places) Note also the title "approximate values" and the comment "the value for [...] metals can vary by 5% or more[...]" preceding the table). If you can spot any specific errors (and come up with a decent source for a better value) then, by all means, raise it here. However, most of these values are easily checked in engineering or materials science textbooks; all the metals listed look about right to me, from my recollection of my studies; the other materials don't appear outrageous, either. Finally, the young's modulus of any given material is a physical property, which as far as I know, can't be copyrighted. If this table was copied wholesale from another source, then there would be copyright issues. That did happen at some point in the history of this article, but it's been extensively edited and expanded since then, so I'm pretty sure it's no longer a problemBlufive 19:16, 3 May 2006 (UTC)

The table appears to be a direct copy from

http://phyastweb.la.asu.edu/classes/phs581-culbertson/students/youngsmodulus/Youngs_Modulus.html

Does HFastedge have permission to use this material?

I found the same table at http://www.answers.com/topic/young-s-modulus. However, the heading for E on that table states the units as GPa, rather than MPa - anyone know which is correct? (the la.asu.edu url 404ed on me, so I can't compare) Bewildebeast 23:08, 4 December 2005 (UTC)
Well you would find the same table in answers.com, since they have become mostly a wikipedia clone site, but I don't think anyone can copyright actual facts. Like, if I found a site that gave the melting points of certain materials (at a certain pressure), I could use it here because facts are facts.--User:Rayc 18:16, 20 December 2005 (UTC)

There seems to be an inconsistency in the dimensions in this article (or I don't understand it): Young's modulus (or modulus of elasticity) has units Pa (N/m2), it says in the table. But in the equation below, energy (N m) is equal to modulus of elasticity times length. So modulus of elasticity has units N.

Modulus times length. (N/M^2) times M = N/M modulus times length = energy. no inconsistency just be careful when you parse the english to get which is supposed to be multiplied by what to equal what.

Furthermore, Young's modulus is the slope of the stress-straincurve, hence has units of [stress]/[strain]. But in the article Stress, I read that the unit of stress is Pa. So strain is dimensionless? Mtcv 14:39, 28 Jun 2004 (UTC)

In Wikibooks Solid Mechanics they say that in fact strain is dimensionless. That leaves open my first question. Maybe x (bottom of page) is dimensionless? Mtcv 14:48, 28 Jun 2004 (UTC)

Strain is dimensionless, it is easiest to understand engineering strain which is roughly current length / initial length in the case of 1-D tensile loading (for small displacements). So yes Young's Modulus has the same units as stress. It's a weird way of looking at it, I agree, but it is self consistent. As strain has to be the same when the material is feeling the same deformation. If the bar is 1 inch long or 15 feet long they should ideally have the same values of strain when they are equivalently deformed, which should be a much larger length for the 15 foot bar vs the 1 inch bar.

There are problems with article: e.g. locusts are not viviparous, so the first entry is invalid. This appears to be a "cartographer's error" to keep track of where this information is copied. (And it appears to be extensively copied.)

The lambda variable (λ) is in units of force - it is the product of the modulus of elasticity (force/length2) and the cross sectional area (length2) of the object. (The area of a slice taken perpendicular to the direction of "l".) That is the reason for the discrepancies noted above. Yes, strain is expressed in terms of length/length.

Oh boy, where to start. I've just done one small change, but I want to do more in the near future. Just so I don't surprise anyone too much, here's what I want to go at:

  • Add notes about directional materials (wood, fibre-reinforced plastic composites)
  • Add notes about variety of values for metals; (most metals come in a variety of alloys (especially steel, which is a term defining a whole group of alloys) and individual alloys can vary by at least as much as 5% from a nominal "pure" metal)
  • Overhaul the table:
    • Remove the column giving values in GPa; it's pretty much redundant - values will just be the MPa values divided by 1000.
    • Amend values for metals to 3 significant figures; Quoting values for metals to five/six significant figures is pointless (see alloys above)
    • What materials should be included? I reckon we should have:
      • Common engineering materials
      • A few "ordinary" things that readers will encounter in day-to-day life
      • Some extremes
    • Remove the "pregnant locust" item; I agree with the anonymous user above, it's probably a deliberate error to catch copyright violations.
    • Remove plywood unless I can get a better value; Wood is a directional material (as already noted); plywood, being an assembled composite based on wood, will have a lower (but less blatantly directional) value. I reckon the plywood value should just be removed unless we can get a much more tightly-defined (and correct) value for it.
    • Remove Beryllium; AFAIK, it's not a significant engineering material (being toxic and difficult to work, amongst other reasons)
    • Add some common composites (GFRP, CFRP, maybe even Boron fibre composites)

Plus anything else I think of  :) Blufive 13:26, 16 Jan 2005 (UTC)

http://en.wikipedia.org/wiki/Beryllium Beryllium is a very useful material, higher modulus than steel, resists corrosion, good X-ray transparancy, light weight. It's a little exotic due to processing difficulities (i.e. toxicity of related compounds) but it's a very useful material, albiet a little expensive.

Maybee add some more common plastics to this list? I noted Polystyrene on one of the tables, but maybee a material with a much lower modulus like Polyethylene or polypropylene for reference. CoolMike 20:53, 27 Feb 2005 (UTC)

Done. --203.206.18.96 12:05, 21 August 2005 (UTC)

Isn't Young's modulus basically the modulus of tensile stress? On the other hand, the modulus of elasticity is a very generalized term, referring to the relation between stress and strain in general, as part of the Hooke's Law; whereas Young's modulus is associated with tensile stress only. It seems that defining the Young's modulus as the modulus of elasticity would be inaccurate, as is mentioned in the first line of the article- ....Young's modulus (also known as the modulus of elasticity or elastic modulus)....

[edit] Error in Table

The table units should read GPa, not MPa.

[edit] Just a suggestion

To quote from the article, This can be experimentally determined from the slope of a stress-strain curve created during tensile tests conducted on a sample of the material. Perhaps we ought to mention that this data can be obtained by compressive testing, too.--Nick 18:54, 15 January 2006 (UTC)

To keep it simple, perhaps we ought also to mention that Young's modulus is the stress required to halve, or to double, the length of the specimen under test (depending on whether the test is compressive or tensile). Mind, my physics is pretty rusty, so this might be downright wrong. --Nick 19:02, 15 January 2006 (UTC)

Sorta-kinda. (Disclaimer: it's late in the day, my engineering is seriously rusty, and I've been consuming some of the west country's finest so I'm slightly addled). If memory serves, the definition of YM assumes, and hence the formulae given here are only correct for, small deformations. Basically, strain is somewhat non-linear, so when the deformation starts to get to be the same order of magnitude as the initial size of the sample, the numbers get messy (I think that's due to complications like Poisson's ratio and hence shear stress starting to kick in as the deformation starts to get more than one-dimensional). A strain of 0.05 is pretty huge, as far as something like a bridge or a wing is concerned, and few engineering materials can withstand that much deformation without plastically deforming anyway. However, if a material were to stay elastic, and maintain a constant YM, the YM does correspond to the force required to double the length of a sample under tension. Not so sure about compression, though (if nothing else, double length = strain 1, half length = strain -0.5; at which point the formulae given on this page don't work any more) Given all those caveats, it may be better to leave it out, to avoid confusing people, or at least putting it down the bottom in some sort of "vaguely interesting but complicated stuff" section, well away from the main definitons. Blufive 21:25, 5 February 2006 (UTC)

Oh, and one last thing, I'm not sure that Young's modulus is a measure of stiffness. Elasticity, surely?--Nick 19:10, 15 January 2006 (UTC)

Well, formally, it's the "modulus of elasticity". In plain English, it's a measure of how stiff things are. The higher the number, the stiffer something is. So, technically, you're correct - but the meaning of "stiffness" is clearer to the lay reader, IMO. Blufive 21:25, 5 February 2006 (UTC)

A grammatical point: i was lead to believe that the correct term is specifically "The Young Modulus":- not "Young's Modulus". However, i suppose that when in general reference "Young's Modulus" may be correct but when refering to a specific material the correct reference would be "The Young Modulus of (eg) Iron" I can't seem to find anything supporting me on this but wondered if anyone had any furthur knowledge of this. [The previous comment added by Silvarbullet1 Blufive 21:25, 5 February 2006 (UTC)]

When I studied engineering, everyone, and I mean everyone, teaching the course referred to it as "Young's modulus". Regardless of how correct that is grammatically, that's what everyone calls it. Personally, I think that's grammtically good, too. Blufive 21:25, 5 February 2006 (UTC)

[edit] GPa

The units should be GPa, not MPa. I have compared the value for steel to a text book and the german wikipedia, which both state that steel has a young modulus of E = 210 000 N/mm2 (= 210 GPa). —The preceding unsigned comment was added by 146.140.3.210 (talk • contribs).

Was changed by a recent edit, either clueless or vandalism. Reverted. Femto 11:14, 3 March 2006 (UTC)

[edit] F/A0 + 0?

why is there a + 0? should there be a note explaining this? Bungalowbill 15:17, 16 May 2006 (UTC)

[edit] "The Young Modulus"

As I mentioned above, every reference I've ever encountered to this property (which is a quite few, given that I studied engineering at university) including the dead-tree edition of Britannica downstairs, is as "Young's Modulus". Since there have now been a couple of editors suggesting "The Young Modulus", I've amended the "also known as" to include that form, but that's as far as I'm willing to go unless someone can come up with several substantive cites for "The Young Modulus" (fx: kicks self for fact that all my relevant textbooks are inaccessible right now) Blufive 18:54, 16 May 2006 (UTC)

[edit] Water?

Can anyone come up with a cite for the figure for water that just got added? I assume the value is under compression, while confined, as any other situation seems seems kinda bizarre with respect to a liquid. Unless the value is for solid water (which is to say, ice). The value given, however, does seem to match the value included for water under bulk modulus - in which case it can't be the correct value for the Young's Modulus, surely? (see elastic modulus for the relationships between values) Blufive 19:15, 26 May 2006 (UTC)

OK, I've removed water from the table. Per the bulk modulus article, Bulk modulus is the only elastic modulus which is meaningful for non-solids. The value quoted appeared to be the bulk modulus, in any case. Blufive 18:46, 27 May 2006 (UTC)


[edit] Conseqence of Pauli principle

"Young's modulus (as well as a bulk modulus of liquids and solids) is a mathematical consequence of the Pauli exclusion principle for fermions (electrons in the outer shell of an atom)."

Isn't it formally true only for compression and not for stretching? When atoms get closer, the electon wave function indeed has increased repulsion due to Pauli repulsion but when they get farther away, the overlap is lowered. When the chemical bond is stretched, it is the lower potential energy due to weaker interaction of the electrons with the nuclei that create this force and not Pauli repulsion. Poszwa 03:52, 9 June 2006 (UTC)

[edit] Table:Virus

Why is there a virus in the table? Maybe I don't understand...please enlighten me.Civil Engineer III 13:13, 22 June 2006 (UTC)

Virus shells are squishy too? This needs some cite and an explanation of its relevance, or it should be removed. Femto 16:45, 22 June 2006 (UTC)

[edit] No citation banner

I put up the no citation banner. I will try to remember to do some work on that myself. Notthe9 16:13, 10 November 2006 (UTC)

[edit] Derivation of Hooke's law

The section "Force exerted by stretched or compressed material" derives Hooke's law from Young's modulus. This derivation assumes that the change in length (From Young's modulus) is equal to the extension of a spring (From Hooke's law). But the change in length when measuring Young's modulus is usually measured in millimeters, whereas the extension of a small spring can easily be measured in tens of centimeters. What I'm asking is: Are the two terms equal, and is the derivation valid? I plugged in a few numbers (Although I had to guess on the radius of the spring, and the length of the wire in the spring), and the spring constant I got back was a few thousand times larger than the spring constant from a simple F=kx equation. I could have done the calculations wrong, but it's still a large error. There doesn't seem to be any references for the derivation, and I couldn't find any with some googling. (Oops - forgot to sign. - 81.152.176.6 22:33, 15 November 2006 (UTC))

Right, the value of k derived in this case is the spring constant of the wire, not a spring. So you can expect the constant to be much larger for a wire than a spring.--81.152.176.6 15:41, 16 November 2006 (UTC)

[edit] Young's modulus and Hooke's Law

The relationship between E and Hooke's k is not clearly spelled out in the article, i think this needs addressing by someone with a bit of expertise in this area. Furthurmore it is not made clear that E is only a (very useful) linear approximation to what is essentially a non-linear property, instead the article state "for small strains", which is not *strictly* true, it is actually valid for strains small enough to give a linear stress-strain response, which to some degree is up to the engineer.

As a second point heat treatment and composition are the only things listed in the small disclaimer at the start of the table, really there are many other properties of the microstructure (natural ageing) etc that can affect this, I would suggest that a better sentence state "Dependant on the exact nature of the microstructure of the material, which can be affected by processes such as heat treatment and minor compositional differences in the material" 129.78.64.106 08:37, 23 November 2006 (UTC)

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