Talk:Thermal expansion

message: I just updated the page with the strain definition, but if you look at the formula it has an empty \frac tag.  If you remove that the equation gets small.  Anyone know how to fix that? - EndingPop 03:00, 12 April 2006 (UTC)
thread_title: Strain definition

message: ----
if:
\frac{}{} \epsilon_{thermal} = \alpha \Delta Tis true, and:
\frac{}{}\alpha  is the coefficient of thermal expansion in inverse kelvins is true, thus:
\epsilon_{thermal} \propto \frac{1}{\Delta T}
must be true, then \epsilon_{thermal} must be inversely related to \Delta T.
Da2ce7 15:55, 30 September 2006 (UTC)
replies: text: Sorry, but you're wrong.  The proportionality is independent of the units on the coefficients.  Think of it this way, if the temperature doubles, the thermal strain doubles.  Therefore: \epsilon_{thermal} \propto \Delta T - EndingPop 17:47, 2 October 2006 (UTC)
thread_title: Inverse relationships

message: "Polymers expand as much as 10 times more than metals, which expand more than ceramics."
its no where near that much, plastics 60-90, metals 10-30, so 4 times is nearer, comparing a rare high expansion plastic to a rare low expansion metal is misleading.  —Preceding unsigned comment added by Asplace (talk • contribs) 13:59, 5 September 2007 (UTC)
thread_title: Expansion of materials

message: Hi Asplace,
Well done on the rewrite.  It motivated me to go through the article editing for style and content.  You will notice that I changed some of your text in the process.  Feel free to change some back if you disagree; we can discuss as needed. --Slashme 08:25, 28 September 2007 (UTC)
thread_title:  Rewrite 

message: The format of this page was pretty messed up and looking at the history there were a couple cases of vandalism a while back which were unnoticed at the time.  I have restored content which was deleted and added some subst:unsignedIP templates in various places as well.  I also added a few headings which were not original just to make it readable. Hopefully this all makes the page more usable.
Dhollm (talk) 20:54, 22 August 2010 (UTC)
thread_title:  Restoration of vandalized talk page content 

message: This section has a table with a sorting function which doesn't work exactly right and I don't have any idea how to fix it. If you sort by linear expansion you'll see gasoline with 317 get sorted into the set of materials with COE of about 3 rather than with other high-COE materials. And what is odder is that it won't do that the first time. Or at least it didn't for me. The first sorting looks OK, with gasoline down with ethanol. To see what I mean, I'd invite the usual editors of this page to play with the sorting functions, then refresh the page and try it again. I'm using Mozilla Firefox, if that has any bearing on it. ???? Trilobitealive (talk) 04:35, 12 January 2011 (UTC)
replies: text: If it makes you feel better, I have the same problem. The first time I hit the sort its fine, after that it's all mixed up. You might want to post the question over at Help talk:Table, although I'm not 100% sure this is the best place to ask. Wizard191 (talk) 14:26, 12 January 2011 (UTC)
thread_title:  Thermal expansion coefficients for various materials 

message: Due to the merger of two articles, this article was left with a mixture of notations for the thermal expansion coefficients. One article used \alpha \beta for the linear and volume coefficients of thermal expansion, respectively. The other article used \alpha_{L}, \alpha_{A}, and _{V} for the linear, area and volume coefficients of thermal expansion, respectively.  The current article uses a mixture of both.  We should pick just one convention, although we could mention the other.  Cardamon (talk) 22:54, 20 January 2011 (UTC)
thread_title:  A mixture of notations 

message: Does the formula for length expansion assume the material is not under any stress or does it merely assume that the material is "free" to expand?  (This question is relevant to how elementary physics is taught.  For example, in the thermodynamics section of an elementary physics video ("The Ultimate Physics2 Tutor") there is the example of finding the work done by a column that has a weight on top of it when the column is heated. It is solved using the linear expansion formula without any discussion of stresses or strains due to the weight on top or the weight of the column itself.)  
Tashiro (talk) 16:08, 15 March 2011 (UTC)
replies: text: A material has to be free to expand in order for the dimensions of the material to change. If the material is not free, internal compressive stresses will result. Think of it like a gas inside of a bottle that wants to expand as it is heated. Because the bottle has put a dimensional constraint on the gas, the gas cannot expand. Instead of expanding, the gas pressure inside the bottle will increase. Solids are very similar in that the material will want to expand when heated and will apply a force to anything trying to prevent that expansion. Hence, the weight on top of the column rises when the column is heated. NedWit (talk) 23:30, 24 June 2013 (UTC)
replies: text: If the material is constrained so it cannot expand, then you can calculate the stress by using the thermal expansion equations and imposing compatibility with the boundary conditions that constrain it. - EndingPop (talk) 13:54, 1 July 2013 (UTC)
replies: text:  Typical data are for a material free of any stress except normal atmospheric pressure (or possibly other value if noted). If a material is under stress is modified a little as the elastic constants usually depend on temperature and so there is an additional change of the elastic strain superimposed to thermal expansion.--Ulrich67 (talk) 21:13, 28 October 2014 (UTC)
thread_title:  Does the formula for length expansion assume the material is not under any stress? 

message: ...differ from those on engineeringtoolbox.com See ethanol and gasoline for eg. 89.176.34.187 (talk) 14:26, 21 November 2011 (UTC)
replies: text: The german wikipedia gives for Ethanol: γ(20 °C) = 1.4 × 10-3 K-1; the source is the CRC Handbook of Chemistry and Physics. Regards, Herbmuell (talk) 13:01, 2 January 2016 (UTC)
thread_title:  Thermal coefficients 

message: The usual formula with ΔT is obviously inconsistent (of course, it is approximate, but why should it be inconsistent?). So, when length of a rod is described as a function of temperature, is this function better approximated as linear or as exponential function?--Ilevanat (talk) 01:06, 21 December 2011 (UTC)
replies: text: The shape of the thermal expansion vs. temperature curve strongly depends on the material and temperature range. There is no general function, but linear approximation works best, at least in a narrow T range. Any strong function like exponent, while giving a better agreement in some very specific cases, will lead to a much stronger disagreement in most other cases. Materialscientist (talk) 01:37, 21 December 2011 (UTC)

text: Sorry, for a quick comment - got to run. Experimentalists measure length of a rod vs. temperature that gives L(T) function, which is unique for every material and can't be approximated by any general analytical function. To simplify life of engineers, they use the universal approximation that any smooth physical function can be expanded into series by a small parameter, which is temperature change in this case. This gives aΔT, with a note of the temperature range where coefficient a is valid. I see no reason to choose exponent, or 0 °C (why not 20 °C then? Note that many materials are aimed for use above or below room temperature). Materialscientist (talk) 00:58, 23 December 2011 (UTC)

text: Sorry, I don't understand. Absolute length is not a material property; thermal coefficient is a material property and gives a relative expansion ΔL/L0. Temperature range for the coefficient a is merely the range where its value is valid. There is no use providing anything else. A properly educated engineer, if needed to calculate expansion of his rod from T1 to T2, measures L0 at T1 (i.e. L(T1)) and calculates expansion as a×(T2 - T1)/L0(T1). Materialscientist (talk) 02:52, 25 December 2011 (UTC)

text: \alpha_L=\frac{1}{L}\,\frac{dL}{dT}
has the exponential function for the solution. For small temperature intervals we can use only the first two terms in Taylor series
f(a)+\frac {f'(a)}{1!} (x-a)+ \frac{f(a)}{2!} (x-a)^2+\frac{f^{(3)}(a)}{3!}(x-a)^3+ \cdots. 
where both the function value f(a) (the "initial length") and its first derivative (the expansion coefficient) are taken at the same "initial temperature". But such details can be dismissed with the claim of small coefficients and simple approximation.--Ilevanat (talk) 02:05, 26 December 2011 (UTC)
thread_title:  Does anybody know whether thermal expansion is closer to linear or exponential? 

message: Vandalism on this page on 11/2/12. Don't know how to fix it.   — Preceding unsigned comment added by 128.111.179.98 (talk) 02:54, 3 November 2012 (UTC)
replies: text: I'm not sure what you see. I saw "boobies" in the lead, which was a remainder of the last revert. I added ?action=purge to the url string and hit <enter> to purge the page and the boobies disappeared. Materialscientist (talk) 03:02, 3 November 2012 (UTC)
thread_title: Vandalism

message: Typically in literature (actually I have never seen β for volumetric expansion before):
Solid
::xΔT = x · (1 + α (ΔT) + β (ΔT)2 + …)
α: 1st greek letter, 1st term in the Taylor series
β: 2nd greek letter, 2nd term in the Taylor series
Liquid/Gas
::VΔT = V · (1 + γ (ΔT) + …)
γ: 3rd greek letter, γ ≈ 3 α  — Preceding unsigned comment added by 87.171.50.251 (talk) 13:19, 14 July 2013 (UTC)
thread_title: Alpha, Beta, Gamma

message: Added lede to heat transfer, here. Prokaryotes (talk) 18:52, 5 April 2014 (UTC)
thread_title:  Heat transfer 

message: The citated value for the volumetric expansion coefficients of Titanium (linear=8.6; volumentric=11–14)
is wrong. It should be about twice the mentioned value, what is a big difference.
This value also is not found in the cited reference [24].
Please correct
———————————————————————————————————————————————————————————————————————————————  — Preceding unsigned comment added by 134.102.240.41 (talk) 12:34, 23 December 2014 (UTC)
replies: text: Thanks for pointing this out. I can't find an explicit citation for the volumetric coefficient, but Titanium has an hcp structure, so I'll just multiply the linear coefficient by 3. RockMagnetist(talk) 16:51, 21 January 2015 (UTC)
thread_title:  Mistake detected 

message: The value for quartz is probably way off. The Crystan Handbook lists it as 7.1/13.2, depending on which direction in the crystal.
131.215.211.195 (talk) 23:38, 13 October 2015 (UTC)
thread_title:  Quartz? 

message: Somebody please add discussion of distinction between secant and instantaneous coefficient of thermal expansion.
108.171.131.170 (talk) 18:14, 13 July 2016 (UTC)
replies: text: Hi Chuck. Thanks for the comment. I agree with you, but am not well-enough versed in math to do it myself. As I recall (and somebody please correct me if I'm wrong), a secant (average) coefficient is one that is tied to a fixed reference point, whereas a tangent (instantaneous) coefficient is one that is tied to the temperatures immediately surrounding the temperature of interest. Beyond that, I can't offer much insight myself, but perhaps someone will come along who can. Zaereth (talk) 00:23, 14 July 2016 (UTC)
thread_title:  Secant Coeff. 

message: Linear expansion coefficient for aluminium nitride is bigger than volumetric one. It seems erroneous. --194.190.225.135 
:I agree. According to this source, both 4.2 and 5.3 are for linear (along two different axes). This source lists the volumetric expansion as 10.1. Zaereth (talk) 18:16, 9 January 2017 (UTC)
thread_title:  Something wrong with Aluminium nitride 

message: The section "Examples and applications" does not contain a single worked example of a common material or situation, which an average person can understand. Eg. "A steel rail expands by X cm over 100 metres for each 10C rise in temperature, because {maths}=X" would be invaluable to most people reading this.
Bards (talk) 22:30, 23 November 2017 (UTC)
thread_title:  Not accessible enough 

message: An editor has asked for a discussion to address the redirect Per kelvin. Please participate in the redirect discussion if you wish to do so.  Utopes (talk / cont) 23:45, 28 March 2020 (UTC)
thread_title:  "Per kelvin" listed at [[Wikipedia:Redirects for discussion|Redirects for discussion]] 

message: Which metal rod expands when heated? 41.115.12.42 (talk) 14:22, 30 January 2022 (UTC)
thread_title:  Physical sciences 

message: Can any one help it? Sanjunepali2007 (talk) 12:01, 12 September 2023 (UTC)
replies: text: It's unclear what you are referring to. In general liquids expand uniformly in all directions, unless they are constrained by the geometry of their container to expand in one or two dimensions. Qflib, aka KeeYou Flib (talk) 17:28, 13 September 2023 (UTC)
thread_title:  Does anybody know why liquid have two coefficient of cubical expansion ? 

message: Describe it if you know? Sanjunepali2007 (talk) 12:03, 12 September 2023 (UTC)
replies: text: The page already has a description of this apparatus. Qflib, aka KeeYou Flib (talk) 17:28, 13 September 2023 (UTC)
replies: text: Thank's for help 2405:ACC0:1100:44A0:B5BB:D634:DCD4:3B14 (talk) 03:01, 14 September 2023 (UTC)
thread_title:  Pullinger Apparatus