Talk:Deformation (mechanics)

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Reason for this article[edit]

Four articles were merged: Finite strain theory, Strain (materials science), Strain tensor, and Deformation (engineering). Why? All this topics refer to one central concept, which is Deformation. In this article, all concepts related to deformation are included, from displacement, strain, Finite strain and infinitesimal strain.

The article is not complete yet. Some parts of Infinitesimal strain are still missing. The same with some figures.

I do not think the article is too big, it is only around 60 KB. - Sanpaz (talk) 01:17, 6 September 2008 (UTC)

Also merged the articles Stretch ratio, Shear strain, and Normal strain. Sanpaz (talk) 20:54, 6 September 2008 (UTC)

Deformation (engineering) article[edit]

Why did I merge and disregard the content on the Deformation (engineering) article? The content of that article does not deal with the concept of deformation per se. It talks about the different relationships between strain and stress (constitutive models). That is more related to an article that deals with Strength of Materials. Additionally, the section on Fatigue does not make sense in deformation. Fatigue is a cause of failure, it is not a "type" of deformation. Then again, this concept is more related to Strength of Materials. Sanpaz (talk) 01:28, 6 September 2008 (UTC)

I have reversed this redirect (and a couple of others that you did without apparently attempting to merge the replaced content). The correct way to express disagreement with the title of an article such as Deformation (engineering) is to propose a change of name at the article's talk page. Simply replacing an article's content with a redirect to your new article is very impolite to the editors who have contributed to the other article's contents. Wikipedia works best when editors seek consensus, rather than making sweeping unilateral changes. Gandalf61 (talk) 15:00, 8 September 2008 (UTC)
I get your point. I will place the merging tags. Sanpaz (talk) 15:07, 8 September 2008 (UTC)

This is by far the worst of the pages pertaining to Continuum Mechanics. This page should follow the same material as an Elasticity Book. Also, the name should be changed from Deformation to Strain.Evolvercode (talk) 04:19, 2 December 2009 (UTC)

To clarify to Evolvercode, deformation is the physical phenomenon, strain is just a way to quantify deformation. This is explained in the article. So, no, this article should not be called strain. Additionally, when you say that this page should follow the material from an Elasticity book you are referring to infinitesimal deformation which is already being covered in that article. For large deformations, not characteristic of elastic materials, there is an article called Finite strain theory. Both, the infinitesimal and finite deformation articles are linked from the Deformation (mechanics) article. sanpaz (talk) 06:05, 2 December 2009 (UTC)
Evolvercode, if you want to contribute to this article and other Continuum Mechanics articles, please follow the references provided in this article on Continuum Mechanics, or other books related to the topic. Once you read books in Continuum Mechanics, you will understand the reason for this having deformation (mechanics) article, and the distinction between infinitesimal and finite deformation. Perhaps, you already know this and I misunderstood your point. It would be better to have just one single article that contains both types of deformation, but that has proven very hard to do as the article becomes huge. sanpaz (talk) 06:10, 2 December 2009 (UTC)
And yes, the article is not good yet. It needs a lot of work. sanpaz (talk) 06:12, 2 December 2009 (UTC)

This article is the target of a redirection of Engineering term "Elongation". Although the physics and mechanics are the same, the Engineering Term "Elongation" is neither defined nor described here. This is misleading. These need to be split. Everything is correct, but by attempting to include so much, the article misses out on fundamental aspects and distracts from understanding. Elongation, which despite the redirect is not at all mentioned, is defined as a strain (change in length per unit length as indicated in the article) at breaking. That concept is a seperate concept which should be in a seperate article. Most engineers do not care about all the material science detail. Strain should be it's own article as well. These are more than just physical concepts applied arbitrarily, but accepted parts of engineering methods and language with standards and standardized testing methods behind them. Defining the physics as is done here, does the engineer (and there are a lot of us) no good at all. Wiredrabbit (talk) 22:58, 15 December 2010 (UTC)

Merging articles[edit]

Previously I unilaterally merged the following articles: Finite strain theory, Deformation (engineering), Normal strain, Shear strain, Strain (materials science), Strain tensor, and Stretch ratio. As it was pointed out, this was not polite towards other editors, and I agreed with that. Therefore, I am proposing to discuss the merging of these articles to this article (Deformation (mechanics). The reasons are:

I apologies for the bold edit. I think it is necessary to do this merge though, but if a better approach to improve the presentation of this concepts within the context of deformation is proposed then it is more than welcome. - Sanpaz (talk) 15:39, 8 September 2008 (UTC)

Another article for merging: Displacement field (mechanics). This topic is addressed in the section Deformation (mechanics)#Displacement - Sanpaz (talk) 15:16, 9 September 2008 (UTC)
  • Oppose merge. Articles have very different styles and are aimed at different audiences. Deformation (mechanics) is a narrow, overly long (59 kB) and highly technical exposition that focuses almost exclusively on infinitesimal strain theory within the elastic behaviour region. Deformation (engineering) is a shorter, more general article, suitable for the general reader, that also discusses plastic deformation and failure modes. The brevity and clarity of Deformation (engineering) will be lost if it is merged into the Deformation (mechanics) mega-article. Gandalf61 (talk) 09:08, 10 September 2008 (UTC)
It is a long article (too long, I will split it), I'll give you that. What I think about the article Deformation (engineering) is that the title does not reflect the content. Perhaps that is a a better suggestion than merging with Deformation (mechanics). The reason for that statement is that the engineering article does not address deformation. What it does address is a description of the different stages of an element before failure. This is more related to an article with a title such as strength of materials, or stress-strain curve, but not deformation. An article about deformation has to address: What is deformation?, How it is described and analysed?, How it is measured?, etc. An that is what Deformation (mechanics) does. - Sanpaz (talk) 16:08, 10 September 2008 (UTC)
  • Oppose merging Deformation (engineering) with Deformation (mechanics) - The Deformation (engineering) gives us the macro view, Deformation (mechanics) the micro. The approaches and content differ enough that it's more useful to have both articles.
  • Support merging Shear strain with Normal strain, and maybe those ultimately into Strain.
  • Support merging Displacement field (mechanics) into Displacement (vector).

I do agree with Sanpaz that some reorganization would be useful. Tom Harrison Talk 00:41, 16 October 2008 (UTC)

I am a latecomer here, but:
  • I would support merging several of the concepts discussed here into a single article on strain, which covers infinitesimal and finite strain.
  • I would suggest that some of the redirects are sent to relevant parts of the merged pages, for greater utility.
*I am worried that significant useful material has been lost because strain tensor has been axed, while its information has not been included in the article into which it was "merged"
  • I would strongly suggest that some consensus on good names for these articles be found first. It seems that a re-organization would be good, in a logical framework. However, the titles for articles that differ in scale, such as deformation (mechanics) and deformation (engineering), doesn't make sense to me. They're both parts of mechanics, and non-engineers use the "engineering" one. I'll try to think of a scheme, but maybe something along the lines of two articles:
    • Strain (with the tensors and finite/infinitessimal strain, as well as a non-technical introduction), this would be the mechanics one as well as Finite Strain Theory. Another option is to break this up into several main articles linked together under an overview article.
    • Something on constitutive relationships between stress and strain, and the behavior (elastic, viscoelastic, plastic, fluid, etc.) of various materials (i.e., the "engineering" one)
Awickert (talk) 19:23, 19 January 2009 (UTC)
Awickert, this article (Deformation (mechanics) has the objective, which you propose, of discussing in one article the concept of deformation (strain). And from here to link to other, more detailed, articles about Finite and Infinitesimal deformation theories.
If some of the material that was in the article strain tensor is not included please bring it back into this article or the Infinitesimal strain theory article. All material in the previous Strain tensor article is included in Infinitesimal strain theory.
Renaming the Infinitesimal strain theory, and Finite strain theory into infinitesimal strain and finite strain it is something I have to think about. My first impression is that the word "theory" is broader than just saying "strain".
Sanpaz (talk) 23:59, 19 January 2009 (UTC)
First - sorry - I saw your merges with this article and wrote on the talk page before I realized that the "strain tensor" material was moved to Infinitesimal strain theory. So therefore the strikethrough on that.
As for the "theory", I was thinking that if someone were looking for information on strain, they probably wouldn't type "theory". And it actually seems narrower to me: "strain" covers both the deformation and the continuum mechanics that describe it, whereas "theory" only describes the latter. For the moment, I'll address the former by creating redirect pages (names without the "theory") to go to the theory pages.
Awickert (talk) 00:15, 20 January 2009 (UTC)
Redirects are a good idea. But I would not mind exploring the idea of changing the names of the other two articles. Deformation is the subject so the article is called that way. Infinitesimal strain is also a subject, so it would be logical to think of its article named accordingly. But, I don know if leaving the term "Theory" allows the article to be more inclusive for more content later on. Sanpaz (talk) 00:22, 20 January 2009 (UTC)
I guess I'm not brushed up enough on my continuum mech - is there something in particular that you're worried about not being able to include in a topic article because it's related to the theory but not to the topic? I created the redirects, at least. Awickert (talk) 05:58, 21 January 2009 (UTC)
I've been thinking about the pros and cons of the word "theory" in the title. The question that one has to ask is what is the topic being addressed? The answer is "deformation". So, I think the title should reflect that, which means that it is better to have something like: "Finite strain (mechanics)" or "Finite deformation (mechanics)", and "Infinitesimal strain (mechanics)" or "Infinitesimal deformation (mechanics)". The word theory then could be included in the content. Let me know what you think sanpaz (talk) 18:47, 4 February 2009 (UTC)
Maybe I'm being a stick in the mud, but I don't think that article titles need to be qualified unless they conflict with each other. As per a google search, "finite strain" and "infinitesimal strain" have only the definitions related to mechanics in all of the hits I got. Therefore, these are the generally-accepted names for the topics, and I think the simpler, less qualified title is appropriate. In the lead section, one could define specifically what they are, in what field they lie, etc. I simply feel like having the most intuitive titles is more important than having the most categorized titles. Awickert (talk) 20:12, 4 February 2009 (UTC)
Sure, that makes sense. If you want to make the change in the title go ahead. sanpaz (talk) 20:15, 4 February 2009 (UTC)
  • Oppose merge of strain into deformation. Per Gandalf above. Different audiences/aspects. Strain calculations are often related to strength; deformation & displacement is a different issue. Finite strain theory (e.g. the calculation method) is different again. However there could be a case for merging some of the strain entries together as they seem to be a bit confusing & overlapping. And their introductions all are horribly written in jargon-laden English! Ephebi (talk) 15:35, 25 January 2009 (UTC)

The article Deformation (mechanics) is very clear in its scope: it is about the study of deformation based on Continuum mechanics, which deals with solids assumes as a continuum. This approach is the one used in Mechanical engineering, Civil engineering (Solid mechanics and Fluid mechanics) for analysis of deformations and stress. On the other hand, the article Deformation (engineering) lacks scope. It is a hybrid between Strength of materials and Deformation (mechanics) without being neither. Because of this, now this article is getting the suggestion of being merge with the article User:Logger9/Plastic_deformation_in_solids. This new suggested content is more related with Material Science than with Mechanics. And the end, what I am looking for is clarity in articles: The title has to reflect the content, and the article has to have a clear scope. sanpaz (talk) 17:46, 4 July 2009 (UTC)

I agree clear scope is key here. I've tried to change the Deformation disambiguation page and the "otheruses" redirects accordingly. Deformation (mechanics) is definitely the best, but I still favour keeping Deformation (engineering) and Plastic deformation in solids if possible. This being a hugely notable subject with broad application to designs from bridges to consumer good , its worth having an introductory article , a technical article and a scientific one. Its not perfect to have the introductory one named Deformation (engineering) but with the new redirect those looking for a serious treatment should quickly come to the mechanics page. Just suggestions, no probs with anyone reversing the minor changes I made if they dont find them helpful. FeydHuxtable (talk) 12:33, 6 July 2009 (UTC).
I added a suggestion here for folks to consider. IDave2 (talk) 03:28, 22 July 2009 (UTC)
I would like to add that the the continuum mechanics articles in general do not reflect mathematicians names for them; I noted that finite strain makes no mention of "Non-Linear Elasticity", which is what I would call it, and "Linear Elasticity" is sometimes referred to as "Linearised Elasticity" by mathematicians. This area of articles seems to have got into a knot of trying to deal with several fields and their notations and terms at once, which is inevitable, since it's an area of research for physicists, materials scientists, engineers and mathematicians! I don't have a solution, but I'd be keen to hear ideas for ways to deal with this; tables of side-by-side notational comparison sounds good to me, but messy.
On the subject of the merger, I think I would:
  • Support merging the articles, since the "engineering" article has a brief explanation for less mathematically trained readers, which would be ideal to expand and add to the "mechanics" article, but is currently otherwise a little pointless. Likewise, I think some trimming needs to go on in this article, but that's doable, and I'm happy to help with it!
  • Additionally support the merging of at least some of linear elasticity and infinitesimal strain theory, since to me they appear to be exactly the same topic, but the latter article simply contains some additional details that the first doesn't. Please let me know if I am wrong on this.Thudso (talk) 01:23, 10 December 2009 (UTC)


Oppose Strongly Oppose This article (and see my comments above as well) does not even begin to describe the engineering term. It is fundamentally incomplete. While I might be interested at some point in the physics or in finding out about what mathematicians call something or what have you. Really, the engineering terms (even if they are not what is used by others) are distinct and widely accepted concepts, which is not at all addressed here. I would suggest separating the engineering terms and providing references to more in depth articles. In engineering there are standard tests and measures and a language surrounding these which needs to be mentioned as well in order to define the limits of discussion. At the moment there are many much better resources for information and clarity on the concepts of strain, deformation, and elongation (all of which are shorthand for more specific concepts) as regards engineering. Certainly, whether by redirection or other mechanism, we should make clear that when an engineering text or datasheet says "strain" or "elongation" without qualifier, that means "engineering shear strain" and "Tensile Elongation usually expressed in %". If possible, it would be useful to expand this engineering article to include the definitions and standards that engineers use when defining these. I certainly wanted to find out more about how % elongation was measured specifically and ended up directed to a page which didn't even explain how elongation and deformation related, much less told me why this term, which is very common is used by engineers all over. Wiredrabbit (talk) 23:16, 15 December 2010 (UTC)

Second anniversary[edit]

It appears this merge discussion has been ongoing for about 2 years, with an apparent stasis in the last year or so.

In order to focus on the remaining open topics, here's a summary table of how all these merge proposals have ended up. (I've tried to represent my best understanding of current consensus (or lack thereof) from reading the above and looking at redirects, and not my own opinions.) I think this is comprehensive, but anyone should just add anything I missed. David Hollman (Talk) 10:37, 7 September 2010 (UTC)

Status of proposed article merges into Deformation (mechanics)
Original article Status Notes
Finite strain theory X mark.svg Not done
Deformation (engineering) Maybe
Normal strain Yes check.svg Done
Shear strain Yes check.svg Done
Strain (materials science) Yes check.svg Done
Strain tensor X mark.svg Not done Went to Infinitesimal strain theory
Stretch ratio Yes check.svg Done
Displacement field (mechanics) X mark.svg Not done

One thought on the long timeframe of this discussion: sometimes it is better to act than to not act. I think this is the spirit of "be bold". Sometimes if the best choice is not clear, acting to make a change can still be positive because it exposes other aspects of a problem. There is nothing wrong with (say) merging three articles together and later splitting the new one into two reformulated ones.

As an analogy, this is also the spirit of refactor mercilessily as I understand it. "Refactor mercilessly to keep the design simple as you go and to avoid needless clutter and complexity."

On the other hand a situation where no action is taken means that progress and improvement are on hold, or only incremental, and opportunities to learn are less forthcoming.

At least, that's my 2 cents/pence. David Hollman (Talk) 10:47, 7 September 2010 (UTC)

Merge of Deformation (engineering)[edit]

Support: As an unsigned comment mentioned already, much of the material in D(e) would work well as an introduction to D(m). The fact that it may cross over into aspects of strength of materials or failure is a good thing because it provides context which I think is needed in the D(m) article. David Hollman (Talk) 10:47, 7 September 2010 (UTC) Support: I agree with the above. Merge D(e) into D(m). —Preceding unsigned comment added by Ebarbero (talkcontribs) 22:16, 27 September 2010 (UTC)

Merge of Displacement field (mechanics)[edit]

(add comments)

In my view, the displacement field article is describing a general concept which might not apply only to rigid body deformation. So I don't think a merge is warranted. Given the long absence of any interest in this topic, I have removed the merge tags. David Hollman (Talk) 21:41, 15 September 2010 (UTC)

Split article[edit]

The article got too long, so I split the article, leaving the core content on general deformation, and moving back the content on finite strain theory and infinitesimal strain theory to their own articles. - Sanpaz (talk) 01:30, 12 September 2008 (UTC)

As this article was split and now discusses only general deformation, the strain(physics) article which is still merged with this one does not sufficiently discuss the use of stress in basic physical terms. Thus, links to other pages no longer make sense or adequately answer the question of the terms stressed used in physics from a definitional sense. As the article stands it does not serve as a useful reference from other pages that discuss strain from a physics perspective. I suggest that the strain(physics) is split off from this one and written to refer to this page for a more general discussion on deformation. Falztobias (talk) 15:55, 4 February 2009 (UTC)
I am not sure if you wrote "stress" instead of "strain". But regardless of that, I do not see the need of splitting content from the deformation (mechanics) article. The reason for this is that the content that use to be addressed in the old article strain (physics) is now addressed in the article Infinitesimal strain theory.
The deformation (mechanics) article tries to address the general physical concept of deformation. From this article it is explained that strain is a way of measuring deformation, and that depending on the magnitude of this strain (the difference between the configuration after and before the deformation) there are different approaches to study deformation: two of them being Finite strain theory and the other infinite strain theory.
Let me know if I understood your concern and suggestion. sanpaz (talk) 17:11, 4 February 2009 (UTC)


Personally, I like the format of smaller articles that provide succinct definitions to terms with hot links to other such topics. I often use the system to look up terms I find in other materials related to engineering and would rather not wade through a big article trying to find a description of a certain term. —Preceding unsigned comment added by 142.176.61.245 (talk) 15:00, 3 May 2009 (UTC)

That is the description of a dictionary. An article deals with a topic: in this case deformation. This topic then may address several terms. There is a balance in the scope of an article that needs to be found, which is not always easy. I think that this article is general enough without being too overstretched. Obviously, this article is not near complete, nor of high quality. sanpaz (talk) 02:40, 4 May 2009 (UTC)
I must agree with the IP reader. Wikipedia is meant to be an encyclopedia; which is a bit more than a dictionary, but defintely not a collection of essays or textbook chapters. Wikipedia is not meant to replace books and should not try to imitate them. Most readers, technical or expert, come here looking for specific information, and they will be frustrated if they have to look for it in a large article (or, worse, if they have to read several large articles and take a crash course in continuum mechanics just to understand the jargon). Merging may feel right to editors who work in the field, are used to books and structured courses, and have all the articles on one field in their head; but is almost always very bad for our readers. --Jorge Stolfi (talk) 18:04, 24 February 2013 (UTC)

Other strains[edit]

See IUPAC's 1997 Recommendations here (PDF, possibly badly made) and here (rtf). Please also confirm that "Cauchy" strain means what it say in the article — it is not obvious that it agrees with the IUPAC definition, which seems prevalent. —DIV (128.250.247.158 (talk) 11:30, 16 June 2009 (UTC))

Plastic deformation in solids[edit]

The article is still under construction. I am working now on getting all the references detailed, and I am wide open to edit suggestions ! -- logger9 (talk) 23:54, 3 July 2009 (UTC)

"Strain, or deformation..."[edit]

Strain is not deformation. This opening sentence needs to be restated. Strain is a resultant of deformation. d=Lf-Lo, where d= deformation, Lf= Length final and Lo= length original. s=d/Lo where s=strain, d=deformation and Lo=length original. Also s=p/E where s=strain, p=strss and E=modulus of elasticity. This is indicative that normal deformation is a resultant of (s*L)/(A*E) where s=stress, L=length, A=area and E = modulus of elasticity.24.58.102.10 (talk) 22:09, 19 September 2010 (UTC)

Agree completely. My feeling is that the bit on different strain measures needs a separate home. But neither infinitesimal strain nor finite strain theory appear to be the right place for strain measures. Examples of deformation are given at the bottom of the page. More can be added. Bbanerje (talk) 21:38, 20 September 2010 (UTC)
The article had the correct definition but at some point some one changed it. The correct definition is that deformation is the change in shape and size, and strain is the geometrical representation of deformation. http://en.wikipedia.org/w/index.php?title=Deformation_%28mechanics%29&oldid=238712279 sanpaz (talk) 23:11, 20 September 2010 (UTC)
Entropy in action:) The older version was perhaps a bit too technical for whoever changed it. It may be time to write a new introduction. Bbanerje (talk) 23:45, 21 September 2010 (UTC)

When was epsilon first used as the symbol to denote strain?[edit]

Hi there,

Just wondering when the symbol epsilon was first used or started being used to denote strain...

Pjoseph 98 (talk) 11:47, 28 April 2011 (UTC)

Deformation includes rotation?[edit]

The head section states that

Deformation in continuum mechanics is the transformation of a body from a reference configuration to a current configuration.<ref name=Truesdell>Truesdell, C. and Noll, W., (2004), ''The non-linear field theories of mechanics: Third edition'', Springer, p. 48.</ref> A configuration is a set containing the positions of all particles of the body. Contrary to the common definition of deformation, which implies distortion or change in shape, the continuum mechanics definition includes rigid body motions where shape changes do not take place (<ref name=Truesdell/> footnote 4, p. 48).

This is rather strange, since a mechanical engineer will hardly say that a train wheel "severly deforms" merely by turning on its axle.
Is that indeed a common convention in continuous mechanics? Certainly the strain tensor is only the symmetric component of the relative displacement; and since "strain tensor" now redirects here, it ought to be the case that deformation excludes rigid rotation.
Perhaps that is a convention that only some authors make? Or that is only made in specific subfields of mechanics (like static stress analysis of fixed structures)?
--Jorge Stolfi (talk) 17:42, 24 February 2013 (UTC)

From the February 4, 2009 edit I found a paragraph I introduced, but later got removed: In general, the displacement of a continuum body has two components: a rigid-body displacement component and a deformation component. If after a displacement of the continuum there is a relative displacement between particles, a deformation has occurred. On the other hand, if after displacement of the continuum the relative displacement between particles in the current configuration is zero i.e. the distance between particles remains unchanged, then there is no deformation and a rigid-body displacement is said to have occurred
I think the right approach is to say that deformation/distortion plus rigid body motions form the motion of body. That is what most books on continuum mechanics say. I cannot access page 48 of Truesdell's books in Google Books to understand the context of the reference. sanpaz (talk) 17:42, 25 February 2013 (UTC)
This is another of those cases where Truesdell and his peers tried to standardize the terminology and failed. I recall seeing a comment from Walter Noll on a Wikipedia article saying that configurations should properly be called placements (but that term has not caught on). To quote Truesdell (p. 45 of his Nonlinear field theories of mechanics) "In the work of HOOKE, POISSON, and CAUCHY, the body is subjected to a rigid deformation." Darn! (boldface mine) Bbanerje (talk) 21:17, 25 February 2013 (UTC)

Merge redux[edit]

Now that someone split out large parts of this article, the main argument against the merge with deformation (engineering) seems to have disappeared. I am usually a splitter, but in this case I thik that a merge is warranted; because, among other things:

  • While the split may seem to make sense to the editors involved, it does not make sense to the outside public and to editors in other areas. If a reader is looking for an article on "deformation", which article should he be directed to? If someone out there needs to wikilink "deformation", which one should he point to? (Pointing to a disamb is a non-solution, since it expects the reader to make a choice that he has no way of making without looking at the articles.)
  • We do not have two different concepts here: "deformation" means exactly the same thing to engineers and physicists. The difference between the articles is only one of digestibility. If anything, this article is badly named and packaged. The strain tensor is not "deformation", it is only one very particular way to describe the deformation mathematically; therefore its definition should be in an article called "strain tensor" or "Cauchy strain tensor" or "Euler strain tensor" etc..
  • This article is also rather indigestible even to specialists. There should be less expanded formulas and more intuition-building. The merging of deformation (engineering) may help set the right tone and drive future edits in the right direction.

--Jorge Stolfi (talk) 21:16, 24 February 2013 (UTC)