# Talk:Stress (mechanics)/Archive 1

## Brittle and ductile

I am skeptical about "By definition, brittle materials fail under normal stress, and plastic or ductile materials fail under shear stress." Don't ductile materials undergo plastic yield before failing whereas brittle materials simply break? (I am in the midst of a stress class; if nobody touches this, I'll come back to it later.)

I added this statement, and agree that it is simplified and can be improved. Please do.
However, I don’t believe the statement is false. Its not only that brittle materials simply break; they break in an orientation where the greatest normal stress is seen. And ductile materials do yield before breaking, but in the orientation of maximum shear stress, and plastic flow is a result of shear stress.
By the way, you can sign and date stamp your talk entries with four tildas (~~~~).
Duk 21:30, 16 Oct 2004 (UTC)
I disagree with the anonymous poster. The article is correct, as is. The above statement by Duk is indeed accurate, and very well written. --Simian, 2005-10-03, 06:44 Z

## This is an article about stress

This is an article about stress. Stress can occure in solids, liquids and gases so it is unhelpful to turn this into an article about stress in solids. I think that it would be systematic to confine discussions about brittle and ductile fracture to the article fracture which really could do with turning into a decent article. Cutler 12:10, Oct 17, 2004 (UTC)

sounds good. Duk 02:48, 19 Oct 2004 (UTC)
I think the article is excellent, as is. It briefly mentions these terms in one or two sentences, as it should. Then if the reader wants further information, (s)he simply clicks on the links. The stress article should briefly mention this as it does now, and is very well written. --Simian, 2005-10-03, 06:44 Z

## Microscopic Interpretation of Stress Force

I am missing any reference to the microscopic interpretation of the stress force in the article, and in particular to the fact that the stress/strain curve is only linear (i.e. obeys Hooke's law) over a much smaller region than one should expect if molecular forces are responsible. I have discussed this issue on my page http://www.physicsmyths.org.uk/hooke.htm and suggested there that in fact plasma polarization fields due to free electrons in the material might actually be responsible for the linear stress/strain curve in the Hooke-region.

Thomas

## Cauchy v. Piola–Kirchhoff

There should be some discussion here about the distinction between the Cauchy and the Piola–Kirchoff stress tensors (corresponding, I believe, to true and engineering stress respectively.) —BenFrantzDale 15:59, 11 October 2005 (UTC)

I feel that we should resist the temptation to make this article too complicated and off-putting. Most people who come here will simply want to know the difference between stress and strain without any math. Technical points like this should go to stress tensor. Cutler 18:45, 11 October 2005 (UTC)
If BenFrantzDale is in agreement, this sounds like a good suggestion by Cutler. This does seem to be a perfect fit for the stress tensor article. --Simian, 2005-10-14, 04:22 Z
I agree, except that stress tensor has something to do with relativity. Perhaps there should be a new page for the nitty-gritty details of stress tensors in engineering? —BenFrantzDale 04:48, 14 October 2005 (UTC)
Good point. That page states up front it's devoted to relativity. So I currently retract my previous comment, and my two posts here can be deleted by the next editor. --Simian, 2005-10-14, 13:05 Z

Gonz - I agree.

I think that the discussion of Cauchy stress vs. Piola-Kirchhoff stress does have a place here. If this article is meant to represent the Continuum Theory of stress it is important to make the distinction between the two stress. They are theoretically and physically easy to understand as to not be "off-putting" yet at the same time important to the development of constitutive laws (where Cauchy is most often used) as compared to actual physical measurement (where the 1st P-K is most often used). A statement as to the conditions where these stresses are equal would be helpful as well.71.199.128.182

## Title

This title is inaccurate. It should read either Stress (Mechanical Engineering) or Stress (Applied Physics).

'Stress (mechanics)' would be better, keeping both physicists and engineers happy. I've changed the first sentence to reflect this and link to mechanics. RDT2 09:49, 15 August 2006 (UTC)

Agree with 'Stress (mechanics)'. And I moved the 'Continuum mechanics' box to the top. --Duk 18:33, 14 January 2007 (UTC)
Agree with 'Stress (mechanics)'. Proposed merger with tensile stress. Katanada (talk) 23:47, 16 December 2007 (UTC)

## formatting

why are so many phrases in boldface? this is distracting and makes the article more difficult to read. i suggest that boldface be removed from everything that doesn't need special emphasis (such as the examples of what constitutes a one-dimensional system and every single appearance of the word stress).

## force on cube face

The force on the cube face is stress*dA, not dV. I've reverted to the previous version.RDT2 10:25, 19 October 2006 (UTC)

## Extending side menu: Continuum mechanics

Hi, I have updated the article about Strain and I think that it should be in this side menu Continuum mechanics, but I don't know how to add it. How do you customise side menus?

Janek Kozicki 13:31, 21 November 2006 (UTC)

I added it to the menu. In the future, you can edit by entering "Template:Continuum mechanics" in the search bar. PAR 17:29, 1 December 2006 (UTC)

great, thanks! Janek Kozicki 21:14, 3 December 2006 (UTC)

## Poisson's Ratio

In the section dealing with nominal and engineering stress, it said "its cross-sectional area reduces by an amount that depends on the Poisson's ratio" I changes this to "may change" to reflect a more general condition where the material my have a negative or zero Poisson's ratio. 71.199.128.182

Poisson's ratio will always be greater than zero and less than or equal to 0.5 —Preceding unsigned comment added by 74.60.57.253 (talk) 23:50, 5 August 2009 (UTC)

## Residual Stresses

"Press fits are the most common intentional use of residual stress." I think this statement needs to be modified if not removed completely. It is unclear what is meant by "most common" and intentional. Many biologic tissues exhibit residual stresses. This is intentional as it helps the tissue function and is more common in the fact that many animals have tissues with residual stresses. I would propose "In material manufacturing, press fits are the most common intentional use of residual stress."71.199.128.182

## Tensor notation

We have three different tensor notations in this article; ${\displaystyle \sigma _{ji}}$, ${\displaystyle \sigma _{ij}}$, and ${\displaystyle \sigma }$ & ${\displaystyle \tau }$. Should try to be more consistent here ? --Duk

## Derivation of the stress vector as a function of the stress tensor

I have made a few changes in this derivation. The argument ${\displaystyle h\rightarrow 0}$ has been replaced by the idea of the parallelogram shrinking to a point. A note has also been added to Fig.3 explaining the sign convention K.sateesh (talk) 05:56, 18 February 2009 (UTC)