Talk:Von Mises yield criterion

message: It may be more accurate to delete or change 
"because the stress tensor has six independent components"
The stress tensor must be positive-definite, so the components are related and only five can be independent.
Tibbits (talk) 17:19, 2 December 2013 (UTC)
thread_title:  only five independent components of the stress tensor 

message: Currently the links take you to the stress page; however, the deviatoric stress invariants aren't defined their. They're defined on the Cauchy stress tensor page. Should they be included on the stress page, or should we simply redirect that link to the Cauchy stress tensor subsection?
Jdc2179 (talk) 12:11, 7 June 2013 (UTC)
replies: text: I changed all wiki links about the stress tensor to the Cauchy stress tensor page. sanpaz (talk) 15:06, 7 June 2013 (UTC)
thread_title:  Better Link to deviatoric stress invariants 

message: I think that two important details should be mentioned in the article: Firstly the fact that we are looking at a /projection/ here from an (at least) 6-dimensional space to a 3-dimensional space. Obviously, during this projection, some information of the Cauchy stress tensor gets lost... And secondly the fact that the /position/ of the stress point inside the yield surface does not have any physical meaning - except that it shows the proximity to possible yielding by its shortest distance to the surface (which in fact could more easily be shown in a one-dimensional plot). Any comments on that? Kassbohm (talk) 04:56, 18 February 2010 (UTC)
thread_title:  Two details to be mentioned 

message: Since the third term is squared, it does not matter whether the sigma(x) or the sigma(z) come first (mathematically).  The mathematical convention, however, is that the terms are presented in order, x then y then z with there complimentary terms following each. —The preceding unsigned comment was added by Samba6566 (talk • contribs) 23:17, 2 March 2007 (UTC)
thread_title:  Subscript order in third term of local coord equation 

message: ----
Was this supposed to say sigma_v over square root of 3?
Readertonight 01:23, 17 August 2007 (UTC)
thread_title:  first equation 

message: I started improving the section on the Yield Criterion, and then realized that both sections within this article are redundant. Which made me think that this article needs to be re-organized and include the following:
1- what the von Mises yield criterion states (definition and assumptions)
2- equations and figures for the yield function and yield surface
3- equations for the different stress conditions (triaxial, biaxial, uniaxial, and pure shear)
4- The Flow Rule Associated with the von Mises Yield Function
I will try to re-organize this article according to these suggestions. Please comment Sanpaz 00:39, 1 December 2007 (UTC)
replies: text: It needs an introductory paragraph and those horizontal lines ought to be removed in favor of sections... I'll get to it later but for now I'll add the page to Wikipedia:WikiProject Engineering. --Explodicle 19:10, 4 December 2007 (UTC)
thread_title:  Re-organization of this article 

message: These changes deviate the intent of the article. The article is about the overall yield criterion, not solely about the interpretation of, or the use of it(von vises stress). However, the concept of von mises stress needs to be included. Sanpaz (talk) 18:36, 19 January 2008 (UTC)
thread_title:  Recent changes (19 Jan 2007) 

message: I found a much more succinct and usefully answer on yahoo answers.
"What is Von Mises Stress in layman terms?
Good question. Von Mises Stress is actually a misnomer. It refers to a theory called the "Von Mises - Hencky criterion for ductile failure".
In an elastic body that is subject to a system of loads in 3 dimensions, a complex 3 dimensional system of stresses is developed (as you might imagine). That is, at any point within the body there are stresses acting in different directions, and the direction and magnitude of stresses changes from point to point. The Von Mises criterion is a formula for calculating whether the stress combination at a given point will cause failure.
There are three "Principal Stresses" that can be calculated at any point, acting in the x, y, and z directions. (The x,y, and z directions are the "principal axes" for the point and their orientation changes from point to point, but that is a technical issue.)
Von Mises found that, even though none of the principal stresses exceeds the yield stress of the material, it is possible for yielding to result from the combination of stresses. The Von Mises criteria is a formula for combining these 3 stresses into an equivalent stress, which is then compared to the yield stress of the material. (The yield stress is a known property of the material, and is usually considered to be the failure stress.)
The equivalent stress is often called the "Von Mises Stress" as a shorthand description. It is not really a stress, but a number that is used as an index. If the "Von Mises Stress" exceeds the yield stress, then the material is considered to be at the failure condition.
The formula is actually pretty simple, if you want to know it:
(S1-S2)^2 + (S2-S3)^2 + (S3-S1)^2 = 2Se^2
Where S1, S2 and S3 are the principal stresses and Se is the equivalent stress, or "Von Mises Stress". Finding the principal stresses at any point in the body is the tricky part."
I find this a lot with engineering articles, they are all written at graduate student level.  But if you think about it, someone of that level, wouldn't need to look this up.  Try to write these kinds of articles in such a way that someone can be like "wait, what is von mises stress anyways", and then they can come here and figure it out.  Not many people ask "wait, what was the mathematical approximation you used to find this von mises stress"  —Preceding unsigned comment added by 75.162.56.142 (talk) 23:43, 9 March 2008 (UTC)
thread_title:  This article lacks layman definition 

message: I have set up a new article for the von Mises stress. I think can take a little bit the pressure away as to how formulate things on this page. Actually, one could delete now the equations stated in the subsection arbitrary loading conditions as they are double now on the new page. I will leave this deletion to other users, since I am not disturbed by this redundancy. Tomeasy (talk) 06:01, 27 April 2008 (UTC)
replies: text: I don't think there is a need to create another article about this, if it is already in this article. I would delete that article.Sanpaz (talk) 23:34, 27 April 2008 (UTC)
thread_title:  [[von Mises stress]] 

message: I have substituted the value k by the fracture strength, as can be done if the yield criterion is stated the way it currently is. This simplifies the whole article enormously. That's why I chose to do so. However, should we decide in the future to step back to the generic critical value (the one that equals the square root of J2) than we will also revert these edits. Please, comment on what you prefer. Tomeasy (talk) 06:05, 27 April 2008 (UTC)
thread_title:  substitution of the generic critical value by the fracture strength 

message: I appreciate this description of Von Mises yield criterion as a graduate-level discussion of the concept. However, when I imagined that my undergraduate students might look up "von Mises stress" on wikipedia, I felt that they would be confused by this article.
The context in which the average person would be searching wikipedia for "von Mises" is its connection to the maximum distortion energy failure theory. I was surprised to discover that there is no article describing the maximum distortion energy failure theory as referenced by this article.
I admit that precedence may be an issue. One undergraduate text, Shigley's Mechanical Design, gives precedence to von Mises, but a similar text, Juvinal and Marshek, attributes several others as potential originators of the max distortion theory concept.
In any case, would it be a good idea for someone to create a distortion energy entry for the benefit of people who require a pedestrian understanding of this topic?
Thanks, Deltapapamike (talk) 04:53, 8 June 2009 (UTC)
thread_title:  An undergraduate-level exposition, or a distortion-energy entry 

message: In the equation → (sigma1)^2-sigma1*sigma2+(sigma2)^2=3k^2=sigmaY^2 ...sigmaY above refers to the yield strength. This equation does not equal yield strength. This equation should equal Sigma_e (Von Mises stress in my mech. design book) or Sigma_v as denoted in this article. Someone take a look at this and fix if this is indeed incorrect. It could be confusing to someone if it is equaling the yield strength instead of the Von Mises stress. I realize that for the Von Mises failure criterion sigma_e=Sy÷n where n is the safety factor and if it is 1, Sy can = Sigma_e but this is not always the case pbviously. So this formula should be changed. 192.91.173.36 (talk) 21:20, 17 December 2009 (UTC)
replies: text: The formula is correct. One reference to confirm it Plasticity for Structural Engineers page 78sanpaz (talk) 17:30, 18 December 2009 (UTC)
thread_title:  Von Mises equation for plane stress 

message: I believe tau13 should be tau12 in the conditions column. I'm not involved in this article. Someone please change it, it's really bugging me. Thanks.--67.59.60.122 (talk) 12:37, 14 December 2011 (UTC)
replies: text: Fixed sanpaz (talk) 16:28, 14 December 2011 (UTC)
thread_title:  Reduced Von Mises Eq. for dif. stress cond. 

message: I like to use \tau (tau) for shear stress, to help make it obviously different from normal stress.  All my engineering books use tau for shear.  I realize that some/older books use sigma for both kinds of stress.  I know of one asme code that uses it both ways.  Is there and advantage to using sigma for shear stress?  Is tau typically used for something else? --Zojj tc 19:20, 25 February 2012 (UTC)
replies: text: In many textbooks stresses are denoted by \sigma_{ij} where i and j indicate the direction of the surface normal and stress, respectively. Hence, \sigma_{11} is the normal stress acting on the surface "1" and \sigma_{12} is the component of the shear stress on the same surface acting in the "2" direction, et c. I guess it makes for more compact writing using tensor notation and stuff. Baxtrom (talk) 16:31, 29 February 2012 (UTC)

text: I agree, it should be \tau. I'm a mechanical engineer, and without exception, none of any of my textbooks used \sigma for shear. All of them used \tau. Also, since the Wikipedia article about Shear uses \tau, consistency dictates this article should too. Xiph1980 (talk) 10:35, 9 May 2016 (UTC)
thread_title:  tau or sigma for shear stress? 

message: Why is there no hint about the physical reasoning that lead to the development of the von Mises yield criterion in the first place? It was well known that shear stress is what drives ductile yielding. This is the reason the Tresca (max shear) criterion was developed. But in multi-axial loading (more than just pure shear and simple tension/compression), it was noted that Tresca led to incorrect (conservative) predictions of yield, and that indeed there was need for terms in the failure criterion that coupled stresses in different directions. So, von Mises proposed that the stress components be decomposed into a hydrostatic (average normal stress) component, and whatever was left over to get the original stress state back (the deviatoric component). He then proposed that the hydrostatic component (because it involves no shear) be ignored, and worked only with the deviatoric component. Using the generalized Hooke's law, he calculated the strain energy density of only the deviatoric component for general 3-D loading. 
He then proposed calculating the deviatoric strain energy density for any specific loading under consideration, and comparing it to the deviatoric strain energy density of a specimen in simple tension or compression at yield. When the two are equal, the specimen will yield. This leads to the conclusion that when the von Mises stress reaches the tensile yield strength of the material, yield occurs.
So, the statement at the end of the section "This implies that the yield condition is independent of hydrostatic stresses" is misleading. That the yield condition is independent of hydrostatic loading is not implied by the von Mises criterion. It was explicitly assumed from the start.  — Preceding unsigned comment added by 157.201.95.254 (talk) 22:11, 21 October 2013 (UTC)
thread_title:  Mathematical Formulation? 

message: The lede is
"The von Mises yield criterion [1] suggests that the yielding of materials begins when the second deviatoric stress invariant J_2 reaches a critical value.
Does the Wikipedia community wish to limit its audience to those who understand all of that introductory sentence?  So for example, does Wikipedia want to exclude every reader who doesn't understand the term "second deviatoric stress"?  — Preceding unsigned comment added by Mcamp@cinci.rr.com (talk • contribs) 00:20, 15 May 2015 (UTC)
replies: text: That is always a problem with technical articles (try to explain the EPR paradox in simple words! and that is arguably only the beginning of "serious" quantum physics…). In that very case though, aren't the blue links to Yield (engineering) and Cauchy_stress_tensor#Stress_deviator_tensor enough? , feel free to change it if you have a better idea, of course. Tigraan (talk) 09:47, 15 May 2015 (UTC)

text: I agree, this article is terribly over-complicated. I generally have little or no problems following theoretically technical documentation, which I very often need to do for my job, but this article got me confounded. Readability is not helped by the fact that using the \sigma/\tau notation, with a Cartesian coordinate system using the (x, y, z) axes, or (\hat{i}, \hat{j}, \hat{k}) vectors (even often without hat) is more common.  Xiph1980 (talk) 10:58, 9 May 2016 (UTC)
thread_title:  Who is the audience of the article? 

message: I am trying to make this article a little more useful. I have been providing edits to this page for over ten years (under various usernames). The applicability of any engineering/scientific information must be listed before the information is presented. If you can't see this value within the article I'd have to assume you are not well versed in it and question why you are editing it. As for inline citations, I was not aware of them and as a courtesy you could have added them then told me it should be done.
I have been dealing with von Mises criterion for over thirty years, it's a fascination with me. It is obvious Wikipedia does not need any help from someone with sufficient and adequate knowledge and experience. Good luck, I'll quit watching this page.
Joseph L. Moore
Senior Aerospace Engineer 
NASA
:, I do not feel you addressed my concerns.
#Nowhere in the article is any definition of F_{sy}/F_{ty}. Maybe it is a notation for the yield stress / Young's modulus or whatever, but it needs to be said.
#I would have put the inline citations myself if I knew which reference to use, but I have no access to most of the existing references. You come with a claim that one of them supports your information: it seems natural that I ask you which one, rather than go and try to find all of them. If you tell me which one supports which part, I can do the editing for you.
#Think of the lead as the abstract of a scientific paper. You do not put the full hypotheses in there. Yes, application criteria must be mentioned - but not in the lead.
#Finally, I will certainly not report you and no administrator should block you over this, but pay attention that "multiple usernames" are subject to WP:SOCK.
:Wikipedia does need competent editors, but while competence in a technical subject is useful, competence in encyclopedia writing is better still. TigraanClick here to contact me 13:53, 19 October 2016 (UTC)
thread_title: =

message: @NearlyMad, provide a more specific citation on this comment:
"Although the given criterion is based on a yield phenomenon, extensive testing has shown that use of a "von Mises" stress is applicable at ultimate loading "
I have read through the Timoshenko text and I cannot find information that agrees with your statement. 
Timoshenko makes reference to R. v. Mises in a footnote on p478 in a discussion about the development of the maximum strain energy theory. He goes on to mention “recent experiments” that showed correlation between maximum strain energy theory and maximum shear theory, and notes that “in most cases the difference between these two theories is not so large as to make it of practical importance”. However, these discussions are focused on defining the yield point for ductile materials, not ultimate failure, so I do not believe it is relevant.
 
Later, on p482, there is a reference to “very extensive experiments” and a footnote regarding applying the theory to ultimate stresses, but this is explicitly noted in reference to brittle materials.
 
I should point out that all of my references above are in “Part II” of the text. Your citation notes “Part I”, but I have not been able to locate a reference to von Mises in that portion of the text. 216.243.30.3 (talk) 22:13, 5 January 2024 (UTC)
replies: text: After reviewing Timoshenko, I felt it was appropriate to remove the note stating that von Mises was applicable to ultimate loading. If the claim can be substantiated with a more precise citation, the edit can be reversed. NGenEar (talk) 23:55, 5 February 2024 (UTC)
thread_title:  Applicability to Ultimate Loading