Talk:Von Mises yield criterion

Ratio of the yield and ultimate strengths.

I believe your sentence, "It is most applicable to ductile materials where the ratio of the yield and ultimate strengths is near 0.577." should better read " It is most applicable to ductile materials where the ratio of the shear yield to tensile yield strengths is appx. 0.577, or 1 over the square root of 3.

---

You are right, this was my mistake.

-samba6566

Subscript order in third term of local coord equation

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).

first equation

---

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

• You are absolutely right! Thanks! Alex Bakharev 04:09, 17 August 2007 (UTC)

Re-organization of this article

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)

I just posted the new version of the article. I know it is a huge change, but I saw necessary to add more content and re-organize the article. There is still more to be added. I apologize for the big change. Please comment Sanpaz 02:39, 4 December 2007 (UTC)

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)

Recent changes (19 Jan 2007)

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)

I reintroduced the concept of Equivalent stress or von Mises stress into the article, but into its correct spot within the context of the article (i.e. in the uniaxial stress condition section ). Sanpaz (talk) 20:06, 19 January 2008 (UTC)

This article lacks layman definition

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"