Difference between vonmises and maximum principal stress 2

[kar99429]

Hi
I need to know two things..

1.what is the difference between vonmises and maximum pricipal stress.
2.I heard that vonmises is apt for static analysis and max. principal is for dynamic analysis..Why?

Hope you guys will help me to understand the concept.. thank u verymuch in advance

 

[rb1957]

sorry (well, not really) for the bluntness, but ...

1) look it up in any text

2) no idea, never heard it. both are failure criteria, wys of combining stress components together to get a scalar stress to compare to an allowable.

the biggest difference between them is that vM is strictly an elastic stress (ie up to yield) but is often applied (conservatively) to ultimate. max principal has no such limitations (it's just a vector combination of stress components).

 

[DanStro]

I use vM for ductile and Max. Principal for brittle materials. But I haven't heard of a distinction based on static and dynamic.

Han primo incensus

 

[corus]

What the OP probably refers to is that the principal stress is used in fatigue assessments, and so could be considered as being 'dynamic'. For the yield criteria to be met it's common to use Von Mises stress, though some design codes use the more conservative Von Tresca stress intensity.

 

[JoshPlumSE]

VonMises is really good for comparison to yielding. That's what it was derived for. It's directionless, so it doesn't tell you much about the orientation of the stress.

I can't say that I'm in a field (civil / structural) where I look at principal stresses very much. However, it may be that the directionality of the principal stresses make it more important for other failure states (fracture, buckling, et cetera).

 

[JpPhysics]

We use the VonMises stress to determine if the part will fail and the principal stress to determine how to make it better. Sometimes knowing the direction is valuable.

 

[kar99429]

Thank you very much guys.. i didnt expect these much of replies in a short span.. really i appreciate this forum..