Principal stresses or Von Mises 2

[visitor]

I like to know which is to be checked whether Principal stresses or Von Mises equation when an element is subjected
to axial,bending stresses in two planes and shear stresses ?

I want to know where Principal stresses govern , where Von Mises equation govern ?

Please help me.

 

[tld23]

Visitor,
The principal stresses and von Mises stresses are derived quantities based on the stress state. If you want to assess a component or structure based on these stresses you need to determin failure criterion. As general rule:

1) von Mises stress is used to assess ductile modes of failure
2) Principal stresses are used to assess brittle failure

therefore which you choose will depend on the materials that you are using. You will need to look at the stress-strain behaviour of the material. If there is lots of plastic deformation then use the Mises. If the deformation up to failure is elastic only use the principal stresses. If you are not sure you can apply both sets of criteria and use the most conservative.

TERRY

 

[visitor]

Thanks Terry,

Normally the standards recommend Von Mises for steel structures like bridges.
But I have seen people checking principal stresses for concrete etc.

Am I correct ?