What is IN-PLANE PRINCIPAL STRESS in Abaqus?

[Ingeniosus]

Hi everybody!

I'm doing a Static analysis of a circular reinforced concrete slab.
I'm using SHELL elements in ABAQUS.

In the OUTPUT there are these variables:

MAX IN-PLANE PRINCIPAL STRESS
MIN IN-PLANE PRINCIPAL STRESS

MAX PRINCIPAL STRESS
MIN PRINCIPAL STRESS


What is the difference? And what is the principal stress that I need?

Thank you

Regards

 

[mechfeeney]

The principal stresses are those that are on the principal plane. The principal plane is a plane oriented in a particular way such that the shear stresses go to zero. At any point in the slab, there exists a plane that (1) intersects that point and (2) has zero shear stresses. Now referencing that plane, there are three stress (1) that is normal to the plane and (2) that are in the plane.

Max in plane principal stress grabs the highest value of (2).
Max principal stress grabs the highest value of (1) and (2).

 

[Ingeniosus]

Thanks for your tip.
But I'm not sure because I'm considering a SHELL element that has a PLANE STRESS hypotheses.

In fact there are only these stresses: S11 S22 (that are normal) and S12 that is a shear stress.
When I find a plane without shear I'll find only 2 stresses (that are normal). I think this is all. Is it correct?

 

[mechfeeney]

How can you have two normals to a plane? "S11 S22 (that are normal)"

 

[mechfeeney]

Don't you mean S11 and S22 that are IN PLANE and S12 that is a shear stress IN PLANE?

 

[Ingeniosus]

Yes I mean S11 and S22 that are IN PLANE and S12 that is a shear stress IN PLANE.
So I should have only 2 principal stresses, shouldn't I?

 

[mechfeeney]

I miss interpreted your comment. You are right in that S11 and S22 will be the normals. Look here

http://www.efunda.com/formulae/solid_mechanics/mat_mechanics/plane_stress_principal.cfm

 

[mechfeeney]

It really depends on your definition of normal haha.

 

[Ingeniosus]

So which ones are the principal stresses max and min that I need?


IN-PLANE PRINCIPAL STRESSES or PRINCIPAL STRESSES ?

 

[mechfeeney]

I don't think there would be any difference in a 2-D model. Can you confirm this for me?

 

[Ingeniosus]

No there are differences between two MAX or two MIN.
In fact I can't understand which I have to consider.

 

[mechfeeney]

Would you query a point on your model (tools query) and compare the max in plane principal with the max principal values?