Large Deformation Vs Small Deformation (Nlgeom on Vs off) 2

[khalidfh]

Hi

I am simulating simple uniaxial tensile test using Standard (Implicit) Abaqus.
Material (Density elasticity and plasticity) has been defined.
Everything is just fine.
The problem is when I turn the Nlgeom on, it show necking.
What is the theory behind this?
And how can Abaqus triger necking at certain time?

Anyone can help me...I looked into the documentation but could not find a lot.

Thank you.

 

[DanStro]

The stress is high enough that, based on your material definition, Abaqus thinks that the material is yielding. This is controlled by the plasticity values that you entered for the material.

Decrease the force to a point that the material should not be yielding and there will be no plastic deformation (and no necking).

 

[khalidfh]

Thanks DanStro
I forget to tell it is steel.
The material yield and plastic deformation starts.
This is good. But the issue is necking occure only when Nlgeom option is On.
I artificially increase the fracture strain from 0.11 and True stress of 1200MPa to fracture strain of 5 (or 500%) and true fracture stress of 1400MPa and still necking occure.

Why? and What is the theory behind this?

 

[ESPcomposites]

Linear geometry does not update the geometric dimensions as the load changes. Nonlinear geometry updates the element geometry at each load increment and has the ability to recognize that the element size/shape/position is different than when the analysis started.

Brian

http://www.espcomposites.com