Elastic vs Plastic analysis 1

[Istructeuk]

Hi all,
I have 2 identical models, first is analysed Elastic and second is analysed Non-linear (Plasticity).

https://s15.postimg.org/hqfyro9nf/image.png

https://s12.postimg.org/qwgh1oae5/image.png

The max. Vonmises stress in the first model = 449 Mpa
The max. Vonmises stress in the second model = 1196 Mpa which is totally out of my mind.
The reason I have used “Multilinear Isotropic Hardening” (see pic below) instead of “Bilinear Isotropic Hardening” is I want to set the limit plastic strain as 5% as marked.

https://s16.postimg.org/ti4smrcv9/image.png

Could anyone please shed some light: Why is the stress in the plastic model so high, more than the limit as defined? And the maximum stress points are different between 2 models?
In case of “Bilinear Isotropic Hardening”, how do we know the strain (i.e 5%) in the final result?

Any comments are truly welcome.

Many Thanks

 

[hendersdc]

Your mesh is way too coarse so the numbers you are getting can't be relied upon, try refining it around the sharp corners. Also if you can add a radius there in your design it would help limit the stress concentration at those points.

 

[NRP99]

You should use brick elements to avoid high stress and to have smooth contours of stress at corners with through thickness at least 3 elements. Another thing your stress-strain is of which material? I guess stress should be in MPa and not in GPa in stress vs strain curve unless you are using very high strength exotic/fictitious material.

 

[inline6]

plot plastic strain and post results

 

[Shu Jiang PEng SE]

It seems that the yield stress is approximately 3e5MPa from the material model. The stresses derived in two analyses both are less than the yield stress.

The reason of nonlinear stress analysis result is higher than the linear analysis maybe is: Nonlinear analysis consider the load application position change while linear analysis does not.

 

[oswald88]

Hi
Try reefing the mesh at the curves, I hope it does not involve contact.