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Checking Stress Triaxiality

Dear All,

I'm researching to investigate JC Flow stress and Failure parameters (A356 T6) for my thesis. I'm encouraging with a problem to verify Stress triaxiality Bridgman Model VS FEA. In addition, I'd like to compare strain at fracture from actual tensile test VS FEA. Could anyone advise me please? By the way, I have efforted to compare stress tri by HyperView. FEA result is quite different from Bridgman model(Fig 3). Please correct me if I'm wrong.

Model setting

Software: Hyperwork 2020.1,Radiouss

Material Law:

Failure Model: Johnson (D1,D2,D3)

Control Cards

/ANIM/BRICK/TENS/STRESS,/ANIM/BRICK/TENS/STRAIN

Fig 3: Stress triaxiality Bridgman VS FEA(Hyperview)

Best regards,

Manop Pagdeevongsa

Master of Engineering Program in Metallurgical Engineering

King Mongkut's University of Technology Thonburi

Community-Pasted-Attachment-1635863337251.png

Community-Pasted-Attachment-1635865685290.png

Inner_rim_BD - Failure.hm

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Radioss

Accepted answers

All comments

Rogerio Nakano_21179

I am not familiar with the Bridgman stress triaxiality

But I think it calculates the stress level, and so the triaxiality, on the surface of the notched region.

The solution that you have in Radioss is in the centroid of the element.

Also, you can improve the result on Radioss if you use tetrahedon full integration formulation with Itetra=1

with the option /H3D/DT and /H3D/SOLID/TENS/OUTER you can have Membrane stress tensor on the outer surface of a solid or thick shell component. The membrane layer is automatically created, and the solid stress tensor is extrapolated to this surface.

I hope this is helpful.

Regards

Mathieu_Courchesne

Hi,

Just wondering if you found a way to have the same triaxiality stress in the FEA vs bridgman model.

I'm currently have the same question.

Thanks,

Polyvios Romanidis

Hi Mathieu,

The Bridgman model and FEA work in a different way, so they can not return the same results.

Bridgman model make some assumptions that are not valid generally. More specifically in Bridgman model:

The plastic strain is assumed not to change through the thickness of the naked region
The radius and azimuth stress components are assumed to be equal

The above assumptions lead to inaccuracies between FEA solution and Bridgman model for stress triaxiality and stress values in different directions, despite the fact that the equivalent (Von Mises) stress is accurate.

For more details you can refer to the next link:

https://apps.dtic.mil/sti/trecms/pdf/AD1077234.pdf

So, generally it is not expected to produce the same results with these methods.

Polyvios

Mathieu_Courchesne

Really nice paper.

Thank you.