Checking Stress Triaxiality

Manop Pagdeevongsa
Manop Pagdeevongsa Altair Community Member
edited February 23 in Community Q&A

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:

 

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Failure Model: Johnson (D1,D2,D3)

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Control Cards

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

Fig 3: Stress triaxiality Bridgman VS FEA(Hyperview)

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image

 

Best regards,

Manop Pagdeevongsa

Master of Engineering Program in Metallurgical Engineering
King Mongkut's University of Technology Thonburi

 

 

 

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Answers

  • Rogerio Nakano_21179
    Rogerio Nakano_21179 New Altair Community Member
    edited November 2021

    Hi 

    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
    Mathieu_Courchesne Altair Community Member
    edited February 2

    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
    Polyvios Romanidis New Altair Community Member
    edited February 23

    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
    Mathieu_Courchesne Altair Community Member
    edited February 23

    Really nice paper.

     

    Thank you.

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