Axisymmetric problem with bi-linear material in Femap

[PetrGrygar]

Hi,
I have another thing, I want to ask. Is there a way, how to solve an axisymmetric job, with bilinear material? I tried, but without success. First I solved axisymmetric job normally, as linear static, and the results look fine. Then I defined material as nonlinera (Elasto-plastic, BI-linear) and entered date for yield stress and plasticity modulus H. After that, I solved this job as nonlinear static. Results from such a job is exactly same as results from previous solved linear job. Did I something wrong, or such analysis doesn't support axisymmetric elements?

Thanks for any reply.

 

[jerza]

Hi,
if the results are same it doesn't mean that the second one is wrong. I suggest create a simple pull beam a check the result for each type of the material. Something like here.

 

[PetrGrygar]

Thanks for reply. Yes, it means, because i forget to wrote that the Von Mises stress is above yield stress. So the results cant be the same.

 

[jerza]

Hi, yes you are right. I'm interested, could you share your problem in more detail?

 

[PetrGrygar]

Ok,
it's a pipe with internal pressure. My calculation was focused on welded bottom. This calculations was finaly solved at one quarter of solid model with symmetric BC's. This problem with axisymmetric is just for future cases that I will solve. If you know something about it, or you already solved something with this approach, I would be grateful if you share your knowledge.

Thanks

 

[jerza]

Hi,
I just read Element Library Reference for NX Nastran (for me v8.5). There is a describe of the axisymmetric solid elements on page 141.

1. The recommended axisymmetric elements CTRAX3, CQUADX4, CTRAX6, and CQUADX8 support all capabilities of the elements described in categories 2 and 3 below , they are defined in the X-Z basic coordinate system, and are supported in solutions 101, 103, 105, 106 (hyperelastic), 107, 108, 109, 110, 111, 112, 153, 159 and 601. They support the materials linear isotropic (MAT1/MATT1), linear orthotropic (MAT3/MATT3), isotropic heat transfer (MAT4/MATT4), thermal material properties for anisotropic materials (MAT5/MATT5), and MATHP or MATHE for hyperelastic solutions.

2. The CTRIAX6 element is a linear axisymmetric element defined in the X-Z basic coordinate system, it is supported in SOLs 101, 103, 107, 108, 109, 110, 111, 112, 153, 159, and it supports the materials linear isotropic (MAT1/MATT1), linear orthotropic (MAT3/MATT3), isotropic heat transfer (MAT4/MATT4), and thermal material properties for anisotropic materials (MAT5/MATT5).

3. The CTRIAX and CQUADX elements are defined in the X-Y basic coordinate system, they are fully nonlinear elements supported in solution types SOL 106 and 601 but only support hyper-elastic material defined on the MATHP bulk data entry . The CTRIAX and CQUADX axisymmetric elements are described in the Hyperelastic Axisymmetric Elements section.

In the NX Nastran User's Guide, on page 129, we can read: Hyperelasticity is the only nonlinear capability that allows axisymmetric analysis.

I think the conclusion is clear. You can't used for these elements your material. If I'm wrong I hope someone correct me.

 

[jerza]

Supposed you are using Femap with NX Nastran

 

[PetrGrygar]

Thanks a lot! So my problem can't be solved by this approach. Yes, I use Femap with NX Nastran.