Nonlinear Analysis

[ToohTaah]

I am performing a nonlinear analysis of a titanium tube using in hydraulic application on I-DEAS. My stress-strain curve has zero slope in non-linear range. This is the first time I use the program to do nonlinear analysis. Before this, I used NASTRAN to do the job. The result from NASTRAN looks good to me. However, for the result from I-DEAS, I got the maximum von-mises stress more than the yield stress. If I understand correctly, the max von-mises stress at the critical load should be not more than the yield stress. I don't know what I did wrong. Here is the information of my model.

- nonlinear analysis of titanium tube using in hydraulic application.
- Arc length method to find the maximum internal pressure.
- Yield strength = 105 ksi
- Young's modulus = 15000 ksi in elastic range and 0 in inelastic range
- Ultimate strength = 125 ksi
- poisson's ratio = 0.361

Can anyone tell me how to perform nonlinear analysis using I-DEAS?

TIA

 

[thirumalai]

hi toohtaah,
One more point i want to add. The values yield & ultimate you are giving are used simply to find the slope of the curve after yield. If that curve is plotted the program gets the stress value from the obtained strain. So the stress will be taken depending on strain whatever the ultimate stress may be. The slope of the curve is going to be the same till you give the next entry as subsequent slope. Hope you understood better.

 

[analyzer]

Any one has any comparative data results between NASTRAN and IDEAS for a specific case of plastic analysis?
thanks