Initial stress read from ODB file, integration point or nodal stresses?

[jfonken]

Hi all,

I'm working on a model to estimate the pre-stress in a measured abdominal aortic geometry. To do so, I use an initial condition in which stress is read from the ODB file of a previous simulation using:
*INITIAL CONDITIONS, TYPE=STRESS, FILE=Cylinder_BI_01.odb

This works fine, but I need to know if this command causes the stresses to be extracted at the element integration points or at the element nodes. I'll need this to compare my results to Ansys simulations. I haven't been able to find an answer to my question. Can anybody at this forum help me?

Thanks in advance!
Kind regards,
Judith

 

[Mustaine3]

With default output requests you do not have stresses at nodes in the .odb.

 

[FEA way]

Initial stresses are specified for material points in elements (not for nodes).

 

[jfonken]

Good to know, thanks!

 

[IceBreakerSours]

FYI

Biomechanics literature has a confusing set of terms so this might be useful - There are three kinds of stress in tissues/organs: a) Residual stress due to the inherent microstructure/microarchictecture evolution, b) Stress due to some small load (preload?) that is hard to measure, and c) Stress due to the day-to-day functioning of the tissue/organ. Most simulations target the third job and there are many issues to consider but I won't bother with it here.

For a simulation to start with a tissue/organ that is "stress-free" means you have estimated its residual stress and its unloaded configuration. For the first job, one option is to take your tissue/organ, cut it in various directions, measure its resultant change, and then do an inverse FEA analysis to estimate the stress-free configuration. Now, the residual stress may very well be tensorial in nature so you may need to make multiple cuts. Tough stuff but one or two cuts might be doable. There are many papers by leading biomechanics figures on estimating the unloaded configuration (see papers that cite Govindjee's classic paper on inverse elastodynamics).

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