Failure Criteria, FEA 1

[martin99]

Hi,

I want to use failure criteria other than Von Mises in the visualiser or even just post processing. Normaly the failure theories are quite simple like Coulomb-Mohr theory:
max princ stress divided by materials UTS minus min princ stress divided by UCS. Fracture occurs if the answer is equal or greater than 1 (but you all knew this anyway)

Can i create a result set that applies formula like the one above then display the result set to see if fracture has occured. I have never created any result sets and i got a bit lost when i tried. I would like to know if i'm on the correct track before diving on in!

Many thanks in advance

Using ideas 9

 

[toothroot]

Hi,

In the I-DEAS postprocessing task, there's a button called "create results", which opens a pop-up menu. Within this menu, you can find some tools that allow you to create your own results. You can directly access the entries of the stress tensor at each node and use standard formulae on them, which should enable you to derive other failure criteria automatically.

If that doesn't satisfy your needs, I would export your FE-model plus results into the Universal format, which is plain ASCII text, and either read it into EXCEL (where you can manipulate the result data) or write a programme that reads the universal file and calculates your failure criterion.

Regards,
Daniel

 

[martin99]

Many thanks, at least i was on the right track. I'll wade in and have a go at creating a results set now. Mind you a bit of messing around with the universal file is tempting, i never thought of that.

Cheers

Martin

 

[martin99]

Maybe I'm being a bit slow but how do i access the individual stress tensors when creating the new results set. I can only apply a formula to whole results set i.e stress and not individual tensors within the results set.

How do i get to the individual stress tensors to apply the formula ??

probably just me having a dense day

Many thanks in advance

 

[toothroot]

You can use the "Reduction" command of the "Create Results" subpanel to derive a scalar value (e.g.a failure criterion) from the entries of a stress tensor of one result set. That should enable you to "programme" your own failure characteristics.

 

[martin99]

I think I’m still being a bit dim! When using 'reduction' in create results you can only get the normal and shear stress not the principal stresses. I vaguely remember the graphical Mohr’s circle way for calculating principal stress etc but surely I can get at the principal stress result values for my equation some how without recalculating them!!

Many thanks

Martin

 

[Irwin]

As I know:
In the select result set you can choose the stress data. If you choose Von-Mises stress, Maximum... etc stress you will get in the list these calculated values.
If you choose normal stresses or shear stresses in these case you can list the items of the stress tensor.

Irwin