Hoffman Failure Theory

[Kristina Sornikova]

Dear experts, I have problem with this.
I have sandwich panel, I make spread sheet with all Hoffman required values.
But question are:
What sign to use for stress allowable values?
What sign to use for applied stresses (normal stresses)?
I have some elements with signma1 value greater than compressive stress allowable value for a ply in a sandwich panel.

But I use all positve allowables and absolute applied stress values, I get positive margin even through sigma1 (compressive) is more than allowable compressive stress along direction 1?

 

[Kristina Sornikova]

Just to clear, if I use as it is stress values but positive allowable values, results seem OK.

 

[SWComposites]

Yes, this is possible with interactive failure theories.

BUT, none of the interactive failure theories work, ie, correlate to test data. Search for previous discussions on this forum. Or see the failure criteria papers by Hinton.

 

[Kristina Sornikova]

Thank you SWComposites! Bad luck no test data to compare for me...

 

[blakmax]

Kristina

SWComposites is correct. Stress based theories are notoriously bad at predicting failure. I urge you to look at Hinton's papers in the ICCM conferences because he provided test cases where the failure conditions were known. Some people have reported good correlation with John Gosse's Strain Invariant Failure Theory (SIFT).

Regards

Blakmax

 

[Kristina Sornikova]

Thanks much blankmax, is there a link I can download Hinton's papers?

 

[blakmax]

Try this:

Link

Regards

Blakmax