Doubts on CZM inputs with TBDATA

[Davide_P]

Hi all,

a short question about something that i cannot understand on CZM inputs with INTER elements and Bilinear formulation. In the table a short recall of C1-C6 constants.

[John Doyle]

As you know, C5 defines ratio of displacement jump at maximum cohesive traction to displacement jump at completion of debonding.
While the same ratio applies equally to normal and tangential directions, your max traction values for normal (C1) and tangential (C3) directions can be defined differently.
Also, if you have mixed mode CZM, you can use C6 to introduce a nondimensional weighting parameter to take into account the difference in the debonding contribution of each mode.
Refer to Section 4.11 of MAPDL Theory Manual (R2022-R1) for graphs and formulas related to these inputs.

[Davide_P]

Thanks for your reply!
Do you basically refer to this (see the picture)?

If yes, the beta term is a sort of correction factor that is required in order to fill the discepancy introduced, for example, by the calcultation of C5 from normal traction values (in terms of separations), to the transversal separation data.
If is not correct, please clarify this point which seems to be quite complicated.
Many thanks,
Davide

[John Doyle]

Yes. This is what I was referring to. I agree it is complicated. I can't advise you on the correct input values other than to calibrate these inputs against benchmark tests. In the absence of benchmark test results, the FEA model might still be helpful for gauging the sensitivity of your design to a range of potential values.

[Davide_P]

Ok, thanks for this clarification!
Based on your feeling, can have sense try to write an explicit relationship between alpha (ratio beetween normal separation quantities) and lambda_cr = beta* ratio on shear separations? (Here i refer to the equation in the above picture after "where")
Thanks Davide