Convergence in contact debonding

[leonardo.barducci]

I have a single lap shear test involving a 2 rectangular shaped specimens (one in aluminum and one in woven cf) bonded together with an adhesive I created with czm formulation (wanting to investigate the decohesion of the specimen within the adhesive interface). Contact is defined as bonded and pure penalty formulation, convergence is not reached. Could you please list a series of suggestions to achieve convergence in this specific contact debonding tool in static structural? And also a checklist of the important settings so that I can check if I missed somethimng

[Dennis Chen]

Hello Leo, this is very normal with CZM models in Ansys Mechanical.   You can potentially change the damping coefficient in the CZM model definition (it is one of the parameter you can adjust) to help with this but there's a limit to how much you can adjust that.    contact debonding is, by definiton, a status-changing nonlinearity so you are suposed to have issues. 

It is, in my opinion, far better to use a tool with cohesive elements explicitly modelled, such as LS-Dyna, to do CZM based modelling.   It is something to consider.    We all must use the proper tool for our problems and applications or we are just giving ourselves unneeded headaches. 

hope this helps. 

[leonardo.barducci]

Hi Dennis! thank you so much for answering! I used static structural following your yt tutorial which helped a lot btw! How do i set up this simulation in LS-Dyna?

 

[Dennis Chen]

Hi Leo, I also made a video about this which is linked below.   Basically, LS-Dyna has several material models you can use (Mat138 vs linear TSC and Mat186 for nonlinear TSC for example).   You will want to use a single layer element to model the cohesive elements.   Elform 19 in section_solid for solid-solid connection.  Elform 20 for shell-shell connection.     Also, based on where you get the CZM material model, it is critical you understand what is the bond thickness from which the CZM model is generated.     The bond thickness defines the process zone for the crack and CZM model is all about capturing the damage initiation and evolution through the traction separation function (which is computed from various tests of that bond thickness). 

Hope this helps! 

https://www.youtube.com/watch?v=EOaYQYGVltw&t=0s