Learning Forum

[h.bahreinizad]

Hi everyone,

I'm looking for a way to include linear viscoelastic behavior in the passive component of the muscles in LS-DYNA.

I'm considering either *MAT_MUSCLE (*MAT_156) or *MAT_SPRING_MUSCLE (*MAT_S15). Ideally, I'd like to model the passive response using a linear viscoelastic formulation (such as a Prony series) while keeping the active muscle behavior unchanged.

Does anyone know if this is possible with either of these material models? Or is there another way to achieve this, such as adding a separate viscoelastic element in parallel?

I'd appreciate any suggestions or examples.

Thanks!

[Dennis Chen]

Hello, I've never tried using this with Mat_Musslce but you can try mat_add_inelasticity.     I believe this is ulitimately the same as a generalized maxwell model imposed by other code like Ansys Mechanical (APDL) to allow you to add what's equivalent to the prony series terms in terms of "weights".    

I also made a video on this topic here:

in the later part of the video, I tried to study the prony series term and dyna's mat_add_inelasticity's weights to get the same answer and you can do so by just inverting the relaxation time of the prony series definition.   I hope this helps. 

[h.bahreinizad]

Hi Dennis,

Thank you for this suggestion. However the mat_add_inelasticity onlt supports solid and shell elements, whereas the muscles are beam elements. Do you know of something similar that works for beams ?

Thanks

[Dennis Chen]

Hi, sorry I didn't check the doc and did not realize it's only for beam elements.     Mat_add_inelasticity is pretty much just based on the genrealized maxwell model where each link is a set of springs and dashpots.   

If I follow that logic, perhaps there's a way to achieve your objective by adding a dashpot between the nodes which forms the beam element.    If you can define the relaxation function you want to achieve, you can tune the dashpot to get what you are looking for at least in principle.  

Please take this just as a passing thought.   If its' a real work project, I would have taken hours to reserach before answering but it's just a forum here. 

Thanks