Learning Forum

[ansysuser]

Hello,

 

Some materials, such as biological materials, are active materials.  This means that they change their own stress and strain state as a function of time.  For example, a muscle contracting behaves differently than a steel beam where external forces are imposed.  I am interested in using ANSYS for this type of material, but I do not know where to start. 


Most papers describe the stress state of an object with this kind of behavior in terms of an active and passive components of the strain energy function.  How would I begin to approach this in ANSYS?

[Bhargava Sista]

Soft tissues are known to have a time-dependent response (stress relaxation and creep) without undergoing any permanent deformations. Such behavior is modeled using viscoelastic material models. At slow deformations, they can be modeled using linear viscoelastic models and for high strain rate deformations, the response is usually nonlinear viscoelastic which is very complicated to model.

In ANSYS, you can use a combination of hyperelastic and linear viscoelastic (Prony series) models to simulate tissue response. This is a very common practice so you should find example studies in the literature. You can search along the lines of "viscoelastic modeling of soft tissues in ANSYS" to find relevant studies that can get you started.

[ansysuser]

Thank you bsista, but my problem is not in dealing with hyperelastic materials per se.  The problem is that muscle moves from internal contractions, not external applied forces and pressures.  I am wondering how to perform analysis with active stresses such as this.

[Bhargava Sista]

In that case, the material model is not what you're looking for, perhaps initial stress or residual stresses might be a what you're looking for. You can introduce some stress into the material using INISTATE command and depending on the boundary conditions the tissue will tend to settle down and move in that process.

For a more realistic representation, you may need to write your own material sub-routine which is a daunting process if you're not experienced. 

[Gina]

 Dear ansysuser, did you discover how can we model muscle contraction in ANSYS?

I am trying to model muscle according to Hill constitutive model, but I am no sure how can I implement this model in ANSYS.

Any help is much appreciated. 

[pedroksm]

I am also looking for a way to implement Hill constitutive model in ANSYS, because I need to introduce some muscles in my model.

Did you discover something about it?