meniscus fiber simulation

[rsantamaria]

I am currently engaged in simulating fiber damage within meniscus tissue, initiating with basic models to grasp the nuances of the software I'm using. Up to now, I've successfully modeled the damage to the viscoelastic material that represents the meniscus tissue matrix. However, I'm encountering challenges in incorporating fibers into the simulation. My approach has been to configure the model as a solid mixture, aiming to integrate fibers with damage, yet I struggle with managing the strain level at which the fibers fracture and adjusting the quantity of fibers that undergo this breakage. As an initial step towards testing the model's functionality, I'm attempting to synchronize the fracture strain level for both the matrix and the fibers, as well as having all the fiber break at the same time. Although I'm unsure if my current setup for the material properties is optimal, I would greatly value any insights or recommendations on how to accurately model the fibers and their damage.

I have attached my .feb file for both the viscoelastic model, the viscoelastic + fibers model and the viscoelastic + fibers model with damage.

[ateshian]

Hi,

Although we have allowed strain to be used as a damage criterion in FEBio, the reality is that most damage theories (for common engineering materials) use an stress-based criterion for damage. This is embodied in the classical failure analyses known as the Mohr-Coulomb failure theory and the maximum distortional strain energy theory (which produces the von Mises stress). These theories are valid for linear isotropic elastic materials. In my opinion, failure of fibrous biological tissues is most likely caused by excessive fiber normal stress (which can be modeled using the maximum principal normal stress as the damage criterion).

Having said this, I noticed in your model that you are using a CDF Step to model fracture of a fiber at a specific threshold of strain. I don't recommend using CDF Step for a fibrous biological soft tissue because fibers typically get recruited progressively (hence the toe region of most fibrous tissue stress-strain responses) therefore one can reasonably presume that they also fail progressively with increasing threshold of the damage criterion.

I also notice that you additionally use the "damage fiber exponential" material in FEBio. I am not as familiar with that model, so I am unable to provide more insight about it.

That's the gist of the insight I can share. Of course, we can discuss further.

Best,

Gerard

[rsantamaria]

Hi Gerard,

Thank you for your detailed insights and recommendations. I understand and agree with your point on the preference for stress-based criteria over strain for modeling damage, especially in the context of fibrous biological tissues. The classical failure analyses you mentioned, like the Mohr-Coulomb theory and the von Mises stress concept, indeed seem more aligned with the nature of the material we're dealing with.

However, I've encountered a challenge in applying these concepts within the FEBio framework. Specifically, among the three damage-fiber material options available in FEBio, I haven't been able to identify a module or parameter where I can explicitly set either stress or strain as a constraint for initiating damage. This limitation has been a stumbling block in accurately modeling the progressive failure of fibers under stress.

Given your expertise, could you advise on how you would configure the material properties in such a scenario? Your guidance on setting up the material to incorporate a stress-based damage criterion effectively would be invaluable as I aim to refine my model for more accurate simulation results.

Best regards,

Raul

[ateshian]

Hi Raul,

Have you checked the Test Suite damage problems in the FEBioStudio Repository? There are many examples of damage models that employ stress as a damage criterion and a continuous CDF that produces progressive damage. For example see dm01.feb.

Let me know.

Best,

Gerard