Simulating skin penetration- viscoelasticity

- April 9, 2020 at 5:54 pm
  
  allisonfurmidge
  Subscriber
  
  I am having a hard time trying to make a simulation for penetration of needles through skin. I was initially trying to simulate PDMS instead of skin, but I found more viscoelastic properties for skin than PDMS. Has anyone here tried to make a simulation using Explicit Dynamics with a viscoelastic material (specifically skin or PDMS)? What material properties are necessary in order to complete this? When I added the viscoelastic instantaneous shear modulus and decay constant, it said it either needed isotropic properties (E modulus, Poisson's ratio) or an equation of state. However, I cant find any equation of state that matches the 2,3,5, or 9 parameters as in the Engineering Data. Any help with simulating this material would be appreciated!
- April 19, 2020 at 1:20 pm
  
  Vahidebrahimi
  Subscriber
  
  Hi mate
  
  I have the same problem, but I am using isotropic properties of skin from literature (E and v). To erode the elements, I introduced failure strain criterion that is between 10-25% to remove elements as penetrating. I am also using explicit dynamics and want to measure the insertion force in time, do you know how I can measure insertion force - time. I am displacing the needle from the end to penetrate using Tabular displacement. In the available results, there is no Force components ! and I am trying to measure the force from the needle back (where the displacement is introduced).
  
  Also, can you tell me what is your "End time" ? cause if I select my end time to be 3 sec. It will take ages to finish. So, I had to change it to smaller value of end times 1e-3. This end time is not realistic as my real end time based on needle movement should be 3 sec. Do you have any idea for my case?
  
  Kind Regards
- May 16, 2020 at 7:42 pm
  
  allisonfurmidge
  Subscriber
  
  Hello,
  
  Just wondering, what literature did you use to find E and v? I was originally trying to use Explicit Dynamics but realized that Static Structural actually was showing Force-time and stress results. It might have been because skin is viscoelastic and I was trying to add a Mooney-Rivlin model that might have been incorrect.
  
  Yes for a while I was using my end time to be 1 e-6. I would say maybe try to begin the needle penetration closer to the skin, or already mid penetration. Or just remove the needle really quickly. I understand the struggle of a long computation time, it was literally crashing my computer at the beginning. Sorry I wish I could be of more help!
  
  Allison