Ls-Dyna model total stiffness

- March 23, 2024 at 7:34 am
  
  Fady Elshazly
  Subscriber
  
  Hello,
  
  Is there a way to check the system total stiffness from the lsprepost or the ouput files?
  
  thanks
- March 26, 2024 at 11:21 pm
  
  Reno Genest
  Ansys Employee
  
  Hello Fady,
  How would you get the total stiffness of the system experimentally? You could put the system in a press and get the stiffness in compression. Or you could put the system in a a tension test machine and get the total stiffness in tension. You can model this test with LS-DYNA and extract the force required to compress or extend the system along with the displacement. You can get the force from the *BOUNDARY_PRESCRIBED_MOTION (bndout) or the contact (rcforc) and the displacement at a node on the press (or extension machine). Then, you can plot the Force vs displacement curve and calculate the stiffness.
  
  Let me know how it goes.
  
  Reno.
  - March 26, 2024 at 11:24 pm
    
    Fady Elshazly
    Subscriber
    
    Thank you so much for your reply. I mean when doing the eigen analysis, is there any way to report the system stiffness used for calculating the modes frequencies.
    
    thanks
- March 27, 2024 at 12:24 am
  Reno Genest
  Ansys Employee
  Hello Fady,
  You should be able to output the stiffness matrix as follows:
  "
```
you can get the stiffness matrix, the mass
matrix, the nodal information to map the rows of the independent system to
the nodes and rigid body center-of-masses, and the unscaled eigenvectors.
See MTXDUMP (2nd field, 2nd line of *CONTROL_IMPLICIT_SOLVER)
and EVDUMP (6th field, 2nd line of *CONTROL_IMPLICIT_EIGENVALUE)."
```
  Let me know how it goes.
  
  Reno.