LS Dyna

LS Dyna

Material Stopped Being Elastic with No Property Changes?

    • Ozen
      Subscriber

      I am working on tuning a armor penetration simulation against a ceramic tile and UHMWPE behind it. Originally it went well but I input a a value incorrectly in the ceramic material properties (hydrodynamic tensile limit was to the E-06 power in kPa instead of to the E06 power). When I fixed the value and ran it, the simulation just completely lost any resemblance of accuracy. The ceramic behaved OK, with only localized failure at impact, but what is broken is the UHMWPE behavior. It is a very elastic material, yet right now all it keeps doing is breaking down the elements where failure occurs. No elasticity whatsoever. Below are input properties.

    • Ozen
      Subscriber
      This is what it keeps doing instead of behaving correctly:
      Notice how the UHMWPE is behaving radically and has random fractures as if it was a ceramic instead. It doesn't make any sense why this is behaving this way and is incredibly frustrating when you fix one problem only to have another massive one delay you further.

    • Chris Quan
      Ansys Employee
      Can you check the UHMWPE material properties carefully? Especially, check the Poisson's ratios YZ & XZ.
      Orthotropic Stress Limit may not work with Explicit Dynamics system. Can you replace it with Principal Stress or Principal Strain failure or Hydro Tensile failure model and then re-run the model to see if the results get improved?
      Since the ceramic material is very hard, the pressure wave created by impact to the ceramic is very strong and is likely causing the material failure in UHMWPE.
    • Ozen
      Subscriber
      Thank you for the reply! Below is a copy of the material property table from the journal I am basing off of titled: "Numerical sensitivity studies of a UHMWPE composite for ballistic protection".

      Being honest, I am not sure what directions they are using for their values, but assuming 1 is X, 2 is Y, and 3 is Z results in an error shown below:
      Instead, I used 1 as Z, 2 as X, and 3 as Y. That gave me good results shown in the first post.
      Orthrotopic Stress limits can work in Explicit Dynamics, it already yielded good data without the ceramic interfering and is causing the material to fail in the inaccurate simulation. I cannot switch and use any other failure method because UHMWPE is a woven fiber composite fabric, it has different strengths in each direction that must be accounted for when determining penetration of a projectile, otherwise results may be skewed.
      I would be more than open to rearranging the property values of UHMWPE as long as the software will accept them. I am currently 4+ days behind schedule so anything that can get this running right I would love to try.
      Lastly, why would there be a pressure wave created by impact? The bullet is harder than the ceramic tile, the tile will fail absorbing some projectile energy and damaging the bullet.

Viewing 3 reply threads
  • You must be logged in to reply to this topic.