Ansys Learning Forum › Forums › Installation and Licensing › Ansys Products › Negative eroding contact energy in impact testing › Reply To: Negative eroding contact energy in impact testing

October 16, 2024 at 7:18 pm
Reno Genest
Ansys Employee

Hello,

It is possible that the negative eroded internal energy is caused by negative volume error. If you get negative volume or out-of-range forces or velocities error messages without a failure criteria, this indicates some degree of instabilities in your model. I would try to fix the negative volume and instability problem first and then try to activate element erosion again. Here are some tips to combat instability and negative volume errors:

  • Make sure you have a good quality mesh. If the element quality is bad, you are more likely to have elements with high distortion and negative volume.
  • Reduce the time safety factor (TSSFAC on *CONTROL_TIMESTEP) from 0.9 to 0.66. This can be effective especially if the impact is very fast.
  • Increase the d3plot output frequency and animate the results to see what is happening and what triggers the instability.

Also, I would try to remove the *CONTACT_AUTOMATIC_SINGLE_SURFACE for now. Having redundant contacts is not recommended.

You will find more information on negative volume and instabilities here:

https://ftp.lstc.com/anonymous/outgoing/support/FAQ/negative_volume_in_brick_element.tips

https://ftp.lstc.com/anonymous/outgoing/support/FAQ/instability.tips

https://lsdyna.ansys.com/have-you-any-tips-on-how-to-to-combat-instability/

https://lsdyna.ansys.com/negative-volumes-in-brick-elements/

 

Let me know how it goes.

 

Reno.