I`m modeling a helmeted head impact to a steel anvil. I used MAT 126 to model the foam of the helmet and it seems like E (the elastic modulus for the compacted honeycomb material) is causing the negative volume error in the contact.I`m pretty sure about the honeycomb material model parameters used in this model as I have validated them in a simple rigid ball-foam cube impact. Also, if I decrease (E) couple of orders of magnitudes the negative volume problem goes away but the foam itself shows very unrealistic behavior. I have modeled this impact with different foam material models (both softer and stiffer than the current foam), and never had this negative volume problem before.
Hi Arghavan, You may get rid of this error by changing the element formulation or introducing a proper hourglass.
Check attached file. There is an option CONTACT_INTERIOR which sometimes can be used to prevent negative volumes in Foam modeling.
This might be caused by your contact formulation. For dissimilar materials like foam and steel the penalty method can lead to very high contact forces.
If you use the SOFT=1 option for your contact the forces are based on nodal mass as well as the step size, which is advantageous in this case.
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