In an earlier post on CONTACT INTERIOR , we saw how adding interior contact can help prevent negative volumes. An additional method that is available in LS-DYNA is the use of SET_SEGMENT_GENERAL to generate the interior segments of solids. When a list of parts are defined using PART_SLDIO in the SET_SEGMENT_GENERAL, LS-DYNA generates both external and internal segments of the parts for inclusion in contact treatment. This allows a very fast method (and reversible) way of including interior segemnts so the solid elements can be prevented from inversion.
It must be noted that the default thickness for these internally generated segments is zero which may still result in nodal release due. To prevent this a non-zero value of SLDTHK and an appropriate stiffness value using SLDSTF must be defined to create a stable contact. When a nonzero value of SLDTHK is specified, solid segments will use a contact thickness that is equal to SLDTHK.