Airbag Internal Contacts

External and internal airbag components including inter-chamber voids and void components used for vents should not have any geometrical intersections.

A combination of /INTER/TYPE7 and /INTER/TYPE11 contact should be used to represent internal airbag contact.

Generic /INTER/TYPE7 airbag contact (kg, mm, ms):

#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/INTER/TYPE7/666700001
Airbag Selfcontact - 666700001
#  Slav_id   Mast_id      Istf      Ithe      Igap                Ibag      Idel     Icurv      Iadm
 666100103 666100101         4         0         0                   1         0         0         0
#          GAP_SCALE             GAP_MAX             Fpenmax
                   0                   0                   0
#              STMIN               STMAX          %MESH_SIZE               dtmin
                   1                1E30                   0                   0
#              STFAC                FRIC             GAP_MIN              Tstart               Tstop
                   1                   0                   1                   0                   0
#     I_BC                        INACTI               VIS_S               VIS_F              BUMULT
       000                             6                   0                   0                   0
#    Ifric    Ifiltr               Xfreq     Iform
         0         0                   0         2
/SURF/PART/666100101
Airbag External Surface by Part - 666100101
 666000001 666000002 666000003 666000004 666000005 666000006 666000007 666000008 666000009 666000013
 666000014 666000015 666000016 666000017 666000018 666000201 666000202 666000203
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|

For /INTER/TYPE7 contact:

All external and internal fabric components including inter-chamber voids and void components for vents should be defined in a self-contact where the components are listed as secondary nodes and main surfaces
I_stf=4 provides correct contact stiffness
I_bag=1 provides vent closure due to contact
St_min=1KN/mm limits smallest contact stiffness
Gap_min=1mm provides a smooth increase of contact force as secondary nodes are approaching main segment
Friction is set to 0
Inacti=6 deactivates initial penetrations

Initial penetration can be checked with HyperCrash's penetrations checker. The airbag model should be depenetrated up to the physical thickness of airbag fabric. For example, if the thickness of airbag fabric is 0.3mm, the airbag should be depenetrated to 30% of Gap_min = 1 value.

Generic /INTER/TYPE11 airbag contact (kg, mm, ms):

#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/INTER/TYPE11/666800001
Airbag Selfcontact Edge - 666800001
#  Slav_id   Mast_id     I_stf               I_gap   Multimp                Idel
 666100102 666100102         4                   0         0                   0
#              STmin               STmax           MESH_SIZE               dtmin     Iform   Sens_Id
                   1                   0                   0                   0         2         0
#              STFAC                FRIC                 GAP              Tstart               Tstop
                   1                   0                 0.9                   0                   0
#     I_BC                        INACTI               VIS_S               VIS_F              BUMULT
       000                             6                   0                   0                   0
/LINE/SURF/666100102
Airbag Line by Surface - 666100102
 666100101
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|

For /INTER/TYPE11 contact:

All external and internal fabric components including inter-chamber voids and void components for vents should be listed both on secondary and main side
I_stf=4 provides correct contact stiffness
St_min=1KN/mm limits smallest contact stiffness
Gap_min=0.9mm provides a smooth increase of contact force as secondary nodes are approaching main segment. This contact gap is 90% of /INTER/TYPE7 contact gap
Friction is set to 0
Inacti=6 deactivates initial penetrations

Initial penetration can be checked with HyperCrash penetrations checker. The Airbag model should be depenetrated till 90% of Gap_min value which would result in a maximum penetration of 10% of the Gap_min value.

Assuming there are no initial intersections in the model, the definition of a TYPE7 and TYPE11 contact prevent node-to-surface and edge-to-edge intersections during airbag simulation. If initial intersections do exist in the model, the model can be unstable because nodes can be stuck on the wrong side of a main surface. In addition to this, the finite volume mesh cannot be created when airbag components have intersections. Therefore, it is important to remove all initial intersections.

When the /DT/INTER/DEL option is used in the Engine file, airbag secondary nodes can be removed from the internal contacts causing local intersections of airbag fabric and decreased accuracy of airbag simulation. When this option is used, define a local dtmin=1e-5ms in the /INTER/TYPE7 and /INTER/TYPE11 internal contacts definition which will override the global /DT/INTER/DEL dtmin value.

Note: Model time step should not be limited by the contact kinematic time step.