Airbag Setup Recommendation

Airbag Materials

Recommendations for fabric material model setup using LAW19.

LAW19 Option	Recommended Value	Recommended Option Details
`R`_E	0.001 < `R`_E < 0.01	If `R`_E > 0.01 the compression stiffness is too high.
`ZeroStress`	1	Airbag pre-strain is applied correctly.
`sens_ID`	Use the same sensor as used in /MONVOL card	Fabric pre-strain through reference geometry must be activated at time to fire.

Recommendations for fabric material model setup using LAW58.

LAW58 Option	Recommended Value	Recommended Option Details
`B`₁ and `B`₂	> 0	`B`₁ and `B`₂ values should be positive.
`Flex`	0.01	The default value is adequate.
`G`₀ < `G`_T	--	Shear parameters should be consistent.
$α_{T}$	Enter value in degrees	Shear locking angle shall be entered in degrees.
`ZeroStress`	1	Airbag pre-strain is applied correctly.
`sens_ID`	Same sensor that is used in /MONVOL card	Fabric pre-strain through reference geometry must be activated at time to fire.

Airbag Properties

Recommendation in fabric properties /PROP/TYPE9 (SH_ORTH) and /PROP/TYPE16 (SH_FABR).

Property Option	Recommended Value (per material)		Recommended Option Details
	LAW19 ¹	LAW58 ²
`I`_sh3n for trias	2	2	This is the default tria formulation.
`I`_smstr for trias	1	4	Best practice recommendation for 3 node trias
`I`_shell for 4-node shells	12	12	This formulation avoids hourglassing.
`I`_smstr for 4-noded shells	11	11	Must be used with `I`_shell =12, 4 node shells.
`N`	1	1	Enable membrane formulation
`Thick`	> 0	> 0	Thickness must be defined
`I`_plas	0	0	Not relevant for fabric
`I`_thick	0	0	Not relevant for fabric
`Vx`, `Vy`, `Vz`	Non-zero vector	Non-zero vector	This input defines a vector which determines first orthotropy direction. If not defined the Global X- axis is used.
`I`_dril	0	0	Not relevant for fabric

Airbag Self-Contact

If all intersections can be removed from the airbag, then surface to surface and edge contact and be defined using /INTER/TYPE19. In some advanced cases, it is better to define the two separate contacts, /INTER/TYPE7 for node to surface and /INTER/TYPE11 for edge contact.

Interface Options	Recommended Value for contacts TYPE7, TYPE11 and TYPE19	Comments
Intersections	No intersections	No intersections are allowed.
Penetrations	Penetrations < 95% gap	All penetrations > 95% gap need to be removed.
`I`_stf	4	Interface stiffness is the minimum of the main and secondary stiffness.
`St`_min (kN/mm)	1	Avoids contact that is too soft.
`I`_del	0	Not relevant for airbag self-contact.
`I`_gap	0	Constant gap is used as defined by `Gap`_min.
`Gap`_min	1.0 mm	For TYPE11, use `Gap`_min =0.9mm
`Inacti`	6	Automatically remove initial penetrations by reducing the contact gap.
`Fric`	0	No friction used in airbag self-contact.
`I`_bag	1	Block vent holes and porous fabrics during contact.

If it is not possible to remove intersections, then /INTER/TYPE23 can be used with these recommended values.

Interface Options	Recommended Value for TYPE23	Comments
Penetrations	Penetrations < 95% gap	All penetrations > 95% gap need to be removed.
`I`_stf	4	Interface stiffness is the minimum of the main and secondary stiffness.
`I`_del	0	Not relevant for airbag self-contact.
`I`_gap	0	Constant gap is used as defined by `Gap`_min.
`Gap`_min	Thickness of fabric material	This value determines both contact gap and contact depth, too high values will mean that intersected nodes will not be released due to too high contact depth.
`Inacti`	6	Automatically remove initial penetrations by reducing the contact gap.
`Fric`	0	No friction used in airbag self-contact.
`I`_bag	1	Block vent holes and porous fabrics during contact.