/INTER/TYPE23

Block Format Keyword

/INTER/TYPE23 - Interface Type 23

Description

Defines a contact interface for airbag fabrics, modeling contact between a master surface and a slave surface which are supposed to belong to an airbag. This is a soft penalty contact which can deal with penetrations and intersections often coming in the folded airbag mesh. This interface can be used for self-impacting.

Format

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
/INTER/TYPE23/inter_ID/unit_ID
inter_title
surf_IDs	surf_IDm	Istf		Igap		Ibag	Idel
Fscalegap		Gap_max		Fpenmax
Stmin		Stmax
Stfac		Fric		Gapmin		Tstart		Tstop
IBC			Inacti	VISs				Bumult
Ifric	Ifiltr	Xfreq

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
C1		C2		C3		C4		C5

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
C6
Blank
Blank
Blank

Field	Contents	SI Unit Example
inter_ID	Interface identifier (Integer, maximum 10 digits)
unit_ID	Optional unit identifier (Integer, maximum 10 digits)
inter_title	Interface title (Character, maximum 100 characters)
surf_IDs	Slave surface identifier (Integer)
surf_IDm	Master surface identifier (Integer)
Istf	Stiffness definition flag (Integer) = 0: Stfac is a stiffness scale factor and the stiffness is computed according to the slave side characteristics = 1: Stfac is a stiffness value
Igap	Gap/element option flag (Comment 3) (Integer) = 0: gap is constant and equal to the minimum gap = 1: variable gap varies according to the characteristics of the impacted master surface and the impacting slave node
Ibag	Airbag vent holes closure flag in case of contact Default = 0 (Integer) = 0: no closure = 1: closure
Idel	Node deletion flag Default = 0 (Integer) = 0: no deletion = 1: non-connected nodes are removed from the slave side of the interface.
Fscalegap	Gap scale factor Default = 1.0 (Real)
Gap_max	Maximum gap = 0: there is no maximum value for the gap. (Real)
Fpenmax	Maximum fraction of initial penetration (Comment 4) (Real)
Stmin	Minimum stiffness (Real)
Stmax	Maximum stiffness Default = 1030 (Real)
Stfac	Interface stiffness (if Istf = 1) Default set to 0.0 (Real)
	Stiffness scale factor for the interface (if Istf = 0) Default = 1.0 (Real)
Fric	Coulomb friction (Real)
Gapmin	Minimum gap for impact activation (Real)
Tstart	Start time (Real)
Tstop	Time for temporary deactivation (Real)
IBC	Deactivation flag of boundary conditions at impact (Boolean)
Inacti	Stiffness deactivation flag of stiffness in case of initial penetrations (Comment 4) (Integer) = 0: no action = 1: deactivation of stiffness on nodes = 5: gap is variable with time and initial gap is computed as follows: , with the initial penetration = 6: gap is variable with time but initial penetration is computed as follows (the node is slightly depenetrated):
VISS	Critical damping coefficient on interface stiffness Default set to 1.0 (Real)
Bumult	Sorting factor (Comments 5 and 6) Default set to 0.20 (Real)
Ifric	Friction formulation flag (Comments 8 and 9) Default = 0 (Integer) = 0: static Coulomb friction law = 1: generalized viscous friction law = 2: Darmstad friction law = 3: Renard friction law
Ifiltr	Friction filtering flag (Comment 10) (Integer) = 0: no filter is used (default) = 1: simple numerical filter = 2: standard -3dB filter with filtering period = 3: standard -3dB filter with cutting frequency
Xfreq	Filtering coefficient (Comment 10) A value should be between 0 and 1. (Real)
C1	Friction law coefficient (Optional) (Real)
C2	Friction law coefficient (Optional) (Real)
C3	Friction law coefficient (Optional) (Real)
C4	Friction law coefficient (Optional) (Real)
C5	Friction law coefficient (Optional) (Real)
C6	Friction law coefficient (Optional) (Real)

(1)-1	(1)-2	(1)-3	(1)-4	(1)-5	(1)-6	(1)-7	(1)-8	(1)-9	(1)-10
							IBCX	IBCY	IBCZ

Field

Contents

IBCX

Deactivation flag of X boundary condition at impact

(Boolean)

=0: free DOF

=1: fixed DOF

IBCY

Deactivation flag of Y boundary condition at impact

(Boolean)

=0: free DOF

=1: fixed DOF

IBCZ

Deactivation flag of Z boundary condition at impact

(Boolean)

=0: free DOF

=1: fixed DOF

1.	For contact stiffness:

if Istf = 0

While,

Ks is an equivalent nodal stiffness of the slave component computed as:

when node is connected to a shell element.

Where,

E is the Young modulus,

B is the bulk modulus of the slave component,

t is the shell thickness,

V is the solid element volume.

2.	If Gapmin is not specified or set to zero, a default value is computed as the minimum of t (average thickness of the slave shell elements).

3.	If Igap = 1, variable gap is computed as:

While,

gs: slave node gap:

with t is the largest thickness of the shell elements connected to the slave node.

If the slave node is connected to multiple shells, the largest computed slave gap is used.

The variable gap is always at least equal to Gapmin.

4.	Inacti = 6 is recommended, in order to avoid numerical (high frequency) effects into the interface before inflation.

Inacti_flag_6

If Inacti = 5 or 6 and if Fpenmax is not equal to zero, nodes stiffness is deactivated if:

5.	The sorting factor, Bumult is used to speed up the sorting algorithm.

6.	The sorting factor Bumult is machine dependent.

7.	One node can belong to the two surfaces at the same time.

8.	For Friction Formulation

➢	If the friction flag Ifric = 0 (default), the old static friction formulation is used:

with ( is Coulomb Friction coefficient)

➢	For flag Ifric > 0, new friction models are introduced. In this case, the friction coefficient is set by a function

Where,

p is the pressure of the normal force on the master segment,

V is the tangential velocity of the slave node.

9.	Currently, the coefficients C1 ~ C6 are used to define a variable friction coefficient for new friction formulations.

The following formulations are available:

•	Ifric = 1 (generalized viscous friction law):

•	Ifric = 2 (Darmstad law):

•	Ifric = 3 (Renard law):

Where,

•	First critical velocity must be different to 0 ().

•	First critical velocity must be lower than the second critical velocity ().

•	The static friction coefficient and the dynamic friction coefficient , must be lower than the maximum friction ( and ).

•	The minimum friction coefficient

10.	Friction filtering

If Ifiltr ≠ 0 , the tangential forces are smoothed using a filter:

Where coefficient is calculated from:

•	If Ifiltr = 1 , simple numerical filter

•	If Ifiltr = 2 , standard -3dB filter, with , and T = filtering period

•	if Ifiltr = 3 , standard -3dB filter, with Xfreq is cutting frequency

The filtering coefficient Xfreq should have a value between 0 and 1

11.	The type of friction penalty formulation is based on the incremental stiffness formulation:

The friction forces are:

While an adhesion force is computed as follows:

with

Where,

Vt is contact tangential velocity.