/INTER/TYPE8

Block Format Keyword This interface is used to simulate drawbeads. It is mainly used in the process industry to model metal forming.

Drawbeads are used to prevent the metal strip from sliding during the stamping process. Normals of the main segments must be oriented toward the secondary nodes (unsorted group).

Format

(1)	(2)	(3)	(4)	(5)	(7)	(9)
/INTER/TYPE8/`inter_ID`/`unit_ID`
`inter_title`
`grnd_ID`_s	`surf_ID`_m		`I`_form
`F`_n		`F`_t		`DEPTH`	`T`_start	`T`_stop
Blank Format

Definition

Field	Contents	SI Unit Example
`inter_ID`	Interface identifier. (Integer, maximum 10 digits)
`unit_ID`	Unit Identifier. (Integer, maximum 10 digits)
`inter_title`	Interface title. (Character, maximum 100 characters)
`grnd_ID`_s	Secondary unsorted node group identifier. (Integer)
`surf_ID`_m	Main surface identifier. (Integer)
`I`_form	Friction penalty formulation type. = 1 Viscous (total) formulation. = 2 (Default) Stiffness (incremental) formulation. Recommended when the loading speed is low. (Integer)
`F`_n	Drawbead normal force per unit length. (Real)	$[\frac{N}{m}]$
`F`_t	Drawbead restraining force per unit length. (Real)	$[\frac{N}{m}]$
`DEPTH`	The drawbead depth. (Real)	$[m]$
`T`_start	Start time for contact impact computation. (Real)	$[s]$
`T`_stop	Temporary deactivation time. (Real)	$[s]$

Comments

The node group for secondary surface must be an unsorted group (/GRNOD).
I_form =1 is not available when using Idt =1 in option /ADMESH/GLOBAL.
When F_n ≠ 0, Normal force is computed. The normal force is due to the bending of the blank into the draw bead as the binder closes on the die. The total contact force is the sum of the restraining force and normal force.
F_n represents a limiting value. The normal force begins to develop when the distance d between the blank and drawbead line is less than the drawbead depth (DEPTH). When the drawbead is close to blank (distance equal to depth), this normal force reaches a plateau F_n. The value of normal force depends on the penetration as described here:

Figure 1.

Where, $δ = DEPTH - d + \frac{{Thickness}_{Blank}}{2}$ .
If DEPTH = 0 or $\frac{F_{n}}{DEPTH} > {Stiffness}_{Blank}$ stiffness, the slope of the linear part of the curve is reset to the stiffness of the blank so that the same time step than the one without normal force is used to guarantee the stability.