/INTER/TYPE6
Block Format Keyword This interface is used to simulate contact between two rigid bodies with tabulated input of the contact force. It works similar to interface TYPE3. Contact force between the bodies can be input as a function of maximum penetration. The interface also allows you to input a force function for unloading.
Description
 The segments of two contact surface must face each other (example: the surface normals must be oriented from one surface to the other)
 The interface only works with segments connected to solid or shell elements; two contact surfaces must not share the same node (must be part of 2 different rigid bodies)
 Userdefined interface stiffness can reduce the time step
Format
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

/INTER/TYPE6/inter_ID/unit_ID  
inter_title  
surf_ID_{1}  surf_ID_{2}  
Sfric  Fric  Gap  T_{start}  T_{stop}  
I_{RS}  I_{Rm}  Inacti  fct_ID_{ff}  fct_ID_{fv}  Ascale_{f}  Ascale_{v}  
fct_ID_{Id}  I_{form}  Ascale_{x}  Fscale_{Id}  Icor  
fct_ID_{ul}  Stiff  Fscale_{ul}  
Visc  fct_ID_{dv}  fct_ID_{df}  Fscale_{v} 
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) 

surf_ID_{1}  Rigid surface 1
identifier. (Integer) 

surf_ID_{2}  Rigid surface 2
identifier. (Integer) 

Sfric  Static friction
force. (Real) 
$\left[\text{N}\right]$ 
Fric  Coulomb
friction. (Real) 

Gap  Gap for impact
activation. (Real) 
$\left[\text{m}\right]$ 
T_{start}  Interface activation
time. Default = 0.0 (Real) 
$\left[\text{s}\right]$ 
T_{stop}  Interface deactivation
time. Default = 1.0e30 (Real) 
$\left[\text{s}\right]$ 
I_{RS}  Renumbering flag for
segments of the first surface.
(Integer) 

I_{Rm}  Renumbering flag for
segments of the second surface (same as I_{RS}).
(Integer) 

Inacti  Deactivation flag of
stiffness in case of initial penetrations.
(Integer) 

fct_ID_{ff}  Friction multiplier
function versus normal force. (Integer) 

fct_ID_{fv}  Friction multiplier
function versus sliding velocity. (Integer) 

Ascale_{f}  Abscissa scale factor for
velocity functions
(fct_ID_{ff}
and
fct_ID_{dv}). (Real) 
$\left[\frac{\text{m}}{\text{s}}\right]$ 
Ascale_{v}  Abscissa scale factor for
force functions
(fct_ID_{ff} and
fct_ID_{dv}). (Real) 
$\left[\text{N}\right]$ 
fct_ID_{Id}  Force versus penetration
curve function identifier. This function should be positive in both force and displacement. (Integer) 

I_{form}  Contact formulation flag.
1
(Integer) 

Ascale_{x}  Abscissa scale factor on
fct_ID_{Id} and
fct_ID_{ul}. Default = 1.0 (Real) 
$\left[\text{m}\right]$ 
Fscale_{Id}  Ordinate scale factor on
fct_ID_{Id}. Default = 1.0 (Real) 
$\left[\text{N}\right]$ 
Icor  Adjusting force flag, due
to initial intersection. 2
(Integer) 

fct_ID_{ul}  Force versus penetration
curve for unload function identifier. This function should be positive in both force and displacement and always less than the loading curve. Not used if I_{form} = 2. (Integer) 

Stiff  Loading/unloading
stiffness used when transitioning between curves. Required input if I_{form} = 1, 2. 
$\left[\frac{\text{N}}{\text{m}}\right]$ 
Fscale_{ul}  Ordinate scale factor for
unload
fct_ID_{ul}. Default = 1.0 (Real) 
$\left[\text{N}\right]$ 
Visc  Damping
coefficient. (Real) 
$\left[\frac{\text{Ns}}{\text{m}}\right]$ 
fct_ID_{dv}  Damping force function
versus penetration velocity. (Integer) 

fct_ID_{df}  Damping multiplier
function versus normal force. (Integer) 

Fscale_{v}  Ordinate scale factor on
fct_ID_{dv}. (Real) 
$\left[\text{N}\right]$ 
Comments
 The loading curve
fct_ID_{Id} should always be
given.
For I_{form} =0, the unloading curve is not considered and loading and unloading use the same curve fct_ID_{Id}.
For I_{form} =1, the unloading curve fct_ID_{ul} is considered and: When the unloading curve fct_ID_{ul} is not defined, then loading follows the fct_ID_{Id} and unloading follows a straight curve with slope Stiff down to zero and remain equal to zero. Reloading Radioss jumps from zero to the loading function fct_ID_{Id} along a straight curve with slope Stiff.
 When both the loading and unloading curves are defined (the unloading curve should be lower than the loading curve) then during unloading Radioss jumps from loading to unloading curve following a straight curve with slope Stiff. Reloading Radioss jumps from fct_ID_{ul} unloading curve to loading curve fct_ID_{Id} along a straight curve with slope Stiff.
Some of the cases are shown below:  If I_{form} =1 and Icor =1, the interface force at t=0 is set to a value from the unloading function fct_ID_{ul}, which corresponds to the initial penetration. If the unloading function is not defined, the initial force is set to zero.
 Tangent friction force,
F_{t} is calculated
as:$${F}_{t}=\mathit{Sfric}+\mu ({F}_{n},{F}_{t})\cdot {F}_{t}$$Where,
 ${F}_{n}$
 The normal force
 $\mu $ ( ${F}_{n}$ , ${F}_{t}$ )
 Dynamic friction coefficient defined as:
$$\mu ({F}_{n},{F}_{t})=\mathit{Fric}\cdot {\mathrm{f}}_{\mathit{ff}}({F}_{n})\cdot {\text{f}}_{\mathit{fv}}({v}_{t})$$Where, ${v}_{t}$
 Sliding velocity
 ${\mathrm{f}}_{ff}$ and ${\mathrm{f}}_{fv}$
 Functions of fct_ID_{ff} and fct_ID_{fv}
 Damping force,
F_{damp} is calculated
as:$${F}_{\mathit{damp}}={\mathrm{f}}_{\mathit{df}}\left({F}_{n}\right)\cdot \left(\mathit{Visc}+{\mathrm{f}}_{\mathit{dv}}\left({v}_{n}\right)\right)$$Where,
 ${v}_{n}$
 Penetration velocity
 ${\mathrm{f}}_{df}$ and ${\mathrm{f}}_{dv}$
 Functions of fct_ID_{df} and fct_ID_{dv}