/FRICTION

Block Format Keyword Specific contact friction between groups of parts or two parts. This friction definition overwrites the friction model defined in the contact interface for the defined set of interfaces.

This friction model is compatible with contact interfaces: TYPE7, TYPE11, TYPE19, TYPE24 and TYPE25.

Format

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
/FRICTION/fric_ID/unit_ID
friction_title
Ifric Ifiltr Xfreq Iform          
Default friction values, used for any parts are not specifically defined below.
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
C1 C2 C3 C4 C5
C0 Fric VISF    
Repeat these 3 lines to define different friction values for specific parts or groups of parts. For orthotropic friction Idir =1, repeat the next 5 lines where the first set of coefficients is for the first direction and the second set defines the second direction.
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
grpart_ID1 grpart_ID2 part_ID1 part_ID2   Idir    
C1 C2 C3 C4 C5
C6 Fric VISF    
If Idir =1, enter 2 additional lines to define friction in the second direction of orthotropy. 7
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
C1 C2 C3 C4 C5
C6 Fric VISF    

Definitions

Field Contents SI Unit Example
fric_ID Friction identifier

(Integer, maximum 10 digits)

 
unit_ID Unit Identifier

(Integer, maximum 10 digits)

 
friction_title Friction model title

(Character, maximum 100 characters)

 
Ifric Friction formulation flag. 1
= 0 (Default)
Static Coulomb friction law.
= 1
Generalized viscous friction law.
=2
(Modified) Darmstad friction law.
=3
Renard friction law.

(Integer)

 
Ifiltr Friction filtering flag. 5
= 0 (Default)
No filter is used.
= 1
Simple numerical filter.
= 2
Standard -3dB filter with filtering period.
= 3
Standard -3dB filter with cutting frequency.

(Integer)

 
Xfreq Filtering coefficient.

This coefficient should have a value between 0 and 1.

Default = 1.0 (Real)

 
Iform Friction penalty formulation type. 6
=0
Set to 1
=1 (Default)
Viscous (total) formulation.
= 2
Stiffness (incremental) formulation.

(Integer)

 
C1 Friction law coefficient.

(Real)

 
C2 Friction law coefficient.

(Real)

 
C3 Friction law coefficient.

(Real)

 
C4 Friction law coefficient.

(Real)

 
C5 Friction law coefficient.

(Real)

 
C6 Friction law coefficient.

(Real)

 
Fric Coulomb friction.

(Real)

 
VISF Critical damping coefficient on interface friction. 4

Default = 1.0 (Real)

 
grpart_ID1 Part group identifier. /GRPART for the first set.

(Integer)

 
grpart_ID2 Part group identifier /GRPART for the second set.

(Integer)

 
part_ID1 Part identifier 1.

Ignored if grpart_ID1 is defined.

(Integer)

 
part_ID2 Part identifier 2.

Ignored if grpart_ID2 is defined.

(Integer)

 
Idir Orthotropic friction flag for a couple of parts.
= 0
Isotropic friction.
= 1
Orthotropic friction.

(Integer)

 

Comments

  1. The friction defined in /FRICTION overrides any friction defined in the contact interface.
  2. Default values listed in the first section are used for any parts whose friction is not specifically defined in the repeating section using grpart_ID1, grpart_ID2, part_ID1, and part_ID2.
  3. If friction between parts is defined more than one time in the model, the friction defined in the last position are used.
  4. The friction value μμ is defined.
    • Ifric = 0 (Coulomb friction):(1)
      μ=Fricμ=Fric
    • Ifric = 1 (Generalized Viscous Friction law):
      (2)
      μ=Fric+C1.p+C2V+C3.pV+C4p2+C5V2μ=Fric+C1.p+C2V+C3.pV+C4p2+C5V2
      Where,
      pp
      Pressure of the normal force on the master segment
      VV
      Tangential velocity of the slave node
    • Ifric = 2 (Modified Darmstad law):(3)
      μ=Fric+C1.e(C2V).p2+C3.e(C4V).p+C5.e(C6V)μ=Fric+C1.e(C2V).p2+C3.e(C4V).p+C5.e(C6V)
      Where,
      pp
      Pressure of the normal force on the master segment
      VV
      Tangential velocity of the slave node
      • Ifric = 3 (Renard law):(4)
        μ=C1+(C3C1)VC5(2VC5)ifV[0,C5]μ=C1+(C3C1)VC5(2VC5)ifV[0,C5]
        (5)
        μ=C3((C3C4)(VC5C6C5)2(32VC5C6C5))ifV[C5C6]
        (6)
        μ=C211C2C4+(VC6)2ifVC6
      Where,
      C1=μs C4=μmin
      C2=μd C5=Vcr1
      C3=μmax C6=Vcr2
      • First critical velocity Vcr1=C5 must be different to 0 ( C50 ).
      • First critical velocity Vcr1=C5 must be less than the second critical velocity Vcr2=C6(C5<C6) .
      • The static friction coefficient C1 and the dynamic friction coefficient C2 , must be less than the maximum friction C3 ( C1C3 and C2C3 ).
      • The minimum friction coefficient C4 must be less than the static friction coefficient C1 and the dynamic friction coefficient C2 ( C4C1 and C4C2 ).
      Table 1. Units of Friction Formulation
      Ifric Fric C1 C2 C3 C4 C5 C6
      1 [1Pa] [sm] [sPam] [1Pa2] [s2m2]
      2 [sm] [sm] [sm]
      3 [ms] [ms]
  5. Friction filtering
    If Ifiltr ≠ 0, the tangential forces are smoothed using a filter:(7)
    Ft=αFt+(1α)Ft1
    Where, α coefficient is calculated from:
    • If Ifiltr = 1: α=Xfreq , simple numerical filter
    • If Ifiltr = 2: α=2πXfreq , standard -3dB filter, with Xfreq=dtT , and T = filtering period
    • If Ifiltr = 3: α=2πXfreqdt , standard -3dB filter, with Xfreq = cutting frequency

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

  6. Friction penalty formulation Iform:
    • If Iform = 1 (default) viscous formulation, the friction forces are:(8)
      Ft=min(μFn,Fadh)
      While an adhesion force is computed as:(9)
      Fadh=CVtwithC=VISF2Km
    • If Iform = 2, stiffness formulation, the friction forces are:(10)
      Fnewt=min(μFn,Fadh)
      While an adhesion is computed as:(11)
      Fadh=Foldt+ΔFtwithΔFt=KVtδt

      Where, Vt is the contact tangential velocity.

      Iform = 2 is recommended for implicit and low speed impact explicit analysis.

  7. Orthotropic friction for shell elements, if Idir = 1.
    • Two sets of friction coefficients must be defined after the line that contains Idir
    • The orthotropic directions are defined only on the master contact surface
    • The 2 ways to define the orthotropic friction direction
      • Use the orthotropic direction from the shell element as defined in /PROP/TYPE9, /PROP/TYPE10, /PROP/TYPE11, /PROP/TYPE17, /PROP/TYPE51, or /PROP/PCOMPP.

        Direction 1 from element.

        Direction 2 is orthogonal to Direction 1 in the segment plane.

      • Use Direction 1 defined from the vector V and angle ϕ defined in /FRIC_ORIENT.
    • Not supported for solid element, beam, truss or spring elements or edge to edge contact.