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/MAT/LAW87 (BARLAT2000)

Block Format Keyword This elasto-plastic law is developed for anisotropic materials, especially aluminum alloys.

Yield stresses can be defined either by user-defined functions (plastic strain versus stress) or analytically by a combination of Swift-Voce model. The model is based on Barlat YLD2000 criterion. 1

Format

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
/MAT/LAW87/mat_ID/unit_ID or /MAT/BARLAT2000/mat_ID/unit_ID
mat_title
ρi                
E ν  Iflag VP c p
If Ifit =0, insert the following two lines
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
α1 α2 α3 α4 Ifit  
α5 α6 α7 α8  
If Ifit =1, insert the following two lines.
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
σ00 σ45 σ90 σb Ifit
r00 r45 r90 rb
Hardening parameter.
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
Chard
Input for material yield and hardening. If Iflag=0 read:
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
  a         Fcut Fsmooth Nrate
Blank line
If Iflag=0, Nrate read line(s):
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
fct_IDi Fscalei ˙εi
If Iflag=1 read:
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
a αsv n Fcut Fsmooth
A ε0 Q B K0
If Iflag=2 read:
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
  a        
Am Bm Cm Dm Pm
Qm ε0 mart VM0    
AHS BHS MHS NHS EPS0HS
HMART K1 K2    
T0   Cp Eta  
Read if Chard > 0:
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
CRC1 CRA1 CRC2 CRA2
CRC3 CRA3 CRC4 CRA4

Definition

Field Contents SI Unit Example
mat_ID Material identifier

(Integer, maximum 10 digits)

 
unit_ID Unit Identifier

(Integer, maximum 10 digits)

 
mat_title Material title

(Character, maximum 100 characters)

 
ρi Initial density

(Real)

[kgm3]
E Young's modulus

(Real)

[Pa]
ν Poisson's ratio

(Real)

 
Iflag Yield stress definition flag.
= 0 (Default)
Tabulated input and function numbers defined in Nrate.
= 1
Swift-Voce analytic formulation and then Nrate = 0.
= 2
Hansel hardening model.

(Integer)

 
VP Strain rate choice flag. 4
= 0 (Default)
Strain rate effect on yield stress depends on the total strain rate.
= 1
Strain rate effect on yield depends on the plastic strain rate.

(Integer)

 
Ifit Material parameter fit flag.
=0 (Default)
Input Barlat parameters in α1 through α8 .
=1
Barlat parameters are calculated from the test data which is input as σ00 , σ45 , σ90 , σb , r00 , r45 , r90 , rb .
(Integer)
 
αi Barlat material parameters with i=1~8.

(Real)

 
σ00 Yield strength in 00 direction (rolling direction).

(Real)

[Pa]
σ45 Yield strength in 45 direction.

(Real)

[Pa]
σ90 Yield strength in 90 direction.

(Real)

[Pa]
σb Yield strength biaxial loading.

(Real)

[Pa]
r00 Lankford r-value in 00 direction (rolling direction).

(Real)

 
r45 Lankford r-value in 45 direction.

(Real)

 
r90 Lankford r-value in 90 direction.

(Real)

 
rb Lankford r-value in biaxial loading.

(Real)

 
Chard Hardening coefficient.
=0
Hardening is a full isotropic model.
=1
Hardening uses the kinematic Chaboche Roussilier model.
= value between 0 and 1
Weight for the combined isotropic kinematic hardening.
(Integer)
 
a Exponent in yield function. 2

Default = 2 (Integer)

 
αsv Swift-Voce weighting coefficient. 2
= 1
Swift hardening law.
= 0
Voce hardening law.

Default = 0.0 (Real)

 
Q Voce hardening coefficient.

(Real)

[Pa]
K0 Voce hardening parameter.

(Real)

[Pa]
B Voce plastic strain coefficient.

Default = 0.0 (Real)

 
A Swift hardening coefficient.

(Real)

[Pa]
n Swift hardening exponent.

Default = 1.0 (Real)

 
ε0 Swift hardening parameter.

Default = 0.00 (Real)

 
Fsmooth Smooth strain rate option flag when VP=0. 4
= 0 (Default)
No strain rate smoothing.
= 1
Strain rate smoothing active.

(Integer)

 
Fcut Cutoff frequency for strain rate filtering, Appendix: Filtering. 7

Default = 10KHz (Real)

[Hz]
c Cowper-Seymonds reference strain rate.

(Real)

[1s]
p Cowper-Seymonds strain rate exponent. 5

(Real)

 
Nrate Number of yield functions. 2
Nrate > 0
Used only if Iflag = 0.

(Integer)

 
fct_IDi Yield stress versus plastic strain identifier.

(Integer)

 
Fscalei Scale factor for ordinate for fct_IDi.

Default = 1.0 (Real)

[Pa]
˙εi Strain rate i corresponding to fct_IDi.
VP =0
Total strain rate for fct_IDi.
VP =1
Plastic strain rate for fct_IDi.

Default = 1.0 (Real) 5

[1s]
Am Parameter A for martensite rate equation.

(Real)

 
Bm Parameter B for martensite rate equation.

(Real)

 
Cm Parameter C for martensite rate equation.

(Real)

 
Dm Parameter D for martensite rate equation.

(Real)

[1K]
Pm Parameter P for martensite rate equation.

(Real)

 
Qm Parameter Q for martensite rate equation.

(Real)

[K]
ε0 mart Parameter ε0 for martensite rate equation.

(Real)

 
VM0 Initial volume fraction VM0 for martensite rate equation.

(Real)

 
AHS Parameter AHS in Hansel hardening law.

(Real)

[Pa]
BHS Parameter BHS in Hansel hardening law.

(Real)

[Pa]
MHS Coefficient m in Hansel hardening law.

(Real)

 
NHS Exponent n in Hansel hardening law.

(Real)

 
EPS0HS Reference strain ε0 in Hansel hardening law.

(Real)

 
HMART Martensite ΔHγα coefficient in Hansel hardening law. [Pa]
K1 Temperature parameter K1 in Hansel hardening law.

(Real)

 
K2 Temperature parameter K2 in Hansel hardening law.

(Real)

 
T0 Initial temperature.

(Real)

[K]
Cp Specific heat per mass unit.

(Real)

[JkgK]
Eta Taylor-Quinney coefficient.

(Real)

 
CRCi Chaboche Rousselier kinematic parameter C i=1~4.

(Real) 3

 
CRAi Chaboche Rousselier kinematic parameter A i=1~4.

(Real) 3

[Pa]

Example 1 (with Barlat parameters input =0 and I=0)

Example 2 (with experiment data input I=1)

Example 3 (with Hansel yield model (=2) and kinematic hardening model (Chard=1))

Comments

  1. The yield function is expressed as:(1)
    f=ˉσσy
    (2)
    ˉσ= 121a(φ(X)+φ(X)) 1a
    (3)
    φ(X)=|X1X2|a 
    (4)
     φ(X)=|2X2+X1|a+|2X1+X2|a
    X' and X" denote the principal values of the tensors X' and X" which are a linear transformation of the stress deviator, which leads to:(5)
    φ(X)= [(XxxXyy)2+4(Xxy)2]a2 
    (6)
     φ(X)=[32(XxxXyy)+12(XxxXyy)2+4(Xxy)2]a+[32(XxxXyy)12(XxxXyy)2+4(Xxy)2]a

    The tensors X' and X" are linear transformations of the stress tensor:

    X=Lσ  and  X=Lσ (7)
    L=13[2α1α10α22α20003α7]
    (8)
    L=19[2α3+2α4+8α52α6α34α44α5+4α604α34α44α5+α62α3+8α4+2α52α60009α8]
  2. The yield stress could be defined either by tabulated input or using the analytic Swift-Voce model.
    • Iflag=0: Tabulated.
      • It is possible to add total strain rate dependency by defining a number Nrate of functions.
    • Iflag=1: The analytic Swift-Voce model is expressed as:(9)
      σy=αsv[A(ˉεp+ε0)n]+(1αsv)[K0+Q(1exp(Bˉεp))]
      Where,
      ˉεp
      Equivalent plastic strain.
    • Iflag=2: Hansel hardening model is considered.(10)
      σy={BHS(BHSAHS)e(m[ˉεp+ε0]n)}(K1K2T)+ΔHγαVm
      Temperature is updated in the law when adiabatic conditions:(11)
      ΔT=ηˉσdˉεpρCp
      The martensite rate equation is computed as follows:(12)
      Vmε={0ifε<ε0BAe(QT)(1VmVm)(B+1B)(Vm)p2(1tanh[C+DT])fεε0
  3. If Chard>0, a kinematic hardening model of Chaboche Rousselier is used:
    • The back stress is calculated as:(13)
      a=4i=1ai
      With,(14)
      ai=AiCidεpCiaiΔˉεp
    • The yield stress is computed as follows when combined isotropic kinematic hardening is chosen:(15)
      σy=(1Chard).σiso_hard+Chard.σkin_hard
  4. The strain rate filtering is available to smooth strain rates when tabulated input is chosen.
    List of Animation output (in /ANIM/SHELL/USRII/JJ):
    • USR 1= plastic strain
    • USR 2= effective stress
    • USR 3= increment of plastic strain
  5. When Iflag=1 (analytic Swift-Voce formulation is used) strain rates effect is taken into account using Cowper-Symonds expression:(16)
    σy=σy(1+(˙εc)1p)

    If VP=0: ˙ε is the total strain rate.

    If VP=1: ˙ε is the plastic strain rate.

    If c=0 or p=0, the strain rate effects are not taken into account.

  6. When Iflag=0 (tabulated formulation) then:

    If VP=0: ˙εi is the total strain rate.

    If VP =1: ˙εi is the plastic strain rate.

  7. Strain rate filtering:

    If VP=0 (dependency on strain rate), the default value of Fcut = 10KHz.

    If VP=1 (dependency on plastic strain rate), Fsmooth and Fcut are ignored.

  8. If Ifit=1, the coefficients αi will be automatically fit in the Radioss Starter. The tensile yield strengths σ00,σ45,σ90 and Lankford ratios r00,r45,r90 must be determined from uniaxial tension experiments along the rolling, diagonal and transverse directions at an amount of plastic work corresponding to a plastic strain equal to 0.2%. σb and rb should be determined from biaxial test, for the same amount of plastic strain.
1
Barlat F., Brem J.C., Yoon J.W, Chung K., Dick R.E., Lege D.J., Pourboghrat F., Choi, E. Chu S.-II, (2003), Plane stress yield function for aluminum alloy sheets part 1: Theory, International Journal of Plasticity, Volume 19, Issue 8, August, Pages 1215-1244.
2
J.L. Chaboche,G. Rousselier, (1983), On the Plastic and Viscoplastic Constitutive Equations-Part I: Rules Developed With Internal variable Concept, Journal of Pressure Vessel Technology, Volume 105, pages 153
3
A. H. C. Hänsel, P. Hora and J.Reissner, (1998), model for the kinetics of strain-induced martensitic phase transformation at nonisothermal conditions for the simulation of steel metal forming processes with metastable austenitic steels, Simulation of Materials Processing: Theory, methods, and Applications