/MAT/LAW4 (HYD_JCOOK)

Block Format Keyword This law represents an isotropic elasto-plastic material using the Johnson-Cook material model. This model expresses material stress as a function of strain, strain rate and temperature.

This material may account for the nonlinear dependence between pressure and volumetric strain when corresponding equation of state is specified. A built-in failure criterion based on the maximum plastic strain is available. This material law is compatible with solid elements only.

Format

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
/MAT/LAW4/mat_ID/unit_ID or /MAT/HYD_JCOOK/mat_ID/unit_ID
mat_title
ρi ρ0
E ν
a b n εpmax σmax
Pmin
c ε˙0 m Tmelt Tmax
ρ0Cp Tr

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]
ρ0 Reference density used in E.O.S (equation of state).

Default = ρ0=ρi (Real)

[kgm3]
E Young's modulus.

(Real)

[Pa]
ν Poisson's ratio.

(Real)

a Yield stress.

(Real)

[Pa]
b Plastic hardening parameter.

(Real)

[Pa]
n Plastic hardening exponent.

Default = 1.0 (Real)

εpmax Failure plastic strain.

Default = 1030 (Real)

σmax Maximum stress.

Default = 1030 (Real)

[Pa]
Pmin Pressure cutoff ( < 0 ).

Default = -1030 (Real)

[Pa]
c Strain rate coefficient.
= 0
No strain rate effect.

Default = 0.00 (Real)

ε˙0 Reference strain rate.

If ε˙ε˙0 , no strain rate effect.

(Real)

[1s]
m Temperature exponent.

Default = 1.00 (Real)

Tmelt Melting temperature.
= 0
No temperature affect.

Default = 1030 (Real)

[K]
Tmax For T > Tmax: m = 1 is used.

Default = 1030 (Real)

[K]
ρ0Cp Specific heat per unit volume.

(Real)

[Jm3K]
Tr Reference temperature.

Default = 300K (Real)

[K]

Example (Aluminum)

Comments

  1. In this model, the material behaves as a linear-elastic material when the equivalent stress is lower than the plastic yield stress. For higher stress values, the material behavior is plastic and the stress is calculated as:
    σ=(a+bεpn)(1+clnε˙ε˙0)(1(T)m)

    Where,

    T*=T-TrTmelt-Tr

    Where,
    εp
    Plastic strain
    ε˙
    Strain rate
    T MathType@MTEF@5@5@+=feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamivaaaa@36CC@
    Temperature
    Tr
    Reference temperature
    Tmelt
    Melting temperature

    When /HEAT/MAT (with Iform = 1) references this material model, the values of Tr and Tmelt defined in this card will be overwritten by the corresponding T0 and Tmelt defined in /HEAT/MAT.

    When the temperature is not initialized using /HEAT/MAT or /INITEMP, the reference temperature (Tr) is also the initial temperature.

    clip0067
    Figure 1.
  2. The plastic yield stress should always be greater than zero. To model pure elastic behavior, the plastic yield stress will be set to 1030.
  3. When εp reaches the value of εpmax (for tension, compression or shear), in one integration point, the deviatoric stress of the corresponding integration point is permanently set to 0, however, the solid element is not deleted.
  4. The plastic hardening exponent, n, must be less than or equal to 1.
  5. To eliminate the effect of the strain rate, either set the value of c equal to 0 or set the reference strain rate ( ε˙0 ) equal to 1030. There is no effect of strain rate when ε˙ is less than ε˙0 .
  6. By default, the hydrostatic pressure is linearly proportional to volumetric strain:
    P=Kμ

    Where, K=E3(12ν) is the bulk modulus and μ=ρρ01 MathType@MTEF@5@5@+=feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbbG8FasPYRqj0=yi0dXdbba9pGe9xq=JbbG8A8frFve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaacqaH8oqBcqGH9aqpdaWcaaqaaiabeg8aYbqaaiabeg8aYnaaBaaaleaacaaIWaaabeaaaaGccqGHsislcaaIXaaaaa@3F42@ is the volumetric strain.

    An additional Equation of State (/EOS) card can refer to this material in order to incorporate a nonlinear dependency between hydrostatic pressure and volumetric strain.