/MAT/LAW38 (VISC

Block Format Keyword

/MAT/LAW38 - Visco-Elastic Foam Tabulated Material

Description

This law describes the visco-elastic foam tabulated material and can only be used with solid elements.

Format

(1)	(2)	(3)	(4)	(5)	(7)	(8)	(9)	(10)
/MAT/LAW38/mat_ID/unit_ID or /MAT/VISC_TAB/mat_ID/unit_ID
mat_title

E0							Iflag	Itota
		H		RD	KR	KD
Kair	NP	FscaleP
P0		RP		Pmax
fct_IDul		Fscaleunload			a		b
Nfunct		CUToff		Iinsta
Efinal					Visc		Tol
Fscale1		Fscale2		Fscale3	Fscale4		Fscale5

fct_ID1L	fct_ID2L	fct_ID3L	fct_ID4L	fct_ID5L
fct_ID1ul	fct_ID2ul	fct_ID3ul	fct_ID4ul	fct_ID5ul

Field	Contents	SI Unit Example
mat_ID	Material identifier (Integer, maximum 10 digits)
unit_ID	Optional unit identifier (Integer, maximum 10 digits)
mat_title	Material title (Character, maximum 100 characters)
	Initial density (Real)
E0	Minimum tension modulus, used for interface and time step computation (Real)
	Maximum Poisson’s ratio in tension Default = 10-30 (Real)
	Maximum Poisson’s ratio in compression (Real)
	Exponent for Poisson’s ratio computation (Real)
Iflag	Analysis formulation type flag (Comment 4) (Integer) = 0: viscoelasticity is computed in each principal stress direction = 1: behavior is linear in both tension and compression
Itota	Incremental formulation flag Default = 0 (Integer) Total: 0 or 1 = 0: behavior in tension is linear = 1: behavior in tension is read from stress curves INCREMENTAL: 2 or 3 = 2: behavior in tension is linear = 3: behavior in tension is read from stress curves
	Relaxation rate for unloading Default = 10-30 (Real)
H	Hysteresis coefficient for unloading Default = 1.0 (Real)
RD	Damping factor on strain rate Default = 0.5 (Real)
KR	Recovery model flag for unloading (hysteresis loop) Default = 0 (Integer) = 0: No stress recovery on unloading (unloading curve=loading curve) = 1: Stress recovery on unloading is computed as: = 2: Stress recovery on unloading is computed as: Where, and are current internal energy and maximum internal energy, respectively. (Comment 6)
KD	Decay model flag, hysteresis type Default = 0 (Integer) = 0: Decay is active during loading and unloading = 1: Decay is only active during loading = 2: Decay is active during unloading
	Integration coefficient for instantaneous module update Default = 0.67 (Real)
Kair	Air content computation flag (Comment 7) Default = 0 (Integer) = 0: No confined air content = 1: Confined air content computation active = 2: Read hydrostatic curve (number defined by NP). The difference between pure compression and hydrostatic are taken into account.
NP	Pressure curve number (pressure vs. relative volume) (Integer)
FscaleP	Pressure curve scale factor (Real)
P0	Atmospheric pressure (Real)
RP	Relaxation rate of pressure Default = 10-30 (Real)
Pmax	Maximum air pressure Default = 1030 (Real)
	Porosity (density of foam/density of polymer) (Real)
fct_IDul	Unloading function identifier > 0: when unloading strain rate is equal to the static one, unloading will use only the function fct_IDul. (Integer)
Fscaleunload	Unloading function scale factor Default = 1.0 (Real)
	Unloading strain rate (must be greater than ) (Real)
a	Exponent for stress interpolation Default = 1.0 (Real)
b	Exponent for stress interpolation Default = 1.0 (Real)
Nfunct	Number of functions defining rate dependency (five or less) (Integer)
CUToff	Tension cutoff stress Default = 1030 (Real)
Iinsta	Material instability control flag Default = 0 (Integer) = 0: No material instability control = 1: Material instability control
Efinal	Maximum tension modulus Default = E0 (Real)
	Absolute value of strain at final modulus Default = 1.0 (Real)
	Modulus interpolation coefficient Default = 1.0 (Real)
Visc	Maximum viscosity (Comment 11) Default = 1030 (Real)
Tol	Tolerance on principal direction update Default = 1.0 (Real)
Fscalei	Scale factor for curve i (Real)
	Engineering strain rate for curve i (Real)
fct_IDiL	Loading function identifier for curve i (Integer)
fct_IDiul	Unloading function identifier for curve i (Integer)

#RADIOSS STARTER

#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|

/UNIT/1

unit for mat

Mg mm s

#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|

#- 2. MATERIALS:

#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|

/MAT/VISC_TAB/1/1

Foam

# RHO_I

2E-10

# E_0 NU_t NU_c R_V Iflag Itota

200 0 0 0 0 0

# Beta H R_D K_R K_D Teta

0 0 0 0 0 0

# K_air Np Fscale_P

0 0 1

# P0 Rp Pmax Phi

0 0 0 0

# fctID_ul Fscale_ul Eps_._ul a b

0 0 0 0 0

# N_funct CUT_off I_insta

1 0 0

# E_final Eps_final Lambda Visc Tol

0 0 0 0 0

# Fscale_i

# Eps_._i

# fct_ID_il

# fct_ID_iul

#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|

#- 3. FUNCTIONS:

#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|

/FUNCT/4

function_4

# X Y

-1 -200

1 200

#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|

#ENDDATA

/END

#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|

1.	Nominal stresses are computed by interpolation from input functions:

for given , read two values of function at for the two immediately lower and higher strain rates.

The example below is for two strain rate curves (up to five may be input).

starter_mat_plas_tab2

with

Where, , , and input are positive in compression.

The parameters a and b define the shape of the interpolation function within each interval. If a = b = 1, the interpolation is linear.

The curves are always nominal stresses versus engineering strains.

2.	The strain is negative in compression. The tensile stress can either be negative or positive. The absolute stress value is used in the material law.

3.	A “coupled” set of principal nominal stresses is computed with anisotropic Poisson’s ratios:

in tension ()

in compression.

Where,

4.	Analysis formulation type Iflag.

Iflag = 0: corresponds to the visco-elastic foam tabulated material (visco-elasticity is computed in each principal stress direction).

Iflag = 1: behavior will be linear in both tension and compression, following Hook’s relations.

For compression, Young Modulus E0 and Poisson’s ratio are used.

Whereas, in tension the instantaneous Young modulus ratio Et is used. The other data is ignored (especially, no viscous effect can be expected).

5.	For stability, is filtered using:

6.	Hysteresis is applied in linear tension case.

If KR = 1, Hysteresis is only applied in compression.

If KR =2, Hysteresis is applied both in compression and in tension.

Hysteresis is applied in linear tension case.

7.	For air pressure Pair (when Kair = 1)

If Np ≠ 0:

where f refers to function number Np.

If Np = 0:

Relaxation is applied as .

Where, RP is the relaxation rate of pressure and t is the time.

8.	When unloading, if the unloading curve is not defined (fct_IDul = 0), is computed from curve one.

starter_mat_visc_tab

If the unloading curve is defined, is interpolated between curve one and curve fct_IDul. In this case, curve 1 must correspond to a quasi-static state.

9.	If fct_IDiul = 0, fct_ID1L, unloading is used instead.

Unloading functions fct_IDiul (Line 12) are used only if the unloading curve fct_IDul is not defined.

10.	The instantaneous modulus is updated using:

with

Where, E0 is the minimum tension modulus, Efinal is the maximum tension modulus and VR is the relative volume computed in RADIOSS, and is the absolute value of the strain corresponding to the maximum compression modulus.

The instantaneous modulus is only used for tension.

11.	If Visc is input, interpolated stress will be limited by this value to have a larger timestep:

12.	The behavior is strain rate independent when .

/MAT/LAW38 (VISC_TAB)

/MAT/LAW38 (VISC_TAB)

/MAT/LAW38 (VISC_TAB)

Format

See Also: