/MAT/LAW65 (ELASTOMER)

Block Format Keyword

/MAT/LAW65 - Elastomer Material

Description

This law describes non-linear elastoplastic material with strain rate dependent loading and unloading behavior.

Format

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
/MAT/LAW65/mat_ID/unit_ID or /MAT/ELASTOMER/mat_ID/unit_ID
mat_title

E
Nrate	Fsmooth	Fcut

Nrate times

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
fct_IDld	fct_IDul	Fscalestress

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)
E	Young’s modulus (Real)
	Poisson’s ratio (Real)
	Failure plastic strain (Real)
Nrate	Number of loading/unloading function pair Default = 50 (Integer)
Fsmooth	Smooth strain rate flag (Integer) = 0: no strain rate filtering (default) = 1: strain rate filtering
Fcut	Cutoff frequency for strain rate filtering Default = 1030 (Real)
fct_IDld	True stress-true strain function identifier for loading (Integer)
fct_IDul	True stress-true strain function identifier for unloading (Integer)
Fscalestress	Stress scale factor Default = 1.0 (Real)
	Strain rate Default = 1.0 (Real)

#RADIOSS STARTER

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/UNIT/1

unit for mat

kg mm ms

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#- 2. MATERIALS:

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/MAT/LAW65/1/1

nitinol-like material

# RHO_I

6E-6

# E0 NU EPS_max

50 .3 0

# Nrate Fsmooth Fcut

1 1 0

# fct_IDld fct_IDul Fscale_stress EPS_rate

3 4 1 0

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#- 3. FUNCTIONS:

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/FUNCT/3

Loading_stress_strain

# X Y

0 0

.0085 .35

.0575 .55

.077 1.262

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

/FUNCT/4

Unloading_stress_strain

# X Y

0 0

.0055 .199

.0502 .25

.077 1.245

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#ENDDATA

/END

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1.	The law is defined by pairs of true stress-true strain functions for loading and unloading at specified strain rates. Each of the curves should begin with point (0,0) and increase monotonically. Each unloading curve should lie below the loading curve for corresponding strain rate.

The loading/unloading curve with the higher strain rate (

) should lie above the curve with lower strain rate (

). The curves between

and

are interpolated linearly for intermediate strain rates. Curves are extrapolated for strain rates higher than maximum specified strain rate. It is advised to duplicate the last curves twice to avoid instability for high strain rates.

3.	Yield stress is determined at the intersection point between loading and unloading curves.

If the load is removed prior to the intersection point between loading and unloading curves, the unloading follows the hyperelastic path with hysteresis (Fig. 1). This path is calculated based on the value of Young's modulus, E until it intersects with the unloading curve. Thereafter it follows the unloading curve back to its initial state (0,0).

If the load is removed after intersection point between loading and unloading curves, the unloading curve is shifted by the value of plastic strain (Fig. 2).

5.	The Young's modulus must be greater than the maximum slope of all stress-strain curves. As mentioned before, Young's modulus is used to determine the unloading path between loading and unloading curves.

6.	When reaches in one integration point, then based on the element type:

•	Shell elements: The corresponding shell element is deleted.

•	Solid elements: The deviatoric stress of the corresponding integral point is permanently set to 0, however, the solid element is not deleted.

mat_law65_strain-stress

Fig 1: Loading and unloading function sets for constant strain rates. Hyperelastic loading/unloading.

mat_law65_plasticstrain

Fig 2: For plastic case the unloading curve is shifted by the value of the actual plastic strain.