/FAIL/NXT

Block Format Keyword Describes the forming limit based on stresses. This failure model is available for Shell only.

Format

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
/FAIL/NXT/`mat_ID`/`unit_ID`
`fct_ID`₁	`fct_ID`₂	`Ifail_sh`

Optional Line

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
`fail_ID`

Definition

Field	Contents	SI Unit Example
`mat_ID`	Material identifier. (Integer, maximum 10 digits)
`unit_ID`	Unit Identifier. (Integer, maximum 10 digits)
`fct_ID`₁	Function identifier of lower limit for fracture (S-R mode). (Integer)
`fct_ID`₂	Function identifier of upper limit for fracture (3D mode). (Integer)
`Ifail_sh`	Shell failure flag. = 0 (Default) Shell is not deleted. = 1 Shell is deleted, if there is one layer in failure zone. = 2 Shell is deleted, only if all layers are in the failure zone. (Integer)
`fail_ID`	Failure criteria identifier. 5 (Integer, maximum 10 digits)

Example (Steel)

In this example material LAW32 with /FAIL/NXT is used. The curve of upper limit for fracture (3D mode) is scaled with /MOVE_FUNCT.

#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/HILL/1/1
void_steel
#              RHO_I
              7.8E-9
#                  E                  NU
              210000                  .3
#                  A           EPSILON_0                   n             EPS_max           SIGMA_max
                 582               0.009                .258                   0                   0
#          EPS_DOT_0                   m
                   0                   0
#                r00                 r45                 r90                       Iyield0
                 1.0                 1.0                 1.0                             0
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/FAIL/NXT/1/1
#  fct_ID1   fct_ID2  Ifail_sh
       100       101         1
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/FUNCT/100
SR-mode
#                  X                   Y
                -1.2                 1.2
                  -1                 1.3
                -0.8                1.36
                -0.6                1.42
                -0.4                1.47
                 0.2                 1.5
                 0.4                1.45
                 0.6                1.33
                   1                 1.5
                 1.5                1.85
                   2                2.25
                 2.5                2.55				 
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/FUNCT/101
3D-mode
#                  X                   Y
                -1.3                1.35
                -1.1                 1.6
                -0.9                 1.9
                -0.7                 2.2
                -0.5                2.55
                -0.3                2.85
                -0.1                3.15
                   0                 3.2
                 0.3                3.15
                 0.7                2.95
                 1.1                 2.7
                 1.3                2.65
                 1.5                 2.7
                 1.9                 2.8
                 2.3                2.95
                 2.7                 3.1
                 3.1                 3.2
/MOVE_FUNCT/101
scale for 3D-mode   
#            Ascalex             Fscaley             Ashiftx             Fshifty                                                              
                   0                 2.0                   0                   0			 
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
#ENDDATA
/END
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|

Comments

A method to predict the fracture limit during a metal forming process based on the localized bifurcation theory and the instability theory for elastoplastic material.
The forming limit diagram as presented in Figure 1 is represented in the $σ / h$ plane where, $σ$ is the stress and h is the current work-hardening modulus. The limit curves, SR and 3D represent the Stӧren-Rice's mode (S-R) limit and the 3-dimensional localized mode limit respectively. The SR limit can be regarded as the lower limit and the 3D limit and the upper limit for fracture. The fracture should occur when the stress level reaches the 3D limit.

Figure 1.
To determine the failure zone, an instability factor is defined as:(1)
$λ_{f} = \frac{σ / h - {(σ / h)}_{S R}}{{(σ / h)}_{3 D} - {(σ / h)}_{S R}} + 1$

According to the value of $λ_{f}$ , the status for fracture is:

Free: if $0 < λ_{f} < 1$

Warning: if $1 < λ_{f} < 2$

Danger: if $λ_{f} > 2$ . In this case, the element failed. In this case, $λ_{f}$ is set equal to 2.
When this failure model is defined, it automatically generates animation files containing three new outputs which are the instability fracture $λ_{f}$ (NXT failure factor), $σ_{1} / h$ (SIGMA1/h), and $σ_{2} / h$ (SIGMA2/h).
Where, $σ_{1}$ and $σ_{2}$ are the two current principal stresses.
The fail_ID is used with /STATE/BRICK/FAIL and /INIBRI/FAIL. There is no default value. If the line is blank, no value will be output for failure model variables in the /INIBRI/FAIL (written in .sta file with /STATE/BRICK/FAIL option).
Available laws with this criterion are LAW2, LAW32, LAW36, LAW43, LAW73, and LAW78.