Block Format Keyword
/FAIL/XFEM_TBUTC - Failure Model for XFEM Crack Initialization (Modified Tuler-Butcher failure)
Description
Describes a XFEM (eXtended Finite Element Method) failure model.
Format
(1)
|
(2)
|
(3)
|
(4)
|
(5)
|
(6)
|
(7)
|
(8)
|
(9)
|
(10)
|
/FAIL/XFEM_TBUTC/mat_ID/unit_ID
|
|
K
|
|
Ifail_sh
|
Iduct
|
|
|
a
|
b
|
|
|
|
|
|
|
Optional line:
(1)
|
(2)
|
(3)
|
(4)
|
(5)
|
(6)
|
(7)
|
(8)
|
(9)
|
(10)
|
fail_ID
|
|
|
|
|
|
Field
|
Contents
|
SI Unit Example
|
mat_ID
|
Material identifier
(Integer, maximum 10 digits)
|
|
unit_ID
|
Optional unit identifier
(Integer, maximum 10 digits)
|
|
|
Exponent
(Real)
|
|
K
|
Critical damage integral
Default = 1030 (Real)
|
|
|
Fracture stress
Default = 1030 (Real)
|
|
Ifail_sh
|
Shell failure flag
Default = 1 (Integer)
= 1: Shell is cracked (not deleted), if D > K for one integration point.
= 2: For each integration point, the stress tensor is set to zero, if D > K; and shell is cracked (not deleted), if D > K for all integration points.
|
|
Iduct
|
Ductile-brittle materials flag
Default = 1 (Integer)
= 1: if a ductile material is used
= 2: if a brittle material is used
|
|
a
|
Material parameter (exponent)
(Real)
|
|
b
|
Material parameter (exponent)
(Real)
|
|
fail_ID
|
(Optional) Failure criteria identifier (see Comment 5)
(Integer, maximum 10 digits)
|
|
|
| 1. | This failure model is available for Shell only. |
| 2. | An element fails once the Tuler-Butcher cumulative damage parameter is greater than the stated critical damage value, K. The damage parameter accumulation is calculated differently for ductile and brittle materials (Iduct = 1 or 2). |
For ductile materials, the cumulative damage parameter is:
where,
 is the fracture stress
 is the maximum principal stress
is the material constant
t is the time when shell cracks for initiation of a new crack within the structure
D is damage integral, another material constant
| 3. | For brittle materials, the damage parameter is: |
| 4. | Current known limitations are: |
| • | /PARITH/ON does not ensure results repeatability, if SPMD > 1; it works in SMP parallel mode only. |
| • | XFEM is currently NOT compatible with either /ANIM/VECT or with /PARITH/OFF. |
| 5. | 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). |
|
