/FAIL/XFEM_TBUTC (Obsolete)

Block Format Keyword Describes a XFEM (eXtended Finite Element Method) failure model.

Format

(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`	Unit Identifier (Integer, maximum 10 digits)
$γ$	Exponent (Real)
`K`	Critical damage integral Default = 10³⁰ (Real)
$σ$ _r	Fracture stress Default = 10³⁰ (Real)	$[Pa]$
`I`_{fail_sh}	Shell failure flag = 1 (Default) 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. (Integer)
`I`_duct	Ductile-brittle materials flag = 1 (Default) If a ductile material is used = 2 If a brittle material is used (Integer)
`a`	Material parameter (exponent) (Real)
`b`	Material parameter (exponent) (Real)
`fail_ID`	(Optional) Failure criteria identifier 5 (Integer, maximum 10 digits)

This failure model is available for Shell only.
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 (I_duct = 1 or 2).
For ductile materials, the cumulative damage parameter is:(1)
$D = \int_{0}^{t} {(σ - σ_{r})}^{λ} dt$

Where,

$σ$ _r

Fracture stress

$σ$

Maximum principal stress

$λ$

Material constant

t

Time when shell cracks for initiation of a new crack within the structure

D

Damage integral, another material constant
For brittle materials, the damage parameter is:
(2)
$\dot{D} = \frac{1}{K} {(σ - σ_{r})}^{a}$
(3)
$σ_{r} = σ_{0} {(1 - D)}^{b}$
(4)
$D = D + \dot{D} Δ t$
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.
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).