# /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/XFEM_TBUTC/mat_ID/unit_ID
$\gamma$ K $\sigma$ r Ifail_sh Iduct
a b

## 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)

$\gamma$ Exponent

(Real)

K Critical damage integral

Default = 1030 (Real)

$\sigma$ r Fracture stress

Default = 1030 (Real)

$\left[\text{Pa}\right]$
Ifail_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)

Iduct 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)

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:(1)
$\text{D}=\underset{0}{\overset{\text{t}}{\int }}{\text{(}\sigma -{\sigma }_{r}\text{)}}^{\lambda }\text{dt}$
Where,
$\sigma$ r
Fracture stress
$\sigma$
Maximum principal stress
$\lambda$
Material constant
t
Time when shell cracks for initiation of a new crack within the structure
D
Damage integral, another material constant
3. For brittle materials, the damage parameter is:
(2)
$\stackrel{˙}{D}=\frac{1}{K}{\left(\sigma -{\sigma }_{r}\right)}^{a}$
(3)
${\sigma }_{r}={\sigma }_{0}{\left(1-D\right)}^{b}$
(4)
$D=D+\stackrel{˙}{D}\text{Δ}t$
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).