The fractal damaged pattern is based on the “random walk” approach proposed by Stefan
Kolling.
Format
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/FAIL/FRACTAL_DAMAGE/mat_ID/unit_ID
Grsh4_1
Grsh3_1
Grsh4_2
Grsh3_2
Damage
Probability
Seed
Nb_walk
Iprint
Optional line:
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fail_ID
Definition
Field
Contents
SI Unit Example
mat_ID
Material identifier.
(Integer,
maximum 10 digits)
unit_ID
(Optional) Unit
identifier.
(Integer, maximum 10 digits)
Grsh4_1
4 node shell element group ID
defining starting elements for “random walkers”. 2
(Integer)
Grsh3_1
3 node shell element group ID
defining starting elements for “random walkers”. 2
(Integer)
Grsh4_2
4 node shell element group ID
defining target elements for “random walkers”. 3
(Integer)
Grsh3_2
3 node shell element group ID
defining target elements for “random walkers”. 3
(Integer)
Damage
Initial damage value (0.0 ≤
Damage ≤ 1.0). Value of 1.0 leads to
deletion of the elements at time zero.
Default = 1.0
(Real)
Probability
Probability of damage
agglomeration. If “random walker” is placed in the neighborhood
of a target element, the current element may also become damaged
with defined probability.
Default = 1.0 (Real)
Seed
Initialization of Random Number
generator.
Default = 0.0 (Real)
Nb_walk
Number of released “random
walkers”.
(integer)
Iprint
Flag to activate print out of each
walker path from starting element until it dies or damage of the
next element.
Default = 0 (Integer)
fail_ID
(Optional) Failure criteria identifier.
(Integer, maximum 10
digits)
Example
Example without starting element groups and only one element in the target element
groups (in the center of the part).
All starting and
target element groups must belong to the /PART defined with the
same mat_ID as the failure model. Usually, start elements are chosen close to part
edges (as in, in windshield) and target elements closer to the center, but
it is not a strict rule. Target elements are those which are already
initially damaged, and the other elements will progressively agglomerate
around them, creating final damage patterns.
If both starting
element groups ID (Grsh4_1, Grsh3_1)
are not defined, a random element from the part will be chosen as starting
point for each consecutive “random walker”.
If both target
element groups ID (Grsh4_2, Grsh3_2)
are not defined, one single random element from the part will be chosen as
initially damaged target.
The number of “random walkers” should be much higher than the number
of starting and target elements.
Each “walker” will begin its path at the random element from the
starting element group. It will change direction at each next element and
may end its “walk” either at the domain border or in the neighborhood of an
already damaged element. In the first case it “dies” with no other effect;
otherwise, there is a probability that the current element will
“agglomerate” to the damaged group. Figure 2. Example of random path from starting element to
target
The final fractal-like damage pattern depends on the number of
“walkers” and on damage agglomeration probability. The small probability
values result on compact patterns, the high probabilities give high spread
fractals. Figure 3. Example
/FAIL/FRACTAL_DAMAGE only initializes element
damage in Radioss Starter. It is not able to
simulate further damage evolution under external loading in Engine. Other
compatible failure models should be applied in parallel to the same mat_ID. Fractal damage initialization is only compatible with /FAIL/BIQUAD, /FAIL/TAB2 and /FAIL/ALTER.Figure 4. Example of results obtained with simulation of impact on
windshield using /FAIL/ALTER
The Iprint flag allows to print in the standard
output file the complete path of each walker from starting element to the
end, either terminating on the domain border, or agglomerating a new damaged
element.
