/FAIL/TSAIHILL
Block Format Keyword Tsai-Hill failure criterion for composite materials failure modeling. This criterion is available for solids and shells.
Format
(1) | (2) | (3) | (4) | (5) | (6) | (7) | (8) | (9) | (10) |
---|---|---|---|---|---|---|---|---|---|
/FAIL/TSAIHILL/mat_ID/unit_ID | |||||||||
Ifail_sh | Ifail_so | ||||||||
Fcut |
(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 | (Optional) Unit
identifier. (Integer, maximum 10 digits) |
|
Longitudinal critical
strength. Default = 1020 (Real) |
||
Transverse critical
strength. Default = 1020 (Real) |
||
Shear critical strength. Default = 1020 (Real) |
||
Ifail_sh | Shell failure model flag.
(Integer) |
|
Ifail_so | Solid failure model flag.
(Integer) |
|
Dynamic time relaxation. 5 Default = 1020 (Real) |
||
Fcut | Stress tensor filtering
frequency. Default = 0.0 (Real) |
|
fail_ID | (Optional) Failure criteria
identifier. 4 (Integer, maximum 10 digits) |
Example
/UNIT/1
Mg mm s
/FAIL/TSAIHILL/1/1
# X11 X22 S12 IFAIL_SH IFAIL_SO
520. 316. 407.5 1 1
# TAU_MAX FCUT
1.0E-4 100.0
Comments
- This failure model is
available for shells and solids. It considers a composite material ply with
the fibers oriented in the direction 1 (also denoted m1) and the matrix
oriented in transverse direction, that is, in directions 2 (and 3 for
solids). Each direction considers a critical strength value valid for both
tension and compression.
Where, , , are respectively the critical strength in direction 1, critical strength in direction 2 and in shear.
- The failure criterion
for shells is written as:
(1) For solids the criterion becomes:(2) The criterion is considered to be reached when . In fact, the damage variable corresponds to the criterion itself .
- Once the criterion is
reached
, two behaviors can be set up:
- If Ifail_sh = 0 or Ifail_so = 0, there is no stress softening and elements are never deleted. In this case, the failure criterion is purely visual using the output of the damage variable.
- If Ifail_sh ≠
0 or
Ifail_so ≠
0, a stress relaxation is generated to decrease
the load carrying capacity of the element.
(3) With and .
Where,- Time.
- Start time of relaxation when the damage criteria is assumed.
- Time of dynamic relaxation.
- Stress tensor when the criterion is reached.
When the stresses reach 1% of the stress value at the beginning of the failure, the element is deleted. This is necessary to avoid instabilities coming from a sudden deletion of an element and a failure “chain reaction” in the neighboring elements. Even if the failure criterion is reached, there will be no element deletion with the default value of . Therefore, it is recommended to define a value for 10 times larger than the simulation time step.
- To avoid “chain
reaction” when deleting elements, you can also define a stress tensor
filtering frequency Fcut. Thus, the stress tensor used to calculate the TSAIHILL criterion is
first be filtered according to:
(4) With
Where, is the current timestep.
If a filtering frequency is not defined (Fcut= 0.0), the filtering effect is deactivated.
- 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).