Tabular Damage Evolution Softening Curve (Trapezoidal cohesive law)
Tabular Damage Evolution Softening Curve (Trapezoidal cohesive law)
(OP)
I am running a model simulating composite delamination using a cohesive interface. The model delaminates correctly using energy based damage evolution, however when I try to use displacement based, tabular data to define the softening curve, it does not delaminate. I am trying to implement a trapezoidal cohesive law. I have defined the tabular displacement by equating the area under the softening curve to the Fracture toughness (1.0755 N/mm) and am using MPa and mm.
Does anyone know why this is not delaminating? Or have experience implementing a trapezoidal cohesive law?
Thanks
** MATERIALS
**
*Material, name="Material 1"
*Elastic, type=ENGINEERING CONSTANTS
159000.,8490.,8490., 0.32, 0.32, 0.32,4610.,2780.
2780.,
**
** INTERACTION PROPERTIES
**
*Surface Interaction, name=Bonding
1.,
*Cohesive Behavior
3.52e+06, 2.78e+06, 2.78e+06
*Damage Initiation, criterion=MAXS
10000., 128.5,10000.
*Damage Evolution, type=DISPLACEMENT, softening=TABULAR
0., 0.
0.989, 0.0042
1., 0.0125
*Damage Stabilization
1e-05
Does anyone know why this is not delaminating? Or have experience implementing a trapezoidal cohesive law?
Thanks
** MATERIALS
**
*Material, name="Material 1"
*Elastic, type=ENGINEERING CONSTANTS
159000.,8490.,8490., 0.32, 0.32, 0.32,4610.,2780.
2780.,
**
** INTERACTION PROPERTIES
**
*Surface Interaction, name=Bonding
1.,
*Cohesive Behavior
3.52e+06, 2.78e+06, 2.78e+06
*Damage Initiation, criterion=MAXS
10000., 128.5,10000.
*Damage Evolution, type=DISPLACEMENT, softening=TABULAR
0., 0.
0.989, 0.0042
1., 0.0125
*Damage Stabilization
1e-05





RE: Tabular Damage Evolution Softening Curve (Trapezoidal cohesive law)
I have been having the same problem, as my tabular cohesive law is also not breaking. The documentation on tabular cohesive laws is very poor. This is what I have understood and applied:
- The damage variable is defined as 1-K/K0, with K0 the stiffness at initiation and the K the stiffness at other points in the diagram.
- The total/plastic displacement is the crack opening displacement (COD) minus the COD at initiation.
Using that interpretation however does not work at all. My cohesive simply does not break for some unknown reason. The traction keeps on increasing.
I have created a two-element model to test a lot of different parameters real quickly, but nothing that I have tried works...
Anyone else have any clue what could be causing this?
Comp
RE: Tabular Damage Evolution Softening Curve (Trapezoidal cohesive law)
I hope this helps!
Comp
RE: Tabular Damage Evolution Softening Curve (Trapezoidal cohesive law)
Thanks for the advice! By using 10,000 data points it finally decohered.
A further complication came up. I tried to replicate the linear, energy based option using tabular, but this gives a slightly different force delta response. Using the tabular damage evolution it fails earlier than the energy based method.
The logic I was using was
For Gc=1.0755 N/mm
K=1000000
max traction=128.5mpa
therefore onset of damage occurs at 0.000128mm (maxtraction/K)
delta critical occurs at 0.0167mm (2*Gc/maxtraction)
Input into the tabular table (10,000 points):
- interpolation of D from 0 to 1 (1-k/ko)
- interpolation of delta minus delta onset from 0 to 0.01661 (delta critical-delta onset)
I've attached the excel with my working
Have you managed to replicate the results between energy and displacement? Do you have any ideas?
Thanks
Sandy