Dear all,
I am modelling bonded interfaces using cohesive element and trying to define the values of Nominal Stress(Normal-only Mode), Nominal Stress(First Direction) and Nominal Stress(Second Direction) for "Damage for traction separation laws"(Maxs Damage) and define.
My question is that how might I determine the values of these terms, i.e. Nominal Stress (Normal-only Mode), Nominal Stress (First Direction) and Nominal Stress (Second Direction).
Can someone please let me know on how to calculate these terms or any other information that relate to finding or working of such terms.
Many thanks in advance for any kind help
Dear Omid,
One way to get you further is to contact the authors here on RG who wrote the papers, they might help you:
Article Mode I fracture in adhesively-bonded joints: A mesh-size ind...
Article Prediction on Nominal Stress-Strain Curve of Anisotropic Pol...
Dear Omid,
One way to get you further is to contact the authors here on RG who wrote the papers, they might help you:
Article Cohesive traction–separation laws for tearing of ductile metal plates
Article Mode I fracture in adhesively-bonded joints: A mesh-size ind...
Article Prediction on Nominal Stress-Strain Curve of Anisotropic Pol...
Hi , late reply but might help someone.
When you are asking for the value of the nominal stresses, I believe you are asking for N max, S max and T max which are the nominal stresses in the normal mode and the two shear modes. It is quite easy.
The biggest consideration in the Traction separation law for Cohesive elements is the Fracture Energy. Fracture Energy (Gc) is the area under the Traction - Separation Triangle. There are two parts in this triangle. The part till Failure Initiation and the part post initiation (till failure).
Let me assume a linear initiation and post initiation part which will give rise to an equilateral triangle. Then area of this triangle = 0.5 * Final separation displacement ( 𝛿 failure) * N max. Again, this 𝛿 failure = Penalty factor * Characteristic Length of the cohesive element.
The length of the cohesive element is based upon the length of the other structural elements in the model. If you have a structural length = 1mm, then the Cohesive element mesh size = 0.2mm (Over meshing factor = 5). Refer Diehl et al paper. Structural mesh size is based upon mesh convergence. So, now you have your cohesive mesh size from your structural mesh size, choose a proper penalty factor from literature and you can arrive at 𝛿 failure.
With this 𝛿 failure, and by determining the fracture energy from experiments (Gic. Giic and Giiic ), you should be able to arrive at N max from area of triangle formula. Do this for the two shear modes too.
The slope of the line from origin to failure initiation is Knn, Kss and Ktt for the normal and the two shear modes respectively. The initiation is controlled by QUADSCRT Criterion.
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