what is Knn, Kss and Ktt in cohesive element?

[isyhadh]

do you have any idea on the meaning and explanation of Knn, Kss and Ktt for cohesive element?
how do we get the value of those values for CFRP?
can we get it from supplier?
is the cohesive value for matrix and fiber cohesive interaction the same with cohesive interaction between interplies in composite (between plies)?

many thanks
regards
isyhadh

 

[compositesFEAguru]

Hi Isyhadh,

do you have any idea on the meaning and explanation of Knn, Kss and Ktt for cohesive element?

The K values are the stiffness values for a Traction (Stress) - Separation curve. I.e., the traction required to separate two surfaces. The nn designates the normal (3) direction and the ss and tt designate the tangential directions in the 1 and 2 element coordinate directions respectively.

how do we get the value of those values for CFRP? can we get it from supplier?

No, these are not material inputs, these values are specific for the mesh density/thickness of the cohesive zone. The best way to determine these values from material data is to recreate a flatwise tension model (using the same thickness and mesh density as you will in your final model) to get normal properties and a lap shear model for shear properties.

is the cohesive value for matrix and fiber cohesive interaction the same with cohesive interaction between interplies in composite (between plies)?

No

Hope this helps


Firehole Composites

http://www.firehole.com