fracturing

I'm modeling rock fracture problem with cohesive element. I konw the propertiey of the solid element around the fracture because we can measure it (rock sample) in the lab. but as regard to how to define the propeties of cohesive element, I'm completely lost.



in fact, the cohseive element is a fictitious one, not a real matearial in the physical world, we can't mearsure its propety by physical means. then how can we know what parameters we should enter ?



need your help, thanks