Need some information on cohesion model

Dear All,

I have two doubts about cohesion model sjkr.

1) In the cohesion model, what is the reference for cohesion energy density values? How do we select the values
for cohesion energy densities? Can we calculate it, if we know the properties of liquid and solid?

2) Cohesion model uses JKR model, and it adds only an additional normal force. What about tangential force?

Any help will be much appreciated.

Thanks,
Narendra