Urgent help - Contact modelling in Abaqus

Dear all
I urgently need the answer to my question. I am modelling a clapping or contact between two surfaces similar to a crack.
I have used abaqus : 1-tangential : frictionless  2-Hard contact
I wanna know what moelling approach does abaqus use for above situation ?
Does abaqsu use hertzian contac ? bilinear stiffness or what ?
Thank you