Hello,
I'm needing to model an interference fit in an assembly and have created a test case of a plain collar on a shaft. I have modelled the shaft OD and the collar ID at the same nominal diameter (28.0mm); I prefer this to creating the mesh with the shaft OD greater than the collar ID, as the interference can be adjusted. 
I have created the surface based contact in the Scenario and attributed a Contact Interference to it. No matter whether I enter the 0.052mm interference that I have specified or increase to a huge 1.0mm, I don't achieve the hoop stress levels that I am expecting, it is <1 MPa, as if the size for size (28 OD, 28 ID) is being solved. The *CONTACT INTERFERENCE keyword is produced in the Abaqus .inp file.
Is there a particular combination of contact and interference input that is required for the interference to work?