Pressure-Overclosure relations

Hello,

I am using Abaqus for nonlinear FEA of contact between material1 (soft foam like) and material2 (hard plastic type) in vertebrae for my thesis. I have encountered many problems during this exercise, because I have to include the results of various contact conditions in this situation with friction. I am trying to get results for 

•  Hard contact (using penalty constraint enforcement)
•  Soft contact (using linear and exponential Pressure-Overclosure relations)

The major problem is convergence during both analyses.