Dear all,
How do you think collision between 2 porous sphere different from a collision between two solid spheres?

Hertz came up with a model for collision between 2 solid elastic spheres and a profile for deformation along the contact surface. Now if we have 2 porous elastic spheres colliding with how can this be visualized??

Any idea for developing a model is welcome!!

Or if you know if someone has already done this literature pls let me know!!