Contact stresses two sphere's in contact same material and different spherical radius.
When a sphere is in contact with anoterh sphere, a small radial contact area is formed, the size of the area depending on the load and materials.
E = Young’s modulus
F = load
r1, r2 =radii
v = Poisson’s ratio
Contact area radius
Mechanical Engineers Data Hanbook, James Carvill 1993 Page 51