Sorry it took so long on this. I apparently forgot how to read.
According to the bible, Roark's, for a ball and socket:
The max compressive stress is:
[tex]\sigma_c = .918\left[ \sqrt[3]{\frac{P}{K_D^2 C_E^2}}\right][/tex]
Where:
[tex]P[/tex]=the compressive load applied
[tex]K_D[/tex]= Load condition factor = [tex]\frac{D_1D_2}{D_1-D_2}[/tex]
[tex]D_1[/tex]= Diameter of the socket
[tex]D_2[/tex]= Diameter of the ball
[tex]C_E[/tex]= [tex]\left[\frac{1-\nu_1^2}{E_1}\right]+\left[\frac{1-\nu_2^2}{E_2}\right][/tex]
[tex]E, \nu[/tex] = Modulus of elasticity and Poisson's Ratio
Also, don't forget that the maximums for Hertzian stresses do not occur at the surface of the bodies.