Elastic Contact Stress Formulae
Consider two bodies in contact identified with the suffixes 1 and 2.
Young's Modulus, E_{1}
Poisson's ratio n_{1}
Young's Modulus, E_{2} Poisson's ratio, n_{2} 
R_{1} and R_{2} are the principal radii of curvature of the two bodies (convex positive).
Effective curvature
Contact Modulus
Hertzian Contact Equations
Line contact (Width 2a; Load P'/unit length) 
Circular contact Diameter 2a; Load P 

Semicontact width or contact radius 


Maximum contact pressure (Hertz stress) 


Approach of centres 


Mean contact pressure 


Maximum shear stress 


Maximum tensile stress  Zero 

An initial estimate of the value of t_{max }for many materials is H/6 where H is the material hardness