Meaning
Localized contact stresses between two curved surfaces under load determine the limits of material deformation and surface fatigue. The calculation of Hertzian contact pressure assumes purely elastic behavior in the contacting bodies. This metric assists in preventing surface yield in high-precision hardware mounts.
Interface Profile
Surface geometry defines the shape and size of the contact zone when the mechanical parts are pressed together. Sphere on flat plane, cylinder on cylinder, and double curved surfaces are analyzed using classic equations. The footprint of the contact expands as the applied force increases.
Stress Limit
Material limits dictate the maximum permissible stress before permanent indentation occurs. The onset of plastic deformation begins below the surface where the shear stress is highest. Hardened materials must be used for contact interfaces to avoid surface pitting.
This is especially true for optomechanical assemblies where shifts in position are unacceptable.
Deformation Behavior
Elastomer pads and metal shims behave differently under identical loading conditions because of their different elastic moduli. Hardened steel spheres on flat sapphire surfaces create extremely high stress concentrations under light loads. The localized deformation is very small but creates a highly stable resting point.
When the system suffers from high shock levels, the material must withstand the peak loads without cracking. Design choices must balance the stability of high pressure with the toughness required for survival.
