In mechanical engineering, Hertz contact stress is a description of the stress within mating parts. In general, this is usually described with respect to contacting spheres of different radii.

Hertz stresses, also called contact stresses or hertz contact stresses, or hertzian (contact) stresses, bearing the name of H. Hertz, refer to the localized stresses that develop as two curved surfaces come in contact and deform slightly under the imposed loads. This amount of deformation is dependent on the elasticity of the the material in contact, i.e. its Modulus of Elasticity.

In gears and bearings in operation, these contact stresses are cyclic in nature and over time lead to subsurface cracks.

These equations form the foundation for the equations for load bearing capabilities in bearings, gears, and any other bodies where two surfaces are in contact.

More about contact stresses and the evolution of bearing stress equations can be found in this publication by NASA Glenn Research Center head the NASA Bearing, Gearing and Transmission Section, Erwin Zaretsky, http://gltrs.grc.nasa.gov/reports/1997/TM-107440.pdf

There is a section on this topic with a full description of the equations in the popular textbook for Mechanical Engineering Design, with the same name by J.E. Shigley and C.R. Mischke, Chapter 2. J.E., Mischke, C.R., "Mechanical Engineering Design", Fifth Edition, McGraw-Hill, Inc, 1989, ISBN 0-07-056899-5

These stresses have nothing to do with the unit of measure of frequence , a Hertz (Hz). They bear the name of H. Hertz who first studied them, and published his work on the topic in “Ueber die Beruehrung elastischer Koerper (On Contact Between Elastic Bodies),” in Gesammelte Werke (Collected Works), Vol. 1, Leipzig, Germany, 1895.

See also

• Bearing (mechanical)