Contact Fatigue | Life - Surface Strength - Hardness Relationships

Here the phenomenon of surface fatigue resulting from contact stress is presented and explained. The reason why surface fatigue results in surface pitting is shown in terms of the subsurface location of worst-case stress. It is discussed how the contact area increases with increasing force, leading to a non-linear relationship between force and stress. The two alternatives for the application of a design factor (i.e. with respect to force v. with respect to stress) are demonstrated. The meaning and usage of each of the terms in the equation for surface stress are discussed, including the AGMA elastic coefficient Cp. An example problem is completed in which the minimum allowable surface hardness is found for a cylindrical elliptical cam where the desired life, the load (via spring deflection), and the geometry are given. The problem is solved for both the case where the design factor is with respect to force, and where the design factor is with respect to stress.

Playlist for MEEN361 (Advanced Mechanics of Materials):
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Playlist for MEEN462 (Machine Element Design):
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This lecture was presented on February 21, 2018. All retainable rights are claimed by Michael Swanbom.

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