Macropitting due to misalignment. Photo courtesy GEARTECH © 2003.

Definition: Macropitting is a fatigue failure driven by Hertzian contact stress. Cracking and detachment of the surface fragments results from cracks that develop in the subsurface of the gear or bearing.

Identification: Macropits on active tooth surface. Cracks on boundaries of the pits. Beach marks in craters.

Discussion: Macropitting is a wear out failure mode. Failure from macropitting early in the design life of a gearbox is abnormal, but a failure of this type at or beyond the end of the gearbox design life could indicate that the gearbox was designed for minimum cost or weight and that the gearbox performed as intended.

Prevention: Reduce contact stress. Increase surface hardness. Increase lubrication film specific thickness.

More Information: For more information on macropitting failures, please submit a question to our “Ask an Expert” link. For assistance with a gearbox failure analysis, please visit our “Consulting” page.