Cracks initiated at the surface of case-hardened gears may lead to typical life-limiting fatigue failure
modes such as pitting and tooth root breakage. Furthermore, the contact load on the flank surface
induces stresses in greater material depth that may lead to crack initiation below the surface if the
local material strength is exceeded. Over time the sub-surface crack propagation may lead to gear
failure referred to as “tooth flank fracture” (also referred to as “tooth flank breakage”). This paper explains the mechanism of this subsurface fatigue failure mode and its decisive influence factors, and presents an overview of a newly developed calculation model.
Many years ago, when asked how the
five-meter gear was checked, the quality manager responded, “When they’re that big, they’re never bad!” That may have been the attitude and practice in the past, but it no longer serves the manufacturer nor the customer. Requirements have been evolving steadily, requiring gears to
perform better and last longer.
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