Look at that picture right over there on the right.
That’s one of the Bronze Wheels of Peru. Looks like a gear, doesn’t
it? If you knew nothing about it or the culture it sprang from and
just happened to see it on the street, you’d probably label it as such. So many people have had that same thought, in fact, that the set has picked up another name: the Bronze Gears of Peru.
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.