Originally Posted by
Geoffersincornwall
riff raff - would it be true to say that the fracture toughness you refer to means that the fracture dynamics are somewhat rapid as a result?
Predicting propagation of a fracture within a metal structure is a fairly complicated task, mostly due to the wide range of variables involved. The fracture propagation analysis is intended to demonstrate that a worst case size/shape flaw in the part structure will not produce propagation of a fracture originating from this flaw that results in a catastrophic failure event.
The rate at which a fracture will propagate is greatly influenced by the stress levels at the fracture tip. The fracture will only propagate if the stress level at the crack tip exceed the local tensile strength of the material. The design of planets gears like the example discussed, having a very thin section rim and internal radial support provided by just a few rollers over a limited angular sector of the bearing, is very difficult to get right. If the planet's spherical roller bearing has excessive internal radial clearance, it can produce higher bending stresses in the gear rim than it was designed for.