Originally Posted by
MechEngr
There are two sorts of fatigue - low cycle and high cycle.
Low cycle fatigue is typically a material issue where the material strength is far below the requirement, such as from an improper heat treatment or incorrect alloy. It can also happen if the manufacturing process has left a fatigue initiator such as using a sharp corner end mill instead of a fillet end mill. Low cycle is found in the 5.0 -100 cycle range. This can be typified by flexing a paper clip. It is from a load near or above the yield strength.
High cycle fatigue is the more typical for manufactured goods. It is typified by a load that is far below the yield strength and is nearly independent of yield strength and can run from 100,000 cycles to well into the millions. If there is a manufacturing process problem it can be as simple as a surface texture that's a bit rougher or an internal inclusion of contamination.
At only 3 months - that is no bueno.
MechEngr,Would the position of this door be subjected to large torsional stresses??