Failure of a Large Fan Assembly

A large fan assembly deformed and broke at multiple locations. The user wanted to know whether the bearing pillow block fracture caused the fan blade assembly to crack, or whether a fan blade assembly fracture caused the pillow block to crack. Close inspection of the entire length of the crack showed the crack probably grew quite a while before it was large enough to cause the final catastrophic event. No evidence of fatigue cracks was visible on the broken pillow blocks. In the absence of some other contradictory information, the usual conclusion would be to presume that the fatigue crack predated the single overload crack.