Neutron fatigue was a breakdown of the nuclear cohesion in a material.

A sub-micron fracture, caused by neutron fatigue, in the metal casing of a dilithium chamber hatch replaced at Earth Station McKinley in 2367 was the cause for an explosion in the USS Enterprise-D's dilithium chamber, and not sabotage by the Klingon spy J'Dan, as was originally suspected. (TNG: "The Drumhead")