fatigue

Definition 1

Human: Physiological and/or psychological state characterized by diminished capacity to perform, and usually accompanied by a feeling of tiredness. It normally results from exertion beyond one's normal ability, but may also be caused or aggravated by ill health, physical and emotional aspects of the work environment, worries, or mental conflict.

Definition 2

Metal: Phenomenon by which a material may fracture under cyclic stresses, even by those below its ultimate breaking strength (called tensile strength). Metal fatigue is one of the most common forms of failure of material under repeated and reversed stresses. See also fatigue strength.