AbstractThe fatigue behavior of metal structures is extremely complex. Many types of uncertainty exist in metal fatigue studies, including member geometry; shape and size of fatigue cracks; type, shape, and size of defects and discontinuities in the structural detail; loading and environmental conditions; and thermal and corrosive effects. This article reviews a number of factors affecting the fatigue behavior of metal members. An example problem is presented to illustrate the use of fuzzy sets to evaluate the acceptability of a welded structural detail