Fatigue is the phenomenon in which a repetitively loaded structure fractures at a load level less than its ultimate static strength. For instance, a steel bar might successfully resist a single static application of a 300 kN tensile load, but might fail after 1,000,000 repetitions of a 200 kN load.

A formal fatigue evaluation accounts for these primary factors that contribute to fatigue failures:

For information about the commands referenced in this documentation, see Part II: Archived Commands.