Fatigue

Fatigue is the catastrophic failure due to dynamic (fluctuating) stresses. It can happen in bridges, airplanes, machine components, etc. The characteristics are: • long period of cyclic strain

• the most usual (90%) of metallic failures (happens also in ceramics and polymers)

•  is brittle-like even in ductile metals, with little plastic deformation

• it occurs in stages involving the initiation andpropagation of cracks.

Cyclic Stresses

These are characterized by maximum, minimum and mean stress, the stress amplitude, and the

stress ratio.