Mechanical Properties

· Periodic loads can cause "Fatigue" fracture at lower stress levels than those found for static load tests.
· Crack initiation and propagation in tensile- compression fatigue failure and the structure of the fracture surface in an Aluminum alloy is shown opposite.
· Local stress concentration that takes the material into the plastic region of its mechanical response is important in this fatigue regime.
· Most engineering systems experience fluctuating stresses, and as light-strong structures become more important fatigue is an essential design consideration.

From: Weidman, Lewis & Reid, "Structural Materials," Butterworths (1990),